ASTM D6334-98(2003)e1
(Test Method)Standard Test Method for Sulfur in Gasoline by Wavelength Dispersive X-Ray Fluorescence
Standard Test Method for Sulfur in Gasoline by Wavelength Dispersive X-Ray Fluorescence
SIGNIFICANCE AND USE
Knowledge of the presence of sulfur in petroleum products, especially fuels, helps predict performance characteristics, potential corrosion problems, and vehicle emission levels. In addition, some regulatory agencies mandate reduced levels of sulfur in reformulated type gasolines.
SCOPE
1.1 This test method covers the quantitative determination of total sulfur in gasoline and gasoline-oxygenate blends. The Pooled Limit of Quantitation (PLOQ) was determined to be 15 mg/kg. Therefore, the practical range for this test method is from 15 to 940 mg/kg.
Note 1—This concentration range is based on that used in the interlaboratory round robin, which shows that the range of sulfur in the round robin samples was from 1.5 to 940 mg/kg; however, below 15 mg/kg, the reproducibility approaches 100 % of the concentration.
1.2 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 limitation prior to use.
1.3 The values stated in SI units are to be regarded as the standard. The preferred units are mg/kg sulfur.
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AnAmerican National Standard
e1
Designation:D6334–98 (Reapproved 2003)
Standard Test Method for
Sulfur in Gasoline by Wavelength Dispersive X-Ray
Fluorescence
This standard is issued under the fixed designation D 6334; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Warning notes were editorially moved into the standard text in August 2003.
1. Scope D 5453 Test Method for the Determination of Total Sulfur
in Light Hydrocarbons, Motor Fuels and Oils by Ultravio-
1.1 This test method covers the quantitative determination
let Fluorescence
of total sulfur in gasoline and gasoline-oxygenate blends. The
D 5842 Practice for Sampling and Handling of Fuels for
Pooled Limit of Quantitation (PLOQ) was determined to be 15
Volatility Measurement
mg/kg. Therefore, the practical range for this test method is
D 5854 Practice for Mixing and Handling of Liquid
from 15 to 940 mg/kg.
Samples of Petroleum and Petroleum Products
NOTE 1—This concentration range is based on that used in the
interlaboratory round robin, which shows that the range of sulfur in the
3. Summary of Test Method
round robin samples was from 1.5 to 940 mg/kg; however, below 15
3.1 The sample is placed in the X-ray beam, and the
mg/kg, the reproducibility approaches 100 % of the concentration.
intensity of the sulfur Ka line at 5.373 Å is measured. The
1.2 This standard does not purport to address all of the
intensity of a corrected background, measured at a recom-
safety concerns, if any, associated with its use. It is the
mended wavelength of 5.190 Å, or if a rhodium tube is used,
responsibility of the user of this standard to establish appro-
5.437 Å, is subtracted from this intensity. The resultant net
priate safety and health practices and determine the applica-
counting rate is then compared to a previously prepared
bility of regulatory limitation prior to use.
calibration curve or equation to obtain the concentration of
1.3 The values stated in SI units are to be regarded as the
sulfur in mg/kg. (Warning—Exposure to excessive quantities
standard. The preferred units are mg/kg sulfur.
of X radiation is injurious to health. Therefore, it is imperative
that the operator avoid exposing any part of his or her person,
2. Referenced Documents
not only to primary X-rays, but also to secondary or scattered
2.1 ASTM Standards:
radiation that might be present.The X-ray spectrometer should
D 2622 Test Method for Sulfur in Petroleum Products by
be operated in accordance with the regulations of recommen-
Wavelength Dispersive X-Ray Fluorescence Spectrom-
dations governing the use of ionizing radiation.)
etry
D 3210 Test Method for Comparing Colors of Films from
4. Significance and Use
Water-Emulsion Floor Polishes
4.1 Knowledge of the presence of sulfur in petroleum
D 4045 Test Method for Sulfur in Petroleum Products by
products, especially fuels, helps predict performance charac-
Hydrogenolysis and Rateometric Colorimetry
teristics, potential corrosion problems, and vehicle emission
D 4057 Practice for Manual Sampling of Petroleum and
levels. In addition, some regulatory agencies mandate reduced
Petroleum Products
levels of sulfur in reformulated type gasolines.
D 4177 Practice for the Automatic Sampling of Petroleum
and Petroleum Products 5. Interferences
D 4294 Test Method for Sulfur in Petroleum Products by
5.1 Fuels with compositions that vary from those specified
Energy-Dispersive X-Ray Fluorescence Spectroscopy
in 9.1 may be analyzed with standards made from base
materials that are of similar composition to minimize matrix
effects.
This test method is under the jurisdiction of ASTM Committee D02 on
5.1.1 Fuels containing oxygenates may be analyzed using
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.03 on Elemental Analysis. standardspreparedwithsimilaramountsofthesameoxygenate
Current edition approved May 10, 2003. Published August 2003. Originally
added to the standard dilution matrix. However, round robin
approved in 1962. Last previous edition approved in 1998 as D 6334–98.
Annual Book of ASTM Standards, Vol 05.01.
Annual Book of ASTM Standards, Vol 15.04.
4 5
Annual Book of ASTM Standards, Vol 05.02. Annual Book of ASTM Standards, Vol 05.03.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
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D6334–98 (2003)
studies done by theWestern States PetroleumAssociation have and representative sample can be taken and analyzed over the
shown no significant bias in determining sulfur in gasolines period of intended use. It is permissible to use calibration
with and without oxygenates at regulatory levels (0 to 2.7 standards for this purpose. Since standard samples are dis-
weight percent oxygen). carded after each determination, it is recommended that a
5.1.2 Methanol fuels (M85 and M100) exhibit interferences lower cost material be used for daily calibration checks.
at this level of detection (<100 mg/kg). They can be analyzed
8. Sampling and Specimen Preparation
using a calibration curve produced by diluting the standards in
a similar matrix of M85 or M100 or by Test Method D 2622. 8.1 Samples shall be taken in accordance with the instruc-
tions in Practice D 4057, D 4177, D 5842, or D 5854, where
6. Apparatus
appropriate.
6.1 Wavelength Dispersive X-Ray Fluorescence Spectrom-
8.2 Clean and dry reusable cells before use. Disposable
eter (WDXRF), equipped for soft ray detection in the 5.37 Å
sample cups are not to be reused. Window material usually is
range. For optimum sensitivity to sulfur, equip the instrument
8 µm polyester, 8 µm polycarbonate, or 6 µm polypropylene
with the following:
film. Renewal of the window of the sample cup is essential for
6.1.1 Optical Path, of helium.
the measurement of each sample.Avoid touching the inside of
6.1.2 Pulse-Height Analyzer, or other means of energy
the sample cup, the portion of the window film in the cup, or
discrimination.
the instrument window that is exposed to X-rays. Oil from
6.1.3 Detector, designed for the detection of long wave-
fingerprints can affect the reading when analyzing for low
length X-rays.
levels of sulfur. Wrinkles in the film will affect the number of
6.1.4 Analyzing Crystal, suitable for the dispersion of sulfur
sulfur X-rays transmitted. Therefore, the importance of the
Ka X-rays within the angular range of the spectrometer
film’s tautness and cleanliness cannot be over stressed. Reca-
employed. Pentaerythritol and germanium are the most popu-
librate the analyzer when you change the type or thickness of
lar, although materials, such as EDDT, ADP, graphite, and
the window film.
quartz, may be used.
8.3 Polyester films often contain impurities that may affect
6.1.5 X-Ray Tube, capable of exciting sulfur K radiation.
the measurement of low levels of sulfur and may vary from lot
a
Tubes with anodes of rhodium, chromium, and scandium are
tolot.Therefore,ifusingapolyesterfilm,checkthecalibration
most popular, although other anodes may be suitable.
with the start of each new roll.
8.4 X-ray films may vary in thickness from batch to batch.
7. Reagents
Check the calibration when starting a new roll of any film.
7.1 Di-n-Butyl Sulfide (MW – 146.30), a high-purity grade
8.5 Samples of high aromatic count may dissolve polyester
standard with a certified sulfur analysis.
andpolycarbonatefilms.Inthesecases,othermaterialsbesides
7.2 Thiophene MW– 84.14), a high-purity (98+ %) grade
these films may be used for X-ray windows, provided that they
standard with a certified sulfur analysis.
do not contain any elemental impurities that can adversely
7.3 2-Methylthiophene MW – 98.17), a high purity (98+ %)
affect the results obtained by this test method.
grade standard with a standard sulfur analysis.
7.4 2,2,4-Trimethylpentane,(isooctane), reagent grade, 9. Calibration
MW-114.23.
9.1 Prepare calibration standards by the careful preparation
7.5 Methylbenzene, (Toluene), reagent grade, MW-92.14.
by mass of a 50:50 mixture (based on sulfur content) of the
7.6 Drift Correction Monitor(s), (Optional), several differ-
certified thiophene and 2-methylthiophene or n-butyl sulfide
ent materials have been found to be suitable for use as drift
with 20 to 80 % mixture of toluene–isooctane or other suitable
correction monitors. Examples of sulfur containing materials
base material (see 5.1). Exact standards of the nominal sulfur
that meet these requirements are renewable liquid petroleum
concentrations listed in Table 1 are recommended.
materials, semipermanent solids, pressed powder pellets, metal
9.2 Preparation of Stock Standard:
alloys, or fused glass disks. Bracket the calibration range with
Weigh approximately 0.657 g of thiophene and 0.767 g of
concentrations of monitor samples. The counting rate for each
2-methylthiopheneandrecordthemassestothenearest0.1mg,
monitor is determined during calibration (see 9.7) and again at
orweigh2.286of n-butylsulfidetothenearest0.1mg.Addthe
thetimeofanalysis(see10.1).Thesecountingratesareusedto
standard materials to a tared 100 mL volumetric flask. Add
calculate a drift correction factor (see 11.1).
mixedsolventof20 %tolueneand80 %isooctane(byvolume)
7.7 Calibration Check Standards, one or more liquid petro-
or other base material (see 5.1) to a net mass of 50.000 + 0.010
leum or product standards of known sulfur content (which do
not represent one of the samples prepared in Section 9) are
TABLE 1 Nominal Sulfur Standards
used to verify the accuracy of the calibration curve.
Range 1 Range 2
7.8 Quality Control (QC) Sample, one or more stable liquid
Sulfur Concentration, Sulfur Concentration,
petroleumorproductsamples,whichareusedtoverifythatthe
mg/kg mg/kg
measurementsystemisincontrol.PreferablytheQCsample(s)
0 100
should be representative of the samples typically analyzed. In 5 250
10 500
cases where volatility of the QC sample(s) may affect the
50 1000
sample integrity, precautions need to be taken to minimize or
100 —
eliminate sample losses prior to analysis to ensure that a stable
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D6334–98 (2003)
g. This stock standard contains approximately 10 mg/g sulfur. This value corresponds to A in Eq 5, Section 11. Many
Correct the concentration by multiplying the measured masses instrumentmanufacturershavebuiltdriftcorrectionprocedures
by the sulfur equivalency in each of the standards, that is into their software.
thiophene grams 3 0.3803 3 purity plus 2-methylthiophene 9.8 At the completion of the calibration, measure one or
grams 3 0.3260 3 purity (or n-butyl sulfide grams 3 0.2191 more independent calibration check standards to verify the
3 purity) = weight of sulfur in the standard solution. Divide accuracy of the calibration curve.These standards (see 7.7) are
this number by the total mass of the standards and base independent of the calibration set. The measured value shall
material added to them, multiply by 1000 mg/g and the result agree with the standard value within 62 % relative or 2 ppm,
istheactualsulfurconcentrationinmg/g.Thiscalculationisas whichever is greater.
follows:
NOTE 3—NIST traceable gasoline standards are available at the 1, 10,
T 3 0.3803 3 P 1 M 3 0.3260 3 P
40, and 300 mg/kg levels. Other concentrations may be prepared by
S, mg/g 5 1000 3 (1)
F dilutionofthesestandardswithasolventofsimilarmatrixtothestandards
previously prepared.
DB 3 0.2187 3 P
S, mg/g 5 1000 3 (2)
F
10. Procedure
where: 10.1 Measure the intensity of the drift correction monitor(s)
S = final sulfur concentration,
used in 9.7. The value determined corresponds to B in Eq 5,
T = mass of thiophene added,
Section 11. This measurement may not be required on high
M = mass of 2-methylthiophene added,
stability instrumentation. Determine the value of F8 in Eq 6,
DB = mass of di-n-butyl sulfide added,
Section 11 at regular intervals by measuring the peak and
P = purity of the standard material, and
background count rates on the solvent blank. This measure-
F = final mass of mixture.
ment may not be needed on some instruments.
9.3 Preparation of Diluted Standard:
10.2 Place the sample in an appropriate cell using tech-
Dilute 25.0 mL of stock standard to 250 mL using the base
niques consistent with good practice for the particular instru-
material. This gives a standard of approximately 1000 mg/kg.
ment being used.Although sulfur radiation will penetrate only
Divide the standard concentration calculated in 9.2 by 10 to
a small distance into the sample, scatter from the sample cup
determine the actual concentration.
and the sample may vary to such an extent that a specific
9.4 Serial Dilutions:
amount or a minimum amount of sample shall be used.
Prepareserialdilutionsofthedilutedstandardbydilutingthe
Generally, filling the cup to one-half capacity is sufficient.
following volumes to 100 mL using the base material:
Once this amount is established for each instrument, this
0.5 mL = 5 mg/kg
volume of sample is used for each measurement.
1.0 mL = 10 mg/kg
10.3 Place the sample in the X-ray beam, and allow the
5.0 mL = 50 mg/kg
X-ray optical atmosphere to come to equilibrium.
10.0 mL = 100 mg/kg
25.0 mL = 250 mg/kg
10.4 Determine the intensity of the sulfur K radiation at
a
50.0 mL = 500 mg/kg
5.373 Å by making counting rate measurements at the precise
Diluted Standard = 1000 mg/kg
angular settings for this wavelength.
NOTE 2—Prepare calibrations up to 1000 mg/kg sulfur, and dilute
NOTE 4—Take a sufficient number of counts to satisfy at least a 1.0 %
samples with higher concentrations of sulfur to within this concentration
expected coefficient of variation when practical. When sensitivity or
range.
concentration, or both, make it impractical to collect a sufficient number
9.5 Establish calibration curve data by carefully measuring
of counts to achieve a 1.0 % coefficient of variation, accepted techniques,
thenetintensityoftheemittedsulfurradiationfromeachofthe
which will allow the greatest statistical precision in the time allotted for
each analysis, should be used. Calculate the coefficient of variation as
standards by the procedure described in Sections 10 and 11.
follows:
9.6 Construct a calibration model by:
9.6.1 Using the software and algorithms supplied by the
Coefficient of variation,% 5 ~100 N 1 N !/~N 2 N ! (4)
=
s b s b
instrument manufacturer.
where:
9.6.2 Fitting the data to an equation of the type:
N = gross number of counts collected at sulfur line, and
s
S 5 aR 1 b (3) N = gross number of counts collected at background wavelength (on
b
the base material) in
...
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