ASTM D2908-91(2001)
(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
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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An American National Standard
Designation:D 2908–91(Reapproved 2001)
Standard Practice for
Measuring Volatile Organic Matter in Water by Aqueous-
Injection Gas Chromatography
This standard is issued under the fixed designation D 2908; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 “ghosting” or memory peaks—an interference, show-
ing as a peak, which appears at the same elution time as the
1.1 This practice covers general guidance applicable to
organic component of previous analysis.
certain test methods for the qualitative and quantitative deter-
3.1.2 internal standard—a material present in or added to
mination of specific organic compounds, or classes of com-
samplesinknownamounttoserveasareferencemeasurement.
pounds, in water by direct aqueous injection gas chromatogra-
2 3.1.3 noise—an extraneous electronic signal which affects
phy (1, 2, 3, 4).
baseline stability.
1.2 Volatile organic compounds at aqueous concentrations
3.1.4 retention time—the time that elapses from the intro-
greater than about 1 mg/L can generally be determined by
duction of the sample until the peak maximum is reached.
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-
3.2 For definitions of other chromatographic terms used in
priate safety and health practices and determine the applica-
this practice, refer to Practice E355.
bility of regulatory limitations prior to use.
4. Summary of Practice
2. Referenced Documents
4.1 This practice defines the applicability of various col-
2.1 ASTM Standards:
umns and conditions for the separation of naturally occurring
D1129 Terminology Relating to Water
or synthetic organics or both, in an aqueous medium for
D1192 Specification for Equipment for Sampling Water
subsequent detection with a flame ionization detector. After
and Steam in Closed Conduits
vaporization,theaqueoussampleiscarriedthroughthecolumn
D1193 Specification for Reagent Water
by an inert carrier gas.The sample components are partitioned
D2580 Test Method for Phenols in Water by Gas-Liquid
betweenthecarriergasandastationaryliquidphaseonaninert
Chromatography
solidsupport.Thecolumneffluentisburnedinanair-hydrogen
D3370 Practices for Sampling Water from Closed Con-
flame. The ions released from combustion of the organic
duits
5 components induce an increase in standing current which is
E260 Practice for Packed Column Gas Chromatography
measured.Although this method is written for hydrogen flame
E355 Practice for Gas Chromatography Terms and Rela-
5 detection, the basic technology is applicable to other detectors
tionships
if water does not interfere.
3. Terminology 4.2 The elution times are characteristic of the various
organiccomponentspresentinthesample,whilethepeakareas
3.1 Definitions—The following terms in this practice are
are proportional to the quantities of the components.Adiscus-
defined in accordance with Terminology D1129.
sion of gas chromatography is presented in Practice E260.
1 5. Significance and Use
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
5.1 This practice is useful in identifying the major organic
Organic Substances in Water.
constituents in wastewater for support of effective in-plant or
Current edition approved Dec. 15, 1991. Published April 1992. Originally
pollutioncontrolprograms.Currently,themostpracticalmeans
published as D2908–70T. Last previous edition D2908–87.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
for tentatively identifying and measuring a range of volatile
this practice.
organic compounds is gas-liquid chromatography. Positive
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 11.02.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2908–91 (2001)
identification requires supplemental testing (for example, mul- 7.1.3 Gas Leaks—The gas system should be pressure
tiple columns, speciality detectors, spectroscopy, or a combi- checkeddailyforleaks.Tocheckforleaks,shutoffthedetector
nation of these techniques).
and pressurize the gas system to approximately 103 kPa (15
psi) above the normal operating pressure. Then shut off the
6. Interferences
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-
7.2 Injection Port—The injection port usually is insulated
nentswillbeenhancedifthesampleismadeneutralorslightly
from the chromatographic oven and equipped with a separate
acidic.Thismayminimizetheformationofnonvolatilesaltsin
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.
increases due to the increasing temperature.An unsteady flow
7.2.2 On-Column Injection—Whileinjectionintotheheated
will create an unstable baseline.
chamber for flash vaporization is the most common injection
7.1.2 Gas Transport Tubing—Newtubingshouldbewashed
set-up, some analyses (for example, organic acids) are better
with a detergent solution, rinsed with Type I cold water, and
performed with on-column injection to reduce ghosting and
solvent rinsed to remove residual organic preservatives or
peaktailingandtopreventdecompositionofthermallydegrad-
lubricants. Ethanol is an effective solvent. The tubing is then
able compounds. This capability should be built into the
dried by flushing with nitrogen. Drying can be accelerated by
installing the tubing in a gas chromatograph (GC) oven and injection system. When using on-column injection a shorter
columnlifemayoccurduetosolidbuildupintheinjectionend
flowingnitrogenorotherinertgasthroughit,whileheatingthe
oven to 50°C. of the column.
D 2908–91 (2001)
7.3 Column Oven—The column ovens usually are insulated cal Society, where such specifications are available. Other
separately from the injection port and the detector. The oven grades may be used, provided it is first ascertained that the
reagent is of sufficiently high purity to permit its use without
should be equipped with a proportional heater and a squirrel-
cage blower to assure maximum temperature reproducibility lessening the accuracy of the determination.
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-
usual choice in trace aqueous analysis. The flame ionization
oussystems,stainlesssteelisthemostdesirablecolumntubing
detectorisrelativelyinsensitivetowatervaporandtomoderate
material. However, when analyzing organics that are reactive
temperature changes if other operating parameters remain
with stainless steel. Fused silica capillary columns have been
unchanged. If temperature programming is used, the detector
demonstrated as having equal, if not better, performance in all
should be isolated from the oven and heated separately to
cases.Columnsof0.25,0.32,and0.53mminsidediameterare
ensure uniform detector temperature.The detector temperature
readily available from most suppliers of fused silica. With a
should be set near the upper limit of the programmed tempera-
flame ionization detector, maximum resolution with packed
ture to prevent condensation. The detector should also be
columns is achieved with long, small-diameter (3.175-mm
shielded from air currents which could affect the burning
(0.125-in.) and smaller) tubing. New tubing should be washed
characteristics of the flame. Sporadic spiking in the baseline
as described in 7.1.2.
indicates detector contamination; cleaning, preferably with
8.4.2
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