ASTM D7994-17

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: D7994 − 17
Standard Test Method for
Total Fluorine, Chlorine, and Sulfur in Liquid Petroleum Gas
(LPG) by Oxidative Pyrohydrolytic Combustion Followed by
Ion Chromatography Detection (Combustion Ion
Chromatography-CIC)
This standard is issued under the fixed designation D7994; 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 ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method covers the individual determination of
mendations issued by the World Trade Organization Technical
total fluorine, chlorine, and sulfur in liquid petroleum gas
Barriers to Trade (TBT) Committee.
(LPG), low molecular weight hydrocarbons, their mixtures,
and dimethyl ether (DME) in the range of 1mg⁄kg to
2. Referenced Documents
300mg⁄kg fluorine and sulfur and 5mg⁄kg to 300mg⁄kg for
chlorine. This test method is applicable to products described
2.1 ASTM Standards:
in Specifications D1835 and D7901 and it can be applicable to
D1193Specification for Reagent Water
process streams with similar properties to LPG and other
D1265Practice for Sampling Liquefied Petroleum (LP)
materials such as butylene, propylene, and olefins.
Gases, Manual Method
D1835Specification for Liquefied Petroleum (LP) Gases
1.2 Thistestmethodcanalsobeappliedtothemeasurement
D3700Practice for Obtaining LPG Samples Using a Float-
of the bromine and iodine in samples covered by the scope of
ing Piston Cylinder
this test method, but the precision and bias statement of this
D6849Practice for Storage and Use of Liquefied Petroleum
test method is not applicable to these halides.
Gases (LPG) in Sample Cylinders for LPG Test Methods
1.3 This test method can be applied to sample concentra-
D7901Specification for Dimethyl Ether for Fuel Purposes
tionsoutsidethescopeofthistestmethodthroughadjustments
E29Practice for Using Significant Digits in Test Data to
of sample injection volume or number of injections combusted
Determine Conformance with Specifications
(or both), adjustment of injection volume to the ion
E288Specification for Laboratory Glass Volumetric Flasks
chromatograph, and adjustment of the final dilution volume of
E969Specification for Glass Volumetric (Transfer) Pipets
the absorbing solution prior to injection to the ion chromato-
2.2 OSHA Standards:
graph. The precision and scope of this test method is not
29 CFR Part 1910.1000Air Contaminants
applicable to samples that are outside the scope of the method.
29 CFR Part 1910.1200Hazard Communication
1.4 The values stated in SI units are to be regarded as
standard.
3. Terminology
1.4.1 Exception—Values given in parentheses are for infor-
3.1 Definitions:
mation only.
3.1.1 combustion ion chromatography (CIC), n—ananalyti-
1.5 This standard does not purport to address all of the
cal system consisting of oxidative pyrohydrolytic combustion
safety concerns, if any, associated with its use. It is the
followed by ion chromatographic detection.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.1.2 halogen (X), n—a generic term which includes the
bility of regulatory limitations prior to use. See Section 9.
elements fluorine, chlorine, bromine, and iodine.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee D02 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Standards volume information, refer to the standard’s Document Summary page on
Subcommittee D02.H0 on Liquefied Petroleum Gas. the ASTM website.
Current edition approved Jan. 1, 2017. Published April 2017. DOI: 10.1520/ Available from Occupational Safety and Health Administration (OSHA), 200
D7994-17. Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7994 − 17
3.1.3 hydrogen halide (HX), n—inorganic compounds with 3.3.3 CRM—certified reference material
the formula HX where X is one of the halogens: fluoride,
3.3.4 DME—dimethyl ether
chloride, bromide, and iodide.
3.3.5 HCl—hydrogen chloride
3.1.3.1 Discussion—Hydrogen halides are gases that dis-
3.3.6 HF—hydrogen fluoride
solve in water to give acids.
3.3.7 HX—hydrogen halide
3.1.4 nitrogen oxides (NO ), n—one or more of the follow-
X
3.3.8 IC—ion chromatograph or ion chromatography
ing compounds: nitric oxide (NO), nitrogen dioxide (NO ).
3.3.9 MW—molecular weight
3.1.5 oxidative pyrohydrolytic combustion, n—a process in
3.3.10 LPG—liquefied petroleum gas
which a sample is burned in an oxygen-rich environment at
temperaturesgreaterthan900°Candinthepresenceofexcess
3.3.11 NO —nitrogen oxides (NO and NO )
X 2
watervapornotoriginatingfromthecombustionofthesample.
3.3.12 NO—nitric oxide
3.1.5.1 Discussion—In oxidative pyrohydrolytic
3.3.13 NO —nitrogen dioxide
combustion, the sample is converted into carbon dioxide, 3–
3.3.14 PO —phosphate
water, hydrogen halides (HX), and elemental oxides such as
3.3.15 RSD—relative standard deviation
NO and SO .
X X
3.3.16 SRM—standard reference material
3.1.6 sulfur oxides (SO ), n—one or more of the following
X
chemical species: sulfur dioxide (SO ), sulfur trioxide (SO ),
3.3.17 SO —sulfur oxides (SO, SO,SO,SO,S O , and
2 3
X 2 3 4 2 3
2–
sulfate (SO ).
S O )
2 7
3.2 Definitions of Terms Specific to This Standard: 3.3.18 SO —sulfur dioxide
3.2.1 LPG calibration blank, n—theLPG(usuallybutaneor
3.3.19 SO —sulfur trioxide
propane) used in the preparation of the LPG calibration
2–
3.3.20 SO —sulfate
standards (3.2.2).
3.2.2 LPG calibration standard, n—a material, usually pre- 4. Summary of Test Method
pared in butane or propane, and subsequently used for calibra-
4.1 Using an LPG sampling device with a fixed volume
tion the CIC System (3.1.1).
liquid injection loop, a pressurized sample is introduced at a
3.2.3 LPG check standard, n—a reference material, usually controlled rate into a high-temperature combustion tube where
prepared in butane or propane, which is used to verify
the sample is combusted in an oxygen-rich pyrohydrolytic
instrument calibration and performance of the CIC system environment. The gaseous by-products of the combusted
prior to sample analysis but is not used in the instrument
sample are trapped in a liquid absorption solution where the
calibration procedure. hydrogenhalides(HX)formedduringcombustiondisassociate
–
into their respective ions (X ), while the sulfur oxides (SO )
X
3.2.4 LPG QC sample, n—a pressurized sample previously
2–
formed are further oxidized to SO in the presence of an
analyzed and used to verify instrument calibration and perfor- 4
oxidizing agent.An aliquot of known volume of the absorbing
mance of the CIC system prior to sample analysis.
solution is then automatically injected into an ion chromato-
3.2.5 LPG system blank, n—the area of the anion(s) of
graph (IC) by means of a sample injection valve. The halide
interest of a combustion ion chromatography (CIC) analysis of
and sulfate anions are separated by the anion separation
the LPG calibration blank (3.2.1) used for preparation of the
column of the IC. The conductivity of the eluent is reduced
LPG calibration standards (3.2.2). The same combustion
with an anion suppression device prior to the ion chromato-
conditions, chromatography, time protocols, and injection vol-
graph’s conductivity detector, where the anions of interest are
umes are used as for the analysis of a LPG sample.
measured.Quantificationofthefluorine,chlorine,andsulfurin
3.2.6 non-LPG liquid check standard, n—a liquid hydrocar-
the original combusted sample is achieved by first calibrating
bon sample not in an LPG matrix that is used to troubleshoot
the system with a series of LPG calibration standards contain-
and check the performance of the CIC system (3.1.1) prior to
ing known amounts of fluorine, chlorine, and sulfur and then
sample analysis. (See Appendix X1 for preparation.)
analyzing unknown pressurized samples under the same con-
ditions as the standards.
3.2.7 non-LPG liquid sample, n—ahydrocarbonsamplethat
is in liquid phase at 15°C and atmospheric conditions.
5. Significance and Use
3.2.8 system blank, n—the area of the anion(s) of interest of
5.1 The total fluorine, chlorine, and sulfur contained in
a combustion ion chromatography (CIC) analysis in which the
LPG, similar low molecular weight hydrocarbons, and DME
same combustion, chromatography, and time protocols are
can be harmful to many catalytic chemical processes, lead to
usedasforasampleanalysis,butwithoutthecombustionofan
corrosion, and contribute to pollutant emissions. While LPG
LPG sample, LPG calibration blank, or LPG calibration
specifications limit sulfur, some specifications also contain
standard.
precautionary statements about fluorine. Chlorine has been
3.3 Abbreviations:
known to contaminate LPG with detrimental consequences.
3.3.1 CIC—combustion ion chromatography
This test method can be used to determine total fluorine (as
3.3.2 conc.—concentration fluoride), chlorine (as chloride), and sulfur (as sulfate ion) in
D7994 − 17
process streams, intermediate and finished LPG products, 7.4.1 Ion Chromatograph (IC), (see Note 1) an analytical
similar low molecular weight hydrocarbons, and DME (1.1). system with all required accessories including columns, sup-
pressor and detector.
6. Interferences
NOTE 1—Many different companies manufacture automatic ion chro-
matographs. Consult the specific manufacturer’s instruction manual for
6.1 Substances that co-elute with the elements (anions) of
details regarding setup and operation.
interest will interfere. A high concentration of one or more
7.4.2 Injection System, capable of delivering a minimum of
elements (anions) can interfere with other constituents if their
5µL to 200µL with a precision better than 1% or as
retentiontimesarecloseenoughtoaffecttheresolutionoftheir
recommended by the manufacturer for this determination. It is
peaks. The potential for interference from specific elements
recommended to use an IC chromatograph configured for
(anions) by means of co-elution is largely dependent on the
pre-concentration or matrix elimination (7.4.5) for injection
manufacturer and type of anion separation column used in the
volumes greater than 500µL.
ion chromatograph.
7.4.3 Pumping System, capable of delivering mobile phase
6.2 Improper sample containers that react with fluorine,
flows between 0.2mL⁄min and 2.5mL⁄min with a precision
chlorine, or reactive sulfur species can give erroneously low
better than 2% or as recommended for this determination by
results (Section 10).
the manufacturer.
7.4.4 Continuous Eluent Generation (Optional), to auto-
7. Apparatus
matically prepare and purify the eluent used in the ion
7.1 LPG Sampling System:
chromatography. Electrolytic eluent generation and auto-buret
7.1.1 LPG Sampling Device, capable of accurately deliver- preparation of eluent via in-line dilution of a stock solution
ing under pressure a known volume or aliquot of pressurized have been found satisfactory for this test method. Other
sample,typicallyintherangeof5µLto30µL.Thesystemand continuous eluent generation devices may be used if the
sample injection loop is swept by inert carrier gas and shall be precision, bias, recovery, and accuracy of this test method are
capable of allowing the quantitative delivery of a known met.
aliquot of pressurized sample into the oxidation zone at a 7.4.5 Anion Pre-Concentration Column (Optional),usedfor
controlled rate. anion pre-concentration and matrix elimination. Pre-
concentration enables larger volumes of absorbing solution
7.2 Pyrohydrolytic Combustion Unit:
(1mL to 3mL) to be analyzed without the associated water
7.2.1 Furnace, an electric furnace that can maintain a
dip. Matrix elimination refers to the elimination of any
minimum temperature of 900°C.
unreacted hydrogen peroxide in the absorbing solution prior to
7.2.2 Gas Flow Control, the apparatus shall be equipped
injectionontotheguardandanionseparatorcolumnsandcould
withflowcontrollerscapableofmaintainingaconstantflowof
potentially interfere with the fluoride peak resolution.
oxygen and inert carrier gas (argon or helium).
7.4.6 Guard Column,forprotectionoftheanalyticalcolumn
7.2.3 Humidifier Delivery System, capable of delivering
from strongly retained constituents. Improved separation is
Type1(orbetter)reagentwater(8.2)tothecombustiontubeat
obtained with additional theoretical plates.
a controlled rate sufficient to provide a pyrohydrolytic envi-
7.4.7 Anion Separator Column, capable of producing satis-
ronment.
factory baseline separations of the anion peaks of interest as
7.2.4 Pyrohydrolytic Combustion Tube, made of quartz and
shown in Fig. 1.
capable of withstanding temperatures up to 1100°C. The
combustion tube shall be of ample volume and may include
quartz wool (or other suitable medium) to provide sufficient
mixing and surface area to ensure complete combustion of the
sample.
7.3 Gas Absorption Unit:
7.3.1 Gas Absorption Unit, having an absorption tube with
sufficient capacity to hold a minimum of 5mL which is
automatically filled with a known volume of absorption solu-
tion by a built-in burette or other similar device. The gas
absorption unit is interfaced to the IC and injects an aliquot of
the absorption solution into the IC after the sample is com-
busted and the by-products of combustion are absorbed. The
gas absorption unit rinses the absorption tube and the transfer
FIG. 1 Anion Peaks of Interest
lines from the combustion tube to the gas absorption unit with
Type I reagent water (8.2) or other appropriate absorption
solution prior to sample combustion and after the absorption
7.4.8 Anion Suppressor Device, reduces the background
solution is injected into the IC to minimize cross-
conductivity of the eluent after separation by the anion
contamination.
separator column. Both chemical and continuous electrolytic
7.4 Ion Chromatograph: suppressors have been found satisfactory for this test method.
D7994 − 17
Other anion suppressor devices may be used as long as the available. Othergradesmaybeused,providedthatthereagent
precision and accuracy of the method are not degraded. is of sufficiently high purity to permit its use without lessening
the accuracy of the determination.
7.4.9 Conductivity Detector, temperature controlled to
60.01°C, capable of at least 0µS⁄cm to 1000µS⁄cm on a
NOTE 2—Purity of reagents is of particular importance when perform-
ing trace analysis of pressurized samples containing 1mg⁄kg or less in
linear scale.
concentration of the elements (anions) of interest. The LPG system blank
7.4.10 Data Acquisition System, an integrator or computer
(3.2.5) should provide a chromatographic area response no greater than
data handling system capable of integrating the peak areas of
50% of the lowest LPG calibration standard (3.2.2) used for calibration.
an ion chromatograph.
8.2 Purity of Water—Unless otherwise indicated, references
to water shall be understood to mean Type I (or better) having
7.5 Balance,analytical,withsensitivityto0.0001gusedfor
a minimum of 18 MΩ·cm resistance and conforming to
preparation of standards and reagents.
Specification D1193 Type I reagent water (or better). Comply
7.6 Optional Apparatus and Accessories:
with all ion chromatograph instrument and column vendor
7.6.1 (Optional) Boat Inlet System—The system provides a requirementsforeluentpreparationandhandling(forexample,
filtering and degassing). The reagent water is critical to the
sampling port for the introduction of non-LPG liquid samples
performance, repeatability, reproducibility, and accuracy of
(3.2.7) into the sample boat and is connected to the inlet of the
this test method. Therefore, the reagent water used shall be of
combustion tube. The system is swept by an inert carrier gas
the highest quality available in the lab. A chart of critical
andshallbecapableofallowingthequantitativedeliveryofthe
specification parameters for Type I reagent water per Specifi-
non-LPG liquid sample into the oxidation zone at a controlled
cation D1193 is listed in Table 1.
rate.TheoptionalboatinletsystemmaybeusedforQCtesting
and troubleshooting of the system with non-LPG liquid check
TABLE 1 Type I Reagent Water Key Specifications
standards (3.2.6) or non-LPG liquid samples (3.2.7) and is not
required for routine pressurized sample analysis. Specification D1193 Standards for Reagent Water
Measurement (unit) Type I Type II Type III
7.6.2 (Optional) Boat Inlet Cooler—The volatility of non-
Resistivity (MΩ·cm) at 25 °C >18 >1 >4
Total organic carbon (µg/kg) <50 <50 <200
LPG liquid samples requires an apparatus capable of cooling
Sodium (µg/kg) <1 <5 <10
thesampleboatpriortoinjectionofthenon-LPGliquidsample
Chloride (µg/kg) <1 <5 <10
into the boat.The boat inlet cooler may be used in conjunction
Total silica (µg/kg) <3 <3 <500
with the optional boat inlet system (7.6.1) for QC testing and
troubleshooting of the CIC system with non-LPG liquid check
standards (3.2.6) or non-LPG liquid samples (3.2.7) and is not
8.3 Quartz Wool (Fine Grade) (Optional), or other suitable
required for routine pressurized sample analysis.
materialthatisstableandcapableofwithstandingthetempera-
7.6.3 (Optional) Quartz or Ceramic Sample Boats, of suf- tures inside the furnace may be used.
ficient size to hold 10µL to 100µL and used in conjunction
NOTE 3—Materials meeting the requirements in 8.3 may be used in the
with the optional boat inlet system (7.6.1). The boat is filled
pyrohydrolytic combustion tube (7.2.4) to provide increased surface area
or to ensure a uniform injection of non-LPG liquid samples into the
with quartz wool or other suitable material (8.3) to wick any
sample boat (7.6.3) of the optional boat inlet system (7.6.1) by wicking
remaining drops of non-LPG liquid sample from the tip of the
anyremainingdropsofnon-LPGliquidsamplefromthetipofthesyringe
gas-tight syringe needle prior to introduction into the furnace.
needle prior to introduction of the sample boat into the furnace. Consult
The optional boat inlet system (7.6.1) and quartz or ceramic
instrument manufacturer recommendations for further guidance.
sample boats (7.6.3) may be used for QC testing and trouble-
8.4 Inert Carrier Gas, such as argon or helium, minimum
shooting of the system with non-LPG liquid check standards
99.98% purity.
(3.2.6) or non-LPG liquid samples (3.2.7) but are not required
8.4.1 Purification scrubbers or filters are recommended to
for routine pressurized sample analysis.
ensure the removal of contaminants, such as a molecular sieve
for moisture and activated charcoal (or equivalent) for hydro-
7.6.4 (Optional) Gas-Tight Sampling Syringe, capable of
carbons.
accurately delivering microliter quantities up to 100µL. The
gas-tightsyringemaybeusedforQCtestingandtroubleshoot-
8.5 Oxygen, combustion gas, minimum 99.75% purity.
ing of the system with non-LPG liquid check standards (3.2.6)
8.6 Nitrogen, inert gas, minimum 99.75% purity, used to
or liquid samples (3.2.7) and is not required for routine
pressurize the calibration standards and samples in the pres-
pressurized sample analysis.
surized sample cylinders prior to analysis. Other inert gases
such argon or helium (8.4) meeting the same minimum purity
8. Reagents and Materials
specification may also be used.
8.1 Purity of Reagents—Reagent grade or higher purity
chemicals shall be used for the preparation of all samples,
Reagent Chemicals, American Chemical Society Specifications, American
standards, eluents, and regenerator solutions. Unless otherwise Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
indicated, it is intended that all reagents shall conform to the
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
specification of the Committee on Analytical Reagents of the
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
American Chemical Society, where such specifications are MD.
D7994 − 17
8.7 Gas Regulators, two-stage gas regulators capable of 8.9.1 Fluka TraceSelect Ultra (trademarked), Fluka Trace-
regulating the pressures in the range of 275kPa to 415kPa Select (trademarked), and EMD Suprapur (trademarked) have
(40psi to 60psi) shall be used for the carrier and combustion all proven to work well for this test method.
gases. Follow instrument manufacturer’s recommendations for
8.10 Eluent Solution—Followthespecificguidelinesforthe
pressure regulation.
preparation of the eluent solution from the manufacturer of the
columns. Other concentrations may be used if precision and
8.8 LPG Calibration Standards, certified calibration stan-
accuracy of the method are not degraded. The recommended
dards gravimetrically prepared and traceable by weight to a
solutions from the column manufacturer may be purchased
national metrology institute (NMI) from commercial sources
from vendors as long as the performance, precision, and
covering the desired calibration range and containing the
accuracy are not degraded (see Section 9 regarding hazards).
elements (anions) of interest with the reported values verified
by one or more analytical techniques. The certified calibration
8.11 Suppressor (Chemical and Electrolytic):
standards are normally prepared in butane or propane but may
8.11.1 Chemical Suppressor Regenerant Solution—Follow
be prepared in LPG or other appropriate pressurized sample
the specific manufacturer’s guidelines for the preparation and
matrices. The calibration standard shall be pressurized to a use of the suppressor solution. The manufacturer’s recom-
constant pressure of 2000kPa to 2760kPa (300psig to
mended solutions may be purchased from qualified vendors as
400psig) with inert gas to ensure sampling consistency and long as the performance, precision, and accuracy are not
uniformity. Check pressure prior to analysis and re-pressurize
degraded.
as needed. 8.11.2 Electrolytic Suppressor Current Setting—Follow the
specific guidelines for the current setting from the vendor of
8.8.1 Recommended Primary Organic Compounds, used as
the suppressor being used based upon the flow rate and eluent
sources for the elements (anions) of interest in the preparation
concentration being used for the analysis.
of the LPG calibration standards (8.8):
8.8.1.1 Fluorine: 8.12 Absorbing Solution—Dilute a sufficient amount of
(1) Fluorobenzene, MW 96.103 g⁄mole, 19.77 % by hydrogenperoxidestocksolutionlistedin8.9toachieveafinal
massF. concentration of approximately 100mg⁄kg or µg/mL.
(2) Fluoropropane,MW62.09g⁄mole,30.60%bymassF. 8.12.1 Approximately 0.7mL of 30% hydrogen peroxide
added to 2L(two liters) of absorbing solution will give a final
8.8.1.2 Chlorine:
approximate concentration of 100mg⁄kg or µg/mL.
(1) Chlorobenzene, MW 112.56 g⁄mole, 32.16 % by
8.12.2 The use of hydrogen peroxide in the absorbing
massCl.
2–
solution ensures that all SO species are converted to SO
X 4
8.8.1.3 Sulfur:
priortodetectionbytheIC.Hydrogenperoxideisnotrequired
(1) Dimethyl sulfide, MW 62.13 g⁄mole, 51.16 % by
if the measurement of sulfur is not being determined.
massS.
8.12.3 Other concentrations of hydrogen peroxide may be
8.8.2 Other primary organic compounds may be used.
used as long as the performance of the method is met.
8.8.3 LPGcalibrationstandardstypicallyhaveausefulshelf
8.12.4 Hydrogen peroxide may not be necessary if the
life between three months and twelve months if properly
concentration of sulfur in the sample is low, since the forma-
stored. Follow the manufacturer’s instructions for proper
tion of SO in the absorption solution becomes insignificant at
storage and use. LPG calibration standards shall not be used
low concentrations. It has been observed that results for
beyond the declared shelf life on the calibration standard’s
pressurized samples at concentrations below 5mg⁄kg sulfur
certificate.
typicallydonotrequirehydrogenperoxide.Ifthedifferencesin
8.8.3.1 It is highly recommended when purchasing LPG area counts of the sulfate peaks are less than 5% with and
without hydrogen peroxide at the maximum LPG calibration
calibration standards (3.2.2) to ensure the LPG calibration
blank (3.2.1) is from the same LPG lot number that was used standard used (3.2.2), then one may assume that the use of
hydrogen peroxide is not necessary.
in the preparation of the LPG calibration standards (3.2.2) and
to use the LPG calibration blank when calibrating the CIC
8.13 Phosphate Stock Solution (Optional) (1.00 mL =
system. The purity of the LPG used in the preparation of the
1.00 mg phosphate)—Dissolve 1.433g of potassium dihydro-
LPG calibration standards is often not fully known and the
gen phosphate (KH PO ) in
...