Qualitative analysis: Identifying the components of a sample ...

Qualitative analysis: Identifying the components of a sample

Quantitative analysis: Measuring the amounts or concentrations of analytes in a sample

The three measurement terms of “analysis”, “determination”, and “characterization”have different meanings.

Analysis = Qualitative and quantitative characteristics of chemical analytes

Determination = Quantitative measurements of specific analytes

Characterization = Experimental description of properties of materials

©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

Steps in an Analysis

Define the Problem Select a Method Obtain a Representative Sample

Prepare the Sample for AnalysisPerform Any Necessary

Chemical SeparationsPerform theMeasurement

Data Processingand Report

1. Define the Problem

Factors:

• What is the problem--what needs to be found? Qualitative and/orquantitative?

• What will the information be used for? Who will use it?

• When will it be needed?

• How accurate and precise does it have to be?• How accurate and precise does it have to be?

• What is the budget?

• The analyst (the problem solver) should consult with the client to plana useful and efficient analysis, including how to obtain a usefulsample.

2. Select a Method

Factors:

• Sample type

• Size of sample

• Sample preparation needed

• Concentration and range (sensitivity needed)

• Selectivity needed (interferences)• Selectivity needed (interferences)

• Accuracy/precision needed

• Tools/instruments available

• Expertise/experience

• Cost

• Speed

• Does it need to be automated?

• Are methods available in the chemical literature?

• Are standard methods available?

3. Obtain a Representative Sample

Factors:

• Sample type/homogeneity/size• Heterogeneity of sample composition increases from the fairly

homogeneous gas and liquid samples to solid samples that must be groundup prior to dissolution.

• Analysis of grains from crops (rice, wheat, etc.) requires dehusking to yieldmeaningful data.meaningful data.

• Milling and blending are usually parts of the sample preparation procedures.

• Sampling statistics/errors• The quality of analytical data must support the measurement objectives and

hence the sampling procedures have to satisfy statistical requirements ofthe analysis.

• The number of samples or sample size, the frequency and time of sampling,and the location of sampling have to be consistent with the analyticalobjectives.

4. Prepare the Sample for Analysis

Factors:

• Solid, liquid, or gas?

• Dissolve?

• Ash or digest?

• Chemical separation or masking of interferences needed?

• Need to concentrate the analyte?• Need to concentrate the analyte?

• Need to change (derivatize) the analyte for detection?

• Need to adjust solution conditions (pH, add reagents)?

5. Perform Any Necessary Chemical Separations

Factors:

• Distillation

• Precipitation

• Solvent extraction

• Solid phase extraction

• Chromatography (may be done as part of the measurement step as inthe hyphenated techniques of GC-MS or LC-MS)

• Electrophoresis (may be done as part of the measurement step as inCE-MS and microfluidics)

6. Perform the Measurement

Factors:

• Calibration• Instruments must be properly calibrated according to analytical protocols; for

instance, the wavelength scale of a spectrometer has to be verified with a standard;all sample preparation equipment from the balances to sample extraction devicesmust also be checked or calibarated

• Validation/controls/blanks• Validation/controls/blanks• Suitable matrix blanks, trip blanks, lab control standards must be analyzed to

support the sample measurements.

• Replicates• Appropriate number of replicates meeting the analytical statistical confidence is

necessary.

7. Data Processing and Report

• Conversion of raw instrumental signals into meaningful results ofchemical identification and determination

• Interpretation of data by correlating chemical parameters of analytes (formulamass, functional groups, etc.) with observed signals (energies of spectral peaks ,retention times of chromatographic peaks, etc.)

• Calibration plot of standards at various concentrations is used to determinequantitative results of sample constituents.

• Statistical analysis of quantitative results (reliability)• Accuracy – Results for standard reference materials (SRMs) from National Institute

Standards and Technology

• Precision – Relative standard of deviation or coefficient of variation

• Blanks, correlation coefficients of calibration plots, spike recovery, detectionlimits, and etc.

• Relating qualitative and quantitative results to the objectives ofanalyses (i.e. how C-14 results are used to determine the age of anarchaeological artifact or whether an art piece is authentic).

The sample size dictates what measurement techniques can be used.


Classification of Analytical MethodsClassical methods

• Gravimetry

• Titrimetry

Instrumental methodsInstrumental methods

• Electroanalytical

• Spectroscopy

• Chromatography

• Radioisotopic measurements

Different methods provide a range of precision, sensitivity, selectivity,and speed capabilities.


Types of Instrumental Methods

Configuration of Instrumentation

Instrument or Process

Control Diagnostics DataProcessing

Raw data

Processed data(Information)

Machine-level commands

Analyst

User InterfaceExplanation(Knowledge)

User-levelcommands

IntegratedComputers

Intelligent System

OutputDevice

(Information)High-levelcommands

Components of a Typical Instrument

Analytical

Electricalor

mechanicalinput

Meteror

Scale

Signalgenerator

Inputtransducer

ordetector

Analyticalsignal

Signalprocessor

inputsignal

12.301

Outputsignal Recorder

Digitalunit

Some Examples of Instrument Components

Selecting an Analytical Method

1. What accuracy and precision are required?

2. How much sample is available?

3. What is the concentration range of the analyte?

4. What components of the sample will cause

Defining the problem:

4. What components of the sample will causeinterference?

5. What are the physical and chemical properties ofthe sample matrix?

6. How many samples are to be analyzed?

Validation involvesdetermining:

•selectivity

•linearity

•accuracy

•precision

•sensitivity

•range

•limit of detection

General process for evaluation/validation of methodology

•limit of quantitation

•ruggedness/robustness

Standard referencematerials (SRMs) best fordetermining accuracy.


Other Characteristics to BeConsidered in Choosing a Method

1. Speed of analysis

2. Ease of use and automation

3. Cost and availability of instrument3. Cost and availability of instrument

4. Per-sample cost (consumables and reagents)

5. Training and learning curve

6. Software features and compatibility withdatabases and data processing programs

COMPONENTS OF A QUALITY CONTROL

PROGRAM

QualityControl

Suitable andwell

maintainedfacilities

Maintainedand well

calibratedequipment

GMP

Welltrained

personnel

GLP Control GMP

CompleteDocumentat

ion

EvaluationSamples

GLP

SOP

IMPORTANT PROCEDURES IN QUALITY CONTROL

Measured parameter Procedure

Accuracy Analysis of reference materials or samplesof know concentration

Precision Analysis of replicate samples

Extraction efficiency Analysis of matrix spikes

Contamination Analysis of blanks

Steps in the analyticalprocess

Contamination sources

Sample collection Equipment, Sample handling steps such as compositing, orfiltering, Sample preserving additives, Sample containers,Ambient contamination

Sample transport and storage Sample containers, Cross contamination from ear reagents orother samples

POTENTIAL SOURCES OF SAMPLE CONTAMINATION

Sample preparation Sample handling, Dilutions, Glassware, Ambientcontamination

Sample analysis Instrument memory effects or carry-over, Reagents, Syringes,Glassware, Apparatus

Blank type Purpose Process

System or Instrument blank Establishes the baseline of an analyticalinstrument, in the absence of sample

Determine the background signal withno sample present

Solvent or Calibration blank To measure the amount of the analytical signalwhich arises from the dilution solvent. The zerosolution in the calibration series.

Analytical instrument is run withdilution solvent only

Method blank To detect contamination from reagents, samplehandling, and the entire analytical process

A simulated sample containing noanalyte is taken through entireanalytical procedure

TYPES OF ANALYTICAL BLANKS FOR QUALITY CONTROL

analytical procedure

Matched-matrix blank To detect contamination from field handling,transportation, or storage

A synthetic sample which matches thebasic matrix of the sample is carried tothe field and is treated in the samefashion as the samples

Sampling media or tripblank

To detect contamination in sampling media suchas filters and sample adsorbent traps

Analyze samples of unused filters ortraps to detect contaminated batches

Equipment blank To determine contamination of equipment andassess the efficiency or equipment clean-upprocedures

Samples of final equipment cleaningrinses are analyzed for contaminants

Metals Regulatorylevel (mg/l)

Pesticides Regulatorylevel (mg/l)

Other organics Regulatorylevel (mg/l)

Arsenic 5 Chlordane 0.03 Benzene 0.07

Barium 100 2,4-D 1.4 Chloroform 0.07

Cadmium 1 Endrin 0.003 Cresol 10

Chromium 5 Lindane 0.06 1,4- 10.8

REGULATORY LEVELS OF TCLP CONTAMINANTS

Chromium 5 Lindane 0.06 1,4-Dichlorobenzene

10.8

Mercury 0.2 2,4,5-TP(Silvex)

0.14 Pentachlorophenol

3.6

Lead 5 Heptachlor 0.001 Trichloroethylene 0.07

Silver 5 Methoxychlor 1.4 TolueneVinyl chloride

14.40.05

Compound Regulatory concentration Averaging period

Ozone 0.12 ppm 1h

Carbon monoxide 35 ppm9 ppm

1h8h

Nitrogen dioxide 0.05 1 year

Sulfur dioxide 0.14 ppm 24h

REGULATORY LEVELS FOR AMBIENT AIR POLLUTANTS

Sulfur dioxide 0.14 ppm0.03 ppm

24h1 year

Particulate matter 150 µg/m3

50 µg/m3

25 µg/m3

24h1 year24h

Sulfates 25 µg/m3 24h

Vinyl chloride 0.01 ppm 24h

Lead 1.5 µg/m3 3 months

You can’t have accuracy without good precision.

But a precise result can have a determinate or systematic error.

Accuracy and precision


Figures of Merit for Precision of Analytical Methods

The precision becomes poorer at low concentrations.

(Also sometimes at high concentrations, as in spectrophotometric measurements–see spectrometric error, Fig. 16.27.)

Dependence of relative standard deviation on concentration©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

Random errors follow a Gaussian or normal distribution.

We are 95% certain that the true value falls within 2σ (infinite population),IF there is no systematic error.

Normal error curve (Gaussian Curve)©Gary Christian,Analytical Chemistry,6th Ed. (Wiley)

Bias

Bias = m - xi

where m => population mean

xi => measured concentration

Sensitivity

2 factors limiting sensitivity:

• slope of calibration curve

– steeper slope, greater sensitivity– steeper slope, greater sensitivity

• reproducibility of measurements

– equal slope, better reproducibility, greatersensitivity

Sensitivity

IUPAC defined calibration sensitivity

S = mc + Sbl

where S => measured signalwhere S => measured signal

c => concentration of the analyte

Sbl => instrumental signal for blank

m => slope of calibration line

ignores precision

Sensitivity

analytical sensitivity => g

g = m/ss

where ss =>standard deviation of the signals

advantages:

- relatively insensitive to amplification factors- relatively insensitive to amplification factors

- independent of units

disadvantage:

- standard deviation of signal can vary withconcentration

Detection Limit & Quantitation Limit

Instrumental detection limit refers to the minimumconcentration or weight of analyte that can bedetected at a known confidence level and isusually defined as being equivalent to 3 times theusually defined as being equivalent to 3 times thesignal background noise or the 3s-level.

Method or practical quantitation limit refers to thelevel at which reliable quantitative analysis canbe performed and is commonly defined at 9s to15s levels.

Detection Limit

minimum distinguishable analytical signal => Sm

Sm = Sbl + ksbl

where Sbl => mean blank signal

k => some multiple (normally 3)k => some multiple (normally 3)

sbl => absolute standard deviation of the blank

measure 20-30 blanks over extended period oftime to determine Sbl and sbl

detection limit => cm = (Sm - Sbl)/m

SNR=17

SNR= 5

SNR=2.8

100 ms, 50 um slit

10 ms, 50 um

10 ms, 20 um

Raman spectra of Calcium ascorbate

400 600 800 1000 1200 1400 1600 1800 2000

SNR=2.8

SNR < 2

10 ms, 20 um

10 ms, 10 um

Raman shift, cm-1

0.1 sec*

1.0 sec

Signal averaging improves S/N

400 600 800 1000 1200 1400 1600 1800 2000

Raman shift, cm-1

30 sec

* spectra were accumulated for period indicated

Linear Dynamic Range

LOL

Inst

rum

ent

resp

onse

Useful range

LOQInst

rum

ent

resp

onse

Concentration

LOQ => limit of quantitativemeasurement

LOL => limit of linearresponse

Selectivity

degree to which a method is free frominterference by other species contained inthe matrix

S = mAcA + mBcB + mCcC + SblS = mAcA + mBcB + mCcC + Sbl

where S => analytical signal

cA, cB, cC=> concentrations of A, B, and C,

mA, mB, cC => calibration sensitivities of A, B, and C,respectively, slope of calibration curve

Sbl => instrumental signal of blank

SelectivitykB,A = mB/mA and kC,A = mC/mA

where kB,A => selectivity coefficient forB with respect to A

k => selectivity coefficient forkC,A => selectivity coefficient forC with respect to A

yielding

S = mA(cA + kB,AcB + kC,AcC) + Sbl

The units ppm or ppb are used to express trace concentrations.

These are weigh or volume based, rather than mole based.


m m

m

m m

This is a time plot for analysis of the same sample, assumed to have only

there is a 1 in 20 chance a value will exceed this only by chance.

This is a time plot for analysis of the same sample, assumed to have onlyrandom distribution, to check for errors in a method.

At 2s, there is a 1 in 20 chance a value will exceed this only by chance.At 2.5s, it is 1 in 100.

Typical quality control chart


Select a confidence level (95% is good) for the number of samples analyzed (N).

Confidence limit = x ± ts/√N.

It depends on the precision, s, and the confidence level you select.


You compare the variances of two different methods to see if there is a

F = s12/s2

2

You compare the variances of two different methods to see if there is asignificant difference in the methods at a given confidence level.


QCalc = outlier difference/range.

If QCalc > QTable, then reject the outlier as due to a systematic error.


The median may be a better indicator of the true value than the mean for

And the range times a factor (K) may be a better measure of spread than the

The median may be a better indicator of the true value than the mean forsmall numbers of observations.

And the range times a factor (K) may be a better measure of spread than thestandard deviation (sr = RKR).


A least-squares plot gives the best straight line through experimental points.

Exel will do this for you.

Straight-line or Linear Regression Plot

©Gary Christian,Analytical Chemistry,6th Ed. (Wiley)

Purpose How Performed Usage Application Examples

Removal of interferences Interferences are allowed to passunretained through the cartridge withanalytes remained sorbed, or analytespass through the cartridge, withinterferences remaining on the cartridge

50% Removal of proteins from biological fluids,fats and lipids from food, ionic compoundsfrom aqueous samples and drugs of abusefrom urine, and extractions of dioxans fromwaste water.

Analyte Concentration Conditions are chose to achieve strongretention values (retentive stationaryphase/ weak mobile phase); elution in asmall volume of volatile organic solvent.

35 Trace enrichment of ppb of polynucleararomatics from water, trace pesticides inurine, caffeine from beverages, andtherapeutic drugs from plasma.

Phase exchange Analyte present in emulsion, suspension, 5 Exchange of aqueous solvent for

Main Purposes of Solid Phase Extraction

Phase exchange Analyte present in emulsion, suspension,or undesirable solvent is sorbed on SPEcartridge, dried, and eluted with desiredsolvent

5 Exchange of aqueous solvent fornonaqueous one with intermediate drynitrogen flush.

Solid-phase derivatization Specifically coated SPE phasesselectively derivatize analytes as theypass through the cartridge.

5 2,4-dinitrophenyl hydrazine-coatedcartridges that selectively derivatizecarbonyl-containing compounds; aminesand polyamines in air; organic acids inwater.

Sample storage andtransport

Vapor or liquid samples are collected atfactory or in field on an SPE cartridge ordisk and transported to laboratory.

5 Soil gas analysis; trace organics in water.

Parameter Sonication Soxhlet

(traditional)

Soxhlet

(modern)

SFE ASE (ESE) Microwave-Assisted(closed

container)

Microwave-Assisted (open

container)

Sample size, g 20-50 10-20 10-20 5-10 5-15 2-5 2-10

Solventvolume, ml

100-300 200-500 50-100 10-20* 10-15 30 20-30

Temperature,°C

Ambient-40 40-100 40-100 50-150 50-200 100-200 Ambient

Pressure Atmospheric Atmospheric Atmospheric 2000-4000 psi 1500-2000 psi 1500-2000 psi Atmospheric

Comparison of Extraction Methods for Sample Preparation of Solids

Time, hr 0.5-1.0 12-24 1-4 0.5-1.0 0.2-0.3 0.2-0.3 0.1-0.2

Degree ofAutomation**

0 0 ++ +++ +++ ++ ++

Number ofSamples***

High 1 6 44 24 12 12

Cost§ Low Very low Moderate High High Moderate Moderate

* When organic modifier is used to effect polarity

** For the most complete commercial instrument;0= no automation, += some automation, ++= mostly automated, ++= fully automated

*** Maximum number that can be handled in commercial instruments

§ Very low = < $1000, Low= $10,000, Moderate= $10,000-20,000, High= > $20,000

Method of Sample Principles of Technique Comments

Accelerated(enhanced) solventextraction (ASE orESE)

Sample is placed in a sealed containerand heated to above its boiling point,causing pressure in vessel to rise;extracted sample is automaticallyremoved and transferred to vial forfurther treatment

Greatly increased speed of liquid-solid extraction process and isautomated. Vessel must withstand high pressure; extracted samplein diluted form requires further concentration; safety provisions arerequired.

Automated Soxhletextraction

A combination of hot solvent leachingand Soxhlet extraction; sample inthimble is first immersed in boilingsolvent then thimble is raised forSoxhlet extraction with solvent

Manual and automated versions are available; uses less solvent thantraditional Soxhlet and solvent is recovered for possible reuse.Extraction time is decreased due to two-step process.

Modern Extraction Methods for Solid Samples

Soxhlet extraction with solventrefluxing.

Supercritical fluidextraction (SFE)

Sample is placed in flow-throughcontainer and supercritical fluid (suchas CO2) is passed through sample; afterdepressurization, extracted analyte iscollected in solvent or trapped onadsorbent, followed by desorption byrinsing with solvent.

Automated and manual versions are available; to affect "polarity"of supercritical fluid, density can be varied and solvent modifiersadded. Collected sample is usually concentrated and pure becauseCO2 is removed after extraction; matrix has an effect on extractionprocess.

Microwave-assistedextraction (MASE)

Sample is placed in an open or closedcontainer and heated by microwaveenergy, causing extraction of analyte.

Extraction solvent can range from microwave-absorbing (MA) ornon-microwave-absorbing (NMA); in MA case, sample is placed inhigh-pressure, non-microwave-absorbing container and heated wellabove its boiling point. Also in MA case, the sample and solventcan be refluxed at atmospheric pressure, analogous to solid-liquidextraction, in NMA case, container can be open, with no pressurerise, safety provisions are required.

Method of Sample Principles of Technique Comments

Accelerated(enhanced) solventextraction (ASE orESE)

Sample is placed in a sealed containerand heated to above its boiling point,causing pressure in vessel to rise;extracted sample is automaticallyremoved and transferred to vial forfurther treatment

Greatly increased speed of liquid-solid extraction process and isautomated. Vessel must withstand high pressure; extracted samplein diluted form requires further concentration; safety provisions arerequired.

Automated Soxhletextraction

A combination of hot solvent leachingand Soxhlet extraction; sample inthimble is first immersed in boilingsolvent then thimble is raised forSoxhlet extraction with solventrefluxing.

Manual and automated versions are available; uses less solvent thantraditional Soxhlet and solvent is recovered for possible reuse.Extraction time is decreased due to two-step process.

Modern Extraction Methods for Solid Samples

refluxing.

Supercritical fluidextraction (SFE)

Sample is placed in flow-throughcontainer and supercritical fluid (suchas CO2) is passed through sample; afterdepressurization, extracted analyte iscollected in solvent or trapped onadsorbent, followed by desorption byrinsing with solvent.

Automated and manual versions are available; to affect "polarity"of supercritical fluid, density can be varied and solvent modifiersadded. Collected sample is usually concentrated and pure becauseCO2 is removed after extraction; matrix has an effect on extractionprocess.

Microwave-assistedextraction (MASE)

Sample is placed in an open or closedcontainer and heated by microwaveenergy, causing extraction of analyte.

Extraction solvent can range from microwave-absorbing (MA) ornon-microwave-absorbing (NMA); in MA case, sample is placed inhigh-pressure, non-microwave-absorbing container and heated wellabove its boiling point. Also in MA case, the sample and solventcan be refluxed at atmospheric pressure, analogous to solid-liquidextraction, in NMA case, container can be open, with no pressurerise, safety provisions are required.

Parameter Sonication Soxhlet

(traditional)

Soxhlet

(modern)

SFE ASE (ESE) Microwave-Assisted (closed

container)

Microwave-Assisted (open

container)

Sample size, g 20-50 10-20 10-20 5-10 5-15 2-5 2-10

Solventvolume, ml

100-300 200-500 50-100 10-20* 10-15 30 20-30

Temperature,°C

Ambient-40 40-100 40-100 50-150 50-200 100-200 Ambient

Pressure Atmospheric Atmospheric Atmospheric 2000-4000psi

1500-2000 psi 1500-2000 psi Atmospheric

Time, hr 0.5-1.0 12-24 1-4 0.5-1.0 0.2-0.3 0.2-0.3 0.1-0.2

Comparison of Extraction Methods

Time, hr 0.5-1.0 12-24 1-4 0.5-1.0 0.2-0.3 0.2-0.3 0.1-0.2

Degree ofAutomation**

0 0 ++ +++ +++ ++ ++

Number ofSamples***

High 1 6 44 24 12 12

Cost§ Low Very low Moderate High High Moderate Moderate

* When organic modifier is used to effect polarity

** For the most complete commercial instrument;0= no automation, += some automation, ++= mostly automated, ++= fully automated

*** Maximum number that can be handled in commercial instruments

§ Very low = < $1000, Low= $10,000, Moderate= $10,000-20,000, High= > $20,000

Sample

Solid Liquid

Organic

Extraction Methods for Various Types of Samples and Analytes

OrganicAnalytes

SupercriticalFluid

Extraction

AcceleratedSolvent

Extraction

SoxhletExtraction

UltrasonicExtraction

Metals

MicrowaveDigestion

AcidDigestion

OrganicAnalytes

Solid PhaseExtraction

Solid PhaseMicro-

extraction

Liquid/liquidExtraction

Dissolved Metals

Chelation/OrganicExtraction

Ion Exchange SolidPhase Extraction

Compound Absorbing solution Analytical method Range Interferences

Ammonia Dilute sulfuric acid React with phenol to form blueindenophenol, Colorimetricmeasurement

20-700micrometers/m3

LOD 0.2micrometers/ml insolution

Some metal ions(EDTA prevents someinterference)

Nitrogendioxide

Triethanol amine, o-methyl-phenol, sodiummetabisulfite

React with sulfanilamide and 8-anilino-1-naphthalenesulfonicacid- colorimetric measurement

20-700micrometers/m3

HNO2, N2O3

Sulfurdioxide

Sodiumtetrachloromercurate

React with formaldehyde andpararosaniline, Colorimetric

500 ml/m3 to 10micrometers/m3

None (note hightoxicity of abs. soln)

METHODS FOR ANALYSIS OF AIR POLLUTANTS BY IMPINGER METHODS

dioxide tetrachloromercurate pararosaniline, Colorimetricmeasurement

micrometers/m toxicity of abs. soln)

Phosgene 4-(4’-nitro-benzyl)pyridine indiethylphthalate

Colorimetric measurement Down to 40microliters/m3

Acid chlorides, highhumidity

Chlorine Methyl orange at pH3 Bleaching of the methyl orange ismeasured colorimetrically

Down to 1 ml/m3 inair. 5-100micromoles/ 100 mlof soln

Free bromine, SO2,NO2, (used for Clspills, in emergences)

Ozone andoxidizers

Buffered KI soln I3 formed is measuredcolorimetrically

0.01-10 ml/ m3 inair

NO2

Acrolein 4-hexyl-resorcinol in ethylalcohol and trichloroaceticacid

Colorimetric measurement Down to 0.01ml/m3 in air

Dienes (slight)

Compound Range Description Interference

Mercury vapor 0.1-2mg/m3

Hg reacts with CuI reagent to give ayellow-orange complex

Cl2 gives lowreadings

Carbonmonoxide

5-150ml/m3

CO reacts with iodine pentoxide giving I2,and a preconditioning layer removeshalogenated hydrocarbons, benzene, etc.

Acetylene willinterfere

EXAMPLES OF COLORIMETRIC AIR SAMPLING TUBES

Ozone 0.05-1.4ml/m3

Blue indigo dye is cleaved and bleached towhite

Cl2 and NO2 whenpresent above 5ml/m3 will turnindigo gray

Sulfur dioxide 0.5-5ml/m3

SO2 react with blue complex of I2 andstarch, changing to white

H2S will makeindicator gray

Tetrachloro-ethylene

5-50 ml/m3 First layer contains MnO4- which cleavesthe analyte forming Cl2, which reacts insecond layer with N,N’-diphenylbenzidineto give a gray-blue product

Free halogens,hydrogen halidesand easily cleavedhalocarbons

Sorbent Useful for Desorption method

Tenax (polyphenylene oxide) Nonpolar VOC with BP fromapprox. 40-200 ̊C

Thermal desorption

Carbon molecular sieve C2-C5 hydrocarbons Thermal desorption

Activated charcoal Low to medium boiling polarand nonpolar organics

Solvent extraction

SORBENT MATERIALS FOR AIR SAMPLING

Polyurethane foam Polar and nonpolarsemivolatile compounds

Solvent extraction

Activated silica Amines and polar organics Solvent extraction

Graphitized carbon C4 to C14 hydrocarbons,heavy organics such as PCBs

Thermals desorption, Solventdesorption

XAD-2 resin Semivolatiles, PAH Solvent desorption

Analyte Color system Measurement wavelength(nm)

Metals

Cr (VI) 1,5-Diphenylcarbazide 540

Pb Dicyclohexyl-18-crown-6-dithizone 512

Fe(III) Thiocyanate 460

Fe(II) Pyrocatecol violet 570

Cd Iodide/Malachite green 685

Hg 2-Pyridylketone 2-quinolylhydrozone

SOME COMMON COLORIMETRIC REAGENTS

Hg 2-Pyridylketone 2-quinolylhydrozone

Organics

Phenol 1-nitroso-2-napthol/Ce(IV)

Inorganic Ions

NO2- TiCl3/sulfanilamide 530

SO42- Fe(III)/HClO4 355

CN- Isonicotinic acid, 3-methyl-1-phenyl-2-pyrazoline-5-one

548

Gases

O3 KI 352

NH3 Glutamate dehydrogenase 340

Candidates for electrochemical detection: Biomedical

Acetylcholine* Neutral phenols

Amino acids* Nitrosothiols

Benzoic acids Oxalate

Cinnamic acids Peptides*

Coenzymes Phenylpropionic acids

DNA adducts Phenylpyruvic acidsDNA adducts Phenylpyruvic acids

Enzymes Thiols and disulfides

Estrogenic hormones Tryptophan metabolites

Glucose* Tyrosine metabolites

Lactic acid* Vitamins

Mandelic acids

* Require chemical or enzymatic derivatization before detection.

Bromide Nitrite

Cyanide Sulfite

Candidates for electrochemical detection: Ions

Alkaloids Disulfides

Analgesics L-DOPA and related

Candidates for electrochemical detection: Pharmaceutical

Analgesics L-DOPA and relatedcompounds

Antibiotics Nitrogen heterocycles

Anticancer Phenothiazines

Antimalarial Thiols

β-mimetics and β-blockers Tricyclic antidepressants

Environmental and Industrial

Analines Herbicides

Antioxidants Naphthols

Aromatic amines PCB metabolites

Candidates for electrochemical detection:

Aromatic amines PCB metabolites

Biphenyls Peroxides

Chelating agents Pesticides

Ethylenethiourea Phenols

Explosives

Typical Functional Groups

Oxidizable Reducible

Aromatic amines Aliphatic nitro

Ascorbic acids Aromatic nitro

Hydroquinones Azo compounds

Indoles AzomethineIndoles Azomethine

Phenols Nitrosamines

Phenothiazenes N-oxides

Thiols Organometallics

Vanillyl Peroxides

Xanthines Quinones and Thioamides

Standard Calomel Reference Electrodes of the Type //KCl/MCl(satd.)/M

MCl/M KCl E˚’ at 25˚C25

D(E˚’)dt

(mV deg-1 at25˚C)

AgCl/Ag 3.5 M (at 25˚C) 0.205 -0.73

Saturated 0.199 -1.01Saturated 0.199 -1.01

Hg2Cl2/Hg 0.1 M (at 25˚C) 0.336 -0.08

1.0 M (at 25˚C) 0.283 -0.29

3.5 M (at 25˚C) 0.250 -0.39

Saturated 0.244 -0.67

Electrode Type ConcentrationRange

Interferences

Ammonia Gas sensing 1-5 X 10-7 M Volatile Amines

Chloride Solid state 1-5 X 10-5 M OH-, S-2, Br-, I-, CN-

Fluoride Solid state Saturated to 0.02 ppm OH-

Lead (Pb+2) Solid state 0.1-10-6 M Ag+, Hg+2, Cu+2, high

EXAMPLES OF ION-SELECTIVE ELECTRODES

Lead (Pb+2) Solid state 0.1-10-6 M Ag+, Hg+2, Cu+2, highCd+2 or Fe+

Oxygen Gas sensing 0-14 ppm

Silver or Sulfide Solid state 1-10-17 M (Ag+ or S-2) Hg+2

Water hardness (M+2) Liquid membrane 1-6 X 10-6 M Na+, Cu+2, Zn+2, Fe+2,Ni+2, Sr+2, Ba+2, K+

Calcium (Ca+2) Liquid membrane 1.0-5 X 10-7 M Pb+2, Na+, Hg+2, H+,Fe+2, NH4, Mg+2

Relative Sensitivity of Some Electrochemical Techniques

Technique Limit of Detection forPb(II)

Ion selective electrode 10-5 M

DC polarography at DME 10-6 M

Differential pulsepolargraphy at SMDE

10-7 Mpolargraphy at SMDE

Differential pulse ASV atHMDE

10-10 M*

DC ASV at mercury film 10-11 M*

Square-wave ASV atmercury film

10-12 M*

* Deposition for 360 seconds; LOD varies with deposition time;S(H)MDE = (hanging)mercury drop electrode

Qualitative analysis: Identifying the components of a sample ...

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