ASTM D6228-98(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D6228–98 (Reapproved 2003)
Standard Test Method for
Determination of Sulfur Compounds in Natural Gas and
Gaseous Fuels by Gas Chromatography and Flame
Photometric Detection
This standard is issued under the fixed designation D6228; 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 D1072 Test Method for Total Sulfur in Fuel Gases by
Combustion and Barium Chloride Titration
1.1 This test method covers the determination of individual
D1265 Practice for Sampling Liquefied Petroleum (LP)
volatile sulfur-containing compounds in gaseous fuels by gas
Gases, Manual Method
chromatography(GC)withflamephotometricdetection(FPD).
D1945 Test Method for Analysis of Natural Gas by Gas
The detection range for sulfur compounds is from 20 to 20 000
Chromatography
picograms (pg) of sulfur. This is equivalent to 0.02 to 20
D3609 Practice for Calibration Techniques Using Perme-
mg/m or 0.014 to 14 ppmv of sulfur based upon the analysis
ation Tubes
of a 1-mL sample.
D4468 Test Method for Total Sulfur in Gaseous Fuels by
1.2 This test method describes a GC-FPD method using a
Hydrogenolysis and Rateometric Colorimetry
specific capillary GC column. Other GC-FPD methods, with
D4626 Practice for Calculation of Gas Chromatographic
differences in GC column and equipment setup and operation,
Response Factors
may be used as alternative methods for sulfur compound
D5287 Practice for Automatic Sampling of Gaseous Fuels
analysis with different range and precision, provided that
D5504 Test Method for Determination of Sulfur Com-
appropriate separation of the sulfur compounds of interest can
pounds in Natural Gas and Gaseous Fuels by Gas Chro-
be achieved.
matography and Chemiluminescence
1.3 This test method does not intend to identify all indi-
E840 Practice for Using Flame Photometric Detectors in
vidual sulfur species. Total sulfur content of samples can be
Gas Chromatography
estimated from the total of the individual compounds deter-
2.2 EPA Standards:
mined. Unknown compounds are calculated as monosulfur-
EPA–15 Determination of Hydrogen Sulfide, Carbonyl Sul-
containing compounds.
fide and Carbon Disulfide Emissions from Stationary
1.4 The values stated in SI units are to be regarded as
Sources, 40 CFR, Chapter 1, Part 60, Appendix A
standard. The values stated in inch-pound units are for infor-
EPA–16 Semicontinuous Determination of Sulfur Emis-
mation only.
sions from Stationary Sources, 40 CFR, Chapter 1, Part
1.5 This standard does not purport to address all the safety
60, Appendix A
concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and
3. Terminology
health practices and determine the applicability of regulatory
3.1 Abbreviations:
limitations prior to use.
3.1.1 A common abbreviation of a hydrocarbon compound
2. Referenced Documents is to designate the number of carbon atoms in the compound.
A prefix is used to indicate the carbon chain form, while a
2.1 ASTM Standards:
subscript suffix denotes the number of carbon atoms, for
example, normal decane = n-C , isotetradecane = i-C .
10 14
ThistestmethodisunderthejurisdictionofASTMCommitteeD03onGaseous
3.1.2 Sulfur compounds commonly are referred to by their
Fuels and is the direct responsibility of Subcommittee D03.05 on Determination of
initials, chemical or formula, for example, methyl mercaptan =
Special Constituents of Gaseous Fuels.
MeSH, dimethyl sulfide = DMS, carbonyl sulfide = COS,
Current edition approved May 10, 2003. Published August 2003. Originally
approved in 1998. Last previous edition approved in 1998 as D6228 – 98. DOI:
di-t-butyl trisulfide = DtB-TS, and tetrahydothiophene = THT
10.1520/D6228-98R03.
or thiophane.
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
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6228–98 (2003)
4. Summary of Test Method including fixed gas and organic components (see Test Method
D1945). This test method dictates the use of a specific GC
4.1 Sulfur analysis ideally is performed on-site to eliminate
technique with one of the more common detectors for mea-
potential sample deterioration during storage. The reactive
surement.
nature of sulfur components may pose problems both in
sampling and analysis. Samples should be collected and stored
6. Apparatus
in containers that are nonreactive to sulfur compounds, such as
6.1 Chromatograph—Any gas chromatograph that has the
Tedlar bags. Sample containers should be filled and purged at
following performance characteristics can be used.
least three times to ensure representative sampling. Laboratory
6.1.1 Sample Inlet System—Gas samples are introduced to
equipment also must be inert, well conditioned, and passivated
the gas chromatograph using an automated or manually oper-
with a gas containing the sulfur compounds of interest to
ated stainless steel gas sampling valve enclosed in a heated
ensure reliable results. Frequent calibration and daily verifica-
valve oven, which must be capable of operating continuously
tion of calibration curve using stable standards are required.
at a temperature of 50°C above the temperature at which the
Samples should be analyzed within 24 h of collection to
gaswassampled.TFE-fluorocarbontubingmadeoffluorinated
minimize sample deterioration. If the stability of analyzed
ethylene propylene (FEP), 316 stainless steel tubing, or other
sulfur components is proved experimentally, the time between
tubing made of nonpermeable, nonsorbing, and nonreactive
collection and analysis may be lengthened.
materials, as short as possible and heat traced at the same
4.2 A 1-mL sample of the fuel gas is injected into a gas
temperature, should be used for transferring the sample from a
chromatograph where it is passed through a 60-m, 0.53-mm
sample container to the gas-sampling valve. A 1.0-mL sam-
inside diameter (ID), thick film, methyl silicone liquid phase,
pling loop made of nonreactive materials, such as deactivated
open tubular partitioning column, or a similar column capable
fused silica or 316 stainless steel is used to avoid possible
of separating sulfur components.
decomposition of reactive sulfur species. Other size fixed-
4.3 Flame Photometric Detectors—When combusted in a
volumesamplingloopsmaybeusedfordifferentconcentration
hydrogen-rich flame, sulfur compounds emit light energy
ranges. A 1- to 2-m section of deactivated precolumn attached
characteristic to all sulfur species. The light is detected by a
to the front of the analytical column is recommended. The
photomultipliertube(PMT).ThePMTresponseisproportional
precolumn is connected directly to the gas sampling valve for
to the concentration or the amount of sulfur. All sulfur
on-column injection. The inlet system must be well condi-
compounds including sulfur odorants can be detected by this
tioned and evaluated frequently for compatibility with trace
technique.
quantities of reactive sulfur compounds, such as tert-butyl
4.4 Other Detectors—This test method is written primarily
mercaptan.
for the flame photometric detector. The same gas chromato-
6.1.2 Digital Pressure Transmitter—A calibrated stainless
graphic (GC) method can be used with other sulfur-specific
steel pressure/vacuum transducer with a digital readout may be
detectors provided they have sufficient sensitivity and selectiv-
equipped to allow sampling at different pressures to generate
ity to all sulfur compounds of interest in the required measure-
calibration curves.
ment range.
6.1.3 Column Temperature Programmer—The chromato-
4.5 Other GC Test Methods—The GC test methods using
graph must be capable of linear programmed temperature
sulfur chemiluminescence, reductive rateometric, and electro-
operation over a range from 30 to 200°C, in programmed rate
chemical detectors are available or under development.
settings of 0.1 to 30°C/min. The programming rate must be
sufficiently reproducible to obtain retention time repeatability
5. Significance and Use
of 0.05 min (3 s).
5.1 Many sources of natural gas and petroleum gases
6.1.4 Carrier and Detector Gas Control—Constant flow
containvaryingamountsandtypesofsulfurcompounds,which
control of carrier and detector gases is critical to optimum and
are odorous, corrosive to equipment, and can inhibit or destroy
consistent analytical performance. Control is best provided by
catalystsusedingasprocessing.Theiraccuratemeasurementis
the use of pressure regulators and fixed flow restrictors. The
essential to gas processing, operation, and utilization.
gas flow rate is measured by any appropriate means and the
5.2 Small amounts, typically, 1 to 4 ppmv of sulfur odorant
required gas flow indicated by the use of a pressure gage. Mass
compounds, are added to natural gas and liquefied petroleum
flow controllers, capable of maintaining gas flow constant to
(LP) gases for safety purposes. Some odorant compounds can
61 % at the required flow rates also can be used. The supply
be reactive and may be oxidized, forming more stable com-
pressure of the gas delivered to the gas chromatograph must be
pounds having lower odor thresholds. These gaseous fuels are
at least 69 kPa (10 psi) greater than the regulated gas at the
analyzed for sulfur odorants to help ensure appropriate odorant
instrument to compensate for the system back pressure. In
levels for safety.
general, a supply pressure of 552 kPa (80 psig) will be
5.3 This test method offers a technique to determine indi-
satisfactory.
vidualsulfurspeciesingaseousfuelandthetotalsulfurcontent
6.1.5 Detector—A flame photometric detector calibrated in
by calculation. Gas chromatography is used commonly and
the sulfur-specific mode is used for this test method. Other
extensively to determine other components in gaseous fuels
detectors as mentioned in 4.4 will not be covered in this test
method. This detector may be obtained from various manufac-
turers; however, there are variations in design. The pulsed
Registered trademark. Available from DuPont de Nemours, E. I., & Co., Inc.,
Barley Mill Plaza, Bldg. 10, Wilmington, DE 19880–0010. flame photometric detector (PFPD) is one of the new FPD
D6228–98 (2003)
designs. The pressure and flow rate of the hydrogen and air tration is calculated by mass loss and dilution gas flow rate.
gases used in the detector may be different. The selection of Impurities permeated from each tube must be detected, mea-
which detector to use should be based on its performance for sured, and accounted for in the mass loss, if they are present
the intended application. The detector should be set according above a level of 0.1 % of the permeated sulfur species. See
to the manufacturer’s specifications and tuned to the best Practice D3609.
performance of sensitivity and selectivity as needed. 7.2 Compressed Cylinder Gas Standards—As an alterna-
6.1.5.1 When sulfur-containing compounds are burned in a tive, blended gaseous sulfur standards may be used if a means
hydrogen-rich flame, they quantitatively produce a S * species to ensure accuracy and stability of the mixture is available.
in an excited state (Eq 1 and Eq 2). The light emitted from this These mixtures can be a source of error if their stability during
species is detected by a photomultiplier tube (PMT) (Eq 3). A storage cannot be guaranteed. (Warning—Sulfur compounds
393-nm bandpass optical filter is normally used to enhance the may be flammable and harmful or fatal if ingested or inhaled.)
selectivityofdetection.Theselectivitynormallyisabout10 to 7.3 Carrier Gas—Helium or nitrogen of high purity
1 by mass of sulfur to mass of carbon. (99.999 % min purity). (Warning—Helium and nitrogen are
compressed gases under high pressure.)Additional purification
RS 1 O → n CO 1 SO (1)
2 2 2
is recommended by the use of molecular sieves or other
2SO 14H →4H O 1 S * (2)
2 2 2 2
suitable agents to remove water, oxygen, and hydrocarbons.
S *→ S 1 hn (3)
2 2
Available pressure must be sufficient to ensure a constant
carrier gas flow rate (see 6.1.4).
where:
7.4 Hydrogen—Hydrogen of high purity (99.999 % min
hn = emitted light energy.
purity) is used as fuel for the flame photometric detector
6.1.5.2 The intensity of light is not linear with the sulfur
(FPD). (Warning—Hydrogen is an extremely flammable gas
concentration but is proportional approximately to the square
under high pressure.)
of the sulfur concentration. The relationship between the FPD
7.5 Air—High-purity (99.999 % min purity) compressed air
response (R ) and the sulfur concentration (S) is given by Eq
D
is used as the oxidant for the flame photometric detector (FPD)
4 and Eq 5. The n-factor usually is less than 2.0.
(Warning—Compressed air is a gas under high pressure that
n
R a [S# (4)
D
supports combustion.).
Log [S# a 1/n Log R (5)
8. Preparation of Apparatus and Calibration
where:
8.1 Chromatograph—Place in service in accordance with
n = exponential factor (1.7 to 2.0).
the manufacturer’s instructions. Typical operating conditions
6.1.5.3 The linear calibration curve can be made using a
are shown in Table 1.
log-log plot. Some instruments use an electronic linearizer to
8.2 FPD—Place the detector in service in accordance with
produce a signal with direct linear response. The dynamic
the manufacturer’s instructions. Hydrogen and air flows are
range of this linear relationship is about 1 3 10 .
critical and must be adjusted properly in accordance with the
6.2 Column—A 60- by 0.53-m ID fused silica open tubular
instruction furnished by the manufacturer. With the FPD flame
column containing a 5-µm film thickness of bonded methyl
ignited, monitor the signal to verify compliance with the signal
silicone liquid phase is used. The column shall provide
noise and drift specified by the manufacturer. The FPD flame
adequate retention and resolution characteristics under the
should be maintained to give consistent and optimum sensitiv-
experimental conditions described in 7.3. Other columns,
ity for the detection range.
which can provide equivalent separation, can be used as well.
8.2.1 Sample Injection—A sample loop of 1.0 mL of suit-
6.3 Data Acquisition:
able size for sample injection may be used for performance
6.3.1 Recorder—A 0- to 1-mV range recording potentiom-
check. A linear calibration curve may be determined by
...