ASTM D2908-91(2011)
(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 concerns, 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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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D2908 − 91 (Reapproved 2011)
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 3.1.1 The following terms in this practice are defined in
accordance with Terminology D1129.
1.1 This practice covers general guidance applicable to
3.1.2 “ghosting” or memory peaks—an interference, show-
certain test methods for the qualitative and quantitative deter-
ing as a peak, which appears at the same elution time as the
mination of specific organic compounds, or classes of
organic component of previous analysis.
compounds, in water by direct aqueous injection gas chroma-
3.1.3 internal standard—a material present in or added to
tography (1, 2, 3, 4).
samplesinknownamounttoserveasareferencemeasurement.
1.2 Volatile organic compounds at aqueous concentrations
3.1.4 noise—an extraneous electronic signal which affects
greater than about 1 mg/L can generally be determined by
baseline stability.
direct aqueous injection gas chromatography.
3.1.5 relative retention ratio—the retention time of the
1.3 This standard does not purport to address all of the
unknown component divided by the retention time of the
safety concerns, if any, associated with its use. It is the
internal standard.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.1.6 retention time—the time that elapses from the intro-
bility of regulatory limitations prior to use.
duction of the sample until the peak maximum is reached.
3.2 For definitions of other chromatographic terms used in
2. Referenced Documents
this practice, refer to Practice E355.
2.1 ASTM Standards:
4. Summary of Practice
D1129Terminology Relating to Water
D1192Guide for Equipment for Sampling Water and Steam
4.1 This practice defines the applicability of various col-
in Closed Conduits (Withdrawn 2003)
umns and conditions for the separation of naturally occurring
D1193Specification for Reagent Water
or synthetic organics or both, in an aqueous medium for
D3370Practices for Sampling Water from Closed Conduits
subsequent detection with a flame ionization detector. After
E260Practice for Packed Column Gas Chromatography
vaporization,theaqueoussampleiscarriedthroughthecolumn
E355PracticeforGasChromatographyTermsandRelation-
by an inert carrier gas.The sample components are partitioned
ships
betweenthecarriergasandastationaryliquidphaseonaninert
solidsupport.Thecolumneffluentisburnedinanair-hydrogen
3. Terminology
flame. The ions released from combustion of the organic
components induce an increase in standing current which is
3.1 Definitions:
measured.Although this method is written for hydrogen flame
detection, the basic technology is applicable to other detectors
if water does not interfere.
This practice is under the jurisdiction ofASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.06 on Methods for Analysis for
4.2 The elution times are characteristic of the various
Organic Substances in Water.
organiccomponentspresentinthesample,whilethepeakareas
Current edition approved May 1, 2011. Published June 2011. Originally
approved in 1970. Last previous edition approved in 2005 as D2908–91 (2005). are proportional to the quantities of the components.Adiscus-
DOI: 10.1520/D2908-91R11.
sion of gas chromatography is presented in Practice E260.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this practice.
5. Significance and Use
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
5.1 This practice is useful in identifying the major organic
Standards volume information, refer to the standard’s Document Summary page on
constituents in wastewater for support of effective in-plant or
the ASTM website.
pollutioncontrolprograms.Currently,themostpracticalmeans
The last approved version of this historical standard is referenced on
www.astm.org. for tentatively identifying and measuring a range of volatile
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2908 − 91 (2011)
organic compounds is gas-liquid chromatography. Positive installing the tubing in a gas chromatograph (GC) oven and
identification requires supplemental testing (for example, mul- flowingnitrogenorotherinertgasthroughit,whileheatingthe
tiple columns, speciality detectors, spectroscopy, or a combi-
oven to 50°C.
nation of these techniques).
7.1.3 Gas Leaks—The gas system should be pressure
checkeddailyforleaks.Tocheckforleaks,shutoffthedetector
6. Interferences
and pressurize the gas system to approximately 103 kPa (15
6.1 Particulate Matter—Particulate or suspended matter
psi) above the normal operating pressure. Then shut off the
should be removed by centrifugation or membrane filtration if
tank valve and observe the level of the pressure gauge. If the
components of interest are not altered. This pretreatment will
preset pressure holds for 10 min, the system can be considered
prevent both plugging of syringes and formation of condensa-
leak-free. If the pressure drops, a leak is indicated and should
tion nuclei.Acidification will often facilitate the dissolving of
be located and eliminated before proceeding further. A soap
particulate matter, but the operator must determine that pH
solution may be used for determining the source of leaks, but
adjustment does not alter the components to be determined.
care must be exercised to avoid getting the solution inside the
6.2 Identical Retention Times—With any given column and
tubing or instrument since it will cause a long lasting, serious
operating conditions, one or more components may elute at
source of interference. Leaks may also occur between the
identical retention times. Thus a chromatographic peak is only
instrument gas inlet valve and flame tip. This may be checked
presumptive evidence of a single component. Confirmation
byremovingtheflametip,replacingitwithaclosedfittingand
requiresanalyseswithothercolumnswithvaryingphysicaland
rechecking for pressure stability as previously noted.
chemical properties, or spectrometric confirmation of the
7.1.4 Gas Flow—The gas flow can be determined with a
isolated peak, or both.
bubble flow meter. A micro-rotameter in the gas inlet line is
6.3 Acidification—Detection of certain groups of compo- also helpful. It should be recalibrated after each readjustment
nentswillbeenhancedifthesampleismadeneutralorslightly
of the gas operating pressure.
acidic.Thismayminimizetheformationofnonvolatilesaltsin
7.2 Injection Port—The injection port usually is insulated
cases such as the analysis of volatile organic acids and bases
from the chromatographic oven and equipped with a separate
and certain chlorophenols.
heater that will maintain a constant temperature. The tempera-
6.4 Ghosting—Ghosting is evidenced by an interference
ture of the injection port should be adjusted to approximately
peakthatoccursatthesametimeasthatforacomponentfrom
50°C above the highest boiling sample component. This will
a previous analysis but usually with less intensity. Ghosting
help minimize the elution time, as well as reduce peak tailing.
occurs because of organic holdup in the injection port. Re-
Should thermal decomposition of components be a problem,
peated Type I water washing with 5-µL injections between
theinjectionporttemperatureshouldbereducedappropriately.
sample runs will usually eliminate ghosting problems. The
Cleanliness of the injection port in some cases can be main-
baseline is checked at maximum sensitivity to assure that the
tained at a tolerable level by periodically raising the tempera-
interference has been eliminated. In addition to water
ture 25°C above the normal operating level. Use of disposable
injections, increasing the injection port temperature for a
glass inserts or periodic cleaning with chromic acid can be
period of time will often facilitate the elimination of ghosting
practiced with some designs. When using samples larger than
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
7. Apparatus
preconditioned. Insertion of a new septum in the injection port
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.
increases due to the increasing temperature.An unsteady flow
7.2.2 On-Column Injection—Whileinjectionintotheheated
will create an unstable baseline.
7.1.2 Gas Transport Tubing—Newtubingshouldbewashed chamber for flash vaporization is the most common injection
set-up, some analyses (for example, organic acids) are better
with a detergent solution, rinsed with Type I cold water, and
solvent rinsed to remove residual organic preservatives or performed with on-column injection to reduce ghosting and
peaktailingandtopreventdecompositionofthermallydegrad-
lubricants. Ethanol is an effective solvent. The tubing is then
dried by flushing with nitrogen. Drying can be accelerated by able compounds. This capability should be built into the
D2908 − 91 (2011)
injection system. When using on-column injection a shorter 8. Reagents and Materials
columnlifemayoccurduetosolidbuildupintheinjectionend
8.1 Purity of Reagents—Reagent grade chemicals shall be
of the column.
used in all instances for gas purification, sample stabilization,
and other applications. Unless otherwise indicated, it is in-
7.3 Column Oven—The column ovens usually are insulated
tended that all reagents shall conform to the specifications of
separately from the injection port and the detector. The oven
theCommitteeonAnalyticalReagentsoftheAmericanChemi-
should be equipped with a proportional heater and a squirrel-
cal Society, where such specifications are available. Other
cage blower to assure maximum temperature reproducibility
grades may be used, provided it is first ascertained that the
and uniformity throughout the oven. Reproducibility of oven
reagent is of sufficiently high purity to permit its use without
temperature should be within 0.5°C.
lessening the accuracy of the determination.
7.3.1 Temperature Programming—Temperature program-
8.1.1 All chemicals used for internal standards shall be of
ming is desirable when the analysis involves the resolution of
highest known purity.
organics with widely varying boiling points. The column oven
8.2 Purity of Water—Unless otherwise indicated, references
should be equipped with temperature programming be-
towatershallbeunderstoodtomeanreagentwaterconforming
tween−15 and 350°C (or range of the method) with select-
to Type I of Specification D1193.
ability of several programming rates between 1 and 20°/min
provided. The actual column temperature will lag somewhat
8.3 Carrier Gas System—Only gases of the highest purity
behind the oven temperature at the faster programming rates.
obtainable should be used in a chromatographic system desig-
Baseline drift will often occur because of increased higher
nated for trace-organic monitoring in water. The common
temperatures experienced during temperature programming.
carrier gases used with a flame ionization detector (FID) are
This depends on the stability of the substrate and operating
helium and nitrogen. Trace contaminants in even the highest
temperature range. Temperatures that approach the maximum
purity gases can often affect baseline stability and introduce
limit of the liquid phase limit the operating range. Utilization
noise. Absorption columns of molecular sieves (14 by 30-
of dual matching columns and a differential electrometer can
mesh) and anhydrous calcium sulfate (CaSO , 8 mesh) in
minimize the effect of drift; however, the drift is reproducible
series between the gas supply tank and the instrument will
and does not interfere with the analysis in most cases.
minimize the effect of trace impurities. These preconditioning
columns,toremaineffective,mustbecleanedbybackflushing
7.4 Detector—The combination of high sensitivity and a
them with a clean gas (nitrogen, helium) at approximately
widelinearrangemakestheflameionizationdetector(FID)the
200°C, or they must be replaced at regular intervals. Use of
usual choice in trace aqueous analysis. The flame ionization
catalytic purifiers is also effective (4).
detectorisrelativelyinsensitivetowatervaporandtomoderate
8.4 Column:
temperature changes if other operating parameters remain
unchanged. If temperature programming is used, the detector 8.4.1 Column Tubing—For most organic analyses in aque-
oussystems,stainlesssteelisthemostdesirablecolumntubing
should be isolated from the oven and heated separately to
material. However, when analyzing organics that are reactive
ensure uniform detector temperature.The detector temperature
with stainless steel. Fused silica capillary columns have been
should be set near the upper limit of the programmed tempera-
demonstrated as having equal, if not better, performance in all
ture to prevent condensation. The detector should also be
cases.Columnsof0.25,0.32,and0.5
...
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