ASTM D7212-06

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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An American National Standard
Designation:D7212–06
Standard Test Method for
Low Sulfur in Automotive Fuels by Energy-Dispersive X-ray
Fluorescence Spectrometry Using a Low-Background
Proportional Counter
This standard is issued under the fixed designation D 7212; 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.
1. Scope 3.1.1 low background proportional counter, n—an X-ray
proportional counter that can suppress the noise generated
1.1 This test method specifies an energy-dispersive X-ray
when incident X rays are absorbed near the wall with resulting
fluorescence (EDXRF) method for the determination of the
incomplete charge collection.
total sulfur content of automotive fuels with a concentration
3.1.1.1 Discussion—An electrode shield close to the wall
range from 7 mg/kg to 50 mg/kg.
detects incomplete charge collection and associated electronic
1.1.1 The pooled limit of quantitation of this test method as
detection circuitry rejects those events. In comparison to
obtained by statistical analysis of interlaboratory test results is
conventional proportional counters, this gives lower spectral
7 mg/kg sulfur.
background and a lower limit of detection.
1.2 The values stated in SI units are to be regarded as the
standard. The preferred concentration units are mg/kg sulfur.
4. Summary of Test Method
1.3 This standard does not purport to address all of the
4.1 The sample is placed in the beam emitted from an X-ray
safety concerns, if any, associated with its use. It is the
source with titanium target and primary filtration so that
responsibility of the user of this standard to establish appro-
excitation is by essentially monochromatic radiation of
priate safety and health practices and determine the applica-
4.51 keV and virtually no background at 2.3 keV. A low
bility of regulatory limitations prior to use.
background proportional counter measures the intensity of the
2. Referenced Documents fluorescent sulfur K series intensity and argon K series inten-
sity (from residual air) and the accumulated counts are com-
2.1 ASTM Standards:
pared with counts from previously prepared calibration stan-
D 4045 Test Method for Sulfur in Petroleum Products by
dards to obtain the sulfur concentration in mg/kg. If chlorine is
Hydrogenolysis and Rateometric Colorimetry
expected to be present in some samples then other regions of
D 4057 Practice for Manual Sampling of Petroleum and
the spectrum must be measured to provide compensation for
Petroleum Products
spectral overlap. One group of calibration standards is required
D 4177 Practice for Automatic Sampling of Petroleum and
to span the concentration range from 0 to 150 mg/kg sulfur.
Petroleum Products
D 6299 Practice for Applying Statistical Quality Assurance
NOTE 1—Operation of analyzers using X-ray tubes is to be conducted
Techniques to Evaluate Analytical Measurement System
in accordance with the manufacturer’s safety instructions and federal,
state, and local regulations governing the use of ionizing radiation.
Performance
E29 Practice for Using Significant Digits in Test Data to
5. Significance and Use
Determine Conformance with Specifications
5.1 This test method determines total sulfur in automotive
3. Terminology
fuels with a typical analysis time around 10 min per sample.
5.2 The quality of automotive fuel is related to the amount
3.1 Definitions of Terms Specific to This Standard:
of sulfur present. Knowledge of sulfur level is necessary for
processing purposes.
This test method is under the jurisdiction of ASTM Committee D02 on
5.3 Sulfur level in automotive fuels affects performance
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
characteristicsandairquality.Federal,state,andlocalagencies
D02.03 on Elemental Analysis.
Current edition approved Feb. 15, 2006. Published March 2006. regulate the level of sulfur in fuel delivered at the pump.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.4 This test method can be referenced in specification
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
documents to determine if the material meets the desired sulfur
Standards volume information, refer to the standard’s Document Summary page on
content.
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7212–06
5.5 If this test method is applied to petroleum matrices with Analytical Reagents of the American Chemical Society where
significantly different composition to those used in the inter- such specifications are available. Other grades may be used,
laboratory precision study, then the caution and recommenda- provided it is first ascertained that the reagent is of sufficiently
tions in Section 6 should be observed when interpreting the high purity to permit its use without lessening the accuracy of
results. the determination.
8.2 Di-n Butyl Sulfide (DBS), a high purity standard with
6. Interferences
certified analysis for sulfur content. Use the certified sulfur
6.1 Spectral interferences result when some sample compo- content when calculating the exact concentrations of the
nent element or elements emit X rays that the detector cannot calibration standards. (Warning—Di-n-butyl sulfide is flam-
resolvefromsulfurX-rayemission.Overlappingpeaklinesare mable and toxic).
theresultofthis.Thisoverlappingeffectmaybebyleadalkyls, 8.3 Mineral Oil, White (MOW),withsulfurcontentlessthan
silicon, phosphorus, calcium, potassium, and halides if their 0.2 mg/kg as certified by a suitable analytical method, likeTest
aggregate concentration is more than 10 mg/kg. The most Method D 4045.
likely interference is chlorine that has been found in biodiesel 8.4 X-ray Transparent Film, any film that resists attack by
derived from recycled waste vegetable oil. the sample, is free of sulfur and other interfering elements (see
6.1), and is sufficiently X-ray transparent may be used.
6.2 The presence of oxygenates or water may alter the
sensitivity for sulfur.
NOTE 2—Polycarbonate with thickness of 5 or 6 µm most closely
6.3 Follow the manufacturer’s operating guide to compen-
matches these requirements and eight of nine participants in the interlabo-
sate for the interferences.
ratorystudy usedoneofthesefilms,whiletheotherlaboratoryused3µm
polyester.
7. Apparatus
8.4.1 Samples of high aromatic content may dissolve poly-
7.1 Energy-dispersive X-ray Fluorescence Analyzer—Any
carbonate film and polypropylene has a tendency to absorb
energy dispersive X-ray fluorescence analyzer may be used if
some hydrocarbons and may stretch during a long measure-
its design incorporates, as a minimum the following features:
ment time.
7.1.1 SourceofX-rayExcitation,X-raysourcewithtitanium
NOTE 3—One laboratory has shown that polycarbonate resists a mix-
target and primary filtration so that excitation is by essentially
ture of 25 mass % isooctane and 75 mass % toluene for 80 min.
monochromatic radiation of 4.51 keV.
8.4.2 In these cases high purity polyester is acceptable, but
7.1.2 Low Background Proportional Counter (see 3.1.1),
overall, polycarbonate offers the best combination of spectral
with sensitivity at 2.3 keV.
purityandresistancetostretching.Othermaterialsmaybeused
7.1.3 Multi-channelAnalyzer,withachannelwidthof10eV
for X-ray windows, provided that they do not contain any
or less, covering the energy range from 0 to 10 keV.
elemental impurities and match the listed films for X-ray
7.1.4 Signal Conditioning and Data Handling Electronics,
transmission.
that include the functions of X-ray intensity counting, a
8.5 Sample Cells, resistant to sample attack and meet the
minimum of four energy regions (to correct for background X
geometry requirements of spectrometer.
rays and spectral overlap), spectral overlap corrections, and
8.6 Calibration Check Samples, portions of one or more
conversions of sulfur X-ray intensity into sulfur concentration.
automotivefuelstandardsofknownsulfurcontentandnotused
7.1.5 Display or Printer, that reads out in mg/kg sulfur.
in the generation of the calibration line. The check samples
7.1.6 Removable Sample Cell, providing a sample depth of
shallbeusedtodeterminetheaccuracyoftheinitialcalibration
at least 4 mm and equipped with a replaceable X-ray transpar-
(see 11.3).
ent plastic film window.
8.7 Quality Control (QC) Samples, preferably portions of
7.1.7 Helium Purged Optical Path, to maximize sensitivity
one or more automotive fuel materials that are stable and
and minimize spectral overlap from argon in air. The helium
representative of the samples of interest.
shall be at least 99.9 % purity.
9. Sampling
8. Reagents and Materials
9.1 Asample shall be taken in accordance with the instruc-
8.1 Purity of Reagents—Reagent grade chemicals shall be
tions in Practice D 4057 or D 4177, where appropriate. Do not
used in all tests. Unless otherwise indicated, it is intended that
shake samples, thus avoiding entrained air. Analyze samples
all reagents conform to the specifications of the Committee on
immediately after pouring into a sample cell and allowing the
escape of the air bubbles caused by mixing.
3 9.2 For the measurement of low sulfur contents disposable
The sole source of supply of the apparatus known to the committee at this time
is the Twin-X ULS from Oxford Instruments Analytical, Halifax Road, High cells are recommended. Preparation of sample cells must be
Wycombe, Bucks, HP12 3SE, England. If you are aware of alternative suppliers,
please provide this information to ASTM International Headquarters. Your com-
ments will receive careful consideration at a meeting of the responsible technical Reagent Chemicals, American Chemical Society Specifications, American
committee, which you may attend. Chemical Society, Washington DC. For suggestions on testing of reagents not listed
The low background proportional counter is covered by a pending patent. by the American Chemical Society, see Annual Standards for Laboratory, BDH
Interestedpartiesareinvitedtosubmitinformationregardingtheidentificationofan Ltd., Poole Dorset, U.K., and the United States Pharmacopeia and National
alternative(s) to this patent-pending item toASTM International Headquarters.Your Formulary, U.S Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
comments will receive careful consideration at a meeting of the responsible Supporting data have been filed at ASTM International Headquarters and may
technical committee, which you may attend. be obtained by requesting Research Report RR: D02-1587.
D7212–06
done with care and by following any advice from the supplier.
where:
Afreshly prepared sample cell including film is required prior
S = mg/kg of sulfur in the stock standard,
Stock
to analyzing the samples. Avoid touching the inside of the
DBS = actual mass of DBS, g,
sample cell or portion of the window film in the cell or in the S = the mass % of sulfur in DBS, typically 21.91 %,
DBS
instrument window that is exposed to X rays. Oil from and
MO = actual mass of white mineral oil, g.
fingerprints affects the reading when analyzing for low level of
sulfur. Ensure that the film is not scratched, especially by the 11.1.2 Preparation of Calibration Standards—Accurately
weigh the nominal quantity of white mineral oil to the nearest
tear-off bar as it is withdrawn from the container. Wrinkles in
the film will affect the intensity of sulfur X rays transmitted. 0.1 mg, as shown in Table 2, into a suitable narrow-necked
container, then accurately weigh in the nominal quantity of
Therefore, it is essential that the film be taut and clean to
ensure reliable results. Film may become electrostatically stock standard. Mix thoroughly (a PTFE-coated magnetic
stirrer is advisable) at room temperature. Calculate the concen-
charged during handling so it is important that the cell window
tration of sulfur in the each standard to 0.1 mg/kg using the
doesnotattractanydust,fiber,andhair.Theanalyzerwillneed
following equation:
recalibration if the type or thickness of the window film is
changed.
S 5 STK 3 S / ~STK 1 MO! (2)
Std Stock
9.3 If the instrument has a replaceable secondary/safety
where:
window, it must be changed for every sample to ensure there is
S = mg/kg of sulfur in the calibration standard, and
Std
no cross-contamination. When changing it, follow the precau-
STK = actual mass of stock standard, g.
tions given in 9.2.
11.2 Storage of Standards and Calibration Check
9.4 Impurities that may affect the measurement of low
Samples—Store all standards and check samples in glass
levels of sulfur have been found in polyester films. All films
bottles in a cool, dark place until required. The glass bottles
may vary in thickness from roll to roll. Therefore, the calibra-
shall be either dark or wrapped in opaque material and closed
tion shall be verified after starting each new roll of film.
with glass stoppers, inert plastic lined screw caps, or other
9.5 Where laboratories use more than one XRF spectrom-
equally inert, impermeable enclosures. As soon as any sedi-
eter or analyze different types of sample, a variety of cell
ment or change of concentration is observed, discard the
window materials may be used.Always ensure that the correct
standard.
film is clearly distinguished.
11.3 Instrument Calibration—Calibrate the instrument fol-
lowing the manufacturer’s instructions. Typically, the calibra-
10. Preparation of Apparatus
tion procedure involves setting up the instrument for recording
offluorescentsulfurKseriesintensity,argonKseriesintensity,
10.1 Set up the apparatus in accordance with the manufac-
andtwointensitiestodeterminespectraloverlapfromchlorine.
turer’s instructions. Whenever possible, the instrument should
Ineffect,sulfurismeasuredsimultaneouslywiththreedifferent
remain energized to maintain optimum stability.
regionsofinterest,whicharethenormalsettingandtwoothers,
10.2 When changing the helium gas cylinder or after a
one narrower, and one wider. All three regions have the same
system has been idle for a day or more ensure that the helium
lower limit. The normal setting is approximately symmetrical
pipes are purged of air by performing a dummy measurement.
around the center of the sulfur peak (1.92 to 2.51 keV), the
narrower setting has its upper limit in the center of the sulfur
11. Calibration and Standardization
peak (1.92 to 2.31 keV), and the wider region has its upper
11.1 Preparation of Calibration Standards:
limit in the center of the chlorine
...