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IS 13270 : 1992

(Reaffirmed 2014)
(Reaffirmed 2019)

(Reaffirmed 2013)

Indian Standard (Reaffirmed 2012)

TESTFORGASESBYORSATAND
CHROMATOGRAPHICMETHODS-
(Reaffirmed 2011)
METHODS

(Reaffirmed 2010)
UDC 543’27 : 543’54

(Reaffirmed 2009)

(Reaffirmed 2008)

(Reaffirmed 2007)

(Reaffirmed 2006)

(Reaffirmed 2005)

@ BIS 1992

BUREAU OF INDIAN STANDARDS

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
&?rch 1992 Price Group 4
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Environmental Protection Sectional Committee, CHD 012

FOREWORD

This lcdian Standard wzs sdopted by the Bureau of Indian Standards, after the draft finalized by
the Environmental Protection Sectional Committee had been approved by the Chemical Division
Council.

Orsat analysis and chromatographic gas analysis are ccmmonly used. Each one has some
advantages and disadvantages. These ar’e listed below:
Orsat Analysis Chromatographic Analysis

Advantages
Gasometric ( volumetric procedures ) Gas chromatographic analysis
1 The equipment required is relatively simple. 1 It has a great advantage of speed.
2 It does not require any calibration. 2 A gas analysis can be completed in few
minutes.
3 When the analysis is done on an infrequent 3 It can be used for low range.
basis, it is very useful.
4 Simple to operate. 4 The method is suitable for continuous
analysis, as the instrument needs calibra-
tion before use.
Disadvantages
1 Errors may be due to collection storage and 1 Instrument must have been previously
handling of samples. calibrated for each gas of interest.
2 Unless special care is taken in the collec- 2 The oven must have reached a constant
tion of samples contamination by air temperature and the detector must be
occurs. giving stable response.
3 Mercury is an ideal confining liquid/fluid 3 It is very difficult to carry instrument to
because of the solubility of all gases in it. the site. If the sample is collected in gas
Rut practically it cannot be used due to holder or any other equipment, collection,
great density and cost. Hence saturated storage or handling becomes a problem.
salt/water is used for ordinary purposes.
4 It cannot measure concentrations of gases 4 It requires inert gas cylinder.
below 0 2 percent.

In reporting the result of a test or analysis made in accordance with this standard, if the final
value, cbserved or calculated, is to be rounded off, it shall be done in accordance with IS 2 : 1960
‘Rules for rounding off numerical values ( revised )‘.
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IS 13270 : 1992

Indian Standard
TESTFORGASESBYORSATAND
CHROMATOGRAPHICMETHODS-
METHODS
1 SCOPE 4.3 Interferences

Errors due to physical absorption can be

This standard prescribes the following two minimized by proper air-solution contact allow-
methods for determination of various gases like ing at least 3 minutes as contact time for proper
oxygen, carbon monoxide, carbon dioxide, equilibrium. Otherwise, no interference is
nitrogen, hydrocarbon, etc, present in gaseous observed from components of ordinary com-
mixtures: bustion air at levels normally encountered.
a) Orsat analysis, and Negligible interference results from the presence
b) Gas chromatographic analysis. of hydrogen sulphide, sulphur dioxide and acid
gases which are absorbed by the caustic solution
In case of dispute the gas chromatographic and reported as carbon dioxide.
method shall be the refree method.
4.4 Apparatus
2 REFERENCES
4.4.1 The apparatus shall consist of the
The Jndian Standards listed below are the conventional orsat type in which volumes are
necessary adjuncts to this standard: made comparable by pressure temperature
compensator, with a manometer interposed
IS No. Title between the compensating tube and burette.

1070 : 1977 Water for general laboratory use 4.4.2 Burette

( second revision )
The burette employed shall have a 600 mm
4167 : 1980 Glossary of terms relating to air length of the graduated section with a volume
pollution. of 100 ml, graduated at 0’2 ml intervals, each
graduation to be separated by a distance of
3 TERMINOLOGY 1‘2 mm. The burette shall be calibrated by
weighed volumes of mercury and shall be
For the purpose of this standard, definitions accurate to within 0’1 ml/100 ml delivery and
given in IS 4167 : 1980 shall apply. to 0’02 ml for each 10 ml intervals. A glass
levelling bulb is connected with rubber tubing
4 ORSAT ANALYSIS to the burette.
4.1 Principle 4.4.3 Pipette
Sample gas is contacted successively by a series Gas absorption pipettes are placed following
of chemically reactive solutions. Each solution the gas measuring burette as given in 4.4.3.4
removes a specific constituent of the sample gas to 4.4.3.6.
mixture with the corresponding decrease in gas
volume at each step representative of the volume 4.4.3.1 A bubbling pipette containing potassium
of the specific gas removed. A levelling bulb hydroxide.
is used to adjust all gas volume measurements
to atmospheric pressure. Ordinarily, the ana- CAUTION : AVOID CONTACT TO SKlN
lysis is apphed in the field using the portable, AND EYES
orsat apparatus to determine the volume com- 4.4.3.2 A bubbling ~pipette containing activated
position of carbon monoxide, carbon dioxide, sulphuric acid.
-oxygen_, and unsaturated hydrocarbons in the
gaseous emission from combustion processes. CAUTION : AVOID CONTACT WITH
Results are usually expressed in volume percent SKIN AND EYES
of each component gas. Methane and ethane
shall be determined by fractional combustion 4.4.3.3 A distributing tip pipette containing
and nitrogen is calculated by difference. alkaline pyrogallol solution.
4.2 Range and Sensitivity 4.4.3.4 A slow combustion pipette with plati-
num spiral.
The limit of detection for each component is
given as 0’2 percent of the total volume based 4.4.3.5 A bubbling pipette containing potassium
on a 100’0 ml sample. hydroxide solution. ( Duplicate of 4-4-3-1).
1
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IS132:0:1992

4.4.3.6
A distributing tip pipette containing 4.5.6 Sodium Hydrate Asbestos Absorbent
alkaline pyrogallol solution ( Duplicate
of 4.4.3.3 ). Used when an unusually accurate measure of
carbon dioxide is required. This absorbent may
also be used to remove sulphur dioxide for
4.4.3.7 These pipettes must possess smooth a more accurate determination of unsaturated
surface which will not entrap gas bubbles, acd hydrocarbons.
shall be so sufficient as to absorb the following
gases from the sample after the required number 4.5.7 Saturated Salt Solution - 75 percent.
of contacts with reagents.
Contains 30 g of sodium chloride or sodium
Gas Number of Contacts sulphate or both, 5 ml of hydrochloric acid,
with Reagents 2 drops of methyl red per 100 ml of distilled
Oxygen 4 to 5 water.
Carbon dioxide 3
4.6 Procedure
Unsaturated hydrocarbons 3
4.6.1 Analysis with Portable Apparatus for
4.4.4 Manometer Carbon Dioxide Oxygen and Carbon Monoxide

The apparatus shall be of reproducibility of The portable orsat apparatus is fitted with a
measurement of 0’02 ml per single contact or metal or wooden carrying case and uses a
0’05 ml on three successive contacts using the shortened form of burette with three gas absorb-
same reference gas or air. ing pipettes. In order, starting from the burette,
the pipettes are filled with potassium hydroxide,
4.5 Reagents pyrogallol and cuprous chloride solution res-
pectively. After filling the above pipettes to the
4.5.1Quality of Reagents engraved mark with the above solutions and
before starting the test adjust the level of each
Unless specified, otherwise, pure chemicals and to atmospheric pressure using the levelling bulb.
distilled water ( see IS 1070 : 1977 ) shall be Open the stopcock of the burette to the atmos-
employed in tests. phere. Raise the levelling bulb until the burette
fills to the stopcock with salt water ( saturated).
NOTE - ‘Pure chemicals’ shall mean chemicals Connect the stopcock -of the burette to the
that do not contain impurities shich affect the atmosphere to be sampled or to a sample con-
results of analysis. tainer and fill the burette with sample gas by
lowering the levelling bulb until the meniscus
4.5.2 Potassium Hydroxide Solution Saturated of the water level reads the desired volume in
the burette ( I’,). Open the stopcock connecting
In 200 ml of distilled water, dissolve solid the burette to manifold of the absorbing system
potassium hydroxide until excess potassium and also open the stopcock of the potassium
hydrcxide remains. Cool the saturated solution -hydroxide pipette. Pass the gas contained in
to at least 3°C below lowest expected tempera- the burette into the potassium hydroxid pipette
ture at which analysis will be carried out. by first raising and then lowering the levelling
Decant and store the supernate liquid. bottle. Repeat until three to five full contacts
have been made. Return the remainder of the
45.3 Activated Sulphuric Acid gas sample to the burette using the levelling
bulb-until the level of potassium hydroxide
Concentrated sulphuric acid containing silver solution returns to the engraved mark, and with
sulphate or vanadium pentoxide. the pipette stopcock closed, again, adjust the
water level in the burette to atmospheric pres-
4.5.4 Alkaline Pyrogallol Solution sure using the levelling bulb. Measure the
volume V, of the remaining gas and record the
Dissolve 17 g of pyrogallol crystals in 100 ml of percent carbon dioxide as follows:
potassium hydroxide solution ( 4.5.2 ). Store
under rcfregeration in a glass-stoppered bottle. Carbon dioxide, percentage = loo ( ‘\- Va )
1
4.5.5 Acidic Copper (II) Chloride Solution
Similarly, oxygen is removed from the remaining
Dissolve 450 g of copper (II) chloride in 2 500 ml gas volume V, by passing this gas into the
of hydrochloric acid ( relative density 1’18 ). If pyrogallol solution in the second pipette.
this solution appears greenish or black in colour Measurement of the remaining volume, V, is
after preparation strips or turnings of copper used to calculate the percent oxygen as follows:
shall be added to the solution until a straw-
yellow coloured liquid is produced on standing. 100 ( V, - Vs )
Oxygen, percent =
Store solution over copper turnings or wire. V1

2
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IS 13270: 1992

Carbon monoxide is measured by mnnipulating 0’5 perc:nt they are best determined using
the remaining gas volume V3 as done previously reaction tubes rather than -pipettes.
to admit this sample into the pipette containing
copper (II) chloride. However, before returning 4.6.4 Combustion Analysis
the gas volume V, to the burette for measure- Prepare nitrogen to be used as a transfer gas by
ment, volume V4 % passed once into the potas- absorption of oxygen from uncontaminated air
sium hydroxide pipette to remove any hydro- by contact with alkaline pyrogallol pipette. Flush
chloric acid vapours evolved from copper (II) the manifold with this nitrogen, then transfer
chloride. approximately 40 ml of the pure nitrogen to the
Carbon monoxide, = 100 ( V, - V4 ) duplicate potassium hydroxide pipette ( 4.4.3.5 )
percent Vl
for storage V,. Transfer approximstely 95 ml
of pure cylinder oxygen V, to the burette;
4.6.2 Analysis by Constant Pressure Volumetry measure and transfer to the slow combustion
pipette for storage. Lst the inert impurities
In the laboratory bench apparatus the burette is shown by the published analysis of this cylinder
filled with mercury and enclosed in a water oxygen be represented as VT. Measure a fresh
jacket. The pipettes are connected to the 30 to 35 ml of sample gas V, through the fuming
burette by a manifold and a bubbling pipette sulphuric acid pipette prior to combustion
containing sulphuric acid ( 4.4.3.2 ) is used analysis.
together with a slow combustion pipette (4.4.3.4)
which is equipped with a separate levelling bulb. With the combustion gas sample contained in
Pipettes (4.4.3.5 and 4.4.3.6 ) are added to the the burette adjust the pressure in the combustion
of both absorption and pipette and the burette to atmospheric and with
system. Results
the platinum wire glowing dull red op:n the
combustion analyses are reported.
combustion pipette and slowly admit the gas
4.6.3 Removal of Gases by Absorption Analysis sample over the hot platinum wire. Allow a
full 15 minutes for the first pass of sample into
Transfer 95 to 100 ml of the sample gas $0 the the bomb combustion tubs. When all of the
burette allowing 2 to 3 minutes for attaining gas sample has been transferred to the combus-
temperature and humidity equilibrium. Using tion pipette, displace the gas contained in the
the leveling bulb bring the sample volume to manometer arm through the distributer into the
atmospheric pressure and read the exact combustion pipette. Over a period of about
volume VI. 5 minutes, return the contents of the combustion
pipette to the burette until the mercury level is
4.6.3.1 Removal of carbon dioxide ( or acid gases ) just below the platinum spiral, then return the
gas slowly to the combustion pipette and repeat
Displace the gas sample into the manifold and the slow combustion three times. Allow the
then transfer into the potassium hydroxide final pass of sample gas in the combustion
pipette. Return the sample gas to the burette. pipette to cool before returning to the burette.
Then contact the potassium hydroxide pipette Measure this residue and record as V,.
twice, finally returning the sample to the burette
and allowing 2 to 3 minutes before equilibrating 4.6.4.1 Removal of carbon dioxide produced by
the sample to atmospheric pressure with the combustion
leveling bulb. Then read the volume V,.
Displace the gas from the manometer and the
4.6.3.2 Removal of amsaturated hydrocarbon contents sample residue in the burette into the
duplicate potassium hydroxide pipette ( 4.4.3.5 )
Displace the gas sample from the manometer three times. Return this sample volume to the
arm and pass twice in and out of the pipette combustion pipette and then repeat contact with
containing activated sulphuric acid. Transfer the potassium hydroxide solution before return-
the sample to the potassium hydroxide pipette ing to the burette for measurement as VIO.
return to the sulphuric acid pipette for two
successive contacts. Finally return to the burette 4.6.4.2 Removal of excess oxygen after
for measurement F’s of the gas after standing combustion
3 minutes in the burette.
Dissolve the sample gas from the manometer and
contact 4 times in the duplicate alkaline pyro-
4.6.3.3 Re.moval of oxygen
gall01 pipette ( 4.4.3.6 ). Then contact once the
Displace the gas sample from the manometer duplicate potassium hydroxide pipette (4.4.3.5 )
and transfer twice to the pipette containing and pass once through the slow combustion
alkaline pyrogallol, then transfer to the potas- pipette before returning -to the alkaline pyro-
sium hgdroxide pipette and the sulphuric acid gall01 pipette. Transfer this residue to the
pipette in sequence. Finally transfer twice to burette and measure VI1.
the alkaline pyrogallol pipette and return to the 4.7 Calibration and Standard
burrette for measurement of the residual
volume ( V4). When acid gases, oxygen and Calibration shall be performed using commer-
.unsaturated hydrocarbons occur at levels below cially purchased oxygen, nitrogen, carbon

3
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IS13270:1992

monoxide and specific hydrocarbon gases as the Balance nitrogen Na = I’,,-VF,-- Vr

application of the method dictates to prepare after subtraction
synthetic mixtures for admission into the appa- of transfer nitro-
ratus as calibration gas. Such calibration gases gen and inert
may be standardized if desired by gas chro- impurities in
matography and/or gravimetric methods. oxygen taken
-for combustion
4.8 Calculation
Other volumes represented:
4.8.1Absorption Analysis vlr=(vl-v,)x~ 1
Carbondioxide, percent = ( P1 v,“) X 100
V ,3=(K3-y4)xg
Unsaturated bydrocar- -_ ( V, - I’s) x loo
bons, percent V5 = volume in ml of nitrogen taken as
Vl
transfer gas.
Oxygen, percent = ( v3 v- v4 ) x 100
4.9 Precision and Accuracy
1
Volume designaticns refer to steps indicated 4.9.1Hydrocarbons
in 4.6.3 ard designated as follows:
Since no more than two hydrocarbons may be
V1 = initial vclume in ml of sample for determined simultaneously by this method errors
absorption analysis may be caused by the presence of other hydro-
V, = volume in ml of sample after removal carbons depending upon type and concentration.
of carbocdioxide ( and the acid gases) Consequently, it is not proper to express ~accu-
racy for individual hydrocarbons although
V, = volume in ml of sample after removal relative precision has been determined for the
of unsaturated hydrocarbons most common combustion related hydrocarbons
V, = volume in ml of sample after removal exclusive of other hydrocarbon interferences.
of oxygen
Gas Reproducibility ( percent )
4.8.2 Combustion Analysis r----- A--__-7
Different Single
Volume designations refer to steps indicated Laboratories Laboratory
in 4.6.4 ard designated as follows: and and
Apparatus Apparatus
V1 = initial volume in ml of sample Unsaturated hydro- - 0’01
va = volume in ml of sample after removal carbons as a group
of carbondioxide ( and the acid gases > Methane 1’0 0’2
vs = volume in ml of sample wafter removal Ethane 1.0 0’2
of unsaturated hydrocarbons
4.9.2
V, = volume in ml of residual gas after Gas Probable Reproducibility (percent )
removal of oxygen. Accuracv* r----h-----
Ethane, percent Different Single
Labor$ories Lab;;;tory
= l/3 [ 603 - 4 ( TC + co2 ) ] x Jg
Apparatus Apparatus
Methane, percent Carbon- 0’05 0’05 0’02
dioxide
=1/3[7(2-c+ COZ) - 9021 x $$) Carbon- 0’1 - -
monoxide
where Nitrogen 0’6 0’6 0’1
Total sample TC = vs + vs - v, Oxygen 0’1 to 0’2 0’1 0'03
contraction after
combustion 5 GAS CHROMATOGRAPHIC ANALYSIS
Carbondioxide pro- COa=V6+ PO- VI,- V~B A dual column/dual thermal conductivity detector
duced upon gas chromatograph is used to separate and
sample com- quantify oxygen, nitrogen, carbon monoxide,
bustion carbon dioxide and methane in gas samples.
Oxygen consumed Oa=Vs- VT-I-VIS The sample is introduced as a plug into the
during com- -( v10- VII ) carrier gas, and after drying in a desiccant tube
bustion it passes successively through two carefully

4
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IS 13270 : 1992

matched gas chromatographic columns. The 5.2 Interferences

first column contains a very polar stationary
liquid phase while the second is packed with Argon is not separated from oxygen, but is
molecular sieve 13-X. Detectors are placed at present in natural air at 0’9 volume percent.
each of the column. The first column retains For samples with low ox-ygen concentration, a
only carbon dioxide which is eluted after passage correction may be necessary depending upon
of the rest of the mixture ( the composite peak). the preparation of the calibration standards.
The first detector thus records two peaks, one
corresponding to the unresolved oxygen, nitrogen 5.2.1 Any compound present in a sample at a
methane and/or carbon monoxide and the second detectable level which elute from either column
to carbon dioxide. The gases are swept into at a time close to that of component of interest
the molecular sieve column which separates all is a potential interference. Polar compounds
the components. The second detector records including acid gases are strongly retained in
the elution of oxygen, nitrogen, carbon mono- both columns at ambient temperature and will
xide and/or methane. The carbon dioxide is not interfere. Heavier hydrocarbons than
irreversibly adsorbed on molecular sieve 13-X methane are retained somewhat by the polar
and does not elute. As shown in Fig. I, the column and elute in order of increasing mole-
retention time of oxygen is sufficiently long to cular weight. Hydrogen is not detected using
allow carbcn dioxide to elute from the polar helium carrier gas, but may be measured using
column before the oxygen elutes from the second argon carrier gas.
column.
5.3 Apparatus
Peak heights are used in conjunction with
calibratron plots for quantitative measurements.
Alternatively, electronic integration of peak 5.3.1 Gas Chromatograph
areas may be used.
Any commercial gas chromatograph equipped
The separation is complete in 8’5 minutes. with dual column fittings, a four channel thermal
conductivity detector and both a six port gas
5.1 Range and Sensitivity sampling valve and a syringe injection port, may
be adopted to this analysis. Commercially
The limits of detection with hot wire thermal available models designed specifically for this
conductivity detectors and helium carrier gas analysis are recommended. A schematic diagram
expressed as ppm of a gas in a 1 ml sample that of one such apparatus is given in Fig. 2.
produces a 0’01 mV signal on a 1 mV recorder,
are given below:
5.3.1.1 Detector
Gas Limits of Detection, ppm
Carbon dioxide 250 Either tungsten filament or thermister thermal
conductivity detector elements are suitable. Gold
Oxygen 300
plated filaments are resistant to oxidation by
Nitrogen 300 oxygen. Greatest detector is thermostated
Carbon monoxide 500 and controlled at a temperature slightly above
Methane 300 ambient.

Sample - 0.5 ml, 5, each component

Carrier Gas - 40 ml/mm of He
Attenuation - 32
Chart Speed - l/2 inch/mm
Columns - DEHS & Molecular Sieve
Recorder - 1 millivolt

FIG. 1 TYPICAL CEROMATOGRAM

5
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IS 13270 : 1992

_ _
CONDUCTIVITY CELL
SAMPLING

COLUMN 7 COLUMN 1

FIG. 2 DUAL COLUMN/DUAL DETECTOR GC SCHEMATIC

5.3.1.2 Currier gas times of the components allow separation of the

carbon dioxide from the oxygen.
A ~cylinder of purified helium with a two stage
regulator is required. Flow rat is measured NOTE - Depending upon the specific use, different
at the exit of the second detector with a soap types of columns are used.
film flow meter.
5.3.1.6 Temperature
NOTE -. Carrier gas may vary for different use.
The columns are operated at room temperature.
5.3.1.3 Sample introducer Best precision results when the detector is
operated slightly above ambient temperature.
A six-port gas sampling valve with a 1 ml sample
loop provides the better precision. Alternatively, 5.3.1.7 Recorder
a 1 rnb precision gas-tight syringe with needle
may be used. Any 1 mV potentiometric strip-chart recorder
with a chart speed of 2’5 cm/min is suitable.
5.3.1.4 Drying tube
5.3.1.8 Electronic integrator
A tube of 200 ml capacity with gas-tight fittings
at either end is filled with indicating desiccant Any suitable electronic integrator compatible
1’70 mm/850 micron ( IO/20 mesh ). The tube with the chromatograph may be used to measure
is installed between the sample introduction peak areas for quantification.
system and the first gas chromatography column.
The desiccant shall be replaced when the 5.4 Reagents
indicator colour changes from blue to pink.
5.4.1 Helium - Of high purity grade
5.3.1.5 Gas chromatography columns ( 99’995 percent ).
Column number 1 is a 1 800 X 6 mm column 5.4.2 Calibration Standards
packed with 30 percent by mass hexamethyl-
phosphoamide ( HMPA ) on 250/180 micron Standard blends encompassing the concentration
( 60/80 mesh ) chromosorb P. Alternatively the range of components in the samples can be
column may be packed with 30 percent by mass obtained from commercial suppliers.
di-2-ethyl-hexyl-sebacate ( DEHS ) or 250/ 180
micron ( 60/80 mesh ) chromosorb P. The 5.5 Procedure
DEHS column has a longer life time than the
HMPA column, but DEHS does not separate 5.5.1 Gas Chromatograph
ethane and ethylene from carbon dioxide.
The carrier gas is turned on and the flow rate
Column number 2 is a 1 950 x 5 mm, column adjusted to 50 ml/min. The flow should be
packed with 425/250 micron ( 40/60 mesh ) checked periodically. After the gas has been
molecular sieve 13-X. The columns shall be flowing for at least 3 min, the thermal conducti-
carefully matched to ensure that the retention vity dectors may be turned on and the currents

6
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IS 13270 : 1992

adjusted to the values specified for the instru- air diluted with pure nitrogen both samples and
ments by its manufacturer. About thirty minutes standards contain argon and no correction is
are required for instrument stabilization. The necessary.
recorder is turned eon and zeroed before samples
are introduced. 5.6.1 The standard curves should be checked
periodically.
5.5.2 Injection of Sample
5.6.2 A severe loss in resolution of the carbon
5.5.2.1 Sampling valve
dioxide composite peaks and/or of the nitrogen/
oxygen peaks indicates the need for replacement
The sample loop is flushed with several volumes of columns. The polar gas chromatography
of calibration standard or sample gas. The column continuously looses stationary liquid
handle is then turned to divert the sample to the phase through volatilization. These vapours are
chromatograph. adsorbed on the molecular sieve column along
with the carbon dioxide, which leads to slow
5.5.2.2 Syringe deterioration of the performance of that column.
Normally this will happen slowly over a long
Sample is withdrawn from the sample vessel and period of time.
quickly injected, guarding against blow-back
of the plunger. 5.7 Calculations
5.5.3 Repetitive Analysis Concentrations are determined directly from the
calibration plots. The following conversion
A new sample may be analyzed immedintely factors apply at 76 mm Hg and 25°C.
after the last peak if the sample has emerged.
Samples should be analyzed in duplicate. Gas ( mglm3 Yupm
Carbondioxide 1’80
5.6 Calibration and Standards Oxygen 1’31
A standard curve of peak height or peak area Nitrogen 1’14
vs volume percent is prepared for each constitu- Carbon monoxide 0’,654
ent of interest by analyzing the calibration Methane 1’14
standards. The calibration should bracket the
sample concentrations. Linear plots should 5.8 Precision and Accuracy
result. However, in the presence of 5 to 7 per-
cent carbon dioxide, the calibration for oxygen Accuracy depends upon the availability of
is not linear up to 20 percent, but the calibration accurate calibration standards. These may be
plot may still be used. If the sample source is obtained with a certificate of analysis from com-
natural air, the result for oxygen may need mercial suppliers. Precision is controlled by the
correction for argon present in the sample but mode of sample introduction, primarily, gas of
not separated from the oxygen. If the oxygen & 0.3 percent. Reproducibility with a 1 ml
calibration standard mixtures contain pure gas-tight syringe is about & 1’5 percent. Pre-
oxygen dilute with pure nitrogen, the apparent cision is also affected by detector drift, which in
volume percent of conductivity detector molar turn depends upon the control of carrier gas,
response factors for oxygen are sufficiently close flow rate and system, temperature. Standard
that no appreciable error will result from assum- commercial gas chromatographic equipment
ing identical relative responses. If the oxygen capable of detector temperature control to rt 0’5
calibration standard mixtures contain natural and flow rate control to f 1 percent is adequate.

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I
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products covered by an Indian Standard conveys the assurance that they have been produced
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of the Standard Mark may be granted to manufacturers or producers may be obtained from
the Bureau of Indian Standards.
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Headquarters :

Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002

Telephones : 331 01 31, 331 13 75 Telegrams : Manaksanstha
( Common to all Offices )

Regional Offices : Telephone

Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg 331 01 31
NEW DELHI 110002 331 13 75

Eastern ~: l/14 C.I.T. Scheme VII M, V.I.P. Road, Maniktola

CALCUTTA 700054 37 86 62

Northern : SC0 445-446, Sector 35-C, CHANDIGARH 160036 53 38 43

Southern : C.I.T. Campus, IV Cross Road, MADRAS 600113 235 0216

Western : Manakalaya, E9 MIDC, Marol, Andheri ( East )

BOMBAY 400093 6 32 92 95

Branches : AHMADABAD. BANGALORE. BHOPAL. BHUBANESHWAR.

COIMBATORE. FARIDABAD. GHAZIABAD. GUWAHATI.
HYDERABAD. JAIPUR. KANPUR. LUCKNOW. PATNA.
THIRUVANANTHAPURAM.

Printed at Swatantra Bharat Press, Delhi, India