ASTM D1945-03(2010)
(Test Method)Standard Test Method for Analysis of Natural Gas by Gas Chromatography
Standard Test Method for Analysis of Natural Gas by Gas Chromatography
SIGNIFICANCE AND USE
This test method is of significance for providing data for calculating physical properties of the sample, such as heating value and relative density, or for monitoring the concentrations of one or more of the components in a mixture.
SCOPE
1.1 This test method covers the determination of the chemical composition of natural gases and similar gaseous mixtures within the range of composition shown in Table 1. This test method may be abbreviated for the analysis of lean natural gases containing negligible amounts of hexanes and higher hydrocarbons, or for the determination of one or more components, as required.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D1945 − 03(Reapproved 2010)
Standard Test Method for
Analysis of Natural Gas by Gas Chromatography
This standard is issued under the fixed designation D1945; 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* into irregular peaks by reversing the direction of the carrier gas
through the column at such time as to group the heavy ends
1.1 This test method covers the determination of the chemi-
eitherasC andheavier,C andheavier,orC andheavier.The
5 6 7
cal composition of natural gases and similar gaseous mixtures
composition of the sample is calculated by comparing either
within the range of composition shown in Table 1. This test
the peak heights, or the peak areas, or both, with the corre-
method may be abbreviated for the analysis of lean natural
sponding values obtained with the reference standard.
gases containing negligible amounts of hexanes and higher
hydrocarbons, or for the determination of one or more
4. Significance and Use
components, as required.
4.1 This test method is of significance for providing data for
1.2 The values stated in inch-pound units are to be regarded
calculating physical properties of the sample, such as heating
as standard. The values given in parentheses are mathematical
value and relative density, or for monitoring the concentrations
conversions to SI units that are provided for information only
of one or more of the components in a mixture.
and are not considered standard.
5. Apparatus
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
5.1 Detector—The detector shall be a thermal-conductivity
responsibility of the user of this standard to establish appro-
type, or its equivalent in sensitivity and stability. The thermal
priate safety and health practices and determine the applica-
conductivity detector must be sufficiently sensitive to produce
bility of regulatory limitations prior to use.
a signal of at least 0.5 mV for 1 mol % n-butane in a 0.25-mL
sample.
2. Referenced Documents
5.2 Recording Instruments—Either strip-chart recorders or
2.1 ASTM Standards:
electronicintegrators,orboth,areusedtodisplaytheseparated
D2597 Test Method for Analysis of Demethanized Hydro-
components. Although a strip-chart recorder is not required
carbon Liquid Mixtures Containing Nitrogen and Carbon
when using electronic integration, it is highly desirable for
Dioxide by Gas Chromatography
evaluation of instrument performance.
D3588 Practice for Calculating Heat Value, Compressibility
5.2.1 The recorder shall be a strip-chart recorder with a
Factor, and Relative Density of Gaseous Fuels
full-range scale of 5 mVor less (1 mVpreferred).The width of
E260 Practice for Packed Column Gas Chromatography
the chart shall be not less than 150 mm. A maximum pen
response time of2s(1s preferred) and a minimum chart speed
3. Summary of Test Method
of 10 mm/min shall be required. Faster speeds up to 100
3.1 Components in a representative sample are physically
mm/min are desirable if the chromatogram is to be interpreted
separated by gas chromatography (GC) and compared to
using manual methods to obtain areas.
calibration data obtained under identical operating conditions
5.2.2 Electronic or Computing Integrators—Proof of sepa-
from a reference standard mixture of known composition. The
ration and response equivalent to that for a recorder is required
numerous heavy-end components of a sample can be grouped
for displays other than by chart recorder. Baseline tracking
with tangent skim peak detection is recommended.
5.3 Attenuator—If the chromatogram is to be interpreted
ThistestmethodisunderthejurisdictionofASTMCommitteeD03onGaseous
using manual methods, an attenuator must be used with the
Fuels and is the direct responsibility of Subcommittee D03.07 on Analysis of
Chemical Composition of Gaseous Fuels.
detector output signal to maintain maximum peaks within the
Current edition approved Jan. 1, 2010. Published March 2010. Originally
recorder chart range.The attenuator must be accurate to within
approved in 1962. Last previous edition approved in 2003 as D1945–96(2003).
0.5 % between the attenuator range steps.
DOI: 10.1520/D1945-03R10.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.4 Sample Inlet System:
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.4.1 The sample inlet system shall be constructed of
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. materials that are inert and nonadsorptive with respect to the
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1945 − 03 (2010)
TABLE 1 Natural Gas Components and Range of
5.5.1 Isothermal—When isothermal operation is used,
Composition Covered
maintain the analyzer columns at a temperature constant to
Component Mol %
0.3°C during the course of the sample run and corresponding
Helium 0.01 to 10
reference run.
Hydrogen 0.01 to 10
5.5.2 Temperature Programming—Temperature program-
Oxygen 0.01 to 20
Nitrogen 0.01 to 100 ming may be used, as feasible. The oven temperature shall not
Carbon dioxide 0.01 to 20
exceed the recommended temperature limit for the materials in
Methane 0.01 to 100
the column.
Ethane 0.01 to 100
Hydrogen sulfide 0.3 to 30
5.6 Detector Temperature Control—Maintain the detector
Propane 0.01 to 100
temperature at a temperature constant to 0.3°C during the
Isobutane 0.01 to 10
n-Butane 0.01 to 10
course of the sample run and the corresponding reference run.
Neopentane 0.01 to 2
The detector temperature shall be equal to or greater than the
Isopentane 0.01 to 2
n-Pentane 0.01 to 2 maximum column temperature.
Hexane isomers 0.01 to 2
5.7 Carrier Gas Controls—The instrument shall be
Heptanes+ 0.01 to 1
equippedwithsuitablefacilitiestoprovideaflowofcarriergas
through the analyzer and detector at a flow rate that is constant
to 1 % throughout the analysis of the sample and the reference
components in the sample. The preferred material of construc-
standard. The purity of the carrier gas may be improved by
tion is stainless steel. Copper, brass, and other copper-bearing
flowingthecarriergasthroughselectivefilterspriortoitsentry
alloys are unacceptable. The sample inlet system from the
into the chromatograph.
cylinder valve to the GC column inlet must be maintained at a
temperature constant to 61°C.
5.8 Columns:
5.4.2 Provision must be made to introduce into the carrier
5.8.1 The columns shall be constructed of materials that are
gas ahead of the analyzing column a gas-phase sample that has
inert and nonadsorptive with respect to the components in the
been entrapped in a fixed volume loop or tubular section. The
sample. The preferred material of construction is stainless
fixed loop or section shall be so constructed that the total
steel. Copper and copper-bearing alloys are unacceptable.
volume, including dead space, shall not normally exceed 0.5
5.8.2 An adsorption-type column and a partition-type col-
mL at 1 atm. If increased accuracy of the hexanes and heavier
umn may be used to make the analysis.
portionsoftheanalysisisrequired,alargersamplesizemaybe
NOTE 2—See Practice E260.
used (see Test Method D2597). The sample volume must be
reproducible such that successive runs agree within 1 % on
5.8.2.1 Adsorption Column—This column must completely
each component. A flowing sample inlet system is acceptable
separate oxygen, nitrogen, and methane. A 13X molecular
as long as viscosity effects are accounted for.
sieve 80/100 mesh is recommended for direct injection. A 5A
column can be used if a pre-cut column is present to remove
NOTE 1—The sample size limitation of 0.5 mL or smaller is selected
relative to linearity of detector response, and efficiency of column interferinghydrocarbons.Ifarecorderisused,therecorderpen
separation. Larger samples may be used to determine low-quantity
must return to the baseline between each successive peak. The
components to increase measurement accuracy.
resolution (R) must be 1.5 or greater as calculated in the
5.4.3 An optional manifold arrangement for entering following equation:
vacuum samples is shown in Fig. 1.
x 2 x
2 1
R~1,2! 5 32, (1)
5.5 Column Temperature Control: y 1y
2 1
FIG. 1 Suggested Manifold Arrangement for Entering Vacuum Samples
D1945 − 03 (2010)
where x ,x are the retention times and y ,y are the peak loop with up to two atmospheres of sample pressure, thus
1 2 1 2
widths. Fig. 2 illustrates the calculation for resolution. Fig. 3 is extending the range of all components. The well type inher-
a chromatogram obtained with an adsorption column. ently offers better precision and is preferred when calibrating
5.8.2.2 Partition Column—This column must separate eth- with pure components. Samples with up to one atmosphere of
anethroughpentanes,andcarbondioxide.Ifarecorderisused, pressure can be entered. With either type manometer the mm
therecorderpenmustreturntothebaselinebetweeneachpeak scale can be read more accurately than the inch scale. Caution
for propane and succeeding peaks, and to base line within 2 % should be used handling mercury because of its toxic nature.
of full-scale deflection for components eluted ahead of Avoid contact with the skin as much as possible. Wash
propane, with measurements being at the attenuation of the thoroughly after contact.
peak. Separation of carbon dioxide must be sufficient so that a
5.12 Vacuum Pump—Must have the capability of producing
0.25-mL sample containing 0.1-mol % carbon dioxide will
a vacuum of 1 mm of mercury absolute or less.
produce a clearly measurable response. The resolution (R)
must be 1.5 or greater as calculated in the above equation. The
6. Preparation of Apparatus
separation should be completed within 40 min, including
6.1 Linearity Check—To establish linearity of response for
reversal of flow after n-pentane to yield a group response for
the thermal conductivity detector, it is necessary to complete
hexanes and heavier components. Figs. 4-6 are examples of
the following procedure:
chromatograms obtained on some of the suitable partition
6.1.1 The major component of interest (methane for natural
columns.
gas) is charged to the chromatograph by way of the fixed-size
5.8.3 General—Other column packing materials that pro-
sample loop at partial pressure increments of 13 kPa (100 mm
vide satisfactory separation of components of interest may be
Hg) from 13 to 100 kPa (100 to 760 mm Hg) or the prevailing
used(seeFig.7).Inmulticolumnapplications,itispreferredto
atmospheric pressure.
use front-end backflush of the heavy ends.
6.1.2 Theintegratedpeakresponsesfortheareageneratedat
each of the pressure increments are plotted versus their partial
NOTE 3—The chromatograms in Figs. 3-8 are only illustrations of
typical separations. The operating conditions, including columns, are also
pressure (see Fig. 9).
typical and are subject to optimization by competent personnel.
6.1.3 The plotted results should yield a straight line. A
5.9 Drier—Unless water is known not to interfere in the
perfectly linear response would display a straight line at a 45°
analysis, a drier must be provided in the sample entering angle using the logarithmic values.
system, ahead of the sample valve. The drier must remove
6.1.4 Any curved line indicates the fixed volume sample
moisture without removing selective components to be deter- loop is too large. A smaller loop size should replace the fixed
mined in the analysis.
volume loop and 6.1.1 through 6.1.4 should be repeated (see
Fig. 9).
NOTE 4—See A2.2 for preparation of a suitable drier.
6.1.5 The linearity over the range of interest must be known
5.10 Valves—Valves or sample splitters, or both, are re-
for each component. It is useful to construct a table noting the
quired to permit switching, backflushing, or for simultaneous
response factor deviation in changing concentration. (See
analysis.
Table 2 and Table 3).
5.11 Manometer—May be either U-tube type or well type 6.1.6 It should be noted that nitrogen, methane, and ethane
equipped with an accurately graduated and easily read scale exhibit less than 1 % compressibility at atmospheric pressure.
covering the range 0 to 900 mm (36 in.) of mercury or larger. Other natural gas components do exhibit a significant com-
The U-tube type is useful, since it permits filling the sample pressibility at pressures less than atmospheric.
FIG. 2 Calculation for Resolution
D1945 − 03 (2010)
FIG. 3 Separation Column for Oxygen, Nitrogen, and Methane (See Annex A2)
FIG. 4 Chromatogram of Natural Gas (BMEE Column) (See Annex A2)
6.1.7 Most components that have vapor pressures of less B 5 ~100 3 V!/i (2)
than 100 kPa (15 psia) cannot be used as a pure gas for a
P 5 i 3 M /100 (3)
~ !
linearity study because they will not exhibit sufficient vapor
where:
pressure for a manometer reading to 100 kPa (760 mm Hg).
B = blend pressure, max, kPa (mm Hg);
For these components, a mixture with nitrogen or methane can
V = vapor pressure, kPa (mm Hg);
be used to establish a partial pressure that can extend the total
i = mol %;
pressure to 100 kPa (760 mm Hg). Using Table 4 for vapor
P = partial pressure, kPa (mm Hg); and
pressures at 38°C (100°F), calculate the maximum pressure to
M = manometer pressure, kPa (mm Hg).
which a given component can be blended with nitrogen as
follows: 6.2 . Procedure for Linearity Check:
D1945 − 03 (2010)
FIG. 5 Chromatogram of Natural Gas (Silicone 200/500 Column) (See Annex A2)
FIG. 6 Chromatogram of Natural Gas (See Annex A2)
6.2.1 Connect the pure-component source to the sample- 6.2.2 Carefully open the needle valve to admit the pure
entry system. Evacuate the sample-entry system and observe
component up to 13 kPa (100 mm Hg) of partial pressure.
the manometer for leaks. (See Fig. 1 for a suggested manifold
arrangement.) The sample-entry system must be vacuum tight.
D1945 − 03 (2010)
FIG. 7 Chromatogram of Natural Gas (Multi-Column Application) (See Annex A2)
FIG. 8 Separation of Helium and Hydrogen
6.2.3 Record the exact partial pressure and actuate the 6.2.5 Plot the area data (x axis) versus the partial pressures
sample valve to place the sample onto the column. Record the (y axis
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.