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है”ह”ह

IS 15302 (2003): Determination of Aluminium and Barium inWater by Direct Nitrous Oxide-Acetylene Flame AtomicAbsorption Spectrometry [FAD 14: Drinks and CarbonatedBeverages]

IS 15302:2003

Indian Standard

DETERMINATION OF ALUMINIUM ANDBARIUM IN WATER BY DIRECT NITROUS

OXIDE-ACETYLENE FLAME ATOMICABSORPTION SPECTROMETRY

ICS 13.060.50

0 BIS 2003

BUREAU OF IN DIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARC

NEW DELHI 110002

April 2003 Price Group 2

Drinks and Carbonated Beverages Sectional Committee, FAD 14

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the brinks andCarbonated Beverages Sectional Committee had been approved by the Food and Agriculture DivisionalCouncil.

This standard is based on direct nitrous oxide-acetylene flame atomic absorption spectrometry to detect microquantities of aluminium and barium in waters. This method is used for the determination of these elements inpackaged waters (packaged natural mineral water as per IS 13428 and packaged drinking water as perIS 14543). In the preparation of this standard, considerable assistance has been derived from standard methodsfor the examination of water and wastewater published by American Public Health Association, Washington,USA, 20th edition, 1998.

In reporting the result of a test or analysis made in accordance with this standard, if the final value, observedor calculated, is to be rounded off, it shall be done in accordance with IS 2: 1960 ‘Rules for rounding offnumerical values (revised)’.

IS 15302:2003

Indian Standard

DETERMINATION OF ALUMINIUM ANDBARIUM IN WATER BY DIRECT NITROUS

OXIDE-ACETYLENE FLAME ATOMICABSORPTION SPECTROMETRY

1 SCOPE

This standard prescribes the determination ofaluminium and barium in bottled water by DirectNitrous Oxide-Acetylene Flame Method

2 APPARATUS

2.1 Atomic Absorption Spectrometer and As-sociated Equipment

2.1.1 Atomic Absorption Spectrometer

Consisting of a light source emitting the line spectrumof an element (hollow-cathode lamp or electrodelessdischarge lamp), a device for vaporizing the sample(usually a flame), a means of isolating an absorptionline (monochromator or filter and adjustable slit), anda photoelectric detector with its associated electronicamplifying and measuring equipment.

2.1.2 Burner

The most common type of burner is a premix, whichintroduces the spray into a condensing chamber forremoval of large droplets. The burner is to be fittedwith a special head for use with nitrous oxide andacetylene.

2.1.3 Readout

Most instruments are equipped with either a digital ornull meter readout mechanism. Most moderninstruments are equipped with microprocessors orstand-alone control computer capable of integratingabsorption signals over time and linearizing thecalibration curve at high concentrations.

2.1.4 Lamps

Use either a hollow-cathode lamp or an electrodelessdischarge lamp (EDL). Use one lamp for each elementbeing measured. Multi-element hollow-cathode lampsgenerally provide lower sensitivity thansingle-el.ement lamps. EDLs take a longer time towarm up and stabilize.

2.1.5 Pressure-Reducing Valves

Maintain supplies of fuel and oxidant at pressuressomewhat higher than the controlled operating

pressure of the instrument by using suitable reducingvalves. Use a separate reducing valve for each gas.

2.1.6 Vent

Place a vent about 15 to 30 cm above the burner toremove fumes and vapors from the flame. Thisprecaution protects laboratory personnel from toxicvapors, protects the instrument from corrosive vapors,and prevents flame stability from being affected byroom drafts. A damper or variable-speed blower isdesirable for modulating air flow and preventing flamedisturbance. Select blower size to provide the air flowrecommended by the instrument manufacturer. Inlaboratory locations with heavy particulate airpollution, use clean laboratory facilities such ascommercially available .Iaminar-flow, clean-airbenches or custom-designed work stations andanalyze blanks that reflect the complete procedure.

2.2 Nitrous Oxide Burner Head

Use special burner head as suggested inmanufacturer’s manual. At roughly 20 min intervalsof operation it may be necessary to dislodge the carboncrust that forms along the slit surface with a carbon rodor appropriate alternative.

2.3 T-junction Valve or Other Switching Valve

For rapidly changing from nitrous oxide to air, so thatflame can be turned ‘ON’ or ‘OFF’ with ?ir as oxidantto prevent flashbacks.

3 REAGENTS

3.1 Air

Cleaned and dried through a suitable filter to removeoil, water and other foreign substances. The sourcemay be a compressor or commercially bottled gas.

3.2 Acetylene, Standard Commercial Grade

Acetone, which always is present in acetylenecylinders, can be prevented from entering anddamaging the burner head by replacing a cylinderwhen its pressure has falleti to 689 kPa ( lOOpsi)acetylene.

1

IS 15302:2003

3.3 Metal-Free Water

Use metal-free water for preparing all reagents andcalibration standards and as dilution water. Preparemetal-free water by deionizing tap water andlor byusing one of the following processes, depending on themetal concentration in the sample: single distillation,redistillation or sub-boiling. Always check deionizedor distilled water to determine whether the element ofinterest is present in trace amounts.

Note — The source water contains Hg or other volatile metals,single m redistilled water may not be suitable for trace analysisbecause these metals distill over with the distilled water. In suchcases, use sub-boiling toprepare metal-free water.

3.4 Hydrochloric Acid, HC1-lN,50p ercentandcone.

3.5 NitricAcid,HNOs—cone.

3.6 Sulfuric Acid, H2S01— Onepercent v/v.

3.7 Hydrofluoric Acid, HF, lN

3.% Nitrous Oxide (Commercially AvailableCylinders)

Fit nitrous oxide cylinder with a special nonfreezableregulator or wrap a heating coil around an ordinaryregulator to prevent flashback at the burner caused byreduction in nitrous oxide flow through a frozenregulator. (Most modern atomic absorptioninstruments have automatic gas control systems thatwill shut down a nitrous oxide-acetylene flame safelyin the event of a reduction in nitrous oxide flow rate).

Caurion — Use nitrous oxide with strict adherence tomanufacturer’s directions. Improper sequencing of gas flows atstartup and shutdown of instrument can produce explosions fromflashback.

3:9 Potassium Chloride Solution

Dissolve 250 g KC] in water and dilute to

3.-10 Aluminium Nitrate Solution

Dissolve 139 g A1(N03)3.9H20 in 150

000 ml.

ml water.

Acidify slightly with cone HN03 to preclude possiblehydrolysis and precipitation. Warm to dissolvecompletely. Cool and dilute to 200 ml.

3.11 Standard Metal Solutions

Prepare a series of standard metal solutions in theoptimum concentration ranges by appropriate dilutionof the stock metal solutions with water containing1.5 ml cone. HNOJ/1. Stock standard solutions areavailable from a number of commercial suppliers.Alternatively, prepare as described in 3.11.1and 3.11.2.

3.11.1 Aluminium

Dissolve 0.100 g ahtminium metal in an acid mixtureof 4 ml 1 + 1 HC1 and 1 ml cone. HNOJ in a beaker.Warm gently to effect solution. Transfer to a 1 Iitreflask, add 10 ml 1+1 HCI, and dilute to 1000 ml withwater; 1.00 ml = 100 ~g alttminium.

3.11.2 Barium

Dissolve 0.1516 g BaClz (dried at 250° for 2 h), inabout 10 ml water with 1 ml 1 + 1 HC1, add 10.0 ml1+ 1 HCI and dilute to 1000 ml with water; 1.00 ml =100 pg barium.

4 PROCEDURE

4.1 Sample Preparation

Required sample preparation depends on metal formbeing measured. When determining aluminittm orbarium, mix 2 ml KC1 solution into 100 ml sample orstandard before aspiration. Drinking water, may beanalyzed directly by atomic absorption spectroscopyfor total metals without digestion. On collectionacidify such samples to pH<2 with concentrated nitricacid (1.5 ml HNOS is usually adequate for drinkingwater) and analyze directly, For further verification orif changes in existing matrices are encountered,compare digested and undigested samples to ensurecomparable results. The digestion procedure isoutlined in Annex A.-For all samples, make certain thatthe concentrations of acid and matrix modifiers are thesame in both samples and standards.

4.2 Instrument Operation

Because of differences between makes and models ofatomic absorption spectrometers, it is not possible toformulate instructions applicable to every instrument.See manufacturer’s operating manual. In general,proceed as prescribed in 4.2.l-to 4.2.4.

4.2.1 Install a hollow cathode lamp for the desiredmetal in the instrument and roughly set the wavelengthdial according to Table 1. Set slit width according tomanufacturer’s suggested setting for the elementbeing measured. Turn on instrument, apply to thehollow cathode lamp the current suggested by themanufacturer, and let instrument warm up until energysource stabilizes, generally about 10 to 20 min.Readjust current as necessary after warm-up.Optimize wavelength by adjusting wavelength dialuntil optimum energy gain is obtained. Align lamp inaccordance with manufacturer’s instructions.

I2

IS 15302:2003

Table 1 Atomic Absorption Concentration Range with Direct Aspiration Atomic Absorption(Ckwse4.2.1)

Element Wavelength, nm Flame Gases Instrument Detection Sensitivity, OptimumLimit, mg/1 miiM Concentration Range,

(1)m@

(2) (3) (4) (5) (6)

Al 309.3 N-Ac 0.1 1 5-ltNlBa 553.6 N-Ac 0.03 0.4 1-20

4.2.2 After adjusting wavelength, install a nitrousoxide burner head. Turn on acetylene (without ignitingflame) and adjust flow rate to value specified bymanufacturer for a nitrous oxide-acetylene flame, turn‘OFF’ acetylene. With both air and nitrous oxidesupplies turned ‘ON’, set T-junction valve to nitrousoxide and adjust flow rate according to manufacturer’sspecifications. Turn switching valve to the air positionand verify that flow rate is the same. Turn acetyleneon and ignite to a bright yellow flame. With a rapidmotion, turn switching valve to nitrous oxide. Theflame should have a red cone above the burner. If itdoes not, adjust fuel ffow to obtain red cone. Afternitrous oxide flame has been ignited, let burner cometo thermal equilibrium before beginning analysis.

4.2.3 Aspir:ite a blank consisting of deionized watercontaining 1.5 ml concentrated HNOJl and checkaspiration rate. Adjust if necessary to a rate between 3and 5 ml/min. Zero the instrument. Aspirate astandard of the desired metal with a concentration nearthe midpoint of the optimum concentration range andadjust bu]mer (both horizontally and vertically) in thelight path to obtain maximum response. Aspirate blankagain and re-zem the instrument. The instrument nowis ready to run standards and samples.

4.2.4 To extinguish flame, turn switching valve fromnitrous oxide to air and turn off acetylene. Thisprocedure eliminates the danger of flashback that may

occur on direct ignition or shutdown of nitrous oxideand acetylene.

4.3 Standardization

Select at least three concentrations of standard metalsolutions (prepared as in 3.11) to bracket the expectedmetal concentration of a sample. Aspirate each in turninto the flame and record absorbance. MOSI modeminstruments are equipped with microprocessors anddigital readout which permit calibration in directconcentration terms. If instrument is not so equipped,prepare a calibration curve by plotting on linear graphpaper absorbance of standards versus concentration.Plot calibration curves for aluminium and barium,based on original concentration of standard beforeadding KCI solution.

4.4 Analysis of Samples

Rinse atomizer by aspirating water containing 1.5 mlcone. HNO#l and zero instrument. Atomize a sampleand determine its absorbance.

5 CALCULATIONS

Calculate concentration of each metal ion in pg/1 byreferring to the appropriate calibration curve preparedaccording to 4.3.

Alternatively, read the concentration directly from theinstrument readout if the instrument is so equipped. Ifsample has been diluted, multiply by the appropriatedilution factor.

3

IS 15302:2003

ANNEX A

(Clause 4.1)

NITRIC ACID DIGESTION

A-1 APPARATUS

A-1.l Hot Plate

A-1.2 Conical (Erlenmeyer) Flasks (125 ml) orGriffin Beakers (150 ml, acid washed and rinsed withwater)

A-1.3 Volumetric Flasks — 100 ml.

A-1.4 Watch Glasses — Ribbed and unnbbed.

A-2 REAGENT

A-2.1 Nitric Acid, HNOS -Concentrated analytical

or trace metal grade.

A-3 PROCEDURE

Transfer a measured volume (100 ml recommended)of well-mixed, acid preserved sample appropriate forthe expected metal concentrations to a flask or beaker.In a hood, add 5 ml concentrated HN03. If a beaker is

used, cover with a ribbed watch glass to minimizecontamination. Boiling chips, glass beads, or Hengargranules may be added to aid boiling and minimizespatter when high concentration levels are beingdetermined. Bring to a slow boil and evaporate on ahot plate to the lowest volume possible (about 10 mlto 20 ml) before precipitation occurs. Continue heatingand adding concentrated HNOJ as necessary untildigestion is complete as shown by a light coloured,clear solution. Do not let sample dry during digestion.

Wash down flask or beaker walls and watch glasscover ( if used ) with metal-free water and then filterif necessary. Transfer filtrate to a 100 ml volumetricflask with two 5 ml portions of water, adding theserinsings to the volumetric flask. Cool, dilute to mark,and mix.thoroughly. Take portions of this solution forrequired metal determinations.

Bureau of Indian Standards

BIS is a statutmy institution established under the Bureau of Indian Standards Act, 1986 to promote

harmonious development of the activities of standardization, marking and quality certification of goodsand attending to connected matters in the country.

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BIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.

Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standards

should ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of‘B1S Cataiogue’ and ‘Standards: Monthly Additions’.

This Indian Standard has been developed from Doc : No. FAD 14( 1323).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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