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IS 13270 : 1992

Indian StandardTESTFORGASESBYORSATANDCHROMATOGRAPHICMETHODS-

METHODS

UDC 54327 : 54354

@ BIS 1992BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

( Reaffirmed 2003 )

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Environmental Protection Sectional Committee, CHD 012

FOREWORDThis lcdian Standard wzs sdopted by the Bureau of Indian Standards, after the draft finalized bythe Environmental Protection Sectional Committee had been approved by the Chemical DivisionCouncil.Orsat analysis and chromatographic gas analysis are ccmmonly used. Each one has someadvantages and disadvantages. These are listed below:

Orsat Analysis Chromatographic AnalysisAdvantagesGasometric ( volumetric procedures ) Gas chromatographic analysis1 The equipment required is relatively simple.

2 It does not require any calibration.3 When the analysis is done on an infrequentbasis, it is very useful.4 Simple to operate.

Disadvantages1 Errors may be due to collection storage andhandling of samples.2 Unless special care is taken in the collec-

tion of samples contamination by airoccurs.3 Mercury is an ideal confining liquid/fluidbecause of the solubility of all gases in it.Rut practically it cannot be used due togreat density and cost. Hence saturatedsalt/water is used for ordinary purposes.4 It cannot measure concentrations of gasesbelow 0 2 percent.

1 It has a great advantage of speed.2 A gas analysis can be completed in fewminutes.3 It can be used for low range.

4 The method is suitable for continuousanalysis, as the instrument needs calibra-tion before use.1 Instrument must have been previouslycalibrated for each gas of interest.2 The oven must have reached a constant

temperature and the detector must begiving stable response.3 It is very difficult to carry instrument tothe site. If the sample is collected in gasholder or any other equipment, collection,storage or handling becomes a problem.

4 It requires inert gas cylinder.

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

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I ndian St andardIS 13270 : 1992

TESTFORGASESBYORSATANDCHROMATOGRAPHICMETHODS-

METHODS SCOPE 4.3 Interferences

prescribes the following twomethods for determination of various gases likexygen, carbon monoxide, carbon dioxide,nitrogen, hydrocarbon, etc, present in gaseousmixtures:a) Orsat analysis, andb) Gas chromatographic analysis.

In case of dispute the gas chromatographicmethod shall be the refree method.2 REFERENCESThe Jndian Standards listed below are thenecessary adjuncts to this standard:

I S No. T i t l e1070 : 1977 Water for general laboratory use( second revision )4167 : 1980 Glossary of terms relating to airpollution.3 TERMINOLOGYFor the purpose of this standard, definitionsgiven in IS 4167 : 1980 shall apply.4 ORSAT ANALYSIS4.1 PrincipleSample gas is contacted successively by a seriesof chemically reactive solutions. Each solutionremoves a specific constituent of the sample gasmixture with the corresponding decrease in gasvolume at each step representative of the volumeof the specific gas removed. A levelling bulbis used to adjust all gas volume measurementsto atmospheric pressure. Ordinarily, the ana-lysis is apphed in the field using the portable,orsat apparatus to determine the volume com-position of carbon monoxide, carbon dioxide,-oxygen_, and unsaturated hydrocarbons in thegaseous emission from combustion processes.Results are usually expressed in volume percentof each component gas. Methane and ethaneshall be determined by fractional combustionand nitrogen is calculated by difference.4.2 Range and SensitivityThe limit of detection for each component isgiven as 02 percent of the total volume basedon a 1000 ml sample.

Errors due to physical absorption can beminimized by proper air-solution contact allow-ing at least 3 minutes as contact time for properequilibrium. Otherwise, no interference isobserved from components of ordinary com-bustion air at levels normally encountered.Negligible interference results from the presenceof hydrogen sulphide, sulphur dioxide and acidgases which are absorbed by the caustic solutionand reported as carbon dioxide.4.4 Apparatus4.4.1 The apparatus shall consist of theconventional orsat type in which volumes aremade comparable by pressure temperaturecompensator, with a manometer interposedbetween the compensating tube and burette.4.4.2 Buret teThe burette employed shall have a 600 mmlength of the graduated section with a volumeof 100 ml, graduated at 02 ml intervals, eachgraduation to be separated by a distance of12 mm. The burette shall be calibrated byweighed volumes of mercury and shall beaccurate to within 01 ml/100 ml delivery andto 002 ml for each 10 ml intervals. A glasslevelling bulb is connected with rubber tubingto the burette.4.4.3 PipetteGas absorption pipettes are placed followingthe gas measuring burette as given in 4.4.3.4to 4.4.3.6.4.4.3.1 A bubbling pipette containing potassiumhydroxide.

CAUTION : AVOID CONTACT TO SKlNAND EYES4.4.3.2 A bubbling ~pipette containing activatedsulphuric acid.

CAUTION : AVOID CONTACT WITHSKIN AND EYES4.4.3.3 A distributing tip pipette containingalkaline pyrogallol solution.4.4.3.4 A slow combustion pipette with plati-num spiral.4.4.3.5 A bubbling pipette containing potassiumhydroxide solution. ( Duplicate of 4-4-3-1).

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IS132:0:19924.4.3.6 distributing tip pipette containingalkaline pyrogallol solution ( Duplicateof 4.4.3.3 ).4.4.3.7 These pipettes must possess smoothsurface which will not entrap gas bubbles, acdshall be so sufficient as to absorb the followinggases from the sample after the required numberof contacts with reagents.

Gas Number of Contactswith ReagentsOxygen 4 to 5Carbon dioxide 3Unsaturated hydrocarbons 3

4.4.4 ManometerThe apparatus shall be of reproducibility ofmeasurement of 002 ml per single contact or005 ml on three successive contacts using thesame reference gas or air.4.5 Reagents4.5.1 uality of ReagentsUnless specified, otherwise, pure chemicals anddistilled water ( see IS 1070 : 1977 ) shall beemployed in tests.

NOTE - Pure chemicals shall mean chemicalsthat do not contain impurities shich affect theresults of analysis.4.5.2 Potassium Hydroxide Solution SaturatedIn 200 ml of distilled water, dissolve solidpotassium hydroxide until excess potassiumhydrcxide remains. Cool the saturated solutionto at least 3C below lowest expected tempera-ture at which analysis will be carried out.Decant and store the supernate liquid.45.3 Activated Sulphuric AcidConcentrated sulphuric acid containing silversulphate or vanadium pentoxide.4.5.4 Alkaline Pyrogallol SolutionDissolve 17 g of pyrogallol crystals in 100 ml ofpotassium hydroxide solution ( 4.5.2 ). Storeunder rcfregeration in a glass-stoppered bottle.4.5.5 Acidic Copper (II) Chloride SolutionDissolve 450 g of copper (II) chloride in 2 500 mlof hydrochloric acid ( relative density 118 ). Ifthis solution appears greenish or black in colourafter preparation strips or turnings of coppershall be added to the solution until a straw-yellow coloured liquid is produced on standing.Store solution over copper turnings or wire.

4.5.6 Sodium Hydrate Asbestos AbsorbentUsed when an unusually accurate measure ofcarbon dioxide is required. This absorbent mayalso be used to remove sulphur dioxide fora more accurate determination of unsaturatedhydrocarbons.4.5.7 Saturated Salt Solution - 75 percent.Contains 30 g of sodium chloride or sodiumsulphate or both, 5 ml of hydrochloric acid,2 drops of methyl red per 100 ml of distilledwater.4.6 Procedure4.6.1 Analysis with Portable Apparatus forCarbon Dioxide Oxygen and Carbon MonoxideThe portable orsat apparatus is fitted with ametal or wooden carrying case and uses ashortened form of burette with three gas absorb-ing pipettes. In order, starting from the burette,the pipettes are filled with potassium hydroxide,pyrogallol and cuprous chloride solution res-pectively. After filling the above pipettes to theengraved mark with the above solutions andbefore starting the test adjust the level of eachto atmospheric pressure using the levelling bulb.Open the stopcock of the burette to the atmos-phere. Raise the levelling bulb until the burettefills to the stopcock with salt water ( saturated).Connect the stopcock -of the burette to theatmosphere to be sampled or to a sample con-tainer and fill the burette with sample gas bylowering the levelling bulb until the meniscusof the water level reads the desired volume inthe burette ( I,). Open the stopcock connectingthe burette to manifold of the absorbing systemand also open the stopcock of the potassium-hydroxide pipette. Pass the gas contained inthe burette into the potassium hydroxid pipetteby first raising and then lowering the levellingbottle. Repeat until three to five full contactshave been made. Return the remainder of thegas sample to the burette using the levellingbulb-until the level of potassium hydroxidesolution returns to the engraved mark, and withthe pipette stopcock closed, again, adjust thewater level in the burette to atmospheric pres-sure using the levelling bulb. Measure thevolume V, of the remaining gas and record thepercent carbon dioxide as follows:

Carbon dioxide, percentage = loo ( \- Va )1

Similarly, oxygen is removed from the remaininggas volume V, by passing this gas into thepyrogallol solution in the second pipette.Measurement of the remaining volume, V, isused to calculate the percent oxygen as follows:Oxygen, percent = 100 ( V, - Vs )V1

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IS 13270 1992Carbon monoxide is measured by mnnipulatingthe remaining gas volume V3 as done previouslyto admit this sample into the pipette containingcopper (II) chloride. However, before returningthe gas volume V, to the burette for measure-ment, volume V4 % passed once into the potas-sium hydroxide pipette to remove any hydro-chloric acid vapours evolved from copper (II)chloride.

Carbon monoxide, = 100 ( V, - V4 )percent Vl4.6.2 Anal ysis by Const ant Pr essure Vol umet ryIn the laboratory bench apparatus the burette isfilled with mercury and enclosed in a waterjacket. The pipettes are connected to theburette by a manifold and a bubbling pipettecontaining sulphuric acid ( 4.4.3.2 ) is usedtogether with a slow combustion pipette (4.4.3.4)which is equipped with a separate levelling bulb.Pipettes (4.4.3.5 and 4.4.3.6 ) are added to thesystem. Results of both absorption andcombustion analyses are reported.4.6.3 Removal of Gases by Absorpt i on Anal ysisTransfer 95 to 100 ml of the sample gas $0 theburette allowing 2 to 3 minutes for attainingtemperature and humidity equilibrium. Usingthe leveling bulb bring the sample volume toatmospheric pressure and read the exactvolume VI .4.6.3.1 Remov al of carbon di oxi de ( or aci d gases )Displace the gas sample into the manifold andthen transfer into the potassium hydroxidepipette. Return the sample gas to the burette.Then contact the potassium hydroxide pipettetwice, finally returning the sample to the buretteand allowing 2 to 3 minutes before equilibratingthe sample to atmospheric pressure with theleveling bulb. Then read the volume V,.4.6.3.2 Remov al of amsat urat ed hyd rocarbonDisplace the gas sample from the manometerarm and pass twice in and out of the pipettecontaining activated sulphuric acid. Transferthe sample to the potassium hydroxide pipettereturn to the sulphuric acid pipette for twosuccessive contacts. Finally return to the burettefor measurement Fs of the gas after standing3 minutes in the burette.4.6.3.3 Re.mova l of oxygenDisplace the gas sample from the manometerand transfer twice to the pipette containingalkaline pyrogallol, then transfer to the potas-sium hgdroxide pipette and the sulphuric acidpipette in sequence. Finally transfer twice tothe alkaline pyrogallol pipette and return to theburrette for measurement of the residualvolume ( V4). When acid gases, oxygen and.unsaturated hydrocarbons occur at levels below

05 perc:nt they are best determined usingreaction tubes rather than -pipettes.4.6.4 Combustion AnalysisPrepare nitrogen to be used as a transfer gas byabsorption of oxygen from uncontaminated airby contact with alkaline pyrogallol pipette. Flushthe manifold with this nitrogen, then transferapproximately 40 ml of the pure nitrogen to theduplicate potassium hydroxide pipette ( 4.4.3.5 )for storage V,. Transfer approximstely 95 mlof pure cylinder oxygen V, to the burette;measure and transfer to the slow combustionpipette for storage. Lst the inert impuritiesshown by the published analysis of this cylinderoxygen be represented as VT. Measure a fresh30 to 35 ml of sample gas V, through the fumingsulphuric acid pipette prior to combustionanalysis.With the combustion gas sample contained inthe burette adjust the pressure in the combustionpipette and the burette to atmospheric and withthe platinum wire glowing dull red op:n thecombustion pipette and slowly admit the gassample over the hot platinum wire. Allow afull 15 minutes for the first pass of sample intothe bomb combustion tubs. When all of thegas sample has been transferred to the combus-tion pipette, displace the gas contained in themanometer arm through the distributer into thecombustion pipette. Over a period of about5 minutes, return the contents of the combustionpipette to the burette until the mercury level isjust below the platinum spiral, then return thegas slowly to the combustion pipette and repeatthe slow combustion three times. Allow thefinal pass of sample gas in the combustionpipette to cool before returning to the burette.Measure this residue and record as V,.4.6.4.1 Removal of carbon di oxide produced bycombustionDisplace the gas from the manometer and thecontents sample residue in the burette into theduplicate potassium hydroxide pipette ( 4.4.3.5 )three times. Return this sample volume to thecombustion pipette and then repeat contact withthe potassium hydroxide solution before return-ing to the burette for measurement as VIO.4.6.4.2 Removal of excess oxygen aftercombustionDissolve the sample gas from the manometer andcontact 4 times in the duplicate alkaline pyro-gall01 pipette ( 4.4.3.6 ). Then contact once theduplicate potassium hydroxide pipette (4.4.3.5 )and pass once through the slow combustionpipette before returning -to the alkaline pyro-gall01 pipette. Transfer this residue to theburette and measure VI1.4.7 Calibration and StandardCalibration shall be performed using commer-cially purchased oxygen, nitrogen, carbon

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IS13270:1992monoxide and specific hydrocarbon gases as theapplication of the method dictates to preparesynthetic mixtures for admission into the appa-ratus as calibration gas. Such calibration gasesmay be standardized if desired by gas chro-matography and/or gravimetric methods.4.8 Calculation4.8.1 bsorption Analysis

Carbondioxide, percent = ( P1 v,) X 100Unsaturated bydrocar- -_ ( V, - Is) x loobons, percent VlOxygen, percent = ( v3 - v4 ) x 100v 1

Volume designaticns refer to steps indicatedin 4.6.3 ard designated as follows:V1 = initial vclume in ml of sample forabsorption analysis

V, = volume in ml of sample after removalof carbocdioxide ( and the acid gases)V, = volume in ml of sample after removalof unsaturated hydrocarbonsV, = volume in ml of sample after removalof oxygen

4.8.2 Combust i on Anal ysisVolume designations refer to steps indicatedin 4.6.4 ard designated as follows:

V1 = initial volume in ml of sampleva = volume in ml of sample after removalof carbondioxide ( and the acid gases >vs = volume in ml of sample wafter removalof unsaturated hydrocarbonsV, = volume in ml of residual gas after

removal of oxygen.

Balance nitrogen Na = I,,-VF,-- Vrafter subtractionof transfer nitro-gen and inertimpurities inoxygen taken-for combustionOther volumes represented:vlr=(vl-v,)x~ 1

V 3=(K3-y4)xgV5 = volume in ml of nitrogen taken astransfer gas.

4.9 Precision and Accuracy4.9.1 ydrocarbonsSince no more than two hydrocarbons may bedetermined simultaneously by this method errorsmay be caused by the presence of other hydro-carbons depending upon type and concentration.Consequently, it is not proper to express ~accu-racy for individual hydrocarbons althoughrelative precision has been determined for themost common combustion related hydrocarbonsexclusive of other hydrocarbon interferences.

Gas Reproducibil it y ( percent )r----- A--__-7Different SingleLaboratories Laboratoryand andApparatus Apparatus

Unsaturated hydro- - 001carbons as a groupMethane 10 02Ethane 1.0 024.9.2Gas Probable Reproducibility (percent )

Accuracv r----h-----Ethane, percent= l/3 [ 603 - 4 (

Methane, percent=1/3[7(2-c+

whereTotal sample

contraction aftercombustion

* Different SingleTC + co2 ) ] x Jg

Labor$ories Lab;;;toryApparatus Apparatus

Carbon- 005 005 002COZ) - 9021 x $$) dioxideCarbon- 01 - -monoxide

Nitrogen 06 06 01TC = vs + vs - v, Oxygen 01 to 02 01 0'035 GAS CHROMATOGRAPHIC ANALYSIS

Carbondioxide pro- COa=V6+ PO- VI,- V~Bduced upon A dual column/dual thermal conductivity detectorsample com- gas chromatograph is used to separate andbustion quantify oxygen, nitrogen, carbon monoxide,carbon dioxide and methane in gas samples.Oxygen consumed Oa=Vs- VT-I- IS The sample is introduced as a plug into theduring com- -( v10- VI I ) carrier gas, and after drying in a desiccant tubebustion it passes successively through two carefully

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matched gas chromatographic columns. Thefirst column contains a very polar stationaryliquid phase while the second is packed withmolecular sieve 13-X. Detectors are placed ateach of the column. The first column retainsonly carbon dioxide which is eluted after passageof the rest of the mixture ( the composite peak).The first detector thus records two peaks, onecorresponding to the unresolved oxygen, nitrogenmethane and/or carbon monoxide and the secondto carbon dioxide. The gases are swept intothe molecular sieve column which separates allthe components. The second detector recordsthe elution of oxygen, nitrogen, carbon mono-xide and/or methane. The carbon dioxide isirreversibly adsorbed on molecular sieve 13-Xand does not elute. As shown in Fig. I, theretention time of oxygen is sufficiently long toallow carbcn dioxide to elute from the polarcolumn before the oxygen elutes from the secondcolumn.Peak heights are used in conjunction withcalibratron plots for quantitative measurements.Alternatively, electronic integration of peakareas may be used.The separation is complete in 85 minutes.5.1 Range and SensitivityThe limits of detection with hot wire thermalconductivity detectors and helium carrier gasexpressed as ppm of a gas in a 1 ml sample thatproduces a 001 mV signal on a 1 mV recorder,are given below:

Gas Limits of Detection, ppmCarbon dioxide 250Oxygen 300Nitrogen 300Carbon monoxide 500Methane 300

IS 13270 : 19925.2 InterferencesArgon is not separated from oxygen, but ispresent in natural air at 09 volume percent.For samples with low ox-ygen concentration, acorrection may be necessary depending uponthe preparation of the calibration standards.5.2.1 Any compound present in a sample at adetectable level which elute from either columnat a time close to that of component of interestis a potential interference. Polar compoundsincluding acid gases are strongly retained inboth columns at ambient temperature and willnot interfere. Heavier hydrocarbons thanmethane are retained somewhat by the polarcolumn and elute in order of increasing mole-cular weight. Hydrogen is not detected usinghelium carrier gas, but may be measured usingargon carrier gas.5.3 Apparatus5.3.1 Gas ChromatographAny commercial gas chromatograph equippedwith dual column fittings, a four channel thermalconductivity detector and both a six port gassampling valve and a syringe injection port, maybe adopted to this analysis. Commerciallyavailable models designed specifically for thisanalysis are recommended. A schematic diagramof one such apparatus is given in Fig. 2.5.3.1.1 DetectorEither tungsten filament or thermister thermalconductivity detector elements are suitable. Goldplated filaments are resistant to oxidation byoxygen. Greatest detector is thermostatedand controlled at a temperature slightly aboveambient.

Sample - 0.5 ml, 5, each componentCarrier Gas - 40 ml/mm of HeAttenuation - 32Chart Speed - l/2 inch/mmColumns - DEHS & Molecular SieveRecorder - 1 millivolt

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IS 13270 : 1992_ _

CONDUCTIVITY CELL SAMPLING

COLUMN 7 COLUMN 1

FIG. 2 DUAL COLUMN/DUAL DETECTOR GC SCHEMATIC5.3.1.2 Currier gasA ~cylinder of purified helium with a two stageregulator is required. Flow rat is measuredat the exit of the second detector with a soapfilm flow meter.

NOTE -. Carrier gas may vary for different use.5.3.1.3 Sampl e i nt roducerA six-port gas sampling valve with a 1 ml sampleloop provides the better precision. Alternatively,a 1 rnb precision gas-tight syringe with needlemay be used.5.3.1.4 Drying tubeA tube of 200 ml capacity with gas-tight fittingsat either end is filled with indicating desiccant170 mm/850 micron ( IO/20 mesh ). The tubeis installed between the sample introductionsystem and the first gas chromatography column.The desiccant shall be replaced when theindicator colour changes from blue to pink.5.3.1.5 Gas chromat ography columnsColumn number 1 is a 1 800 X 6 mm columnpacked with 30 percent by mass hexamethyl-phosphoamide ( HMPA ) on 250/180 micron( 60/80 mesh ) chromosorb P. Alternatively thecolumn may be packed with 30 percent by massdi-2-ethyl-hexyl-sebacate ( DEHS ) or 250/ 180micron ( 60/80 mesh ) chromosorb P. TheDEHS column has a longer life time than theHMPA column, but DEHS does not separateethane and ethylene from carbon dioxide.Column number 2 is a 1 950 x 5 mm, columnpacked with 425/250 micron ( 40/60 mesh )molecular sieve 13-X. The columns shall becarefully matched to ensure that the retention

times of the components allow separation of thecarbon dioxide from the oxygen.NOTE - Depending upon the specific use, differenttypes of columns are used.

5.3.1.6 TemperatureThe columns are operated at room temperature.Best precision results when the detector isoperated slightly above ambient temperature.5.3.1.7 RecorderAny 1 mV potentiometric strip-chart recorderwith a chart speed of 25 cm/min is suitable.5.3.1.8 Electronic integratorAny suitable electronic integrator compatiblewith the chromatograph may be used to measurepeak areas for quantification.5.4 Reagents5.4.1 Hel i um - Of high purity grade( 99995 percent ).5.4.2 Calibration StandardsStandard blends encompassing the concentrationrange of components in the samples can beobtained from commercial suppliers.5.5 Procedure5.5.1 Gas Chromat ographThe carrier gas is turned on and the flow rateadjusted to 50 ml/min. The flow should bechecked periodically. After the gas has beenflowing for at least 3 min, the thermal conducti-vity dectors may be turned on and the currents

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IS 13270 : 1992adjusted to the values specified for the instru-ments by its manufacturer. About thirty minutesare required for instrument stabilization. Therecorder is turned eon and zeroed before samplesare introduced.5.5.2 I nject i on of Sampl e5.5.2.1 Sampling valveThe sample loop is flushed with several volumesof calibration standard or sample gas. Thehandle is then turned to divert the sample to thechromatograph.5.5.2.2 SyringeSample is withdrawn from the sample vessel andquickly injected, guarding against blow-backof the plunger.5.5.3 Repetitive AnalysisA new sample may be analyzed immedintelyafter the last peak if the sample has emerged.Samples should be analyzed in duplicate.5.6 Calibration and StandardsA standard curve of peak height or peak areavs volume percent is prepared for each constitu-ent of interest by analyzing the calibrationstandards. The calibration should bracket the

air diluted with pure nitrogen both samples andstandards contain argon and no correction isnecessary.5.6.1 The standard curves should be checkedperiodically.5.6.2 A severe loss in resolution of the carbondioxide composite peaks and/or of the nitrogen/oxygen peaks indicates the need for replacementof columns. The polar gas chromatographycolumn continuously looses stationary liquidphase through volatilization. These vapours areadsorbed on the molecular sieve column alongwith the carbon dioxide, which leads to slowdeterioration of the performance of that column.Normally this will happen slowly over a longperiod of time.5.7 Calculations

sample concentrations. Linear plots shouldresult. However, in the presence of 5 to 7 per-cent carbon dioxide, the calibration for oxygenis not linear up to 20 percent, but the calibrationplot may still be used. If the sample source isnatural air, the result for oxygen may needcorrection for argon present in the sample butnot separated from the oxygen. If the oxygencalibration standard mixtures contain pureoxygen dilute with pure nitrogen, the apparentvolume percent of conductivity detector molarresponse factors for oxygen are sufficiently closethat no appreciable error will result from assum-ing identical relative responses. If the oxygencalibration standard mixtures contain natural

Concentrations are determined directly from thecalibration plots. The following conversionfactors apply at 76 mm Hg and 25C.Gas ( mglm3 YupmCarbondioxide 180Oxygen 131Nitrogen 114Carbon monoxide 0,654Methane 114

5.8 Precision and AccuracyAccuracy depends upon the availability ofaccurate calibration standards. These may beobtained with a certificate of analysis from com-mercial suppliers. Precision is controlled by themode of sample introduction, primarily, gas of& 0.3 percent. Reproducibility with a 1 mlgas-tight syringe is about & 15 percent. Pre-cision is also affected by detector drift, which inturn depends upon the control of carrier gas,flow rate and system, temperature. Standardcommercial gas chromatographic equipmentcapable of detector temperature control to rt 05and flow rate control to f 1 percent is adequate.

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I tandard MarkThe use of the Standard Mark is governed by the provisions of the Bureau of I ndianSt andar ds Act, 1986 and the Rules and Regulations made thereunder. The Standard Mark onproducts covered by an Indian Standard conveys the assurance that they have been producedto comply with the requirements of that standard under a well defined system of inspection,testing and quality control which is devised and supervised by BIS and operated by the pro-ducer. Standard marked products are also continuously checked by BIS for conformity tothat standard as a further safeguard. Details of conditions under which a licence for the useof the Standard Mark may be granted to manufacturers or producers may be obtained fromthe Bureau of Indian Standards.

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Bureau of Indian StandardsBIS is a statutory institution established under the B-creau ofIndian Standards Act, 1936 to promoteharmonious development of the activities of standsrdizstion, marking and quality certification ofgoods and attending to connected matters in the country.CopyrightBIS has the copyright of all its publications. No psrt of these publications mzy be reproduced inany form without the prior PErmission in writing of BIS. This do:s not preclude the free use, inthe course of implem:nting the standsrd, of necessary details, such as symbols and sizes, type orgrade designations. Enquiries relating to copyright b: addressed to the Director ( Publications >, BIS.Revision of Indian StandardsIndian Standards are reviewed periodically and revised, when necessary and amendments, if any,are issued from time to time. Users of Indian Standards should ascertain that they are inpossession of the latest amendments or edition. Comments on this Indian Standard may be sentto BIS giving the following reference :Dot : No. CHD 12 ( 9402 )

Amendments Issued Since PublicationAmend No. Date of Issue Text Affected

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