ASTM D2908-91(2005)
(Practice)Standard Practice for Measuring Volatile Organic Matter in Water by Aqueous-Injection Gas Chromatography
Standard Practice for Measuring Volatile Organic Matter in Water by Aqueous-Injection Gas Chromatography
SIGNIFICANCE AND USE
This practice is useful in identifying the major organic constituents in wastewater for support of effective in-plant or pollution control programs. Currently, the most practical means for tentatively identifying and measuring a range of volatile organic compounds is gas-liquid chromatography. Positive identification requires supplemental testing (for example, multiple columns, speciality detectors, spectroscopy, or a combination of these techniques).
SCOPE
1.1 This practice covers general guidance applicable to certain test methods for the qualitative and quantitative determination of specific organic compounds, or classes of compounds, in water by direct aqueous injection gas chromatography (1, 2, 3, 4).
1.2 Volatile organic compounds at aqueous concentrations greater than about 1 mg/L can generally be determined by direct aqueous injection gas chromatography.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D2908–91(Reapproved 2005)
Standard Practice for
Measuring Volatile Organic Matter in Water by Aqueous-
Injection Gas Chromatography
This standard is issued under the fixed designation D2908; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E355 Practice for Gas Chromatography Terms and Rela-
tionships
1.1 This practice covers general guidance applicable to
certain test methods for the qualitative and quantitative deter-
3. Terminology
mination of specific organic compounds, or classes of com-
3.1 Definitions—The following terms in this practice are
pounds, in water by direct aqueous injection gas chromatogra-
2 defined in accordance with Terminology D1129.
phy (1, 2, 3, 4).
3.1.1 “ghosting” or memory peaks—an interference, show-
1.2 Volatile organic compounds at aqueous concentrations
ing as a peak, which appears at the same elution time as the
greater than about 1 mg/L can generally be determined by
organic component of previous analysis.
direct aqueous injection gas chromatography.
3.1.2 internal standard—a material present in or added to
1.3 This standard does not purport to address all of the
samplesinknownamounttoserveasareferencemeasurement.
safety concerns, if any, associated with its use. It is the
3.1.3 noise—an extraneous electronic signal which affects
responsibility of the user of this standard to establish appro-
baseline stability.
priate safety and health practices and determine the applica-
3.1.4 relative retention ratio—the retention time of the
bility of regulatory limitations prior to use.
unknown component divided by the retention time of the
2. Referenced Documents internal standard.
3.1.5 retention time—the time that elapses from the intro-
2.1 ASTM Standards:
duction of the sample until the peak maximum is reached.
D1129 Terminology Relating to Water
3.2 For definitions of other chromatographic terms used in
D1192 GuideforEquipmentforSamplingWaterandSteam
this practice, refer to Practice E355.
in Closed Conduits
D1193 Specification for Reagent Water
4. Summary of Practice
D3370 Practices for Sampling Water from Closed Conduits
4.1 This practice defines the applicability of various col-
E260 Practice for Packed Column Gas Chromatography
umns and conditions for the separation of naturally occurring
or synthetic organics or both, in an aqueous medium for
subsequent detection with a flame ionization detector. After
This practice is under the jurisdiction ofASTM Committee D19 on Water and
vaporization,theaqueoussampleiscarriedthroughthecolumn
is the direct responsibility of Subcommittee D19.06 on Methods for Analysis for
by an inert carrier gas.The sample components are partitioned
Organic Substances in Water.
betweenthecarriergasandastationaryliquidphaseonaninert
Current edition approved Dec. 1, 2005. Published January 2006. Originally
approved in 1970. Last previous edition approved in 2001 as D2908–91 (2001).
solidsupport.Thecolumneffluentisburnedinanair-hydrogen
DOI: 10.1520/D2908-91R05.
flame. The ions released from combustion of the organic
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
components induce an increase in standing current which is
this practice.
measured.Although this method is written for hydrogen flame
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
detection, the basic technology is applicable to other detectors
Standards volume information, refer to the standard’s Document Summary page on
if water does not interfere.
the ASTM website.
4.2 The elution times are characteristic of the various
Withdrawn. The last approved version of this historical standard is referenced
on www.astm.org. organiccomponentspresentinthesample,whilethepeakareas
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D2908–91 (2005)
are proportional to the quantities of the components.Adiscus- increases due to the increasing temperature.An unsteady flow
sion of gas chromatography is presented in Practice E260. will create an unstable baseline.
7.1.2 Gas Transport Tubing—Newtubingshouldbewashed
5. Significance and Use
with a detergent solution, rinsed with Type I cold water, and
solvent rinsed to remove residual organic preservatives or
5.1 This practice is useful in identifying the major organic
lubricants. Ethanol is an effective solvent. The tubing is then
constituents in wastewater for support of effective in-plant or
dried by flushing with nitrogen. Drying can be accelerated by
pollutioncontrolprograms.Currently,themostpracticalmeans
installing the tubing in a gas chromatograph (GC) oven and
for tentatively identifying and measuring a range of volatile
flowingnitrogenorotherinertgasthroughit,whileheatingthe
organic compounds is gas-liquid chromatography. Positive
oven to 50°C.
identification requires supplemental testing (for example, mul-
tiple columns, speciality detectors, spectroscopy, or a combi-
7.1.3 Gas Leaks—The gas system should be pressure
nation of these techniques). checkeddailyforleaks.Tocheckforleaks,shutoffthedetector
and pressurize the gas system to approximately 103 kPa (15
6. Interferences psi) above the normal operating pressure. Then shut off the
tank valve and observe the level of the pressure gauge. If the
6.1 Particulate Matter—Particulate or suspended matter
preset pressure holds for 10 min, the system can be considered
should be removed by centrifugation or membrane filtration if
leak-free. If the pressure drops, a leak is indicated and should
components of interest are not altered. This pretreatment will
be located and eliminated before proceeding further. A soap
prevent both plugging of syringes and formation of condensa-
solution may be used for determining the source of leaks, but
tion nuclei.Acidification will often facilitate the dissolving of
care must be exercised to avoid getting the solution inside the
particulate matter, but the operator must determine that pH
tubing or instrument since it will cause a long lasting, serious
adjustment does not alter the components to be determined.
source of interference. Leaks may also occur between the
6.2 Identical Retention Times—With any given column and
instrument gas inlet valve and flame tip. This may be checked
operating conditions, one or more components may elute at
byremovingtheflametip,replacingitwithaclosedfittingand
identical retention times. Thus a chromatographic peak is only
rechecking for pressure stability as previously noted.
presumptive evidence of a single component. Confirmation
7.1.4 Gas Flow—The gas flow can be determined with a
requiresanalyseswithothercolumnswithvaryingphysicaland
bubble flow meter. A micro-rotameter in the gas inlet line is
chemical properties, or spectrometric confirmation of the
also helpful. It should be recalibrated after each readjustment
isolated peak, or both.
of the gas operating pressure.
6.3 Acidification—Detection of certain groups of compo-
nentswillbeenhancedifthesampleismadeneutralorslightly
7.2 Injection Port—The injection port usually is insulated
acidic.Thismayminimizetheformationofnonvolatilesaltsin
from the chromatographic oven and equipped with a separate
cases such as the analysis of volatile organic acids and bases
heater that will maintain a constant temperature. The tempera-
and certain chlorophenols.
ture of the injection port should be adjusted to approximately
6.4 Ghosting—Ghosting is evidenced by an interference
50°C above the highest boiling sample component. This will
peakthatoccursatthesametimeasthatforacomponentfrom
help minimize the elution time, as well as reduce peak tailing.
a previous analysis but usually with less intensity. Ghosting
Should thermal decomposition of components be a problem,
occurs because of organic holdup in the injection port. Re-
theinjectionporttemperatureshouldbereducedappropriately.
peated Type I water washing with 5-µL injections between
Cleanliness of the injection port in some cases can be main-
sample runs will usually eliminate ghosting problems. The
tained at a tolerable level by periodically raising the tempera-
baseline is checked at maximum sensitivity to assure that the
ture 25°C above the normal operating level. Use of disposable
interference has been eliminated. In addition to water injec-
glass inserts or periodic cleaning with chromic acid can be
tions, increasing the injection port temperature for a period of
practiced with some designs. When using samples larger than
time will often facilitate the elimination of ghosting problems.
5µL,blowbackintothecarriergassupplyshouldbeprevented
6.4.1 Delayed Elution—Highly polar or high boiling com-
through use of a preheated capillary or other special design.
ponents may unpredictably elute several chromatograms later
When using 3.175-mm (0.125-in.) columns, samples larger
and therefore act as an interference. This is particularly true
than 5 µL may extinguish the flame depending on column
with complex industrial waste samples. A combination of
length, carrier gas flow, and injection temperature.
repeatedwaterinjectionsandelevatedcolumntemperaturewill
7.2.1 Septum—Organics eluting from the septum in the
eliminatethisproblem.Backflushvalvesshouldbeusedifthis
injection port have been found to be a source of an unsteady
problem is encountered often.
baseline when operating at high sensitivity. Septa should be
preconditioned. Insertion of a new septum in the injection port
7. Apparatus
at the end of the day for heating overnight will usually
7.1 Gas System: eliminate these residuals. A separate oven operating at a
7.1.1 Gas Regulators—High-quality pressure regulators temperaturesimilartothatoftheinjectionportcanalsobeused
shouldbeusedtoensureasteadyflowofgastotheinstrument. to process the septa.The septa should be changed at least once
If temperature programming is used, differential flow control- a day to minimize gas leaks and sample blowback. Septa with
lers should be installed in the carrier gas line to prevent a TFE-fluorocarbonbackingsminimizeorganicbleedingandcan
decrease in flow as the pressure drop across the column be used safely for longer periods.
D2908–91 (2005)
7.2.2 On-Column Injection—Whileinjectionintotheheated former may be required in addition to the one incorporated
chamber for flash vaporization is the most common injection within the chromatographic instrument.
set-up, some analyses (for example, organic acids) are better
8. Reagents and Materials
performed with on-column injection to reduce ghosting and
peaktailingandtopreventdecompositionofthermallydegrad- 8.1 Purity of Reagents—Reagent grade chemicals shall be
able compounds. This capability should be built into the used in all instances for gas purification, sample stabilization,
injection system. When using on-column injection a shorter and other applications. Unless otherwise indicated, it is in-
tended that all reagents shall conform to the specifications of
columnlifemayoccurduetosolidbuildupintheinjectionend
theCommitteeonAnalyticalReagentsoftheAmericanChemi-
of the column.
cal Society, where such specifications are available. Other
7.3 Column Oven—The column ovens usually are insulated
grades may be used, provided it is first ascertained that the
separately from the injection port and the detector. The oven
reagent is of sufficiently high purity to permit its use without
should be equipped with a proportional heater and a squirrel-
lessening the accuracy of the determination.
cage blower to assure maximum temperature reproducibility
8.1.1 All chemicals used for internal standards shall be of
and uniformity throughout the oven. Reproducibility of oven
highest known purity.
temperature should be within 0.5°C.
8.2 Purity of Water—Unlessotherwiseindicated,references
7.3.1 Temperature Programming—Temperature program-
towatershallbeunderstoodtomeanreagentwaterconforming
ming is desirable when the analysis involves the resolution of
to Type I of Specification D1193.
organics with widely varying boiling points. The column oven
8.3 Carrier Gas System—Only gases of the highest purity
should be equipped with temperature programming be-
obtainable should be used in a chromatographic system desig-
tween−15 and 350°C (or range of the method) with select-
nated for trace-organic monitoring in water. The common
ability of several programming rates between 1 and 20°/min
carrier gases used with a flame ionization detector (FID) are
provided. The actual column temperature will lag somewhat
helium and nitrogen. Trace contaminants in even the highest
behind the oven temperature at the faster programming rates.
purity gases can often affect baseline stability and introduce
Baseline drift will often occur because of increased higher
noise. Absorption columns of molecular sieves (14 by 30-
temperatures experienced during temperature programming.
mesh) and anhydrous calcium sulfate (CaSO , 8 mesh) in
This depends on the stability of the substrate and operating
series between the gas supply tank and the instrument will
temperature range. Temperatures that approach the maximum
minimize the effect of trace impurities. These preconditioning
limit of the liquid phase limit the operating range. Utilization
columns,toremaineffective,mustbecleanedbybackflushing
of dual matching columns and a differential electrometer can
them with a clean gas (nitrogen, helium) at approximately
minimize the effect of drift; however, the drift is reproducible
200°C, or they must be replaced at regular intervals. Use of
and does not interfere with the analysis in most cases.
catalytic purifiers is also effective (4).
7.4 Detector—The combination of high sensitivity and a 8.4 Column:
widelinearrangemakestheflameionizationdetector(FID)the 8.4.1 Column Tubing—For most organic analyses in aque-
oussystems,stainlesssteelisthemostdesirablecolumntubing
usual choice in trace aqueous analysis. The flame ionization
detectorisrelativelyinsensitivetowatervaporandtomoderate material. However, when analyzing organics that are reactive
with stainless steel. Fused silica capillary columns have been
temperature changes if other operating parameters remain
demonstrated as having equal, if not better, performance in all
unchanged. If temperature programming is used, the detector
cases.Columnsof0.25,0.32,and0.53mminsidediameterare
should be isolated from the oven and heated separately to
readily available from most suppliers of fused silica. With a
ensure uni
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