Analytical Chemistry User Com · acidified with sulfuric acid and the mix- ... The solutions...

12User Com

Collini has produced hard chromium coatings for the machine industry since 1890 in Vienna. In the past twenty years, the company has become a specialist for “tribological coatings” for the auto-mobile industry. The range of products includes coatings such as hard chro-mium, Triflon®, Glatox® and Skintech® as pure metal coatings, metal oxide coatings, or dispersion composite coat-ings. They fulfill a large number of the requirements of suppliers of components to the automobile industry for wear resistance, controlled friction target val-ues, corrosion resistance and decorative appearance for safety systems, drive sys-tems, fuel systems, or locking systems. The coatings have a thickness of 2 to

In Vienna, the capital of Austria, a fully automated Titration Excellence system is installed that can independently determine the nickel, hypophosphite and orthophosphate concentration of nickel baths. It takes care of the entire sample preparation, analysis and calculation and closes the beakers after the analysis. To do all this, it uses several very interesting tricks.

Analytical ChemistryTitration, pH Systems, Density- & Refractometers

Contents 1/2007

Customer Reports- Automated titration of coating baths 1

- Titrate precious metals to strict standards 4

Applications - Automated determination of

conductivity in high purity water 6

- Density, refractive index, pH and color simultaneously 9

- Determination of the complex stability constant by potentiometric titration 13

- Automated measurement of conductivity, pH and turbidity in potable water 16

Expert Tips - Titrimetric analysis of acid or basic

polyol samples 20

- Accurate determination of the concentration of etching acids 23

- Tailor-made laboratory electrodes for pH measurement in difficult products 26

New Products- Titration Excellence Version 2.0 28

- pH- and conductivity meters FiveEasy™ and FiveGo™ 30

- A new generation of InLab® sensors 30

- Brix meter Quick-Brix™ 31

Automated titration of coating baths

L. Candreia

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and the titrator determines the point of inflection of the curve.

Ni2+ + Murexide-¶ Ni-Murexide+

Ni-Murexide+ + EDTA4- ¶ Ni-EDTA2- + Murexide-

The titration of sodium hypophosphite is somewhat more involved. It can be oxidized in solution, which would allow direct titration. A relatively weak oxidiz-ing agent would however have to be used because otherwise other bath constitu-ents would also be oxidized. An iodine solution is the best choice. The oxidation of hypophosphite with iodine is, however, a relatively slow reaction, which is why iodine cannot be used for direct titration – the titration would take hours. This difficulty is overcome by perform-ing a back titration: a defined excess of iodine is added to the sample previously acidified with sulfuric acid and the mix-ture allowed to stand closed for at least 25 min at room temperature in darkness until the entire hypophosphite content has been oxidized:

I2 + H2PO2- + H2O ¶ 2I- + HPO3

2- + 3H+

The excess iodine can now be simply and quickly titrated back with sodium thio-sulfate according to the following reac-tion equation:

2S2O32- + I2 ¶ S4O6

2- + 2I-

The equivalence point is detected with the DM140-SC Redox electrode and the titra-

50 µm and are deposited exclusively from aqueous systems (electrolytically).

The solutions require daily quality con-trol testing in the in-house control labo-ratory. The density, pH and conductiv-ity are checked and the main inorganic constituents quantified by titration. The results are immediately used to make any necessary corrections to the baths.

At least seventy samples have to be proc-essed daily. Up until now, they have been manually prepared and titrated. Ing. Günther Krimshandl, laboratory techni-cian in the central analytical laboratory, wanted to automate the nickel and hypo-phosphite determination. The automated system should as far as possible free the user from all preparative tasks and pro-vide quicker and more repeatable results. No easy challenge!

Simply allow to complex and oxidize The nickel determination is a simple equivalence point titration with EDTA after murexide indicator and ammonia have been added to the sample. Murexide forms a green complex with nickel at pH 10. The EDTA displaces the murexide and forms a more stable complex with nickel. At the equivalence point, only nickel ions complexed with EDTA and free murexide indicator are present. This is shown by the color change from green to purple.

The DP5 Phototrode™ detects the sharp color change at a wavelength of 550 nm

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tor automatically calculates the original hypophosphite content.

The content of orthophosphate is deter-mined in a similar way. In contrast to the hypophosphite titration, however, sodium hydrogen carbonate is first added and not sulfuric acid in order to make the solution alkaline for the oxidation. Immediately before the titration, the solution is acidified with acetic acid. The following section describes the hypo-phosphite method in more detail. The orthophosphate titration is performed in a similar way.

Titration Excellence operates in parallelThe three titrations do not present any problems for the Excellence titrators. The T90 was connected to two Rondo 20 sample changers and can simultane-ously and independently perform the dif-ferent analyses: the first Rondo is used to determine the nickel content of up to 20 samples, while the hypophosphite or orthophosphate of the same samples is titrated on the second Rondo.

Special attention was paid to the automa-tion of the sample preparation steps. For example, in the nickel determination, the ammonia is added using an SP250 peristaltic pump and the water for dilu-tion with a membrane pump. Similarly, in the hypophosphite titration, the sul-furic acid and the water are automati-cally dispensed into the titration beaker using SP250 pumps. The iodine solution for back titration is very accurately dosed with a burette.Since each hypophosphite sample is first prepared and then allowed to stand for 25 min, other samples can be prepared in the meantime. For this reason, the automation method employed uses two sample loops: the first loop executes the preparation of all samples. Afterward, the first sample is sent to the Rondo titra-tion tower and the second loop (titration) started provided that at least 25 min have elapsed since the first sample was pre-pared (Fig. 2).

Figure 1: The Titration Excel-lence system titrates nickel and hypo-phosphite in parallel including sample preparation.

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Figure 2: First, all samples run through Loop 1. After the last sample has been prepared, all samples run through Loop 2.

Otherwise, the system waits for the remaining time to elapse before starting the back titration.

Timing optimizes efficiencySince the number of samples in a series can vary between 1 and 19 samples, valu-able time would be wasted if the sample waiting time between loops were always the same. Short series need less time to prepare than long series, so that with short series the waiting time before titra-tion must be longer than with larger series.

This problem is solved through clever timing: an auxiliary value is defined before the first loop and set to zero. After each sample, this auxiliary value is defined as the sum of its previous value plus tUSE, where tUSE is the time that has elapsed since the start of the particu-lar sample. When all samples have run through the first loop, the auxiliary value has increased to exactly the time that has elapsed since the preparation of the first sample.

Now the second loop begins in the method process, at the beginning of which there are four special stirrer functions. The first function stirs for 20 min, the second for 15 min, the third for 10 min and the fourth for 5 min. The stirrer speed is set to 0%, in other words, it does not actu-ally stir. It merely introduces a waiting time. Not all the stirrer functions are processed, only those that are needed to allow the first sample to wait for at least 25 min so that the iodine can completely react with the hypophosphite.

To select the right stirrer function, each of the four functions includes a condi-tion that takes into account the value of the auxiliary value determined in the first loop: if this is less than 10 min, stir-ring is for 20 min. If it is between 10 and 15 min, stirring is for 15 min and so on. If the auxiliary value is already greater than 25 min, no stirring occurs and the titration is immediately begun (Fig. 3).

In this way, sufficient time is always allowed for the reaction to occur irre-spective of the number of samples but without any time being wasted.

Reaction in the dark thanks to CoverUp™

The reaction of iodine with hypophos-phite must be performed in complete darkness. For this reason, red titration beakers are used that do not transmit light of wavelengths that interfere with the reaction. The samples are equipped with a lid that blocks light transmission and prevents iodine escaping, which would of course affect the result. The lid also largely suppresses the unpleasant smell of ammonia vapor. The reliable CoverUp™ lid handling device removes the lid from the titration beaker imme-diately before the titration and replaces it again afterward (Fig. 4).

This ensures that the reaction goes to completion free from any outside dis-turbances.The sample data is entered at the PC and the analyses started. The LabX titration PC software controls the Titration Excellence system and stores the data for easy retrieval.

Rapid and reliable resultsCollini is very pleased with the advan-tages the system offers and with the sup-port provided by METTLER TOLEDO for

Figure 3: Depending on how long the first loop takes to prepare all the samples, the first sample is not titrated until the first sample has been allowed to react for at least 25 min.

H = Auxiliary value: total time for the preparation of all samples in the first loop.


Mass production of copperThe joint stock company “Uralelekromed” (UEM) is a modern industrial plant and one of the biggest copper producers in the Ural region of Russia. The impressive amount of 350’000 tons of copper is pro-duced per year. UEM was established in 1934 and employs now more than 11’000 people. It is a unique plant which covers

nical re-equipping and chose METTLER TOLEDO instrument solutions for their departments. The main reasons for their choice were:

A wide range of instrument models for specific solutions and complete support of the analytical workflow comprising weighing, titration and software solutionsTechnical excellence and application competence to provide optimal spe-cific customer solutionsHigh product quality and a conse-quent long life timeExcellent regional customer support and service close to the plant site

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Figure 4: CoverUp™ removes the lid im-mediately before the titration and closes the titration beaker again immediately after the titration. This prevents unpleasant vapors from escaping.

Figure 1: Bird’s eye view of the Uralelekromed plant.

applications and service. The Excellence titrators are easy to use in routine opera-tion but allow complete flexibility in a development environment. The results are more reliable than before when up to three different people per-formed the analyses. The titration time for the daily load of at least 70 samples has been significantly reduced thanks to clever automation. The results are known earlier so that it is possible to react more quickly to any changes that occur in the baths.

Furthermore, the entire sample prepara-tion is automated resulting in a substan-tial time saving: the total analysis time

has been reduced from 10 man hours to 4.5 titrator hours. Günther Krimshandl is very satisfied: “The system has fulfilled our require-ments regarding the degree of auto-mation and exceeded our expectations regarding stability. The time from tak-ing the sample to the availability of the measurement value has significantly decreased, while at the same time the reproducibility of the measurement val-ues has improved.”

Collini Vienna

Your Partner for “Tribological coating systems” Visit us at www.collini.eu

the whole cycle of copper processing from ore to blister copper and to copper alloys. Besides copper silver, gold and other pre-cious metals are produced.

Excellent instrument solutions from METTLER TOLEDOUEM has 18 departments within their quality control system that use a wide range of different analytical techniques: atomic emission spectroscopy (AES), inductive coupled optical emission spec-troscopy (ICP-OES), atomic absorption spectroscopy (AAS), voltammetry, amper-ometry, and last but not least weighing and titration. Over the last few years UEM has been conducting a program of tech-

At first glance, the titration of silver is very straightforward, however in content determination within alloys it becomes challenging since demanding requirements with respect to accuracy have to be met. Experience how METTLER TOLEDO supports an important precious metal producer in Russia throughout the complete titration workflow with excellent instrument solutions.

Titrate precious metals to strict standards

I. Orlov D. Chirkin

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Figure 2: Performing a silver titration.

Titration of silver with the highest accuracyIn 2004 UEM was included in the “Good Delivery” list of the London Bullion Market Association for silver and in 2006 for gold. In order to comply with the “Good Delivery” rules for produced sil-ver and gold bars UEM must fulfill strict requirements with respect to the result accuracy of the analyses of finished products. For instance, silver in alloys must be determined with an accuracy of ±0.01% (deviation from the true value).

The workflow of the titration analysis for silver alloys with silver contents of 10 to 30% (silver scrap), 92 to 99% (Ag/Au alloy) as well as 99.99% (pure silver) consists of several steps:

Weigh a small sample of alloy/metal (approximately 0.5 g, depending on silver content) with a resolution of ±0.00001 g.Dissolve the sample in concentrated nitric acid and dilute the solution with deionized water in a volumetric flask (50 or 100 mL, depending on the sil-ver content).Take an aliquot of the solution and titrate with 0.465 mol/L NaCl using a DL55 titrator.

Every step is extremely important for the overall success of the analysis, Mr. Mazgalin, Head of Central Laboratory at UEM confirmed: “We chose the analyti-cal balance AX105DR for weighing silver samples because of its high resolution, accuracy and ease-of-use. Furthermore, the high stabilization speed of the AX105DR saves us a lot of time due to our high sample throughput per day”.

The DL55 titrator is used with a com-bination of a silver selective (DX308) and a reference electrode (DX200); this combination gives excellent results for silver content determination over a wide concentration range. The reason for this superb performance is mainly due to the very low signal noise and the high reso-lution of the titration curves which show a distinct jump at the equivalence point.

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Mr. Mazgalin, Head of central laboratory of UEM: “With the DL55 titrator we are both able to increase sample through-put and improve accuracy, precision and reliability of results. Furthermore all METTLER TOLEDO titrators have a Russian interface, which is very impor-tant for us because it helps UEM to avoid costly mistakes”.

Expansion of the titration systemUEM is very satisfied with the METTLER TOLEDO equipment in their laborato-ries since the accuracy and reliability of the analytical results are excellent. This assures UEM that they will not receive any claims from customers since all results are completely traceable with respect to the assigned quality and quan-tity of their precious metals.

UEM is now planning to upgrade the DL55 titrator by adding a Rondo sample changer, this will efficiently manage the increasing number of samples for analy-sis along with LabX titration PC software to ensure secure documentation and easy development of methods.

UEM is currently using manual titra-tion for the determination of the copper content in electrolysis baths. Titration is performed with sodium thiosulphate and uses starch as indicator. In order to improve the quality of the analysis and be

able to cope with increasing throughput, UEM is planning to further upgrade their laboratories with automated titration sys-tems using the new Titration Excellence series.

Figure 3: Silver bullions


The conductivity of water is a direct measure of the ability of the water to pass a current. The amount of current flow-ing depends on the concentration of ions present, and their mobilities.

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The conductivity of a solution also varies as a function of temperature, the pH of the solution and the amount of dissolved carbon dioxide. The standard describes conductivity due to these factors as “intrinsic conductivity”.Conductivity contributions from other ions dissolved in the water (notably Sodium, Ammonium and Chloride) are referred to as “extraneous conductivity”

The standard specifies a three step proc-ess to measure these effects:

Stage 1 Measurement of Conductivity (intrinsic and extraneous) and TemperatureThe temperature and conductivity of the water test sample are measured with-out agitation and without temperature compensation. The measured values are compared to limiting values given in the USP table 1 (cf. table 1). If the value for the limiting conductivity is not exceeded, then the test is passed and the water may be used in the manufacturing process.

Stage 2 The effect of Carbon dioxide absorption (intrinsic conductivity)For samples that fail the requirement of stage 1, the effect of CO2 is checked by holding a sample at a constant tempera-ture of 25 °C ±1 °C. it is then stirred vig-orously to encourage the uptake of CO2. The conductivity is monitored during this stirring, and when the value changes by no more than 0.1 µS/cm over 5 minutes the final reading is taken. If the final val-ue is below 2.1 µS/cm the test is passed.

Stage 3 Combined effect of pH and Carbon dioxideThe final stage, for samples failing at stage 2, must be performed within 5 min-utes of the sample failing stage 2. First, saturated KCl solution at 0.3 mL per 100 mL test sample is added. The tem-perature is again held constant at 25 °C ±1 °C and the pH value of the solution is measured. The pH should lie in the range 5.0 to 7.0, and for each intermedi-ate value there is a limiting conductivity (cf. table 2). If this limiting conductivity is not exceeded, the test is passed at stage 3. If the requirements of stage 3 are not met, then the water is deemed unsuitable for use in the manufacture of pharma-ceutical products.

AutomationThe USP standard makes demanding rec-ommendations as to the performance of the measurement systems, and up until recently the automation of the test proc-ess was difficult. With the enhanced capabilities of the T90 Excellence titrator, in combination with the Rondo sample changer and LabX titration PC software, automation of the entire process and secure data manage-ment is now possible. The benefit that this brings is large, with large amounts of operator time freed up for use on more productive tasks.

The analysis stages are separated into two methods:Stage 1 & 2 performed for every sample using the Rondo 20 sample changer with CoverUp™

The use of high purity water in the manufacture of vaccines and other injectable pharmaceutical products is controlled by the requirements of USP26 <645>. In this monograph, the conductivity of the water is specified as the key indicator of its suitability for use in production processes.

S. Vincent

Automated determination of conductivity in high purity water

Table 1: Conductivity limits for stage 1.

Temperature [°C]

Conductivity [µS/cm]

0 0.6

5 0.8

10 0.9

15 1.0

20 1.1

25 1.3

30 1.4

35 1.5

40 1.7

45 1.8

50 1.9

55 2.1

60 2.2

65 2.4

70 2.5

75 2.7

80 2.7

85 2.7

90 2.7

95 2.9

100 3.1

Figure 1: The principle of con-ductivity measure-ment.


Stage 3 performed on a manual titration stand as and when required

The CoverUp™ lid handling device en-sures that samples waiting on the sam-ple changer rack are protected from the uptake of CO2 from the atmosphere. The sample beakers are uncapped imme-diately prior to measurement, so spu-rious conductivity results are avoided (cf. Fig. 2).

Temperature control for both titration stands is by means of a thermo-circu-lation heater/chiller programmed to a set temperature of 25 °C. Using heat exchangers immersed in the samples a stable temperature can quickly be attained whatever the initial sample tem-perature. The temperature is set at 25 °C for compliance with the requirements of stage 2, and also to allow a direct com-parison of the stage 1 result a single limiting value from table 1 (in this case 1.3 µS/cm).

The stage 1 & 2 method follows the fol-lowing sequence, which is summarized on the flow diagram in figure 3:

Thorough pre-rinsing of the electrode assembly, in the fixed rinsing beaker with 3 cycles of 25 mL of high purity water for injection. A second pump aspirates the rinse water to waste, pre-venting overflow in the rinsing beaker. This pre-treatment avoids falsely high results in the stage 1 measurement.Remove sample lid from 1st sample beaker.Measure temperature using DT1000 probe.Measure temperature until value <set value 25.5 °C – condition T>25.5 °C. Measure temperature until value >set value 24.5 °C – condition T<24.5 °C. Measure conductivity to nearest 0.01 µS/cm, using InLab®740 elec-trode at 0% stir speed and with no temperature compensation.Report values for temperature and stage 1 conductivity to LabX titration

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If the sample has failed the requirements of stage 1, the method proceeds to test stage 2. If the sample has passed, all of the stage 2 method steps (except for rins-ing) are skipped.

This is made possible using the T90 Excellence titrator by adding a condi-tion statement (E[4]>1.3) to all of the subsequent method functions up to the rinse function. Some functions require more than one condition to be fulfilled in order for them to be executed. Again this is no problem for the T90.

The sample is stirred at high speed whilst the conductivity is measured using the InLab®740. When the signal is stable within the defined limits, the value is taken.The temperature and stage 2 values are reported to LabX titration.If the value for the conductivity exceeds 2.1 µS/cm an instruction is displayed to conduct a separate stage 3 test. The condition here is:

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pH Conductivity [µS/cm]

5.0 4.7

5.1 4.1

5.2 3.6

5.3 3.3

5.4 3.0

5.5 2.8

5.6 2.6

5.7 2.5

5.8 2.4

5.9 2.4

6.0 2.4

6.1 2.4

6.2 2.5

6.3 2.4

6.4 2.3

6.5 2.2

6.6 2.1

6.7 2.6

6.8 3.1

6.9 3.8

7.0 4.6

Table 2: Conductivity limits for stage 3.

Figure 2: Detail of the setup for the automated conductivity meas-urement according to USP 26 <645>.

Heat exchanger

InLab®740 conductivity sensor

Rondo 20 Sample changer

CoverUp™ lid handling device

DT1000 temperature sensor


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E[4]>1.3ANDE[5]>2.1.Rinsing is conducted using the same protocol as before.Recap the sample beaker and move to next sample.

The method for stage 3 follows a similar pattern, with the temperature stability followed by pH measurement using the DG117-Water electrode. The measured pH value is exported to LabX titration, where a comparison is made with the values in table 2.

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SummaryThe results of the sample series show excellent precision, which allow a reli-able characterization of the water for subsequent use.

Through the efficient, multi-cycle spray and dip rinsing between samples, protec-tion of samples from CO2 uptake, temper-ature control and decision making logic statements; the Excellence titrator shows that it is capable of working to the most stringent specifications.

Sample No. Stage 1 [µS/cm]

Stage 2 [µS/cm]

Stage 3 [pH]

Outcome

1.1 0.28 - - Pass

1.2 0.30 - - Pass

1.3 0.29 - - Pass

1.4 0.28 - - Pass

Mean n=4 0.2875

s 0.00957

srel 0.33% 2.1 1.62 1.91 - Pass

2.2 1.64 1.90 - Pass

2.3 1.65 1.92 - Pass

Mean n=3 1.637 1.91

s 0.01528 0.01

srel 0.933% 0.524% 3.1 3.81 4.21 6.82 Fail

Figure 3: The method flow-chart.

Table 3: Results of the stage 1, 2 and 3 conductivity/pH measurements


In the quality control of liquids, den-sity and refractive index are often deter-mined together. The METTLER TOLEDO compact DR40 and DR45 combined meters for density and refractive index are ideal solutions for such applications. The instruments can be optionally oper-ated with an SC1 single automation unit or an SC30 sample changer.

Measurement systems are therefore already available that, at the press of a button, perform the simultaneous determination of density and refractive index or of concentrations derived from them of single samples or sample series. These systems significantly simplify the determination of the density and refrac-tive index but often still do not offer the degree of automation the user would like and that is technically possible.

Nowadays, systems are required that automatically determine as many parameters as possible in one run,ensure that the measurements are properly performed,allow easy integration into any LIMS/ERP systems,have an advanced user management system andcan if necessary be expanded and adapted to meet special needs.

In response to this, METTLER TOLEDO has developed LiQC (Quality Control of Liquids) in cooperation with well-known customers from dif-ferent industries. LiQC systems offer flexible solutions for

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the automatic quality control of homoge-neous liquids and thereby increase pro-ductivity and data security.

More results in one runIn the quality control of homogeneous liquids, pH, conductivity or color are also frequently measured besides density and refractive index. For example, often only the pH and refractive index or the density and color of samples need to be measured.

With LiQC, automatic measurement sys-tems for the simultaneous determination of these parameters can be easily real-

ized. The concept is simple: a PC con-trols an automatic measurement system consisting of a DE density meter, an RE refractometer or a DR combined meter together with an SC1 or SC30 automation unit. Up to two additional measuring instruments (conductivity or pH meter and colorimeter) as well as a barcode reader can if necessary be integrated into such a measurement system.

With LiQC, there is also the possibil-ity to simultaneously operate a DE den-sity meter and an RE refractometer. The advantage of this system is that only one automation unit is necessary for the

Density and conductivity, refractive index and pH, density, refractive index and conductivity or density, refractive index, color and pH? In the quality control of liquids, several different physical properties are often determined in each sample. In practice, this usually means performing several measurements one after the other, compiling the results, and checking whether the values are within the given tolerances. METTLER TOLEDO LiQC systems allow analytical workflow processes like this to be completely automated.P. Wyss

Density, refractive index, pH and color simultaneously

Figure 1: Overview of an LiQC system.


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simultaneous determination of several parameters. This significantly simpli-fies the analytical workflow process and saves time, space and money.

Secure resultsQuality assurance (QA) can be defined as that part of the quality management sys-tem which provides confidence that qual-ity-related requirements are fulfilled. An important part of quality assurance is the control of inspection, measuring and test equipment. As a manufacturer, we help customers ensure that METTLER TOLEDO instruments provide results that are within the required limits of meas-urement accuracy. With LiQC, the meas-urement accuracy of the density meters and refractometers integrated in the sys-tem can be rapidly and reliably checked.

If this check is performed with a com-bined density/refractive index standard from METTLER TOLEDO, the procedure is extremely simple: Put the standard in the automation unit - scan in the barcode on the certificate – and click <Check>. The measurement accuracy is automati-cally checked and the results displayed and stored together with the data of the certificate.A regular check of measurement accu-racy alone cannot however ensure that the results determined with a measure-ment system are within the required lim-its of measurement accuracy. Experience shows that the most frequent cause of measurement errors is not inaccurate test equipment but incorrect measure-

ment procedures. In practice, it also often occurs that the result determined is correct but wrongly interpreted. Furthermore, usually the requirements for the absolute accuracy of measure-ments performed with the test equipment are not identical for all products because the samples cannot all be measured with the same accuracy due to their different composition.

These additional sources of error are mainly due to the manner in which measurements are normally performed in routine quality control. For example, let us assume that the density of a prod-uct is to be determined and the measure-ment result is to be transferred to a LIMS (Laboratory Information Management System).

A typical procedure is:The method is selected at the density meter.The sample is injected into the meas-uring cell.The result is read.The density measuring cell is cleaned.The result is transferred together with the sample data to the LIMS.

Each of these five steps involves potential sources of error:

The operator must ensure that the measurement is performed under cor-rect conditions (instrument settings such as measurement temperature, viscosity correction, etc.).The operator must make sure that the

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measuring cell is clean and dry before injecting the sample and that the sample is properly introduced into the measuring cell (e.g. no air bubbles).The operator is responsible for ensur-ing that the measurement is correctly performed. He must judge whether the result obtained is within the limits of measurement accuracy required and must repeat the determination if this is not the case (e.g. if the measure-ment is affected by air bubbles).It is the operator’s responsibility to make sure that the measuring cell is clean and dry after the cleaning.If the measured values are automati-cally transferred to the LIMS System, the operator must make sure that the sample description is correctly entered and that only results of measurements that have been correctly performed are transferred. If the measured values are entered manually, typing errors must be excluded.

With LiQC, it is possible to eliminate these sources of error. An important aspect of the LIQC concept is responsible for this: In contrast to most present-day measuring instruments and analysis sys-tems, LiQC is product orientated and not method orientated. The characteristics of all the products to be measured with the system can be stored in an MS ACCESS® database. In the database, the following information can be specified for each product:

how the measurement is to be per-formed (sample delivery, measure-ment and cleaning)which measurement parameters are to be determined for the productthe measurement accuracy with which the individual parameters are to be determined the range in which the individual measured values must lie for a par-ticular product

To determine one or more measurement parameters with an LiQC system, the operator now only has to enter the sam-ple identification and select the type of

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Figure 2: The LiQC system.


product. LiQC performs the determina-tion and cleans the measuring cell using the settings specified for the product. The results of the determination are only saved and automatically transferred to a LIMS (or ERP) system if all the parame-ters have been determined without error. If the system was not able to determine all the parameters with the measure-ment accuracy specified for the product type, the operator is requested to repeat the measurement. If the measurement was correctly performed, it can immedi-ately be seen whether the sample satisfies the quality requirements for all the para-meters determined.

However, two important potential sources of error still remain in the above proce-dure because entry of the sample identi-fication and selection of the product type are done manually. Here again, LiQC offers a simple solution: LiQC systems are not only able to read barcodes, they can also interpret them correctly. If barcodes are used that contain both the sample identification and the information about the type of product, then no manual entries at all need to be performed in the measurement process. The barcode can be read in manually or, if working with a sample changer, automatically.

The measurement process becomes more secure and in addition simpler because only two steps are needed to the perform the quality control of homogeneous liq-uids namely:

For single sample automation (SC1): Scan the barcode and place the sample in position (no keystroke required!).For multi-sample automation (SC30 sample changer): Place the sample in position and click Start.

Easy LIMS IntegrationAn important reason for the develop-ment of LiQC was the requirement of many customers for easy integration of our automatic measurement systems into existing LIMS/ERP systems. The start-ing position is the same in most cases:

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The higher-level system (LIMS, ERP) can automatically import measurement results in the form of ASCII text files (or XML files). Where the data is (i.e. the file, folder) and in what form it should be available (i.e. the format) for export to a LIMS system is however different in almost every case.

For this reason, with LiQC, the format of files generated for data export can be freely specified in an easy-to-under-stand menu. Depending on the system, the results also have to be grouped dif-ferently in files. In some cases, all the results must be written into one file that is sporadically imported into and deleted from the higher-level system. There are, however, systems that expect a file for every result; the file must usually have a unique name (with a counter). In other cases, the LIMS expects one result file per product type or per measurement series. LiQC can accommodate all these requirements, without the need to write a single line of code.

Integration into LIMS systems, however, concerns not only the export of data but also the import in the form of sample files. LiQC also offers a solution in this respect: the system is told the folder in which the LIMS generates the sample files. If the user clicks Start and if a sample file exists, the list of samples to be meas-ured is directly displayed. The samples now only have to be placed in the sam-

ple changer in the correct order and the measurement series started.

If desired, LiQC creates additional local copies of measurement results. These files can be opened if necessary in a spread-sheet program (e.g. with MS EXCEL®) and printed. There is also the possibility of creating a file that contains only the results of samples in which one or more of the measured parameters are outside the limits specified for the product type. This means that the user always has an overview of all the samples that do not satisfy the quality criteria.

Advanced user managementA major requirement of automatic meas-urement systems is simple and secure operation. Unauthorized use must be impossible. This makes user manage-ment essential. With a classical user management based on user names and passwords that have to be typed in and changed at regular time intervals [1], operation of the system can be made more secure – but certainly not easier.

Figure 3: SC30 with built-in barcode reader.

Figure 4: Fingerprint reader.


Nowadays, user management systems are possible that make the operation of meas-urement systems easier and more secure and which are also recognized by the responsible authorities [1]. This is due to the rapid development of biometric meth-ods. METTLER TOLEDO recognized and patented the advantages of user manage-ment with biometric user identification for measurement systems early on and now offers it with LiQC for the first time.

LiQC is always delivered with a finger-print reader. This allows all users of the measurement system to be identified and their rights defined. In routine operation, all the functions of the measurement system (i.e. LIQC software, density meter and refractometer keyboards) are blocked by default except for an emergency stop. The user gains access to the system by placing his finger on the reader. LiQC

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automatically recognizes who is access-ing the system and the rights this per-son has and activates the corresponding functions or the keyboard of the measur-ing instrument. When the measurements are completed, LiQC blocks access to the system again. Through this, the system unambiguously documents whoever per-forms a measurement, adjustment or sys-tem check.

Flexible expansionLiQC is extremely flexible and in most cases meets the requirements of the users of automatic measurement systems, namely by providing better results in a shorter time and at lower cost.

There are however applications that require special procedures. To accom-modate this, the system can be expanded with plug-ins. The use of plug-ins avoids

adding numerous menus for each special application, which would make normal operation unnecessarily complicated. In addition, plug-ins ensure that LiQC cov-ers a very wide range of requirements. Plug-ins are dynamic link libraries (dll) whose interface is exactly described in the LiQC documentation.

Two such plug-ins are supplied as stand-ard equipment with the LiQC. One plug-in is for the calculation of the content of alcohol and extract in spirits, and the other allows the content of alcohol, apparent extract and wort in beer to be calculated.

Literature[1] Code of Federal Regulations, 21

CFR Chapter 1, Part 11, § 11.100 - § 11.300 (April, 2005)

Figure 5: Beer plug-in


to one central metal ion. For n ligands, the corresponding stepwise reactions can be given as:

ML n-1 + L D ML n

where Kn is defined as the stepwise reac-tion constant.

Correspondingly, the overall reaction bet-ween n ligands and a metal ion is given as:

Thanks to its excellent complexing action, EDTA is used in titration analy-sis for the determination of metal ion contents in aqueous solutions. The most well-known example is the determina-tion of total hardness in water, which is given by the sum of calcium and mag-nesium ions titrated with EDTA, and expressed as calcium carbonate.

EDTA, binds with di- or trivalent metals ions via two amine and four carboxy-late groups of its structure (Fig. 1). In particular, EDTA forms specially strong complexes with manganese (Mn(II)), copper (Cu(II)), iron (Fe(III)), and cobalt (Co(III)) [1, 2].

What is the complex formation constant?To characterize the binding strengths of the complexing agent with metal ions, the complex formation constant is meas-ured in aqueous solutions. In general, the formation of a complex between a metal ion M and a ligand L can be illustrated by the following chemical reaction (electri-cal charges have been omitted) [2]:

M + L D ML

This process is quantitatively described by the equilibrium constant of this reaction:

M + L D ML

Usually, more than one ligand L is bound

IntroductionMetal complexes have an important role in our daily life. As an example, the hardness of water has to be reduced to avoid damages to the pipelines, the wash-ing machines and to improve efficiency of washing action. Water hardness is due to the presence of calcium and magnesium carbonate, i.e. the white spots visible on the metal sur-faces. Complexing agents (water soften-ers) are added into washing detergents to decrease water hardness. They sequester calcium and magnesium ions present in water by tightly complexing them, and therefore, no carbonate compounds are formed.

EDTA (ethylenediamine tetraacetic acid), a well-known titrant in quantitative volumetric analysis [1], and other simi-lar compounds are typical complexing agents which are used as water softeners for instance. Due to their ability to com-plex metal ions they are also employed to safely bind with poisonous metal agents such as mercury, arsenic and lead.

Furthermore, ligands can be used in pharmaceutical sciences for e.g. a spe-cific therapy of iron dosing or removal. In earth sciences it is known that organ-isms produce organic complexing agents, which have the ability to decompose minerals and rocks by removing metal ions. In general, complexing agents are relevant to the mobilization of metals in the soil, the uptake and the accumu-lation of metals into plants and micro-organisms.

Figure 1: EDTA (black) binds with a central metal ion (red) by means of two nitrogen atoms and four oxygen atoms.

Metal ions play a crucial role in life, nature and environment. They are mainly present as metalligand complexes, where a metal ion is bound to organic ligands. The formation of such complexes is one of the most relevant steps in (bio)chemistry. Thus, the detailed understanding of the complex formation is a prerequisite for a deep understanding of life processes. Automated titration measurements can contribute to this since they allow for accurate determination of the complex formation constant between a metal ion and different organic ligands.

The determination of the complex stability constant by potentiometric titration

Dr. C. De Caro


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M + nL D ML n

ßn is the overall complex formation con-stant.

As an example, selected values for the stepwise complex formation constant Ki are indicated at given temperature and ionic strength in table 1 [1]. The great-er the value of Ki, the more stable is the metal complex.

Why is the complex stability constant determined?The complex stability constant indicates the strength of chemical bonds between a central metal ion and its ligands. The value is generally measured at a specific temperature and at a given ionic strength. This quantity is not only relevant for basic research, in particular for the char-acterization of a metal ion in aqueous solutions and for the study of chemical equilibria, but is also of importance for practical applications.

Herewith a list of typical applications where complexing agents are used:

Solubilization of metal ions in various processes.Removal of poisonous metals from e.g. soil.Remediation of radioactive metals from environment (contaminated soil).Transportation of metal ions into the human body (iron, zinc) for therapeu-tic reasons.

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Quantitative volumetric analysis (con-tent determination of metal ions such as nickel, zinc, aluminum, iron in e.g. electroplating baths).

In particular, the determination of the complex formation constant is an impor-tant analysis in the pharmaceutical and environmental sciences. For instance, the presence of metal ions in soil due to complex formation with humic sub-stances can be characterized by a system-atic study of model organic ligands with selected metals ions simulating humic substances. This allows for for a detailed study of the metal speciation in soils.

How is the complex stability constant determined?Several techniques have been developed for the determination of the complex sta-bility constants in aqueous solutions [2]. Among others, potentiometric titrations are well-known procedures and have been used for many years for this purpose. In fact, almost all ligands are organic com-pounds containing one or more groups which can be protonated by addition of strong acids e.g. hydrochloric acid.

Therefore, the complex formation be-tween the protonated organic ligand HL and the metal ion Mz+ can be moni-tored by measuring the pH value during a potentiometric titration with a strong base: the organic ligands HL are depro-tonated, and the ligand L- can form a complex with the metal ion. In the case of monoprotic ligand, e.g. HL, and of a 1:1 complex formation the corresponding

• chemical equilibrium in solution can be described as it follows (electrical charges have been omitted):

M + HL D ML + H

More precisely, there is a direct competi-tion between complex formation and pro-tonation of the ligands in aqueous solu-tion. For this reason, to study the stability of metal complexes and their formation it is necessary to consider the dissociation equilibria of the ligand. When the com-plex formation constant KM is stronger than the protonation constant of the ligand KL, then the formation of a metal-ligand complex is the predominant reac-tion in solution.

M + L D HL

M + L D ML

Two different potentiometric titrations are needed for the determination of the com-plex formation constant [2]: First, an aqueous, acidic solution of the ligand is titrated with a strong base. In this acidic solution the ligand is com-pletely protonated. From the obtained titration curve the protonation constant of the ligand can be calculated. Note that the protonation constant is the reciprocal value of the acid dissociation constant [3].

Ligand, L Metal ion, M log K1 log K2 log K3 log K4 T [°C] Ionic strength [mol/L]

Ammonia, NH3 Ag+ 3.31 3.92 25 0.0

Cu2+ 3.99 3.34 2.73 1.97 30 0.0

Hg2+ 8.8 8.7 1.00 0.78 22 2.0

Ni2+ 2.67 2.12 1.61 1.07 30 0.0

Acetate, CH3COO- Ag+ 0.73 -0.09 25 0.0

Cu2+ 2.23 1.40 25 0.0

Fe3+ 3.38 3.70 2.60 20 0.1

Ethylenediamine Ag+ 4.70 3.00 2.00 20 0.1

Cu2+ 10.66 9.33 20 0.0

Zn2+ 5.77 5.06 3.28 20 0.0

Table 1: Examples for se-lected values for the stepwise complex formation constant Ki at given tem-perature and ionic strength.


Figure 2: Titrations of proto-nated EDTA with 0.1 M NaOH:a) 8 mL 0.1 M EDTA only (green line), b) 8 mL 0.1 M EDTA and an equimolar calcium solution (blue line).Due to the binding with calcium ions protons are re-leased by EDTA and the pH becomes more acidic.

The protonation constant will be used for the calculation of the complex forma-tion constant. In a second titration, an aqueous acidic solution of the ligand and metal ion is titrated with the same strong base. In both cases, the initial pH value must be the same, and the titrations are stopped at pH 10.5 (Fig. 2).

The titrations have to be determined under controlled conditions [2], [3], i.e. at specific temperature, pressure, ionic strength and inert atmosphere (to avoid intake of CO2 by the strong base, and thus to suppress carbonate formation). The titrations are both performed in a ther-mostated beaker connected to a water bath circulator where the temperature is usually set to 20 or 25 °C. Nitrogen gas is blown into the solution to eliminate CO2 absorption from the air to avoid any interference on the measurement. The titration is generally performed by adding constant titrant increments of e.g. DV = 0.1 mL and subsequently measuring the pH value after a fixed time interval of e.g. Dt = 45 s. During this time, equilibrium has been reached and the signal is very stable. At the end, a complete titration curve is obtained consisting of several pairs of measured values (titrant volume, pH) [3]. Using the LabX titration soft-ware, the titration data can be stored on a PC and exported into an MS EXCEL®‚ spreadsheet for subsequent calculation.

From the experimental known quantities, i.e. the pH value, the titrant consump-tion, and the total concentration of metal ions and ligands, the complex stability constant can be calculated. In particu-lar, two mathematical functions can be calculated for each measured points (mL, pH) of the second titration:

The mean number of ligands bound to one metal ion, The concentration of free ligand, [L].

To solve the resulting equations, the man-ual procedure and their related graphical evaluations can become very complex, especially if more than one ligand is bound to the metal ion. Thus it is referred

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to the relevant literature for comprehen-sive information [2].

Nowadays, powerful computer programs are available for the determination of the complex formation constant from poten-tiometric titrations. The measured values can be e.g. imported and fitted by a math-ematical procedure to obtain the complex stability constant. Briefly, the program calculates the theoretical pH value and compares it with the measured one. Through several iteration steps the dif-ference between them is minimized and the complex formation constant is cal-culated. BEST [2], [4] and HYPERQUAD [5] are examples for the most well-known and widespread PC programs used for this application.

Summary The complex stability constant can be eas-ily determined using modern autotitrators

and dedicated computer programs. The Excellence titrators together with the LabX titration PC software, allow for a user- friendly determination of experimental data needed for the computer evaluation.

Literature[1] D.C. Harris, “Quantitative Chemical

Analysis”, 5th Edition, 1999, W.H. Freeman and Co.

[2] A. E. Martell, R. J. Motekaitis, “The Determination and Use of Stability Constants”, 1988, VCH Publishers.

[3] C. A. De Caro, “The determination of the acid dissociation constant”, USER-COM 11, November 2006, METTLER TOLEDO ME-51724499. (download-able from www.mt.com)

[4] R. J. Motekaitis, A. E. Martell, “A new program for rigorous calculations of equilibrium parameters of complex multicomponent systems”, Can. J. Chem., Vol. 60, 1982, pp 2403-2409.

[5] See: www.hyperquad.co.uk P. Gans, A. Sabatini, A. Vacca, “Investigation of equilibria in solu-

tion. Determination of equilibrium constants with the HYPERQUAD suite of programs”, Talanta 43, 1996, pp 1739-1753.


TurbidityTurbidity in water is caused by colloidal matter such as clay, silt, plankton and other microscopic organisms. Turbidity is an expression of the optical property that causes light to be scattered in a water sample. Turbidimeters with scat-tered light detectors located at 90º to the incident beam are called nephelometers. The turbidity is reported in nephelomet-ric turbidity units (NTUs, Fig. 1).

Nephelometers are particularly suitable for measuring turbidities of water that fall within the range of 0 to 1 unit [1], [2]; such low values are, for example, obtained for potable water. Today nephe-lometers are specified as the standard instrument for measurements of low tur-bidities [1], [2].

The water sample should be measured immediately after it is taken without altering the original sample conditions such as temperature or pH.

According to the U.S. environmental pro-tecting agency and according to ASTM D1889–00, nephelometers should permit detection of differences as follows [1], [2], (cf. Table 1).

Automated method from METTLER TOLEDOAn automated method for pH, conductivi-ty and turbidity measurement was deve-loped by pumping the water from sample containers on the Rondo sample changer (pH, conductivity) and into the turbidi-meter via a flow-through cell.

This system enables easy sampling of po-table water samples in the laboratory and gives a fast measurement of the three parameters. Since the Excellence titra-tors can be equipped with a conductivity board, the conductivity can be determi-ned directly with no need of an additio-nal meter. The following configuration was used for this purpose:

T90 with conductivity board Rondo sample changer with 2 towers (towers A and B) HACH 2100 AN IS Nephelometer (Fig. 2)Flow-through cell kit from HACH (Fig. 3)Jack-Lemo cable to connect the analogue output of the nephelometer (Jack) to the titrator sensor input (Lemo)

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The two towers are required in order to separate the conductivity and pH measurements. This separation is ne-cessary, because the efflux of the KCl reference electrolyte from the pH sensor into the sample solution will increase the conductivity of the water sample; in low conductivity samples this efflux can lead to a significant error in measure-ment. The T90 Excellence titrator was used because a total of 5 sample loops is required to fully automate all analysis steps (cf. Fig 4).

For conductivity and pH measurements no special treatment of the water sam-ples was necessary. The DG115-SC (for pH) and InLab®730 (for conductivity) sensors were calibrated before the sam-ple measurement. These calibration steps are part of the method (cf. method flow chart in Fig. 4 and [3]).

The automation sequence without the calibration of the pH and conductivity sensor is as follows:

An empty titration beaker is moved to tower A.A water sample is pumped from the reservoir with pump 1 into the titra-tion beaker.The conductivity of the sample is measured at Tower A with the InLab®730 conductivity probe.The fixed rinse beaker is moved to tower A.The equipment of tower A is rinsed in the fixed rinse beaker (simulta-neous rinsing with the diaphragm pump on tower A and aspiration of

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and also in the analysis of surface and process water. The water clarity, i.e. the turbidity is also an important parameter. Beverage producers as well as potable water treatment plants commonly apply fluidparticle separation techniques such as sedimentation and filtration in order to increase clarity and so ensure high product quality.

Automated measurement of conductivity, pH and turbidity in potable water

Figure 1: Formazine solutions (from left to right: <0.1 NTU, 200 NTU and 7500 NTU).

NTUrange Report to nearest [NTU]

0…1,0 0.05

1…10 0.1

10…40 1

40…100 5

100…400 10

400…1000 50

> 1000 100

Table 1: Turbidity differences of water that must be detectable [1].

Dr. T. Hitz


the rinse solution with pump 3).The titration beaker carrying the sample is moved from tower A to tower B.The pH of the sample is measured with the DG115-SC.The fixed rinse beaker is moved to tower B.The equipment of tower B is rinsed in the fixed rinse beaker (simulta-neous rinsing with the diaphragm pump on tower B and aspiration with pump 2).A water sample is pumped with pump 5 into the Nephelometer.The turbidity measurement is performed.The turbidity measuring cell is emp-tied with pump 4 and rinsed with fresh sample solution.

The conductivity (tower A) and pH sam-ples (tower B) were directly pumped in using SP250 peristaltic pumps from the sample water reservoir into the titration beaker on the Rondo sample changer.

After conductivity and pH measurement the water sample was directly pum-ped into the flow through cell from the same water reservoir. In total, 5 peris-taltic pumps (SP250) were used to pump the water samples and to rinse the flow through cell, tubes and sensors on the two towers after each measurement (Figs. 5 and 6):

Pump 1: Addition of the water sample from the water reservoir on the Rondo sample changer.

Pump 2 and 3: Rinse cycles on the Rondo sample changer (towers A and B).

Pump 4 and 5: Rinse cycles on the turbidity meter and sample addition into the f low- through cell.

From the analogue output of the tur-bidimeter a mV signal is obtained. The

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settings on the turbidimeter were defined as follows: 0 to 1000 mV corresponds exactly to 0 to 2 NTU. This leads to the factor of 0.002 NTU/mV ([3], Table 2). For the accurate calibration of the turbidimeter formazine standard solutions were ap-plied (Fig. 1).

After the flow through cell had been filled with the water a stir method function at a stirrer speed of 0% for 120 s was inserted, which served as a waiting time in order to obtain a stable turbidity signal.

ResultsThe results for the conductivity (R1), pH (R2) and turbidity (R4) measurements of tap water are shown in table 2.

The results of the pH and conductivity measurements showed excellent precisi-on, as indicated by the low relative stan-dard deviation (srel). The standard devia-tion of the turbidity measurements is also

Figure 2: Nephelometer from HACH with flow through cell inserted.

Figure 4: Flow chart of the method.

Figure 3: Flow through cell.


low at 0.148 ±0.01, therefore this fully automated method allows easy and reli-able detection of differences of 0.05 NTU, as required by the ASTM D1889–00 stan-dard for an NTU range between 0 and 1.

Advantages and conclusionsFor potable water with low turbidity the automated system in question offers se-veral benefits:

The automated water sampling from the same container makes the water sample addition and distribution sim-ple and fast. This saves time.

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numerous different titrations in ana-lytical water laboratories. The meas-urements are fully automated and can be started with one click on the termi-nal of the Excellence titrators. No time consuming and expensive training of operating personnel is required.

Literature[1] ASTM D1889: Standard Test Method

for Turbidity of Water.[2] U.S. ENVIRONMENTAL PROTECTION

AGENCY. 1993. Methods for Deter-mination of Inorganic Substances in Environmental Samples. EPA-6000/R/93/100 - Draft. Environmental Monitoring Systems Lab., Cincinnati, Ohio.

[3] Mettler method M439 (Autom. Con-ductivity, pH and Turbidity Measure-ment of Potable Water).

There is no possibility of contamina-tion of the water sample prior to the turbidity analysis, result integrity is therefore ensured and costly repeat measurements are avoided. The flow through cell of the turbi-dimeter increases the speed of the measurement and assures a constant optical path. The cell is cleaned simply by rinsing with the next water sample, this significantly contributes to the accuracy and precision of the turbidity results. Additional dosing units, attached to the main unit of the titrator, enable

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Figure 5: Automated system at work. The num-bers indicate the pumps 1 to 5.

Table 2: Statistics for con-ductivity, pH and turbidity measure-ment.

Rx Name n Mean Unit s srel [%]

R1 Conductivity 10 265.084 µS/cm 0.643 0.243

R2 pH 10 8.313 pH 0.003 0.041

R3 Potential 10 73.99 mV 4.81 6.501

R4 = R3 * 0.002 Turbidity 10 0.148 NTU 0.01 6.512


Figure 6: Graphical illustra-tion of the titration system.

20 METTLER TOLEDO UserCom 1/200720 METTLER TOLEDO UserCom 1/2007

Expe

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ps

IntroductionPolyols are chemical compounds, usually alcohols, containing multiple hydroxyl groups. When these hydroxyl groups are made readily available for chemical reaction, they can formulate a vast array of different products ranging from food additives to fabrics to plastics.

Some of the most common products associated from this type of reaction are polyurethanes, which are formulated by reacting a diisocyanate and a polyol in the presence of a catalyst under extreme-ly tight acidity control (Fig. 2).

Determining acidity and basicity in nonaqueous matricesMonitoring the levels of acidity/basic-ity of the raw polyol products is very important to catalyze the polyurethane reaction and if not correctly monitored can lead to undesired side reactions. The traditional method for determining acid-ity/basicity in a non-aqueous matrix is to utilize KOH/HCl in an alcohol medium respectively in two distinctive titration methods. One of the limitations to this chemistry is the inability to quantitative-ly differentiate between acidity and basic-ity in a single analysis. Further, KOH has

a negative tendency to react with atmos-pheric carbon dioxide to form carbonates and bi-carbonates rapidly distorting its integrity and introducing a special-case variation.

These two limitations were direct factors in METTLER TOLEDO teaming up with Dr. Ross Koile to perfect an analytical test method that not only differentiates acidity from basicity in single test meth-ods but also could yield quantitative lev-els of both while at the same time elimi-nating the undesirable KOH titrant. The importance of this single test method is compounded by the fact that the desired range of acidity/basicity of the raw polyol is usually exactly neutral or marginally acidic.

Simple but very effectiveThe basics of the chemistry are very sim-plistic in nature. A known amount of an atmospherically stable bi-carbonate solu-tion was accurately dispensed and titrat-ed with p-toluenesulfonic acid. If the polyol samples have an excess of H+ ions (sample is acidic) they will react imme-diately with the bi-carbonate dispensed as part of the back titration. This results in the amount of titrant needed to reach

the equivalence point being less than the blank. If the polyol sample has an excess of OH- ions (sample is basic) they will not react with the bi-carbonate dispensed and results in an excess of titrant needed to neutralize the sample.

Defined conditions for the electrodeA key to this analysis is to define neutral-ity. This becomes more convoluted as you move away from the aqueous realm with which the pH electrodes where originally designed. In an aqueous system, an elec-trode filled with KCl as the reference solu-tion should have an isopotential point very close to 0 mV, however, as organi-cally optimal reference solutions are sub-stituted for KCl an isopotential shift can be observed. This phenomenon forces us to define neutrality in non-absolute mV terms. For this analysis, the bi-carbon-ate/carbonic acid couple was chosen to define neutrality. It turns out that this system can be used in a non-aqueous environment – particularly if the solvent is polar.

Balance the sample solubility and electrode performanceNext a suitable solvent must be chosen that the sample is very soluble in and optimal for electrode performance. The sample in this case is a polyether gly-col that is soluble in most alcohols. The larger the alkyl chain of the alcohol (up to a point), the better the solubility of the polyol. The solubility of this mate-rial in methanol is somewhat limited, but ethanol and the propanols are quite good. The problem with ethanol is all the

Uniquely quantifying varying levels of acidity or basicity in polyol samples has traditionally required two different methods utilizing less than desirable titrants with less than optimal results. It is an extremely important production determination as the quality of yield is dependant on the small variances in the results.

Titrimetric analysis of acid or basic polyol samples with only one method

Ch. Hynes Dr. R. Koile

Figure 1: The basic com-ponents of Poly-urethane.

A diisocyanate and a diol. The diisocyanate has two cyanate groups (shown in blue) and the diol has two alcohol groups.

21METTLER TOLEDO UserCom 1/2007 21METTLER TOLEDO UserCom 1/2007

government regulations surrounding its use in the United States of America and the cost of obtaining it in the anhydrous state. Both n-propanol and isopropanol are very good as solvents, but their vis-cosity slows electrode response. The opti-mal solution is to mix equal volumes of methanol and isopropanol. The isopro-panol allows for excellent sample solubil-ity and the methanol reduces the overall solution viscosity so that the electrode will respond in a reasonable time frame. Some longer chain polyols will necessi-tate an extra solubility push for full dis-solution of the sample into solution.

In these cases, Tetrahydrofuran (THF stabilized with butylated hydroxytolu-ene, BHT) is an excellent choice. A very easy way to tell if THF is required is to take a look at the curve in a titration that does not use it. If the sample is not fully dissolved, the curve will be very flat and demonstrate a very shallow inflection. An immediate addition of THF will solve this solubility issue (cf. Figs. 3 a and b).

Good ionic conductivityGood solution ionic conductivity is another key to this analysis when mak-ing potentiometric measurements and if this were an aqueous solution just a salt would be added to the mixture to increase conductivity: however, most ionic salts are not soluble in alcoholic solutions. This being the case Lithium Chloride is very soluble in the lower alcohols and solves the problem. There are other salts that can be used (like a quaternary ammonium salt), but ionic compound is required that will not influ-ence the acid/base balance of this solvent mixture.

Selection of the appropriate titrantThe choice of titrant needs to take into account that the matrix of the sample is of a non-aqueous nature thus should also be non-aqueous. The introduction of an aqueous titrant could make the water content of the final sample/solvent/titrant solution so high that the “leveling” effect

of water could become an issue, which should be limited. The titrant must be an strong acid which needs to be soluble in polar organic solvents. p-Toluenesulfonic acid works quite nicely and is readily available at a reasonable price. As men-tioned earlier, the matrix of the titrant should be non-aqueous to limit water content. Alcohols would be the first logi-cal choice; however, p-Toluenesulfonic acid reacts with alcohols to form esters which drastically affect the stability of the solvent. Thus, an aprotic solvent

would be a better choice as it prevents the esterification reaction leading to greater solution stability. Acetonitrile fits this requirement very well and is opti-mal considering the acid’s solubility as well as the fact it can be purchased in an anhydrous state.

In summary, here is how this measure-ment was made work. First the titration solvent is going to be an equal part mix-ture of methanol and isopropanol (addi-tion of THF in cases of long chain poly-ols or if needed for solubility of sample). This solution is going to be enhanced

with about 0.25 g/L of LiCl and a very small amount of aqueous 0.2 mol/L NaHCO3. The titrant will be 0.005 N p-Toluenesulfonic acid in acetonitrile. The electrode needs to have a fast flow rate filled with Lithium Chloride in etha-nol, as it is most soluble in this matrix. Analytical results can be either positive or negative. Positive results mean the sample is basic and negative results mean the sample is acidic. The sample should be taken and stored in polyethylene bot-tles because this procedure is sensitive enough to detect the leaching of sodium by the sample from ordinary glass.

Figure 2: An example of a Polyurethane-based product

Figure 3: Typical titration curves of the Polyol titration:

3a) sample that is hardly soluble in the solvent mixture – THF to enhance solubility is re-quired,

3b) titration curve obtained with a well adjusted solvent mixture.


Excellent results with the right equipmentThe titration breaks will be quite pro-nounced and easy to see (cf. Fig. 3b). The METTLER TOLEDO DGi116-Solvent electrode was used (cf. Fig. 4). A rela-tive standard deviation (rsd) of 0.2% on blank samples and on samples that were 0.0045 mg KOH/g a rsd of 5.0% was obtained.

This was very promising con-sidering the very low level of acidity. In addition, the testing was done on a 5 mL burette with equivalence points rou-tinely realized at 0.3 mL (vol-ume to the Equivalence Point) which is well outside the opti-mum range of the 5 mL burette. A 95% confidence interval of 1.0 nEq/g (nano equivalent/g) is quite possible with the pro-cedure described. The theory of this titration can be used in additional applications where the level of acidity/basicity needs to be determined.

One of the key attributes of this method is the fact it can be run on the basic model of the Excellence titrators, the T50. Since this is a typical back titration, an addi-tional dosing unit with a 20 mL burette is required. Greater analytical flexibility can be realized by putting this method on either the T70 or T90 units which can handle a total of 4 or 8 burette drives respectively. This added degree of flex-

ibility will allow for both the Acid/Base Balance and Molecular Weight/Hydroxyl number titrations to be on the same instrument as they are both typical back titrations and common analytical test methods required in Polyol production.

Reliable results thanks to automation A second key attribute to optimizing this method is keeping the electrode clean. The Polyol sample had an affinity to stick to the electrode which resulted in decreasing electrode sensitivity over time. A cleaning procedure that includes a THF soaking is strongly recommended. This can be done manually; however, a too much variability from operator to opera-tor was noticed to recommend this as the most effective utilization of resources.

This problem was solved by inserting two conditioning steps into the method and running each sample on the Rondo sam-ple changer. Upon the completion of each sample, the sample changer would soak the electrode in a THF beaker for 30 sec-onds with stirring to facilitate cleaning. Then it would allow the electrode to condi-tion in a 50% isopropanol/50% deionized water solution for 60 seconds. This proved to be a very reliable means to assure the electrode was clean and hydrated at the end of each sample.

Curriculum vitae of Dr. Ross KoileDr. Ross Koile who co-authored this arti-cle received his Ph.D. from Iowa State

University in 1981. He has worked in the chemical industry for 33 years and has specialized in the practical application of analytical research technologies to indus-trial manufacturing operations. Dr. Koile has authored or co-authored over 300 industrial analytical methods such as the measurement of the acid/base balance of organic products at the nanoequiva-lent per gram level and industrial solvent characterization.

He has also taught both organic and inorganic chemistry at the college level, and has taught a problem solving course for the American Chemical Society. He is currently the President of his own chemi-cal consulting firm and a member of the PURMAC (Polyurethane Raw Materials Analysis) committee of the American Chemical Council.

Figure 5: The T50 Excellence titrator with two additional burette drives/burettes for dosing purposes

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Figure 4: The DGi116-Solvent electrode.


To determine the titer, 0.9 to 1.1 g of the primary standard, potassium hydrogen phthalate (KHP), is weighed into a glass titration beaker on an XP205 balance. In this case, glass titration beakers are par-ticularly recommended because problems due to static electricity, for example bal-ance errors, are effectively avoided.

The weight is transferred directly to the series template. The series template was previously stored as a Shortcut on the Excellence Terminal to simplify entries afterward. The number of standards and samples in the template is already defined in the template so that now only the sample weight has to be transferred from the balance. The optimum weights

LabX titration PC softwareGlass titration vessels1 mol/L sodium hydroxide

The system is set up with the titrator and balance connected to the laboratory computer network – the titrator directly and the balance via an e-Link Box.

For an accurate determination of the concentration of the sulfuric acid, it is very important that the concentration of the titrant does not change. The titer determination of the 1 mol/L sodium hydroxide must be performed daily. In the titrant Setup, the expiration date and lifespan can be defined.

For the user, this means that the titrant cannot be used after the defined time has elapsed and that a titer determination is requested.

A warning message appears on the titra-tor screen or in the LabX titration PC software.

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IntroductionFor etching semiconductor structures, it is very important to know whether the sulfuric acid concentration is 9.0 or 9.2% because etching properties can differ quite significantly even with small devia-tions.

This can result in the material being too strongly or insufficiently etched. The danger is then that the desired structure is destroyed or that unwanted material is not completely dissolved away.

The analyst in the laboratory needs an analytical method that fulfills the fol-lowing requirements:

Highly accurate determination of the acid concentration, for example absolute deviations that are <0.2% of the actual valueHigh repeatability (e.g. srel <0.1%)Robustness and easy applicability for routine operation

Furthermore, it must be possible to fully automate the measurement and to evaluate the data using PC software. In practice, the determination can be easily performed using a system consisting of an Excellence titrator, LabX titration PC software and a sensitive pH electrode.

System descriptionT70 Excellence titrator DG111-SC pH electrodeRondo sample changer with 20-position sample rackSP250 peristaltic pumpMETTLER TOLEDO XP205 balance (resolution ±0.0001 g)

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In the semiconductor industry, high demands are put on the accuracy of the concentration of acids used for etching. This article describes how the Excellence titrator can fully automatically perform an accurate determination of the concentration of dilute sulfuric acid and how it is used for routine analysis.

Accurate determination of the concentration of etching acids in the semiconductor industry

C. Schreiner

Figure 1: The titration system used.


of the primary standard and the sulfu-ric acid samples are defined with limits and displayed on the balance and in the series template. The user therefore knows the weight range that is required or per-missible (Fig. 2a and 2b).

Five identical samples are now prepared and the sample weights transferred to the series template (see Table 1). The opti-mum sample weight refers to a 10 mL burette and an optimum consumption of 4 to 6 mL 1 mol/L sodium hydroxide.Afterward, the Rondo sample changer is loaded with series of primary stand-

ards and samples and the measurement started directly at the titrator using the Shortcut.

After this, the titer of the sodium hydrox-ide titration solution is determined in the first method loop. To do this, 60 mL deionized water is pumped by the SP250 peristaltic pump and the solution stirred for 90 s. The titration is performed with 1 mol/L sodium hydroxide to the first equivalence point (EQP). The titer is cal-culated in the calculation function and stored in the intelligent titrant burette. The titer can be viewed as soon as it has been calculated and stored in the Setup under titrant data while the method is running.

The titration of the samples takes place automatically in the second method loop. Once again, 60 mL deionized water is dosed, stirred for 10 s and titrated with

1 mol/L sodium hydroxide up to the first EQP. During the measurement, the indi-vidual menus can be switched as much as desired. Among other things, a new method can be created while a method is running or settings necessary for the next measurement can be made in the Setup without interrupting the current measurement.

After the titration has been completed, the DG111-SC pH electrode, the propel-ler stirrer and the burette tips are thor-oughly cleaned from top to bottom by the PowerShower™ rinsing system. Deionized water supplied by a membrane pump is directed in a sharp stream from sixteen jets arranged in the form of a ring direct-ly onto the accessory during the upward movement out of the titration beaker (Fig. 3).

The rinsing solution is collected in the titration beaker. This practically elimi-nates sample carry-over and improves the quality of the results.

Titration method parametersThe parameters were taken from the standard measurement functions already stored in the titrator and where neces-sary adapted. For titer determination, the standard parameters for an EQP titration (acid/base) of normal application mode were used. In the titrator, and in LabX titration, the most frequently used appli-cations are already stored as templates.

There are also settings already stored for EQP, EP or titrations that allow the user to create new methods easily and effi-ciently. If necessary, the parameters can be adapted to individual requirements and sample properties (see Table 2).

To determine the sulfuric acid concen-tration, the standard parameters for an EQP titration (acid/base) were selected. They were slightly modified after the trial experiments (see Table 2). The dVmax setting, the parameter for the maxi-mum increment of the titrant addition, was reduced to keep the deviation in the

Figure 2a: Balance display with sample weight, limits and sample ID, titrator terminal display of the cor-responding series template .

Figure 2b: Titrator terminal display of the cor-responding series template.

Concentration of sulfuric acid [%]

Sample weight [g]

5 3.9 – 5.9

10 2.0 – 3.0

15 1.3 – 2.0

20 1.0 – 1.5

Table 1: Optimum sample weights for sulfuric acid determination.

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automatically stored in the RFID chip of the burette. This reduces errors and the new titer is already taken into account in the next determination. Furthermore, all entries can be made via the titrator and LabX titration where the data is stored and archived..

The data can be evaluated in an office PC if LabX titration is installed in a client-server configuration.

mathematical evaluation of the curve as small as possible. This has a very large influence with these small concentration differences.

The mode was changed from Normal to User to do this. The titrant additions are performed dynamically in both methods and the measured value acquisition is equilibrium controlled.

Discussion and summaryExcellent results were obtained for the sulfuric acid concentration in series of six sulfuric acid samples. The results deviate only 0.01% from the actual val-ue and show excellent repeatability of 0.047% (see Table 3).

The high demands of the semiconduc-tor industry for the determination of the concentration of sulfuric acid are com-pletely satisfied.

The system can be automated with the Rondo sample changer to such a level that the user has only to prepare the samples and start the measurement with a single click via the Shortcut. In the titer determination, the titer is afterward

Figure 3: PowerShower™ in action.

Parameter Unit Titer method Concentration of sulfuric acid method

Titrant addition Dynamic

dE mV 8.0

dV min mL 0.005

dV max mL 0.05 0.02

Mode Equilibrium controlled

dE mV 1

dt s 1

t min s 3

t max s 30 20

Mode Acid/Base User

Sample Concentration [% (g/100g)]

Titer s srel [%]

n

KHP 0.99849 0.00151 0.152 5

Sulfuric acid 9% 8.99 -- 0.0042 0.047 6

Table 2: Titration method parameters for the determination of ti-ter and sulfuric acid concentration.

Table 3: Results


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Do difficult samples necessarily mean difficult measurements?Samples from the cosmetics industry represent one of the greatest challenges for pH measurement. Very often, sample consistency alone is enough to increase the difficulty of measurement quite con-siderably, for example if one thinks of highly viscous samples such as creams and gels. Furthermore, these care prod-ucts are usually based on oily or fatty basic substances. This adds to the prob-lems still further (Fig. 1).

In addition, products such as hair dyes or hair tinting lotion contain coloring com-ponents, partly as microfine pigments, which can accumulate in the diaphragm of electrodes.

If one looks at the different samples as a whole, it becomes clear that measure-ments must cover a very large pH range because the pH of some samples can be quite low (acidic) or quite high (alka-line). All the properties mentioned above for samples from the field of cosmetics can have a negative affect on the accu-racy, reproducibility and duration of the measurement. At the same time, high accuracy and reliability in the determination of pH is

essential for cosmetic products because the end-user ultimately applies these products to his skin.

Special samples need tailormade solutions …METTLER TOLEDO recently had the opportunity to tailor-make a pH sensor to measure samples from the cosmetics branch. The project was carried out in coopera-tion with a well-known cosmetics manu-facturer. The specific problems associated with this product segment were carefully analyzed and possible solutions consid-ered based on previous experience with our existing range of electrodes.

The availability of real samples from a wide range of products that have to be measured on a daily basis in laboratories of the cosmetic branch meant that a very targeted and practical approach could be taken. The numerous measurements per-formed allowed valuable experience to be gained on analytical problems that occur in daily laboratory practice.

The first thing that became apparent from the measurements was the wide pH range exhibited by the different samples. Samples with a pH of 1.8 in the acidic range or 12.7 in the alkaline range had not been expected in cosmetic products. Practice proved otherwise!

For this reason, there was a clear tenden-cy right from the outset to use HA glass for the development of sensor prototypes because this type of glass shows good lin-earity even at high pH.

The second problem was the blocked dia-phragm. Further measurements showed that this was in fact the main problem.

Ready? Steady? Force!It soon became clear that a new approach was needed to overcome these difficul-ties. The basic idea was to achieve a con-stant and permanent flow of electrolyte solution through the diaphragm because as long as the diaphragm is flushed with electrolyte it cannot be blocked by sam-ple substance. This idea was realized by incorporating an internal pressure sys-tem in the electrode.

This generated a permanent overpres-sure in the reference chamber and thus provided a constant outflow of electrolyte from the reference system. The technol-ogy has been perfected to such an extent that a constant outflow of electrolyte is achieved throughout the entire lifetime of the sensor. The system is referred to as the SteadyForce™ reference system. It has now become an important part of the electrode portfolio, for example in the METTLER TOLEDO InLab®Viscous and InLab®Power electrodes.

Performance strengths become apparent in routine operationTo make sure the newly developed pro-totypes prove their performance in daily laboratory work, there was only one solu-tion: to perform and document as many measurements as possible.

To obtain meaningful measurement results, the repeatability of 15 measure-ments for each sample and measurement

Most problems that arise in the determination of the pH of a sample have to do with particular sample properties such as viscosity, stickiness, or the presence of microparticles. This makes it impossible to develop a standard electrode that can measure all possible samples equally well and effectively. The following article describes the approach adopted to develop a customerspecific solution for the measurement of difficult samples in the cosmetics segment.

Tailormade laboratory electrodes for pH measurement in difficult products

M. Hefti

Figure 1: Shower gels and shampoos are relatively easy to measure; with sun cream (rear beaker) things become more difficult.


instrument was first determined. In addi-tion, the reproducibility was checked with a series of 9 measurements performed by different laboratory technicians. A total of four hundred measurement values were obtained for each sensor tested, which resulted in a total of about two thousand measurements (each with the recorded measurement times).

To process and evaluate such a large flow of data required electronic acquisition of individual measurements. This was very easily and efficiently accomplished with the LabX direct pH PC software. The flexibility of the software even allowed the results to be directly import-ed into MS EXCEL® so that all the data was already in the right format for evalu-ation (see Table 1).

Summary Two new sensors have been developed based on experience with existing sensor types. They are known as the InLab®Viscous and the InLab®Semi-Micro. Both sensors are ideally suited for samples from the cosmetics industry and can be regarded as “specialists” for this particular field. Their special properties also make them very advantageous for the measurement of samples from other areas such as paints, lacquers, resins, butter, or similar products.

The InLab®Viscous is easy to maintain, easy to clean and extremely resistant to contamination due to the special con-struction of the diaphragm in connection with the SteadyForce™ system. It is there-fore the ideal sensor for really difficult samples such as sticky, highly viscous, or colored substances.

The InLab®Semi-Micro provides results that are often equally as good as those obtained for many samples using the InLab®Viscous. It is, however, more suit-able for easier samples and for the meas-urement of small sample quantities or measurements in small or narrow neck vessels. With its A41 glass, it is also par-ticularly good for biological samples.

Care must, of course, be taken with color-ed samples because the XEROLYT®EXTRA polymer of the reference system tends to become colored. However, this was not found to influence the measurement results.

These two new electrodes are excellent examples that show how innovative ideas can be developed and put into practice through close cooperation with custom-ers (Fig. 2).

Figure 2: The InLab® Viscous and the InLab® Semi-Micro sur-rounded by samp-les from the cosme-tics branch.

Face lotion

Acceptable pH range: from pH 3.50 to pH 4.10

Measurement InLab®412 InLab® Viscous

InLab® SemiMicro

1 3.823 3.802 3.832

2 3.827 3.801 3.814

3 3.842 3.807 3.853

4 3.856 3.814 3.830

5 3.876 3.808 3.884

6 3.856 3.794 3.826

7 3.865 3.799 3.823

8 3.854 3.801 3.810

9 3.861 3.798 3.808

10 3.865 3.798 3.823

11 3.877 3.798 3.827

12 3.872 3.807 3.828

13 3.836 3.803 3.822

14 3.860 3.809 3.823

15 3.863 3.797 3.879

Mean value 3.856 3.802 3.832

s 0.017 0.006 0.023

srel [%] 0.432 0.145 0.590

Highest result 3.877 3.814 3.884

Lowest result 3.823 3.794 3.808

± from mean value 0.027 0.010 0.038

Mean measurement time 00:46 00:38 00:59

Table 1: Excerpt from the data obtained.


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New Plug & Play sensorsA comprehensive range of titration elec-trodes consisting of 17 Plug & Play pH glass, platinum and silver sensors is now available. The sensors cover the entire applications spectrum from routine pH measurements to specialist titrations in difficult sample matrices.

The sensor chip in the electrode head stores all relevant data such as electrode type, serial number, and calibration data with monitoring of expiration date and lifespan. The data is automatically read into the titrator Setup when the sensor is connected. This requires no user interac-tion and ensures that only the right sen-sor with valid sensor data is used.

The new Plug & Play sensors are fully compatible with old and new firmware versions of the Excellence titrators. To use the new Plug & Play functionality, only the latest titrator and sensor board firmware need to be sent to the titrator and a new electrode cable connected. No costly hardware changes are necessary – it couldn’t be easier!

Everything is under control with LabX titration 2.6The new version of the LabX titration soft-ware offers numerous improvements to the Titration Excellence line. All instal-

lation, preparation and analysis tasks can now be performed from the PC and are therefore tracked in the Audit Trail. All resources such as titrants, calibration and titrant standards, reagents, auxil-iary or blank values as well a pumps and peripheral instruments can be edited in the PC and printed.

Plug & Play sensors or burettes are auto-matically recognized and all relevant data is sent to LabX where it is moni-tored with regard to the lifespan and the expiration date of the calibration or titer determination.

Version 2.6 therefore fully supports com-pliance with the requirements of FDA 21 CFR Part 11 due to the comprehensive user and group manager and other secu-rity features. This ensures that only users with the appropriate rights are allowed to perform changes.

A new step in twophase surfactant titration: the DS800TwoPhaseThe new DS800 TwoPhase sensor is a real breakthrough in the potentiometric two-phase titration of anionic and cationic surfactants according to DIN EN 14480 and other standards.

The electrode offers a real alternative to the established Epton method with short-er titration times as well as excellent result quality thanks to high accuracy and precision.

Toxic hazards are eliminated because poisonous chloroform is no longer used. All types of ionic surfactants can be titrated directly in the emulsion without having to wait for phase separation.

Instant documentation with the compact RSP26 printerThe RS-P26 printer delivers GxP-com-pliant printouts on thermally stable and lightfast paper. The RS-P26 has a foot-print of only 203 x 120 mm!

The new version 2.0 firmware offers complete Plug & Play functionality for sensors, burettes, burette drives and accessories as well as new functionality and even easier operation. Together with the new LabX titration version 2.6 PC software as well as numerous new innovative accessories, titration has never been so simple, efficient and secure.

As simple, efficient and secure as possible: Titration Excellence Version 2.0


New functionalities and simpler operating proceduresThe Excellence line titrators now com-municate in Russian and Polish, several burettes can be rinsed at the same with the press of a button, sample series can be interrupted at any time, modified and continued without loss of the sample series information. Two methods running in parallel can be elegantly synchronized using the result buffer. The new version 2.0 firmware offers this and much more.

Flexible automation of large sample batches with the Rondo 30With the new Rondo 30 sample changer, up to 30 samples can be titrated directly in 80 mL polypropylene titration beakers with just a single click. Reliable results are obtained with single sample deter-minations and in sequences of different series of samples.

This is facilitated by the very effective PowerShower™ rinsing system, as well as by numerous conditioning possibili-ties on the sample rack. There are hardly any limits to flexibility in applications: up to three semi-micro electrodes can be used for all aqueous acid/base, Redox, or precipitation titrations. Even complex automated processes can be easily solved with the intuitive method editor of the Excellence titrators both on the terminal and with the LabX titration version 2.6 PC software.

Everything for the automated titration: the Rondo sample changerRondo 30 is a powerful example of the modular Rondo sample changer plat-form. Six different Rondo configurations can be set up to solve specific automation application problems:

Rondo 12: Direct titration of large sample volumes in 250 mL polypropyl-ene titration beakers as well as 400 and 600 mL standard glass beakers.Rondo 15: Direct titration of medium to large sample volumes in 150 or 250 mL standard glass beakers.Rondo 20: The all-rounder for the highest level of automated flexibility for the direct titration of medium sized series of up to 20 samples in 100 mL polypro-pylene or glass titration beakers.Rondo 30: The flexible Rondo system for titrations of large sample series of up to 30 samples in 80 mL polypropylene beakersRondo 60: The sample delivery system for fully automatic sampling of up to six-ty samples in standard test tubes in com-bination with the SU24 sampling unit.Rondo 60 plus: Everything the Rondo 60 can do plus direct pH measurement in up to 60 samples in standard test tubes, separated from the titration.

For more Information: www.mt.com/titration

Rondo 12

Rondo 15

Rondo 20

Rondo 30

Rondo 60

Rondo 60 plus


metic, biological, and many other labo-ratories and production facilities.

Reliable solutions for the No. 1 problem in pH measurementMETTLER TOLEDO offers a number of solutions for the problem most commonly encountered in pH measurement, namely

New

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Amazing functionalityFive measurement parameters: pH, mV (Redox), conductivity, TDS and salt contentAutomatic calibration with automatic buffer recognitionAutomatic or manual temperature compensationData storage in the portable meter for 30 measurements

Intuitive operationLarge, well-organized display that simultaneously shows readings, temperature, endpoint criteria and helpful iconsSelf-explanatory buttons for easy starting and ending a measurement or calibrationSaving and accessing measurement and calibration data at the press of a button

Useful accessoriesElectrode arm for the bench meter can be mounted on the left or the rightElectrode clip and wrist straps are supplied standard with every portable meterQuick guide – laminated just in case of splashesHandy carry bag with room for meter, electrode, buffer pack, sample bottles, operating instructions, quick guide and replacement batteries

The entry-level meters of course come with METTLER TOLEDO quality for reliable measurements and are backed by over 50 years of sensor know-how.

Learn more about these products at: www.mt.com/pH

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The compact FiveEasy™ bench meters and the portable splashprotected FiveGo™ meters are ideal for anyone who needs a simple, easytouse instrument but nevertheless rapid and reliable measurement results.

FiveGo™ and FiveEasy™ – the easy and inexpensive entry into the world of electrochemistry

Figure 1: FiveGo™ pH

Figure 2: FiveEasy™ pH

Practically for every industry and applicationThe new models complete the InLab® portfolio and broaden the spectrum of applications. These range from routine measurements to specialist applications in chemical, pharmaceutical, food technology, cos-

The new sensors all have appropriate names, and combine innovative technologies and glassblowing tradition for rapid pH and Redox measurements. Their high precision and reliability coupled with low maintenance make these sensors the ideal choice for a wide range of applications.

Rapid and reliable results – the new generation of InLab® sensors sets new standards


the contaminated reference diaphragm. Whether you prefer the tried and tested ARGENTHAL™ reference system, the XEROLYT® polymer electrolyte technolo-gy or the new revolutionary SteadyForce™ reference system, the choice is yours.

Viscous samples – no problem for the revolutionary InLab®ViscousThe InLab®Viscous was specially devel-oped for pH measurements in high-ly viscous and sticky samples. The

In the quest for better food products, sugar content (Brix) plays a crucial role for determining the best harvesting time and assessing the quality of food ingredi-

ents. Quick-Brix™ is very easy to operate, rugged and splash-proof and fits into any coat pocket.

Farmers determine the Brix value directly in the orchard, vineyard or field and can therefore harvest products at exactly the right time. This improves the quality of the fresh produce and influences subse-quent processes such as vinification.

In food or drink production, Quick-Brix™ is used in incoming goods reception, to determine the quality of ingredients such as fruit juice, concentrate, jam or honey before a consignment is unloaded from

the delivery vehicle. During production it may serve to control the sugar con-centration in mixtures before bottling or packaging and in final quality control to analyze random samples.

Quick-Brix™ combines ease of use and ruggedness required by the food indus-try with METTLER TOLEDO quality and precision.

For more information: www.mt.com/quickbrix

SteadyForce™ reference system guar-antees a constant outflow of electrolyte even in the greasiest and stickiest of samples, such as cosmetics, paints, or resins. Highly viscous and sticky sam-ples are now no problem at all with the InLab®Viscous.

Would you like to know more about our new high performance electrodes?

Visit us at: www.mt.com/quickbrix

Fruit and vegetable farmers, as well as juice and food manufacturers appreciate the new METTLER TOLEDO QuickBrix™ portable Brix meters.

Fabulous Food –a matter of QuickBrix™

www.mt.comFor more information

The application chemists of the Analytical Chemistry market support group have prepared several publications and a series of application brochures to support customers in their routine work in the laboratory. Each brochure is dedicated either to a particular branch of industry (such as paper, petroleum and beverages), a particular titrator or a specific analysis technique. The following list shows all the publications together with their order numbers. They are available from your local METTLER TOLEDO marketing organization.

Publications, reprints and applications German English

Basics of Titration 51725008Fundamentals of Titration 704152 704153Applications Brochure 1 Customer Methods 724491 724492Applications Brochure 2 Various Methods 724556 724557

Applications Brochure 3 TAN/TBN 724558 724559Applications Brochure 5 Determination in Water 51724633 51724634Applications Brochure 6 Direct measurement with ISE 51724645 51724646Applications Brochure 7 Incremental Techniques with ISE 51724647 51724648Applications Brochure 8 Standardization of titrants I 51724649 51724650Applications Brochure 9 Standardization of titrants II 51724651 51724652Applications Brochure 11 Gran evaluation DL7x 51724676 51724677Applications Brochure 12 Selected Applications DL50 51724764 51724765Applications Brochure 13 Nitrogen Determination by Kjeldahl 51724768 51724769Applications Brochure 14 GLP in the Titration Lab 51724907 51724908Applications Brochure 15 Guidelines for Result Check 51724909 51724910Applications Brochure 16 Validation of Titration Methods 51724911 51724912Applications Brochure 17 Memory card “Pulp and paper” 51724915Applications Brochure 18 Memory card “Standardization of titrants” 51724916 51724917Applications Brochure 19 Memory card “Determination in Beverages” 51725012 51725013Applications Brochure 20 Petroleum 51725020Applications Brochure 22 Surfactant Titration 51725014 51725015Applications Brochure 23 KF Titration with DL5x 51725023Applications Brochure 24 Edible oil and fat 51725054Applications Brochure 25 Pharmaceutical Industry 51710070 51710071Applications Brochure 26 METTLER TOLEDO Titrators DL31/38 * 51709854 51709855Applications Brochure 27 KF Titration with Homogenizer 51725053Applications Brochure 32 METTLER TOLEDO Titrators DL32/39 51725059 51725060Applications Brochure 33 METTLER methods for DL15, DL22 F&B and DL28 51725065Applications Brochure 34 Selected METTLER TOLEDO Methods for

Titration Excellence T50, T70, T9051725066

Applications Brochure 36 Selected METTLER TOLEDO Methods for Biofuel Analysis

51725070

Applications Brochure KF Chemical 724353 724354Applications Brochure KF Food, Beverage, Cosmetics 724477 724478Applications Brochure KF 10 DL35 Applications 724325 724326Applications Brochure DL12 724521Applications Brochure DL18 724589 724590Applications Brochure DL25 724105 724106Applications Brochure DL25 Food 51724624 51724625Applications Brochure DL25 Petro / Galva 51724626 51724627Applications Brochure DL25 Chemical 51724628 51724629Applications Brochure DL70 Gold and Silver 724613

* Also available in French (51709856), Spanish (51709857) and Italian (51709858)

Publications

Editorial boardMETTLER TOLEDO AG, AnalyticalSonnenbergstrasse 74CH-8603 Schwerzenbach, SwitzerlandPhone ++41 44 806 7711Fax ++41 44 806 7240Internet : www.titration.net

Authors L. Candreia, I. Orlov / D. Chirkin, S. Vincent P. Wyss, Dr. C. De Caro, Dr. T. Hitz, C. Hynes / Dr. R. Koile, C. Schreiner, M. Hefti

MettlerToledo AG, AnalyticalPostfach, CH-8603 SchwerzenbachPhone ++41 44 806 73 87Fax ++41 44 806 72 60

©11/2007 Mettler-Toledo AG MarCom Analytical, ME-51724610Printed in Switzerland

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