NB/SH/T 0842-2017 Determination of sulfur content in light liquid fuels by monochromatic wavelength dispersive X-ray fluorescence spectrometry

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Card type: Test method

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

• Standard number: NB/SH/T 0842—2017 (on the cover source-text extraction is written as "NB/SHVT 0842—2017", requires confirmation against the source standard (source-text extraction))
• Chinese title: Determination of sulfur content in light liquid fuels by monochromatic wavelength dispersive X-ray fluorescence spectrometry
• English title: Standard test method for sulfur in light liquid fuels by monochromatic wavelength dispersive X-ray fluorescence spectrometry (the original text source-text extraction spelling is noisy, requires confirmation against the source standard (source-text extraction))
• Replacement relationship: replaces NB/SH/T 0842—2010 "Determination of sulfur content in gasoline and diesel fuels by monochromatic wavelength dispersive X-ray fluorescence spectrometry"; NB/SH/T 0842—2010 was developed by modified adoption of ASTM D7039-07.
• Adoption relationship: This standard uses the redrafting method to modified adopt ASTM D7039-15a.
• Publication/implementation: published on 2017-12-27, implemented on 2018-06-01; issued by the National Energy Administration.
• Secretariat: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC 280/SC 1).
• Drafting organization: Sinopec Research Institute of Petroleum Processing; participating drafting organization: Heilongjiang Provincial Institute of Quality Supervision and Inspection.
• Main drafters: Gao Ping, He Pei, Liang Zhenfen, Wu Fan.

2. Scope of application and non-applicability

• Applicable to the determination of total sulfur content in gasoline, diesel, various distillate oils used in refineries for blending gasoline and diesel, jet fuel, kerosene, biodiesel, biodiesel blended fuels, and ethanol gasoline.
• Sulfur mass fraction determination range: 3.2 mg/kg ~ 2822 mg/kg.
• PL0Q (combined determination limit value) is 3.2 mg/kg (determined according to the method of ASTM D6259).
• Note: Due to volatilization of light components during analysis, highly volatile samples such as high vapor pressure gasoline or lighter hydrocarbons may not meet the specified precision.
• If the matrix of the standard sample used matches the sample matrix, or if the matrix correction in Appendix A is applied to the analysis results, gasoline samples with added oxygenates can also be analyzed by this standard.
• After dilution with a suitable solvent, samples with sulfur mass fraction exceeding 2822 mg/kg can also be analyzed by this standard (see 5.2); this standard does not investigate the precision and bias of sulfur content determination in diluted samples.
• When the elemental composition of the sample differs significantly from that of the standard samples used to establish the calibration curve, the precautions and recommendations in Chapter 5 should be followed; otherwise the analysis results will be subject to interference.
• Not applicable: the original text does not explicitly list "not applicable" clauses.

3. Method principle

Monochromatic X-rays with a suitable wavelength capable of exciting sulfur K-shell electrons are irradiated onto the test sample placed in a sample cell (see Figure 1). The Kα X-ray fluorescence with a wavelength of 0.5373 nm emitted by the sulfur element is collected by a fixed monochromator, and the collected sulfur element X-ray fluorescence intensity is detected by a detector and converted into the sulfur content in the test sample using a calibration equation. Compared with the polychromatic excitation used in traditional wavelength dispersive X-ray fluorescence analysis techniques, monochromatic X-ray excitation reduces background, simplifies matrix correction, and improves the signal-to-noise ratio.

• Warning: Exposure to excessive X-rays is harmful to health. Operators should take appropriate measures to prevent any part of the body from being exposed to primary, secondary, or scattered X-rays; the operation of X-ray spectrometers must comply with the instrument manufacturer's safety guidelines and national and local safety regulations.

4. Reagents and materials (purity / preparation)

• 7.1 Reagent purity: All chemical reagents used in the test are of analytical grade or above; if other purity reagents can ensure that the accuracy of the determination results is not reduced, they may also be used.
• 7.2 Calibration check sample: used to verify the accuracy of the calibration curve; the sulfur content is known and has not been used when establishing the calibration curve; a standard sample from the same batch as the standard samples used to establish the calibration curve can also be used as a calibration check sample.
• 7.3 Di-n-butyl sulfide: not lower than premium grade, molecular formula (C₄H₉)₂S (the original text source-text extraction is written as "(C,Hg)zS", requires confirmation against the source standard (source-text extraction)); labeled with certified sulfur content (generally sulfur mass fraction 21.9%), use this content to calculate the precise sulfur content in the prepared standard sample. Warning: flammable and toxic, the prepared standard solution is not easy to store for a long time. Note: Because impurities may also contain sulfur, it is necessary to know not only the purity of the n-butyl sulfide used but also its sulfur content; its sulfur content can be determined by high-fold dilution with sulfur-free white oil and direct comparative analysis using NIST or standard substances from other national standard material organizations.
• 7.4 Drift monitoring sample (optional): used to determine and correct instrument drift over time (see 10.4, 11.1 and 12.1). Stable sulfur-containing substances in various states are applicable, such as liquid samples, solid samples, pressed powder pellets, metal alloys, and 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% (see Appendix B). Note 1: Standard reference materials can also be used as drift monitoring samples; it is recommended to use inexpensive materials as daily drift monitoring samples. Note 2: The effect of drift correction on the precision and bias of this standard has not been studied.
  • 7.4.1 The calculation can be easily completed through general data processing; if the instrument is equipped with a drift correction function, drift correction can be performed automatically.
• 7.5 Quality control sample: used to establish and check the stability and precision of the analytical instrument (see Chapter 14). Use samples that are similar in composition to the test sample, homogeneous, and available in large quantities for long-term regular use. Note 1: It is recommended to use quality monitoring samples and control charts to verify that the system is in control. Note 2: Suitable quality control samples can be prepared by mixing typical samples.
• 7.6 White oil: high-purity mineral oil; when calculating the sulfur content of standard samples, its sulfur content should be considered.
• 7.7 Helium gas (the original text source-text extraction is written as "ammonia gas", requires confirmation against the source standard (source-text extraction)): purity greater than volume fraction 99.9%, used as the optical path.
• 7.8 Ethanol: analytical grade or premium grade; when calculating the sulfur content of standard samples, its sulfur content should be considered. Warning: flammable, irritating to eyes and skin, harmful if inhaled or swallowed.
• 7.9 2,2,4- Trimethylpentane (isooctane): analytical grade or premium grade; when calculating the sulfur content of standard samples, its sulfur content should be considered. Warning: flammable, irritating to eyes and skin, harmful if inhaled or swallowed.
• 7.10 Toluene: analytical grade or premium grade; when calculating the sulfur content of standard samples, its sulfur content should be considered. Warning: flammable, irritating to eyes and skin, harmful if inhaled or swallowed.
• 7.11 Polysulfide oil: usually nonyl polysulfide with known sulfur content diluted with a hydrocarbon-based solvent. Warning: may cause skin sensitization. Note: Polysulfide oil is a high-molecular-weight oil with a relatively high sulfur content, which can be as high as mass fraction 50%.
• For the calculation of standard sample preparation, see 10.1.1 formula (1); for the method of preparing standard samples with polysulfide oil, see 10.1.2.

5. Instruments and equipment

• 6.1 Monochromatic wavelength dispersive X-ray fluorescence spectrometer (MWDXRF): equipped with a 0.5373 nm X-ray detector; any such instrument that meets the following conditions and whose determination results can achieve the precision and bias described in Chapter 15 may be used.
• 6.2 X-ray source: can generate X-rays capable of exciting sulfur. It is recommended to use an X-ray tube with a power greater than 25 W that can generate RhLα, PdLα, AgLα, TiKα, ScKα and CrKα radiation.
• 6.3 X-ray monochromator: capable of focusing and selecting a single wavelength of characteristic X-rays as the excitation source.
• 6.4 Optical path: vacuum or gas-filled, to minimize absorption of excitation and fluorescence X-rays. It is recommended that the vacuum degree be less than 2.7 kPa. Calibration and testing must use the same optical path, vacuum degree, or helium pressure.
• 6.5 Fixed-channel monochromator: capable of separating sulfur Kα X-rays.
• 6.6 Detector: capable of effectively detecting sulfur Kα X-rays.
• 6.7 Single-channel analyzer: energy analyzer, monitoring only sulfur radiation.
• 6.8 Sample cell: open at the end, suitable for the geometry required by the MWDXRF spectrometer, using a replaceable film transparent to X-rays (see 6.9) to hold the liquid sample, with a sample loading depth of at least 5 mm. After the film is installed, the sample cell must not leak. The sample cell is preferably disposable.
• 6.9 Film transparent to X-rays: used to hold the sample in the sample cell (see 6.8), while providing a window with low absorption for X-rays. Any film that can withstand the chemical corrosion of the sample, contains no sulfur, and allows sufficient passage of X-rays may be used. For example: polyester, polypropylene, polycarbonate, polyimide. However, samples with high aromatic content may dissolve polyester and polycarbonate films.

6. Recommended operating conditions

• Counting time (T): For the expected lowest sulfur content of the sample, use the counting time recommended by the instrument manufacturer; generally each measurement time is 2 min ~ 3 min (see 9.1.2); the procedure in Appendix B may also be referenced to determine the counting time to achieve the required precision (see 9.1.3).
• Optical path: vacuum or gas-filled; it is recommended that the vacuum degree be less than 2.7 kPa; calibration and testing must use the same optical path, vacuum degree, or helium pressure (see 6.4).
• X-ray source: recommended power greater than 25 W, capable of generating RhLα, PdLα, AgLα, TiKα, ScKα and CrKα radiation (see 6.2).
• Analysis time: generally the analysis time for one sample is 5 min (see Chapter 4).
• Sample cell loading depth: at least 5 mm; generally filling the sample cell to three-quarters depth is sufficient (see 9.2.1).
• Gasoline sample storage: 0 ℃ ~ 4 ℃ (see 8.2).
• Drift monitoring sample count rate: the relative standard deviation should be less than 1% (see 7.4; the specific counting time is not provided in the available source).

7. Sampling and sample preparation

• 8.1 Sample according to the method specified in GB/T 4756 or GB/T 27867.
• 8.2 For gasoline samples, special care must be taken during sampling and sample preparation to prevent volatilization of the sample from causing changes in sulfur content. Gasoline must be stored in a closed container and kept in an environment of 0 ℃ ~ 4 ℃ until analysis and testing. If possible, maintain this temperature during any intermediate handling. After the sample is removed from the original container, it should be tested as quickly as possible, and the original container should not be left open for too long.
• 8.3 Use a new film for each sample measurement, avoid touching the inner wall of the sample cell, the liquid, and the film exposed to the X ray beam, and avoid touching the instrument's window (it is recommended to use clean disposable rubber or plastic gloves when preparing test samples). Oil stains on fingers and wrinkles in the film can cause deviations in sulfur content analysis results. Ensure that the window film is taut and clean. If the type and thickness of the film used change, recheck the calibration curve using a calibration check sample (see 7.2). After the sample is poured into the sample cell, the top should be open to air to prevent the film from bending due to sample evaporation. If a reusable sample cell is used, ensure that the sample cell is clean and dry before use. Do not reuse disposable sample cells.
• 8.4 Because the impurities and thickness of film materials on the market may vary, and may vary greatly. Therefore, when starting to use a new film, use a calibration check sample to determine the reliability of the calibration.
• 9.2 Preparation of test sample or standard sample:
  • 9.2.1 Pour the test sample into the cell from the open end of the sample cell, ensuring a minimum depth of 5 mm; exceeding this depth will not affect the results. Generally, filling the sample cell to three-quarters depth with the test sample is sufficient.
  • 9.2.2 Place an unused film on the open end of the sample cell and secure it firmly. Use the same film for both the analysis sample and the standard samples used to establish the calibration curve. When starting to use a new film, determine the reliability of the calibration according to clause 8.4. When the results of the calibration check sample do not meet the standard (see Chapter 10), recalibrate the instrument using a new film. Avoid touching any part of the inner wall of the sample cell, the liquid, and the film exposed to the X ray beam, and also avoid touching the instrument window. Ensure that the film is taut, free of wrinkles, and leak-free.
  • 9.2.3 A small hole must be made above the sample cell to prevent the film from becoming arched due to liquid evaporation.
  • 9.2.4 After the test sample or standard sample is loaded, analyze immediately. The shorter the storage time of the test sample or standard sample in the sample cell before analysis, the better.

8. Analysis Procedure

• 9.1 Preparation of the analytical instrument
  • 9.1.1 Ensure that the MWDXRF analyzer is installed and debugged according to the manufacturer's instructions. Allow sufficient time for the instrument to stabilize. Complete any required instrument inspection procedures. Keep the instrument running continuously as much as possible to maintain optimal stability.
  • 9.1.2 For the expected minimum sulfur content of the sample, use the counting time recommended by the instrument manufacturer (T). Generally, each measurement time is 2 min ~ 3 min.
  • 9.1.3 Alternatively, refer to the procedure in Appendix B to determine the counting time (T) to achieve the required precision.
• 10 Calibration
  • 10.1 Select a suitable matrix material (BM) to dilute di-n-butyl sulfide (DBS) (see Chapter 5) to prepare a set of standard samples whose sulfur content covers the expected range of the samples to be tested (maximum mass fraction of 3000 mg/kg). The two commonly used matrix materials are white oil (see 7.6, using the correction factors in Table 3) and ethanol (see 7.8, using the correction factors in Table 4). All standard substances used in the analysis must be from reliable and consistent sources. The recommended sulfur content range of standard samples is shown in Table 5.
  • 10.1.1 Calculate the mass fraction of sulfur in each standard sample (mg/kg), taking into account the mass fraction of sulfur in the matrix material, see formula (1): S = (DBS·S_DBS + BM·S_BM) / (DBS + BM). Where: S— mass fraction of sulfur in the standard sample, mg/kg; DBS— mass of n-butyl sulfide, g; S_DBS— mass fraction of sulfur in n-butyl sulfide, mg/kg; BM— mass of matrix material, g; S_BM— mass fraction of sulfur in matrix material, mg/kg.
  • 10.1.2 As an alternative, a series of standard samples can be obtained by diluting polysulfide oil (see note to clause 7.11) with sulfur-free white oil. The calibration curve established with polysulfide oil standard samples must be verified with traceable standard substances with accurate sulfur content and matching matrix.
  • 10.2 According to the instrument manufacturer's instructions and the description in clause 11.2, measure the X fluorescence intensity (total counts) of sulfur in each standard sample. Divide the total counts by the counting time (T, in seconds) to obtain the count rate (Rs) (see 9.1.1, 9.1.2 and formula (2)): Rs = N/T. Where: Rs— sulfur X fluorescence intensity count rate, counts/s; N— total counts at 0.5373 nm; T— counting time, s.
  • 10.3 Establish a linear calibration model
    • 10.3.1 Use the software provided by the instrument manufacturer.
    • 10.3.2 Perform linear regression on the calibration measurements. The linear regression equation is shown in formula (3): Rs = Y + (E×S). Where: Rs— sulfur X fluorescence intensity count rate, counts/s; Y— intercept of the calibration curve, counts/s; E— slope of the calibration curve, counts·kg/ (s·mg); S— mass fraction of sulfur, mg/kg.
  • 10.4 If drift correction is used, measure the total counts of sulfur X fluorescence intensity of the drift monitoring sample during calibration. Divide the total counts by the counting time (T) to obtain Rs. The Rs obtained from the drift monitoring sample during calibration is the A factor in formula (4) of clause 12.1.
  • 10.5 After measuring the standard samples, immediately measure the sulfur content of one or more calibration check samples (see 7.2). The results obtained should be within the range of their standard values plus or minus the precision of this method. If this standard is not met, there may be problems with the calibration process and standard samples. Take appropriate measures and repeat the calibration process. When evaluating the calibration, consider the degree of matrix matching between the calibration check samples and the standard samples.
• 11 Test Procedure
  • 11.1 If drift correction is used, analyze the drift monitoring sample measured during calibration before analyzing the test sample. Divide the measured total counts by T to obtain Rs. This Rs is the B factor in formula (4) of clause 12.1.
  • 11.2 Analyze the test sample according to the following steps:
    • 11.2.1 Prepare the test sample according to clause 9.2.
    • 11.2.2 According to the instrument manufacturer's instructions, place the sample cell containing the test sample into the instrument and allow the X ray optical path to equilibrate.
    • 11.2.3 Measure the total counts of sulfur fluorescence intensity, divide it by the total counting time T to obtain Rs (see formula (2)).
  • 11.3 If the Rs of the sample to be tested is greater than the maximum count rate on the calibration curve, quantitatively dilute the sample with the same matrix material used to prepare the standard samples so that its count rate is within the range of the calibration curve. Repeat the steps of clause 11.2 for the diluted sample to be tested.
  • 11.4 Calculate the mass fraction of sulfur in the test sample according to the method in Chapter 12.

9. Qualitative and Quantitative and Calculation Formulas

• 12.1 Drift correction factor (F): F = A/B. Where: A— the Rs measured for the drift monitoring sample during calibration, counts/s (see 10.4); B— the Rs measured for the drift monitoring sample during sample analysis, counts/s (see 11.1). If no drift monitoring sample is used, F is equal to 1.
• 12.2 The count rate of the test sample corrected by drift correction R_corr: R_corr = F × Rs. Where: F— drift correction factor; Rs— the sulfur X fluorescence intensity count rate of the test sample, counts/s.
• 12.3 Substitute R_corr for Rs in formula (3) of 10.3 to calculate the mass fraction of sulfur in the test sample.
• 12.4 If the test sample has been quantitatively diluted, calculate the mass fraction of sulfur in the original sample. The mass fraction of sulfur in the original undiluted sample is calculated according to formula (6): S_o = [S_d × (M_o + M_d) / M_o] − [S_d × (M_d/M_o)]. Where: S_d— mass fraction of sulfur in the diluted sample, mg/kg (obtained from 12.3); M_o— mass of the original sample, g; M_d— mass of the matrix material used to dilute the sample, g; S_d— mass fraction of sulfur in the diluent, mg/kg. (The symbols in the original formula (6) have duplicated/noisy typesetting, requires confirmation against the source standard (source-text extraction))
• 12.5 If a matrix correction factor is to be used to correct for matrix differences between the sample to be tested and the standard samples (see Chapter 5), multiply the mass fraction of sulfur S obtained in formula (3) by the correction factor.
• Appendix A Matrix Correction (Normative Appendix):
  • A.1 For differences in carbon, hydrogen, and oxygen composition between the sample to be tested and the standard samples, a matrix correction factor (C) can be calculated according to formula (A.1), formula (A.2), and formula (A.3). If no matrix correction is used, C is 1. The subscript "cal" refers to the standard sample, and the subscript "test" refers to the sample to be tested. The variable μ refers to the average value of the mass absorption coefficient.
  • A.1 The original text of formula (A.1), formula (A.2), and formula (A.3) source-text extraction is incomplete and requires confirmation against the source standard (source-text extraction). Among them, it gives: μ_w = 198.3W_C + 468.3W_O + 0.581W_H (the original text source-text extraction writes "^w=198.3W.+468.3W. + 0. 58IH", requires confirmation against the source standard (source-text extraction)). In the formula: G— is a constant, determined by the angles between the sample surface and the incident and emergent light; the instrument manufacturer will provide the value of G; for the analyzer G shown in Figure 1, the value is generally 0.87; μ_λ0— is the average value of the mass absorption coefficient for incident light with a wavelength of λ0, cm²/g; μ_S— is the average value of the mass absorption coefficient of the sulfur radiation generated at λ = 0.5373 nm, cm²/g; μ_C— is the mass absorption coefficient of carbon for λ0, cm²/g (for CrKα excitation it is 14.8); μ_O— is the mass absorption coefficient of oxygen for λ0, cm²/g (for CrKα excitation it is 37.7); μ_H— is the mass absorption coefficient of hydrogen for λ0, cm²/g (for CrKα excitation it is 0.34); W_C— is the mass fraction of carbon in the standard sample or the sample to be tested, %; W_O— is the mass fraction of oxygen in the standard sample or the sample to be tested, %; W_H— is the mass fraction of hydrogen in the standard sample or the sample to be tested, %.
  • A.2 Calculate the count of the sample to be tested after matrix correction according to formula (A.4) (R_c): R_c = C × Rs. In the formula: R_c— is the corrected sulfur X fluorescence intensity count rate of the sample to be tested, counts/s; C— is the matrix correction factor calculated by formula (A.1); Rs— is the sulfur X fluorescence intensity count rate of the sample to be tested, counts/s.
  • A.3 Substitute the matrix-corrected count rate (formula (A.4)) into formula (3) in 10.3 to calculate the sulfur content in the sample to be tested.
  • A.4 Figure 2 gives an example of matrix correction, in which the mass ratio of the sample to be tested M_O/M_H ranges from 5 to 10, and the oxygen content (mass fraction) ranges from 0 to 3.0%. The correction factor was calculated using formula (A.1) for CrKα excitation; the standard sample has M_O/M_H of 6.2 and does not contain oxygen-containing compounds.
• Appendix B Determination of counting time (informative appendix):
  • B.1 The quality of X ray fluorescence analysis is a function of counting precision; increasing the counting time (T) can improve counting precision. When sensitivity and content permit (see B.3), it is recommended to collect enough counts so that the relative standard deviation (RSD) of the net fluorescence intensity reaches 1.0% or better.
  • B.2 In order to determine the counting time required to achieve the expected relative standard deviation (RSD), use T = 100 s to analyze the sample to determine Rs and R_B, then use formula (B.1) to calculate T: RSD% = 100 T^(-0.5) (Rs + R_B)^0.5/ (Rs − R_B). (The original text source-text extraction writes "RSD% = 1007-05 (Rs + Ra)"S/ (Rs-Rp)", requires confirmation against the source standard (source-text extraction))
    • B.2.1 If the sulfur content of the sample to be tested is approximately known, then the existing calibration equation can be used to estimate Rs. The background count rate R_B in formula (B.1) can be estimated by the intercept Y from the most recent linear regression calibration (see 10.3.2).
    • B.2.2 If using T can achieve the expected precision, then T is also applicable to samples with the same or higher sulfur content as the sample used to determine T.
    • B.2.3 Because a single-channel analyzer is used to measure sulfur radiation, R_B cannot be directly determined from a sulfur-containing sample. R_B can be obtained by measuring a blank sample containing no sulfur, or replaced by the intercept Y from the most recent calibration curve.
  • B.3 When the sulfur content is low, in order to achieve the expected precision, the counting time should be increased. If in actual operation the same counting time needs to be used for all samples, then the counting time is determined by the sample with the expected lowest sulfur content.
• Table 5 Recommended sulfur mass fraction ranges in standard samples:
  • Range 1: 0 ~ 3000 mg/kg; standard sample 1: 0.0; standard sample 2: 25; standard sample 3: 100; standard sample 4: 500; standard sample 5: 1000; standard sample 6: 3000.
  • Range 2: 0 ~ 500 mg/kg; standard sample 1: 0.0 (matrix substance); standard sample 2: 5; standard sample 3: 15; standard sample 4: 50; standard sample 5: 250; standard sample 6: 500.
  • Note: The sulfur mass fraction range of the standard samples used should cover the expected sulfur mass fraction range of the samples to be tested. For example: if the sulfur mass fraction of the samples to be tested will not exceed 500 mg/kg, there is no need to use a calibration range of mass fraction 0 ~ 3000 mg/kg.
• Table 1 Correction methods used for different sample types:
  • Biodiesel and biodiesel blended fuel: correction table number 2; correction factor (Appendix A) used; matrix matching used.
  • Gasoline-ethanol mixture: correction table number 3 or 4; correction factor (Appendix A) used; matrix matching used.
  • Other types of samples: correction table number not used; correction factor (Appendix A) used; matrix matching used.
• Table 2 Correction factors for determining biodiesel blended fuel using a calibration curve of white oil matrix standard samples: oxygen mass fraction 0 ~ 19% (the original table source-text extraction is severely garbled, values require confirmation against the source standard (source-text extraction)). Note: The table lookup method is based on the known oxygen content of the sample (for example: oxygen mass fraction 11%), look up the corresponding values in the first row and first column (for example: 11 = 10 + 1), and the intersection of the two values is the correction factor (for example: 1.1914). Apply the correction factor according to clause 12.5.
• Table 3 Correction factors for determining gasoline-ethanol mixture using a calibration curve of white oil matrix standard samples: ethanol volume fraction 0 ~ 90% (the original table source-text extraction is severely garbled, values require confirmation against the source standard (source-text extraction)). Note: The table lookup method is based on the known ethanol content of the sample (for example: ethanol volume fraction 15%), look up the corresponding values in the first row and first column (for example: 15 = 10 + 5), and the intersection of the two values is the correction factor (for example: 1.0881). Apply the correction factor according to clause 12.5.
• Table 4 Correction factors for determining gasoline-ethanol mixture using a calibration curve of ethanol matrix standard samples: ethanol volume fraction 0 ~ 90% (the original table source-text extraction is severely garbled, values require confirmation against the source standard (source-text extraction)). Note: The table lookup method is based on the known ethanol content of the sample (for example: ethanol volume fraction 85%), look up the corresponding values in the first row and first column (for example: 85 = 80 + 5), and the intersection of the two values is the correction factor (for example: 0.9492). Apply the correction factor according to clause 12.5. Refer to clauses 7.8 and 10.1 for using ethanol correction.
• Figure 2 Relationship curves between matrix correction factor and M_O/M_H at different total oxygen contents (using CrKα radiation): four curves for oxygen mass fractions 0.0%, 1.0%, 2.0%, 3.0%; the horizontal axis is the sample to be tested M_O/M_H (the original text source-text extraction writes "M1/MH", requires confirmation against the source standard (source-text extraction)), range approximately 4 ~ 10; the vertical axis is the correction factor C, range approximately 0.94 ~ 1.12.

10. Precision

• 15.1 Precision: calculated from experimental data obtained by nine instruments in nine different laboratories measuring 22 sulfur-containing substances. Including five gasolines, seven diesel and biodiesel blended fuels, three jet fuels, one kerosene, three biodiesels, and three ethanol gasolines. The sulfur content range is 1.1 mg/kg ~ 2822 mg/kg (the highest value among the series of samples used in the test). Judge the reliability of the test results according to the following provisions (95% confidence level).
• 15.1.1 Repeatability: For consecutive determinations of the same test sample by the same operator, in the same laboratory, using the same instrument, the difference between the two test results obtained shall not exceed the value obtained by formula (7): Repeatability (r) = 0.4998 × X^0.54 (the original text source-text extraction writes "0.4998 X0. S4", requires confirmation against the source standard (source-text extraction)). In the formula: X— is the average mass fraction of the two replicate test results, mg/kg.
• 15.1.2 Reproducibility: For determinations of the same test sample by different operators, in different laboratories, using different instruments, the difference between the two single and independent test results obtained shall not exceed the value obtained by formula (8): Reproducibility (R) = 0.7384 × X^0.54 (the original text source-text extraction writes "0.7384X0.S4", requires confirmation against the source standard (source-text extraction)). In the formula: X— is the average mass fraction of the two independent test results, mg/kg.
• Table 6 Typical precision values for various types of samples (sulfur mass fraction / repeatability r / reproducibility R):
  • 3.2 mg/kg: r = 0.9 mg/kg, R = 1.4 mg/kg
  • 5.0 mg/kg: r = 1.2 mg/kg, R = 1.8 mg/kg
  • 10.0 mg/kg: r = 1.7 mg/kg, R = 2.6 mg/kg
  • 15.0 mg/kg: r = 2.2 mg/kg, R = 3.2 mg/kg
  • (The remaining row values source-text extraction in Table 6 of the source text are garbled, requires confirmation against the source standard (source-text extraction))
• 15.2 Bias: The test method was verified using NIST gasoline and diesel reference materials SRM2298, SRM2723a, SRM2714b (content ranges are given in Table 7), and no statistically significant bias was found. Other types of fuel oil were not tested, but bias caused by differences in the carbon-to-hydrogen ratio or oxygen content between the sample to be tested and the reference sample can be corrected according to the method in Chapter 5.
• Comparison of the standard values of Table 7 NIST SRM with the results of the ASTM laboratory interlaboratory test (ILS):
  • SRM2298 Gasoline: NIST standard value 4.7 mg/kg; NIST 95% confidence level lower limit 3.4 mg/kg; NIST 95% confidence level upper limit 6.0 mg/kg; ILS measured mean 4.6 mg/kg; ILS whether the measured mean is within the 95% confidence level limits: yes.
  • SRM2723a Diesel: NIST standard value 10.9 mg/kg; NIST 95% confidence level lower limit 10.59 mg/kg; NIST 95% confidence level upper limit 11.21 mg/kg; ILS measured mean 11.1 mg/kg; ILS whether the measured mean is within the 95% confidence level limits: yes.
  • SRM2724b Diesel: NIST standard value 426.5 mg/kg; NIST 95% confidence level lower limit 420.8 mg/kg; NIST 95% confidence level upper limit 432.2 mg/kg; ILS measured mean 431 mg/kg; ILS whether the measured mean is within the 95% confidence level limits: yes.
  • (The number source-text extraction of Table 7 in the source text is written as "2724b", while the foreword/main text writes it as "SRM2714b", requires confirmation against the source standard (source-text extraction))

11. Report

• 13.1 Report the sulfur mass fraction of the test sample calculated in Chapter 12, in units of mg/kg. For samples with a mass fraction less than 100 mg/kg, round to a mass fraction of 0.1 mg/kg; for samples with a mass fraction greater than or equal to 100 mg/kg, round to a mass fraction of 1 mg/kg.
• 14 Quality control:
  • 14.1 To ensure that the instrument and measurement procedure are in a satisfactory state, at least one quality control sample (see 7.5) shall be measured each day before using the instrument.
  • 14.2 If the laboratory has already established quality control or quality assurance measures, they may be used as long as they include steps for monitoring the reliability of test results.
  • 14.3 If the laboratory has not established quality control or quality assurance measures, the system described in Annex C may be used.
• Annex C Quality control procedures (informative annex):
  • C.1 Monitor and control the stability and precision of the instrument by periodically analyzing quality control (QC) samples.
    • C.1.1 The type of QC sample should be similar to the samples routinely analyzed by the instrument. QC samples should be supplied in sufficient quantity to serve as quality control over a long period and be able to remain homogeneous and stable under the storage conditions met.
    • C.1.2 The testing frequency of QC samples depends on the instability of the analysis, the stability exhibited by the testing process, and customer requirements. Generally, QC samples should be tested before analysis every day. If there are many samples in routine analysis, the frequency of QC sample testing should be increased. However, when the testing process is very stable, the frequency of QC sample testing may be reduced.
  • C.2 Record the test results of QC samples, and analyze the statistical control state of the testing process based on control charts or other equivalent statistical techniques.
    • C.2.1 Before using the QC sample control chart to evaluate the testing process, the user of the test method should have collected at least 15 sets of suitable measurement results for the QC sample and calculated the mean and control limits.
    • C.2.2 When any QC sample result exceeds the control limits, the root cause shall be investigated; the investigation may result in recalibration of the instrument or other remedial measures.
    • C.2.3 The laboratory repeatability of the QC sample measurement shall be compared with the reproducibility specified in the standard, and the former should be less than or equal to the latter.
• Annex D Helpful information for analysts (informative annex):
  • D.1 Operations for obtaining the best measurement results include: cleaning procedures to reduce contamination; correct sample preparation and measurement; analytical quality control. These steps are especially important when measuring low-content samples.
    • D.1.1 For more guidance on optimization, sample handling, calibration, and confirmation of X-ray spectrometer methods, please refer to ASTM D7343.
  • D.2 Keep the sample preparation environment clean to reduce sample contamination. Ensure that sample cells, X-ray films, and pipettes are stored in dust-free places, such as plastic bags, containers with lids, or drawers. If a hole-punching tool is used (it is not necessary to pre-punch the sample cell), ensure that the hole-punching tool is also kept in a dust-free environment, and that reusable hole-punching tools are cleaned with a suitable solvent after each use.
  • D.3 Consult the manufacturer about how to clean the analyzer and which cleaning solvents may be used. The instrument's sample chamber shall be cleaned at least once a day, and whenever suspicious measurement results appear.
    • D.3.1 It is recommended to use canned air during cleaning and sample preparation, as a drying agent after cleaning, to remove airborne contaminants such as dust. Do not shake the can before use, as this may produce a visible propellant stream and form a contaminated layer. If this occurs, perform the cleaning process again to remove contamination or replace the disposable window film.
    • D.3.2 The sample chamber, including the inside of the lid, the sample holder, and adjacent areas (except the film), may be cleaned with a clean lint-free cloth moistened with isopropyl alcohol, and then dried with canned air.
    • D.3.3 Disposable films can only be replaced, not cleaned. Before installation, purge the film with canned air, and ensure that the installed film has no wrinkles. Be sure to recalibrate the instrument when using a new batch of film.
    • D.3.4 Carefully clean non-disposable windows according to the instrument instructions. Polyimide windows may be cleaned with a foam cleaning swab or lint-free cloth moistened with isopropyl alcohol. Shake the cloth to remove excess alcohol, then hold the cloth parallel to the top of the analyzer and carefully wipe the main window. Because polyimide windows are fragile, be careful during cleaning to prevent breakage. Dry the main window with canned air. If the canned air stream is visible when drying the window, repeat the main window cleaning operation.
  • D.4 For information about samples and sample handling, please refer to Chapter 8. For information about the instrument and sample preparation, please refer to Chapter 9. In addition, it is recommended to use canned air during sample preparation, and to purge the sample cell with canned air during sample preparation (it is not necessary to pre-purge the sample cell).
    • D.4.1 Use appropriate sample storage and mixing procedures. Before transferring the sample to the sample cell, ensure that the sample is homogeneous. If necessary, filter the sample to remove water and particles. It is recommended to use a disposable pipette to transfer the sample rather than pouring the sample from the container. Do not reuse disposable pipettes.
    • D.4.2 Before placing the X-ray film on the sample cell, purge the side of the film that contacts the sample with canned air. When turning the sample cell over to punch the vent hole, ensure that the sample cell is placed on a rack or lint-free cloth to prevent film contamination. If a sample cell with a pre-made vent hole is used, this step is not necessary.
    • D.4.3 Purge the sample cell film with canned air. Before placing the sample cell into the analytical instrument, inspect the window film surface for leaks, wrinkles, or particles. Be sure to confirm the integrity of the calibration when using a new film. Measure the sample promptly after sample preparation is complete, and remove it from the instrument promptly after analysis. Check whether the sample leaks after analysis. If