ASTM D2908-91(2024)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2908 − 91 (Reapproved 2024)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E260 Practice for Packed Column Gas Chromatography
E355 Practice for Gas Chromatography Terms and Relation-
1.1 This practice covers general guidance applicable to
ships
certain test methods for the qualitative and quantitative deter-
mination of specific organic compounds, or classes of
3. Terminology
compounds, in water by direct aqueous injection gas chroma-
tography (1, 2, 3, 4).
3.1 Definitions—The following terms in this standard are
defined in accordance with Terminology D1129. For defini-
1.2 Volatile organic compounds at aqueous concentrations
tions of other chromatographic terms used in this standard,
greater than about 1 mg/L can generally be determined by
refer to Practice E355.
direct aqueous injection gas chromatography.
3.1.1 “ghosting” or memory peaks, n—an interference,
1.3 This standard does not purport to address all of the
showing as a peak, which appears at the same elution time as
safety concerns, if any, associated with its use. It is the
the organic component of previous analysis.
responsibility of the user of this standard to establish appro-
3.1.2 internal standard, n—a material present in or added to
priate safety, health, and environmental practices and deter-
samples in known amount to serve as a reference measurement.
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
3.1.3 noise, n—an extraneous electronic signal which affects
dance with internationally recognized principles on standard-
baseline stability.
ization established in the Decision on Principles for the
3.1.4 relative retention ratio, n—the retention time of the
Development of International Standards, Guides and Recom-
unknown component divided by the retention time of the
mendations issued by the World Trade Organization Technical
internal standard.
Barriers to Trade (TBT) Committee.
3.1.5 retention time, n—the time that elapses from the
2. Referenced Documents
introduction of the sample until the peak maximum is reached.
2.1 ASTM Standards:
D1129 Terminology Relating to Water 4. Summary of Practice
D1192 Guide 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
D1193 Specification for Reagent Water
or synthetic organics or both, in an aqueous medium for
D3370 Practices for Sampling Water from Flowing Process
subsequent detection with a flame ionization detector. After
Streams
vaporization, the aqueous sample is carried through the column
by an inert carrier gas. The sample components are partitioned
between the carrier gas and a stationary liquid phase on an inert
This practice is under the jurisdiction of ASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.06 on Methods for Analysis for solid support. The column effluent is burned in an air-hydrogen
Organic Substances in Water.
flame. The ions released from combustion of the organic
Current edition approved April 1, 2024. Published April 2024. Originally
components induce an increase in standing current which is
approved in 1970. Last previous edition approved in 2017 as D2908 – 91 (2017).
measured. Although this method is written for hydrogen flame
DOI: 10.1520/D2908-91R24.
The boldface numbers in parentheses refer to the list of references at the end of
detection, the basic technology is applicable to other detectors
this standard.
if water does not interfere.
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
4.2 The elution times are characteristic of the various
Standards volume information, refer to the standard’s Document Summary page on
organic components present in the sample, while the peak areas
the ASTM website.
are proportional to the quantities of the components. A discus-
The last approved version of this historical standard is referenced on
www.astm.org. sion of gas chromatography is presented in Practice E260.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2908 − 91 (2024)
5. Significance and Use increases due to the increasing temperature. An unsteady flow
will create an unstable baseline.
5.1 This practice is useful in identifying the major organic
7.1.2 Gas Transport Tubing—New tubing should be washed
constituents in wastewater for support of effective in-plant or
with a detergent solution, rinsed with Type I cold water, and
pollution control programs. Currently, the most practical means
solvent rinsed to remove residual organic preservatives or
for tentatively identifying and measuring a range of volatile
lubricants. Ethanol is an effective solvent. The tubing is then
organic compounds is gas-liquid chromatography. Positive
dried by flushing with nitrogen. Drying can be accelerated by
identification requires supplemental testing (for example, mul-
installing the tubing in a gas chromatograph (GC) oven and
tiple columns, speciality detectors, spectroscopy, or a combi-
flowing nitrogen or other inert gas through it, while heating the
nation of these techniques).
oven to 50 °C.
7.1.3 Gas Leaks—The gas system should be pressure
6. Interferences
checked daily for leaks. To check for leaks, shut off the detector
6.1 Particulate Matter—Particulate or suspended matter
and pressurize the gas system to approximately 103 kPa
should be removed by centrifugation or membrane filtration if
(15 psi) above the normal operating pressure. Then shut off the
components of interest are not altered. This pretreatment will
tank valve and observe the level of the pressure gauge. If the
prevent both plugging of syringes and formation of condensa-
preset pressure holds for 10 min, the system can be considered
tion nuclei. Acidification will often facilitate the dissolving of
leak-free. If the pressure drops, a leak is indicated and should
particulate matter, but the operator must determine that pH
be located and eliminated before proceeding further. A soap
adjustment does not alter the components to be determined.
solution may be used for determining the source of leaks, but
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
by removing the flame tip, replacing it with a closed fitting and
requires analyses with other columns with varying physical and
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
nents will be enhanced if the sample is made neutral or slightly
of the gas operating pressure.
acidic. This may minimize the formation of nonvolatile salts in
cases such as the analysis of volatile organic acids and bases 7.2 Injection Port—The injection port usually is insulated
and certain chlorophenols. from the chromatographic oven and equipped with a separate
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
peak that occurs at the same time as that for a component from
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
the injection port temperature should be reduced appropriately.
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.
5 μL, blowback into the carrier gas supply should be prevented
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.
repeated water injections and elevated column temperature will
7.2.1 Septum—Organics eluting from the septum in the
eliminate this problem. Back flush valves should be used if this
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 temperature similar to that of the injection port can also be used
should be used to ensure a steady flow of gas to the instrument. 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-fluorocarbon backings minimize organic bleeding and can
decrease in flow as the pressure drop across the column be used safely for longer periods.
D2908 − 91 (2024)
7.2.2 On-Column Injection—While injection into the heated fluctuations affect baseline stability, a voltage regulating trans-
chamber for flash vaporization is the most common injection former may be required in addition to the one incorporated
set-up, some analyses (for example, organic acids) are better within the chromatographic instrument.
performed with on-column injection to reduce ghosting and
8. Reagents and Materials
peak tailing and to prevent decomposition of thermally degrad-
able compounds. This capability should be built into the
8.1 Purity of Reagents—Reagent grade chemicals shall be
injection system. When using on-column injection a shorter
used in all instances for gas purification, sample stabilization,
column life may occur due to solid build up in the injection end
and other applications. Unless otherwise indicated, it is in-
of the column.
tended that all reagents shall conform to the specifications of
the Committee on Analytical Reagents of the American Chemi-
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
should be equipped with a proportional heater and a squirrel-
reagent is of sufficiently high purity to permit its use without
cage blower to assure maximum temperature reproducibility
lessening the accuracy of the determination.
and uniformity throughout the oven. Reproducibility of oven
8.1.1 All chemicals used for internal standards shall be of
temperature should be within 0.5 °C.
highest known purity.
7.3.1 Temperature Programming—Temperature program-
ming is desirable when the analysis involves the resolution of 8.2 Purity of Water—Unless otherwise indicated, references
organics with widely varying boiling points. The column oven to water shall be understood to mean reagent water conforming
should be equipped with temperature programming be- to Type I of Specification D1193.
tween −15 °C and 350 °C (or range of the method) with
8.3 Carrier Gas System—Only gases of the highest purity
selectability of several programming rates between 1°/min and
obtainable should be used in a chromatographic system desig-
20°/min provided. The actual column temperature will lag
nated for trace-organic monitoring in water. The common
somewhat behind the oven temperature at the faster program-
carrier gases used with a flame ionization detector (FID) are
ming rates. Baseline drift will often occur because of increased
helium and nitrogen. Trace contaminants in even the highest
higher temperatures experienced during temperature program-
purity gases can often affect baseline stability and introduce
ming. This depends on the stability of the substrate and
noise. Absorption columns of molecular sieves (14 by 30
operating temperature range. Temperatures that approach the
mesh) and anhydrous calcium sulfate (CaSO , 8 mesh) in
maximum limit of the liquid phase limit the operating range.
series between the gas supply tank and the instrument will
Utilization of dual matching columns and a differential elec-
minimize the effect of trace impurities. These preconditioning
trometer can minimize the effect of drift; however, the drift is
columns, to remain effective, must be cleaned by back flushing
reproducible and does not interfere with the analysis in most
them with a clean gas (nitrogen, helium) at approximately
cases.
200 °C, or they must be replaced at regular inter
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