GB/T 17040-2019 Determination of sulfur in petroleum and petroleum products — Energy-dispersive X-ray fluorescence spectrometry

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: GB/T 17040—2019
• Chinese title: Determination of sulfur in petroleum and petroleum products — Energy-dispersive X-ray fluorescence spectrometry
• English title: Determination of sulfur in petroleum and petroleum products—Energy dispersive X-ray fluorescence spectrometry
• Replacement relationship: replaces GB/T 17040—2008 "Determination of sulfur in petroleum and petroleum products — Energy-dispersive X-ray fluorescence spectrometry"
• Previous versions: GB/T 17040-1997, GB/T 17040—2008
• Publication/implementation: published on 2019-03-25, implemented on 2019-10-01
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC280)
• Drafting organization: Sinopec Research Institute of Petroleum Processing; participating drafting organization: CNOOC (Qingdao) Heavy Oil Processing Engineering Technology Research Center
• Main drafters: Gao Ping, He Pei, Fan Yanxuan, Tian Maohong

2. Scope of application and non-applicability

• Applicable to the determination of petroleum and petroleum products that are single-phase, liquid at room temperature or with appropriate heating, or that can be dissolved in hydrocarbon solvents, including motor gasoline, ethanol gasoline, diesel, biodiesel and its blended fuels, jet fuel, kerosene, other distillates, naphtha, residual oil, crude oil, lubricant base oils, hydraulic oils, and similar petroleum products.
• Determination range of sulfur mass fraction: 0.0017% (17 mg/kg) to 4.6% (46000 mg/kg).
• When the content of ethanol and methanol in oxygenated fuels exceeds the range in Table 1, this standard can still be used for analysis, but the precision and bias do not apply (see Appendix B).
• For samples with relatively high oxygen content (mass fraction greater than 3%), the sample should be diluted or matrix-matched standard samples should be used to ensure the accuracy of the determination results.
• For samples with sulfur mass fraction exceeding 4.6%, the sample may be diluted so that the sulfur mass fraction falls within the applicable range of this standard; this standard has not investigated the precision and bias of the determination of sulfur content in diluted samples, and the precision of the determination results of diluted samples does not apply to the precision and bias of Chapter 15.
• When the sulfur mass fraction is lower than 20 mg/kg, the applicability of this standard shall be determined according to the specific conditions of the sample.
• The data are usable only when the content of interfering substances in the sample is less than that shown in Table 1.
• The repeatability, reproducibility, and bias values in this standard do not include M85 and M100 samples.

3. Method principle

Place the test specimen in a beam emitted from a X-ray source, measure the intensity of the sulfur Kα characteristic X-rays excited at an energy of 2.3 keV, and compare the accumulated counts with the counts of pre-prepared standard samples, thereby obtaining the sulfur content expressed as mass fraction (see ASTM D7343). At least 3 sets of standard samples are required, covering the mass fraction ranges: 0.0% to 0.1%, 0.1% to 1.0%, 1.0% to 5.0%.

4. Reagents and materials (purity / preparation)

• 6.1 Reagent purity: all chemical reagents used in this standard are of analytical grade or above.
• 6.2 Di-n-butyl sulfide (DBS): not lower than premium grade, molecular formula (C4H9)2S. Used as a reference material, labeled with a certified sulfur content [generally sulfur content (mass fraction) is 21.91%], and this content is used to calculate the exact sulfur content in the prepared standard samples (see 8.1). Warning — n-butyl sulfide is a flammable and toxic compound. Note: It is necessary to know the sulfur content in di-n-butyl sulfide, not just its purity, because impurities may also be sulfur-containing compounds.
• 6.3 Drift monitoring sample (optional): sulfur-containing substances in various states that remain stable under repeated irradiation by X-rays can be used as drift monitoring samples, such as polysulfide oil, glass, or metal samples. Liquids, pressed powders, and solid materials that decompose under repeated irradiation by X-rays should not be used. Usable sulfur-containing substances include liquid petroleum products that can be used for a long time, metal alloys, or fused glass discs. At a suitable counting time, the count rate displayed by the monitoring sample should satisfy a relative standard deviation of less than 1%. The count rate of the monitoring sample should be measured during calibration (see 8.2.1) and measured again during analysis (see 11.2). The count rate will be used to calculate the drift correction factor (see 14.6). Although the calculation can also be done manually, drift correction is usually performed automatically by software. For relatively stable X-ray spectrometers, the magnitude of the drift correction factor generally does not change significantly overall.
• 6.4 Polysulfide oil: nonyl polysulfide with a known sulfur content, usually diluted with a solvent in a hydrocarbon matrix. Warning — may cause skin sensitization. Note: Polysulfide oil is a high-molecular-weight oil whose sulfur content can be as high as mass fraction 50%. They still have excellent physical properties after being fully mixed with white oil, such as low viscosity, low volatility, and a long shelf life. The polysulfide oil is diluted with white oil, and then the sulfur content of the polysulfide oil is obtained by direct comparison with the corresponding certified reference material.
• 6.5 White oil: sulfur content less than 2 mg/kg. Used in this standard as a diluent for preparing standard samples (the sulfur content of other types of diluents used in this standard is less than 2 mg/kg). When performing low-sulfur tests (mass fraction less than 200 mg/kg), the calculation of the sulfur content of the standard samples should include the sulfur content in the matrix substance (see 8.1). When the sulfur content in the solvent or reagent is uncertain, it needs to be determined, or a higher-purity reagent should be used to prepare the standard samples.
• 6.6 Film permeable to X-rays: any film that can withstand chemical corrosion by the sample, does not contain sulfur, and allows X-rays to pass through sufficiently can be used. Suitable ones include polyester film, polypropylene film, polycarbonate film, and polyimide film. However, if the aromatic hydrocarbon content in the sample is high, it will dissolve polypropylene film, polycarbonate film, and polyester film.
• 6.7 Helium (optional): purge gas; when needed, select the corresponding specification according to the instrument manufacturer's recommendations.
• 6.8 Counting gas: for instruments equipped with a flow proportional counter, the purity of the counting gas should meet the instrument manufacturer's specifications.
• 6.9 Calibration check sample: one or more liquid petroleum products or standard samples with a determined sulfur content (including polysulfide oil, di-n-butyl sulfide, thiophene, etc.) that have not been used in establishing the calibration curve. The calibration check sample can be used to determine the accuracy and precision of the initial calibration curve (see Chapter 8).
• 6.10 Quality control (QC) sample: a stable petroleum product or other solid sample measured periodically to ensure that the measurement system is in a satisfactory state (see Chapter 14). It is recommended to verify the system state through QC samples and quality control charts. The quality control process should be completed independently by each laboratory. Typical samples that can remain stable for a long time can be used as QC samples. For drift monitoring samples, solid materials are recommended.

5. Instruments and equipment

• 5.1 Energy-dispersive X-ray fluorescence spectrometer
  • 5.1.1 Any energy-dispersive X-ray fluorescence spectrometer that can be used for this test method should at least include the components specified in 5.1.2 to 5.1.8 and give the same test results for samples.
  • 5.1.2 X-ray excitation source: the effective energy of the X-ray tube is higher than 2.5 keV. When using a X-ray tube as the excitation source in a spectrometer, operate according to the instrument manufacturer's safety instructions.
  • 5.1.3 Removable sample cell: a window film made of replaceable polyester film that can be penetrated by X-rays can hold the sample and fit the geometry of the X-ray fluorescence spectrometer; the minimum sample depth is 4 mm, and the minimum diameter is 10 mm. For measuring low-sulfur samples (mass fraction less than 50 mg/kg), disposable sample cells are preferred.
  • 5.1.4 X-ray detector: relatively high sensitivity to the sulfur Kα characteristic X-rays at an energy of 2.3 keV, with a resolution not exceeding 800 eV.
  • 5.1.5 Filter: a device that can distinguish the sulfur Kα spectral line from other X-rays.
  • 5.1.6 Signal conditioning and data processing electronic system: has the functions of counting X-ray intensity, subtracting background X-rays, smoothing correction of spectral lines, and converting sulfur X-ray intensity into mass fraction.
  • 5.1.7 Under optimized conditions, the sensitivity of this spectrometer should be able to measure samples with a sulfur content of about mass fraction 0.05%, and the error should be due to counting statistics, with a standard deviation not greater than 0.5%.
  • 5.1.8 Display or printer: capable of reading or printing the sulfur mass fraction.
• 5.2 Analytical balance: readability 0.1 mg, maximum weighing range 100 g.

6. Recommended operating conditions

• Counting time (Table 4):
  • Sulfur mass fraction range 0.0000% to 0.1000%: counting time 200 s to 300 s
  • Sulfur mass fraction range 0.1% to 5.0%: counting time 100 s
  • Sulfur mass fraction range 1.0% to 5.0%: counting time 100 s
• The test specimen is loaded into the sample cell, and the specimen occupies about 75% of the sample cell.
• If the test specimen is viscous, before loading it into the sample cell, it should first be heated to make it easier to pour into the sample cell.
• Ensure there are no bubbles between the window and the liquid.
• After the sample is poured into the sample cell, analyze it immediately and allow bubbles generated by agitation to escape.
• The instrument should be operated continuously as much as possible to maintain optimal stability.
• Other operating conditions (such as tube voltage, tube current, filter type, etc.): not provided in the available source.

7. Sampling and test specimen preparation

• 10 Sampling: sample according to the method specified in GB/T 4756 or GB/T 27867.
• 7 Preparation of sample cell:
  • 7.1 If a reusable sample cell is used, it should be ensured that it is clean and dry before use. Disposable sample cells should not be reused. Polyester or polycarbonate film (see 6.6) with a thickness of less than 10 μm is often selected as the window film because it has high transmittance for sulfur characteristic X rays. A new window film should be used for each sample measurement. Avoid touching the interior of the sample cell and the window film exposed to X rays and the instrument window. When measuring samples with low sulfur content, oil on fingers can affect the measurement result. Wrinkles on the window film will affect the transmittance of sulfur X rays. Therefore, to ensure reliable measurement results, the window film should be kept flat and clean.
  • 7.2 When the type or thickness of the window film changes or before starting to use a new batch of polyester film, the instrument should be recalibrated.
  • 7.3 For samples with high aromatic content, it is advisable to use other films that do not contain impurity elements as the window film; a polyimide film with a thickness of 6 μm may be preferentially selected.
• For petroleum samples containing suspended water, be sure to remove the water before measurement or completely homogenize the sample and measure immediately (see A.5).

8. Analysis Procedure

• 8 Calibration:
  • 8.1 Standard Samples
    • 8.1.1 Prepare standard samples by diluting di-n-butyl sulfide with sulfur-free white oil or other suitable matrix material (see 6.5). The sulfur content of unknown samples should be within the range of the calibration curve used. Table 2 gives the recommended sulfur content of standard samples. When the sulfur mass fraction of the standard sample is lower than 0.02% (200 mg/kg), the sulfur content in the matrix material should be taken into account, as shown in Formula (1). Accurately weigh the recommended amounts of di-n-butyl sulfide and matrix diluent, calculate the sulfur content of the prepared standard sample, and input it into the instrument for calibration. The sulfur content in the standard sample can be calculated according to Formula (1).
      • Formula (1): w(S) = [m_DBS × w(S_DBS) + m_MO × w(S_MO)] / (m_DBS + m_MO)
      • Where: w(S)—— mass fraction of sulfur in the standard sample, %; m_DBS—— mass of n-butyl sulfide, in grams (g); w(S_DBS)——DBS mass fraction of sulfur in it, generally 21.91%; m_MO—— mass of white oil, in grams (g); w(S_MO)—— mass fraction of sulfur in white oil, %.
      • If other sulfur-containing substances are used, the sulfur content in the standard sample can be calculated according to Formula (2): w(S) = [m_SC × w(S_SC) + m_D × w(S_D)] / (m_SC + m_D)
      • Where: w(S)—— mass fraction of sulfur in the standard sample, %; m_SC—— mass of the sulfur-containing substance, in grams (g); w(S_SC)—— mass fraction of sulfur in the sulfur-containing substance, %; m_D—— mass of the diluent, in grams (g); w(S_D)—— mass fraction of sulfur in the diluent, %.
    • Table 2 Composition of Initial Standard Samples:

      Sulfur mass fraction/%	Diluent mass/g	Di-n-butyl sulfide mass/g
      5	48.6	14.4
      0.1	43.6	0.200

    • 8.1.2 Certified reference materials mixed with the same matrix material as the sample to be tested can be used to obtain standard samples, but the certification body needs to provide the sulfur content and uncertainty of the mixture.
    • 8.1.3 In addition, standard samples can be obtained by diluting polysulfide oil with sulfur-free white oil. The sulfur content of polysulfide oil standard samples can have a wide range. The calibration curve established with polysulfide oil standard samples should be verified with traceable reference materials with accurate sulfur content and matching matrix. After the polysulfide oil calibration curve is established, the standard samples should be stored in brown glass bottles protected from light at room temperature, and should be fully shaken before sampling to ensure uniform mixing. Note: If the sulfur content of commercially available reference materials is known and approximately the same as the concentrations in Table 3, they can also be used.
    • 8.1.4 According to the proportions shown in Table 2, accurately weigh an appropriate amount of diluent, place it in a suitable narrow-mouth container, then accurately weigh an appropriate amount of di-n-butyl sulfide, and mix thoroughly at room temperature (a magnetic stirrer coated with polytetrafluoroethylene may be used).
    • 8.1.5 According to the expected sulfur content of the sample to be tested, prepare 1 or more series of standard samples by diluting the initial standard sample according to Table 3. Or prepare by mixing certified reference materials (8.1.2) and by diluting polysulfide oil (8.1.3). Note: Other standard samples can also be prepared if needed, with concentrations within the range of Table 3 (see 8.1.2).
    • Table 3 Sulfur Standard Calibration Range:

      Sulfur mass fraction/(mg/kg)	Sulfur mass fraction/%	Sulfur mass fraction/%
      0.0 a, b	0.100	1.0
      5 b	0.250	2.0
      10 b	0.500	3.0
      100 b	1.00	4.0
      250	—	5.0
      500	—	—
      750	—	—
      1000	—	—
      a Blank sample. b Repeat testing is required; either the average result or the result of a single sample may be used in the calibration curve.

    • 8.1.6 If commercially available, standard samples within the range of Table 3 can be purchased.
    • 8.1.7 If the diluent used contains sulfur, then add this portion of sulfur to the sulfur content of the prepared standard sample according to Formula (1). (Ask the supplier for the exact sulfur content in the diluent or test it with another low-sulfur determination method).
  • 8.2 Certified Standard Calibration Samples
    • 8.2.1 When the matrix is the same as that of the test sample, certain certified reference materials can also be used as standard samples in this standard.
    • 8.2.2 Standard samples with a sulfur mass fraction less than 100 mg/kg shall be tested repeatedly. Either a single result or an average result may be selected when making the calibration curve.
  • 8.3 Calibrating the Instrument: According to the instrument manual, select an appropriate range to calibrate the instrument according to Table 3. Usually, the calibration process adjusts the instrument so that it can record the net intensity of sulfur X rays, followed by measurement of standard samples with known content. Using the counting time recommended in Table 4, one intensity count is obtained for each standard sample. When the sulfur mass fraction of the standard sample is less than 100 mg/kg, use a new sample cell and a newly taken standard sample and repeat the test immediately. After all standard samples have been analyzed, establish the optimal calibration curve according to the instrument manual based on the net intensity counts of sulfur obtained for each standard sample. Warning—Avoid spilling flammable liquids inside the instrument.
  • 8.4 Quality Control (QC) Samples: It is necessary to use QC samples. QC samples can be prepared according to 8.1, or suitable certified reference materials can be used (see 8.2). The concentration of the QC sample should be close to the expected concentration of the test sample.
  • 8.5 Storage of Standard Samples: All standard samples, when not in use, should be stored in brown glass bottles or glass bottles wrapped with opaque material and stoppered with glass or other inert material, in a dark, low-temperature environment. If precipitation is found or the concentration changes, the standard sample shall be discarded.
• 9 Instrument Preparation: Install the instrument according to the instructions provided by the instrument manufacturer. The instrument should be operated continuously as much as possible to maintain optimal stability.
• 11 Test Procedure:
  • 11.1 Before analyzing unknown samples, measure the QC sample first to verify whether the measurement system is in a satisfactory state. If the repeatability of the QC sample is worse than the repeatability required at this concentration (see Table 5), it indicates that the instrument has deviated and recalibration is required. A synthetic solid QC sample may be used instead of a liquid sample (see Chapter 14).
  • 11.2 Determination of Test Sample: Place the test sample into the sample cell, with the sample occupying about 75% of the sample cell. If the sample is viscous, heat it before placing it into the sample cell to make it easier to pour into the sample cell. Ensure there are no bubbles between the window and the liquid. Measure each test sample. If the sulfur mass fraction measured for the first time is less than 100 mg/kg, then repeat the determination using a new sample cell and a newly taken test sample; the average of the two determination results is the sulfur content of the test sample.
  • 11.3 If multiple test samples are analyzed, at the end of a series of analyses (no more than 10 test samples), the QC sample should be measured to determine whether the system is in a satisfactory state. If the deviation of the QC sample exceeds the repeatability tolerance at that concentration (see Table 5), the analysis should be stopped, the cause identified and corrected. The concentration of the QC sample used should be similar to the concentration of the test sample (see Chapter 14).
  • 11.4 For test samples with a sulfur mass fraction less than 100 mg/kg, repeated determination should be carried out. Each determination shall use a newly taken test sample according to 11.1 and 11.2. If the difference between the results of repeated determinations is greater than the repeatability tolerance in 15.1.2, consider whether it is caused by contamination during sample preparation, and then repeat the determination. Note: The information in Table 1 indicates the error situation when using this standard to determine the sulfur content of ethanol gasoline, methanol gasoline (or M85 and M100).
• 14 Quality Control:
  • 14.1 Each laboratory should establish a quality control procedure to ensure that the measurement system of this standard is in a satisfactory state. A method of periodically measuring QC samples and making quality control charts may be used (see 6.10). At least one representative QC sample should be selected for measurement (see NB/SH/T 0843).
  • 14.2 In addition to periodic determination of the QC sample (see 6.10), the calibration blank sample (for example, diluent) should also be determined before analyzing test samples each day. The sulfur mass fraction of the blank sample should be less than 2 mg/kg. If the test result sulfur mass fraction is greater than 2 mg/kg, the instrument should be recalibrated and the blank sample should be re-determined (using a new sample cell and a new sample). If the result is still not within the acceptable range, a full calibration should be performed. If the instrument injection port is contaminated, when analyzing samples with sulfur mass fraction less than 20 mg/kg, it should be cleaned according to the instrument manual. In order to obtain a better calibration curve at low concentrations, the regression weighting factor may be changed.
  • 14.3 Result confirmation: At the end of each test, the test should be confirmed, and it is necessary to check whether the sample has obvious damage, for example, sample cell leakage, wrinkles in the sample cell film, or double-layer film.
  • 14.4 Observe the analysis result; if the result is considered abnormal, repeat the test to confirm.
  • 14.5 Periodically check to ensure that the purge gas meets the instrument manufacturer's specifications.
  • 14.6 Periodically determine drift monitoring samples and quality control standard samples. Set a limit; when the result exceeds the limit, drift correction or full calibration should be performed. Samples between the last monitoring sample with a normal result and the monitoring sample found to exceed the acceptable range should all be retested.

9. Qualitative and Quantitative and Calculation Formulas

• 12 Calculation: The sulfur content in the test sample is automatically calculated from the sulfur X ray intensity count on the calibration curve.
• Calculation formula for sulfur content in standard samples:
  • Formula (1): w(S) = [m_DBS × w(S_DBS) + m_MO × w(S_MO)] / (m_DBS + m_MO)
  • Formula (2): w(S) = [m_SC × w(S_SC) + m_D × w(S_D)] / (m_SC + m_D)
• Oxygenated fuel correction formula (Appendix B):
  • Formula (B.1): w(S_M85) = w'(S_M85) / 0.59
  • Formula (B.2): w(S_M100) = w'(S_M100) / 0.55
  • Where: w(S_M85)—— mass fraction of sulfur in M85 after correction, in milligrams per kilogram (mg/kg); w'(S_M85)—— mass fraction of sulfur in M85 measured for a standard sample with a matrix of white oil not containing methanol, in milligrams per kilogram (mg/kg); w(S_M100)—— mass fraction of sulfur in M100 after correction, in milligrams per kilogram (mg/kg); w'(S_M100)—— mass fraction of sulfur in M100 measured for a standard sample with a matrix of white oil not containing methanol, in milligrams per kilogram (mg/kg).

10. Precision

• 15.1.1 The precision of this standard was obtained by statistical analysis of test results from multiple laboratories for 27 samples; the 27 samples include: distillate oils, oxygenated or non-oxygenated gasoline, ethanol gasoline, kerosene, diesel, biodiesel and its blended fuels, residual oil, and crude oil, with sulfur mass fraction ranging from 0.0001% (1 mg/kg) to 4.6% (46000 mg/kg). The PLOQ (pooled determination limit) for all types of samples is determined as 16 mg/kg (calculated according to the ASTM D6259 method). Due to differences in manufacturer or model, the instruments used in this standard will have differences in sensitivity; when the sulfur mass fraction is lower than 20 mg/kg, the applicability of this standard should be determined according to the specific situation of the sample. The estimated values of the detection limit and quantification limit of this standard are 3 times and 10 times the reproducibility standard deviation, respectively. For samples with sulfur mass fraction exceeding 4.6%, the sample may be diluted so that the sulfur mass fraction is within the applicable range of this standard. This standard does not investigate the precision and bias of sulfur content determination in diluted samples; the precision of test results for diluted samples does not apply to the precision and bias of Chapter 15, and will be greater than the bias of test results for undiluted samples. Appendix C and Appendix D respectively state the precision for diesel and gasoline. The precision within the sulfur content range of this standard is shown in 15.1.2 and 15.1.3. The data are usable only when the content of interfering substances in the sample is less than that shown in Table 1. Judge the reliability of test results according to the following provisions (95% confidence level). Note: Volatile samples may not achieve the stated precision; possible reasons include: volatilization of light components before or during analysis, and sulfur enhancement effect at the sample cell window, leading to high results.
• 15.1.2 Repeatability (r): For the same operator, in the same laboratory, using the same instrument, under the same conditions, and using the correct operating method on the same test sample, the difference between two test results obtained shall not exceed the value of Formula (3) or Formula (4). Table 5 gives typical precision values.
  • Formula (3): r = 0.4347 X^0.6446
  • Formula (4): r = [0.4347 (10000Y)^0.6446] / 10000
  • Where: X—— average mass fraction of two replicate test results, in milligrams per kilogram (mg/kg); Y—— average mass fraction of two replicate test results, %.
• 15.1.3 Reproducibility (R): For different operators, in different laboratories, using different instruments, and using the correct operating method on the same test sample, the difference between two single, independent test results obtained shall not exceed the value of Formula (5) or Formula (6). Table 5 gives typical precision values.
  • Formula (5): R = 1.9182 X^0.6446
  • Formula (6): R = [1.9182 (10000Y)^0.6446] / 10000
  • Where: X—— average mass fraction of two single, independent test results, in milligrams per kilogram (mg/kg); Y—— average mass fraction of two single, independent test results, %.
• Table 5 Typical precision values for samples of different concentrations:

  Sulfur mass fraction/(mg/kg)	Repeatability r/(mg/kg)	Reproducibility R/(mg/kg)
  16.0	2.6	11
  25.0	3.4	15
  50.0	5.4	24
  100.0	8.5	37
  500	24	105
  1000	37	165
  5000	105	465
  10000	165	727
  46000	440	1943

• 15.1.4 Appendix C and Appendix D respectively give the repeatability and reproducibility for diesel and gasoline.
• Appendix C Diesel precision:
  • C.1 In the multi-laboratory study there were 6 diesel samples (see Table C.1), with total sulfur mass fraction ranging from 20 mg/kg to 5500 mg/kg.
  • Table C.1 Precision determination samples: No. 5 diesel; No. 7 NIST SRM 2770; No. 8 NIST SRM 2724b; No. 15 diesel; No. 17 diesel; No. 22 B5 biodiesel blended fuel.
  • C.2 Repeatability (r): r = 1.6658 X^0.3300 or r = [1.6658 (10000Y)^0.3300] / 10000
  • C.3 Reproducibility (R): R = 8.9798 X^0.3300 or R = [8.9798 (10000Y)^0.3300] / 10000
  • Table C.2 Typical precision values for diesel samples:

    Sulfur mass fraction/(mg/kg)	Repeatability r/(mg/kg)	Reproducibility R/(mg/kg)
    25	4.8	26
    100	7.6	41
    500	13	70
    1000	16	88
    5500	29	154

• Appendix D Gasoline precision:
  • D.1 In the multi-laboratory study there were 5 gasoline samples (see Table D.1), with total sulfur mass fraction ranging from 11 mg/kg to 5500 mg/kg.
  • Table D.1 Precision determination samples: No. 2 gasoline containing 13% ETBE; No. 3 reformulated gasoline; No. 4 gasoline containing 5% ethanol; No. 11 gasoline; No. 20 E85.
  • D.2 Repeatability (r): r = 1.4477 X^0.3661 or r = [1.4477 (10000Y)^0.3661] / 10000
  • D.3 Reproducibility (R): R = 7.1295 X^0.3661 or R = [7.1295 (10000Y)^0.3661] / 10000
  • Table D.2 Typical precision values for gasoline samples:

    Sulfur mass fraction/(mg/kg)	Repeatability r/(mg/kg)	Reproducibility R/(mg/kg)
    50	6.0	30
    100	7.8	38
    500	14	69
    1000	18	89
    5500	34	167

• 15.2 Bias:
  • 15.2.1 Multiple laboratories measured 10 NIST reference materials (SRM). Table 6 gives their standard values, laboratory round-robin measured values, bias, and relative bias. It is assumed that the mC/mH of white oil is 5.698 (C22H46), and the carbon-to-hydrogen ratio will not cause significant bias.
  • 15.2.2 The interlaboratory measurement results for 8 NIST reference materials show that for various types of samples there is no statistically significant bias between the standard values and the measured values.
  • Table 6 Comparison of the results of the ASTM interlaboratory cooperative test with the NIST standard values:

    NIST SRM number	Sulfur mass fraction NIST standard value/(mg/kg)	Cooperative test sample number	Matrix	Sulfur mass fraction measured average/(mg/kg)	Sulfur mass fraction bias/(mg/kg)	Mass fraction relative bias/%	Bias significance
    2296	40.0	2	Reformulated gasoline (gasoline containing 13% ETBE)	46.3	+6.3	+15.8	No
    2299	13.6	3	Reformulated gasoline	18.1	+4.5	+33.1	No
    2770	41.6	7	Diesel fuel	49.4	+7.8	+18.8	No
    2724b	426.5	8	Diesel fuel	430.8	+4.3	+1.01	No
    2721	15832	9	Light high-sulfur crude oil	16118	+288	+1.82	Yes
    2722	2104	10	Heavy low-sulfur crude oil	2082	-21	-1.00	No
    1619b	6960	12	Residual fuel oil	6654	-306	-4.40	Yes
    1620c	45610	13	Residual fuel oil	45801	+191	+0.42	No

11. Report

• 13 Test report: The test result is the total sulfur content of the sample. For mass fractions greater than 0.01%, report the result as mass fraction (%), rounded to three significant figures; for mass fractions less than 0.01%, report the result as mass fraction (mg/kg), where mass fractions between 10 mg/kg and 100 mg/kg are rounded to two significant figures, and those below mass fraction 10 mg/kg are rounded to one significant figure (see GB/T 8170). It shall be stated that the test was conducted using this standard method. For samples with sulfur mass fraction less than 100 mg/kg, report the average of duplicate test results.

12. Normative references

• GB/T 4756 Petroleum liquids—Manual sampling
• GB/T 8170 Rules for rounding off numerical values and expression and judgment of limiting values
• GB/T 27867 Petroleum liquids—Automatic pipeline sampling
• NB/SH/T 0843 Evaluation of analytical testing systems in the petrochemical industry—Statistical techniques
• ASTM D6259 Standard practice for determining pooled measurement limit values (Practice for determination of a pooled limit of quantitation for a test method)
• ASTM D7343 X Standard practice for optimization, sample handling, calibration, and validation of X-ray fluorescence spectrometry for determination of elements in petroleum products and lubricants (Practice for optimization, sample handling, calibration, and validating of X-ray fluorescence spectrometry methods for elemental analysis of petroleum products and lubricants)