NB/SH/T 0253-2021 Determination of total sulfur content in light petroleum products - Electrometric method

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Card type: Test method

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

• Standard number: NB/SH/T 0253—2021
• Chinese full name: Determination of total sulfur content in light petroleum products - Electrometric method
• English name: Determination of trace quantities of sulfur in light petroleum products—Oxidative microcoulometry method
• Replacement relationship: Replaces SH/T 0253—1992 "Determination of total sulfur content in light petroleum products (Electrometric method)"
• Previous versions: First published in 1983 as SY 2506—83; first revision in 1992, standard number changed to SH/T 0253—1992; this is the second revision
• Publication / implementation: Published on 2021-11-16, implemented on 2022-05-16
• Issuing authority: National Energy Administration
• Secretariat: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, Shandong Chambroad Petrochemicals Co., Ltd.
• Main drafters: Liu Yaqiong, He Pei, Wang Yaowei, Liu Jianli

2. Scope of application and non-applicability

• Applicable to the determination of total sulfur content in light petroleum products with boiling point range between 26 ℃ and 380 ℃, such as: motor gasoline, motor ethanol gasoline, distillate, diesel, biodiesel blend fuel, jet fuel, denatured fuel ethanol, etc.
• Total sulfur content determination range: 0.5 mg/kg to 1000 mg/kg.
• Not applicable to samples with total sulfur content higher than 1000 mg/kg; for samples with total sulfur content higher than 1000 mg/kg, appropriate dilution may be used to bring them into the above specified concentration range before determination.
• Interference limits (Chapter 6): Applicable to samples with total halogen content not greater than 10 times the total sulfur content, or total nitrogen content not greater than 1000 times the total sulfur content; not applicable to samples with heavy metal content (e.g., Ni, V, Pb, etc.) greater than 500 mg/kg.
• Changes in scope of application compared with the 1992 edition: Changed from "light petroleum products with boiling point of 40 ℃ to 310 ℃" to "total sulfur content in light petroleum products with boiling point range between 26 ℃ and 380 ℃"; added determination of oxygenated fuels such as motor ethanol gasoline, biodiesel blend fuel, jet fuel, denatured fuel ethanol, etc. (see Chapter 1, Chapter 1 of the 1992 edition).

3. Method principle

The liquid sample is introduced into a high-temperature pyrolysis tube, with the temperature maintained at 900 ℃ to 1200 ℃, the reaction gas is oxygen, and the carrier gas is an inert gas (such as argon, nitrogen, etc.). The sample is pyrolyzed and oxidized in the mixed gas flow of reaction gas and carrier gas, sulfur is converted to sulfur dioxide, which enters the titration cell with the gas flow and reacts with triiodide ions in the electrolyte according to equation (1):

(Equation 1, original source-text extraction is: +SO₂+H₂O→SO₃+3I⁻+2H⁺, requires confirmation against the source standard (source-text extraction))

The triiodide ions in the titration cell are consumed, the concentration decreases, the indicator-reference electrode pair indicates this change and compares it with a given bias voltage, then this signal is input to the microcoulometer amplifier, after amplification the output voltage signal is added to the electrolysis electrode pair, and at the electrolysis anode the reaction of equation (2) occurs:

(Equation 2, original source-text extraction is: 3I⁻→I₃⁻+2e, requires confirmation against the source standard (source-text extraction))

The consumed triiodide ions are replenished, the quantity of electricity consumed is the integral of the electrolysis current over time, and according to Faraday's law of electrolysis the total sulfur content of the sample can be calculated.

4. Reagents and materials (purity / preparation)

• 8.1 Water: Meets the requirements for analytical laboratory water of grade two water standard in GB/T 6682—2008.
• 8.2 Quartz wool.
• 8.3 Acetic acid (CH₃COOH): Relative density 1.05. Warning: Toxic, corrosive, flammable. Harmful if inhaled.
• 8.4 Phosphoric acid (H₃PO₄): Orthophosphoric acid, mass fraction not less than 85%. Warning: Toxic, corrosive.
• 8.5 Inert gas: Argon or nitrogen, high purity, used as carrier gas. Warning: High-pressure gas.
• 8.6 Oxygen: High purity, used as reaction gas. Warning: Oxygen can intensify combustion.
• 8.7 Gas regulator: Two-stage gas regulator for adjusting reaction gas and carrier gas.
• 8.8 Sodium azide (NaN₃). Warning: Highly toxic.
• 8.9 Potassium iodide (KI).
• 8.10 Potassium chloride (KCl): Used for the Ag/AgCl double-junction reference electrode of 1 mol/L.
• 8.11 Potassium nitrate (KNO₃): Used for the Ag/AgCl double-junction reference electrode of 1 mol/L.
• 8.12 Iodine (I₂): Particle size not greater than 100 μm (original source-text extraction is "100km", requires confirmation against the source standard (source-text extraction)), used for saturated reference electrode.
• 8.13 Solvent: Toluene, xylene, isooctane, or other solvents similar to the components of the sample to be tested, used for preparing standard solutions and diluting samples. Warning: Flammable.
• 8.14 Dibenzothiophene: Sulfur mass fraction is 17.40% (see note to clause 8.16).
• 8.15 n-Butyl sulfide: Sulfur mass fraction is 21.92% (see note to clause 8.16).
• 8.16 Benzothiophene: Sulfur mass fraction is 23.90% (see note to clause 8.16). Note: If necessary, the purity of the reagent may be corrected.
• 8.17 Quality control (QC) sample: Homogeneous, stable, representative petroleum sample or certified reference material with known sulfur content. Used to verify the accuracy of the entire test process, see Chapter 12.

Electrolyte preparation (10.1): Dissolve 0.5 g potassium iodide (KI) and 0.6 g sodium azide (NaN₃) in about 1000 mL water, then add 5 mL acetic acid (CH₃COOH). Note: A large amount of electrolyte should be stored in a brown bottle or in the dark, and should be re-prepared at least 1 times every 3 months.

Sulfur standard solution preparation (10.2):

• 10.2.1 Preparation of 1000 mg/L sulfur standard solution (stock solution): Weigh about 0.5748 g dibenzothiophene (or 0.4562 g n-butyl sulfide or 0.4184 g benzothiophene) into a 100 mL volumetric flask, then dilute to the mark with the selected solvent, the stock solution concentration (Ca) is calculated according to equation (3). The stock solution can be further diluted to various concentrations required for determination.
• 10.2.2 Preparation of sulfur standard solutions of different concentrations: Use a pipette to transfer the stock solution, dilute with solvent, as shown in Table 1. The sulfur concentration (Cs) in standard solutions of different concentrations is calculated according to equation (4).
• Note 1: According to the frequency of use and validity period of the standard solution, it needs to be re-prepared regularly. Generally, the validity period of the stock solution and standard solution is 3 months.
• Note 2: If the standard solution is prepared and diluted by mass ratio, unit conversion should be considered when calculating the determination results.
• Note 3: Commercially available certified reference materials may be purchased.

Table 1 Preparation of sulfur standard solutions of different concentrations

a Sulfur standard solution with mass concentration of 500 mg/L.

5. Instruments and equipment

• 7.1 The diagram of the apparatus for determining total sulfur content by electrometric method is shown in Figure 1.
• 7.2 Pyrolysis furnace: Control temperature between 900 ℃ and 1200 ℃, so that organic matter can be completely pyrolyzed and organic sulfur oxidized to SO₂. A pyrolysis furnace capable of independently controlling the inlet and outlet zone temperatures may be selected. An electric furnace may also be used as a pyrolysis furnace.
• 7.3 Pyrolysis tube: Quartz material, the sample is vaporized in the inlet zone before the furnace, enters the center of the pyrolysis tube with the carrier gas and is pyrolyzed. The inlet zone should be designed large enough so that the sample boat can completely enter the center of the pyrolysis tube, and the sample may also be directly injected into the center of the pyrolysis tube. The construction of a conventional pyrolysis tube is shown in Figure 2.
• 7.4 Titration cell: The titration cell shall have two pairs of electrodes. One pair is the indicator-reference electrode pair, used to detect changes in triiodide ion concentration; the other pair is the electrolysis electrode pair, used to maintain the triiodide ion concentration. The reference electrode may be a Ag/AgCl double-junction reference electrode or a platinum wire electrode; the indicator electrode and the electrolysis electrode pair are both platinum foil or platinum wire electrodes. The titration cell has a conduit connected to the pyrolysis tube. The electrolyte in the titration cell needs to be stirred and mixed by a magnetic stirrer, gas flow, or other methods. Note: When stirring excessively, the stirring bar may damage the electrodes; slight ripples from stirring are sufficient.
• 7.5 Microcoulometer: Can control the attenuation and increase of current, used to measure the potential of the indicator-reference electrode pair and compare it with the bias voltage. It has an adjustable amplification control system, amplifies this potential difference, outputs the amplified potential difference signal and applies it to the electrolysis electrode pair, the potential difference signal is proportional to the electrolysis current, and has variable range attenuation.
• 7.6 Recorder (optional): Records and plots the potential of the titration cell during analysis.
• 7.7 Flow controller: In order to ensure stable flow rates of oxygen and carrier gas, a gas flow controller should be installed in the instrument.
• 7.8 Drying tube: If the water vapor generated after sample oxidation condenses between the outlet zone of the pyrolysis tube and the titration cell, it will absorb the SO₂ generated by the reaction, resulting in reduced recovery. Therefore, effective measures need to be taken to prevent this from occurring. The usual method is to place a phosphoric acid drying tube between the titration cell and the outlet zone of the pyrolysis tube. Under the premise of ensuring precision, other methods such as heating tape or permeation tube may also be used.
• 7.9 Microsyringe: A microsyringe of 10 μL, 25 μL, 50 μL, 100 μL, or 250 μL may be used. The injection volume should not exceed 80% of the syringe capacity.
• 7.10 Injection system: A boat injection system and a syringe injection system may be used.
  • 7.10.1 Boat injection system: The injection tube is inserted into the pyrolysis tube, the connection is airtight, and the front end of the injection tube has a carrier gas inlet. The injector can push the sample boat completely into the central region of the pyrolysis tube and can also pull it out from the center of the pyrolysis tube. The sample boat pulled out from the central region retreats to the injection port, where there is a cooling device that can completely cool the sample boat (at least stay for 2 min). After the sample boat is completely cooled, the next sample measurement can be performed. The speed of the injector is controllable and repeatable.
    • 7.10.1.1 Cooling device (optional): Depending on the volatility of the sample and the injection volume, a cooling device may be equipped to cool the sample boat. An electronic refrigerator or a cooling jacket may be used. The cooling jacket requires an additional quartz sleeve on the outer layer of the injection tube, and the coolant circulates in the sleeve to achieve the purpose of cooling the sample boat.
    • 7.10.1.2 Sample boat: Quartz material. The sample boat must not react with the sample or sulfides and must be able to withstand the extreme temperature of the central region of the pyrolysis furnace in this test method 1200 ℃.
  • 7.10.2 Syringe injection system: Use an injector to inject the sample in the syringe into the mixed gas stream of the pyrolysis tube at a constant speed of 0.5 μL/s～1.0 μL/s. The sample vaporizes in the inlet region and is carried by the mixed gas stream to the center of the pyrolysis tube. The speed of the injector is controllable and repeatable. Note: Pushing the sample too quickly into the center of the pyrolysis tube will overload the combustion capacity of the pyrolysis tube. Set the speed of the injection system so that it delivers the sample at a controllable and repeatable speed to prevent the formation of incompletely burned by-products at the outlet of the pyrolysis tube.
• 7.11 Balance: sensitivity 0.01 mg.
• 7.12 Volumetric flask: 50 mL, 100 mL, 1000 mL.
• 7.13 Pipette: 2 mL, 5 mL, 25 mL.

6. Recommended operating conditions

Table 2 Recommended instrument operating parameters

(10.3.3) Adjust the gas flow rate and set the furnace temperature and instrument parameters according to the instructions. The recommended instrument operating conditions are shown in Table 2.

7. Sampling and sample preparation

• 9.1 Sample according to method GB/T 4756 or GB/T 27867. Samples containing volatile components should be analyzed as soon as possible after sampling to avoid sulfur loss and contamination. Note: Samples taken below room temperature expand at room temperature and may even damage the sample container. Therefore, when filling such samples into a container, sufficient expansion space must be left above the sample.
• 9.2 After the sample is collected in the container, if it is not analyzed immediately, the sample must be thoroughly mixed before analysis.
• 13.1 Obtain the test sample according to Chapter 9. The total sulfur content of the test sample should be similar to the total sulfur content of the standard solution. If necessary, the test sample may be diluted by mass dilution or volume dilution to meet the concentration range requirements.
  • 13.1.1 Mass dilution method (m/m): Record the mass of the test sample, and the total mass of the test sample and solvent.
  • 13.1.2 Volume dilution method (m/V): Record the mass of the test sample, and the total volume of the test sample and solvent.
• 13.4 Determine the density of the test sample at room temperature when tested according to method GB/T 1884, GB/T 29617, or SH/T 0604.

8. Analysis procedure

• 10.3 Instrument preparation
  • 10.3.1 Install the instrument according to the manufacturer's instructions and perform a leak check. Rinse the titration cell several times with electrolyte. If there are bubbles in the side arms of the reference electrode and the electrolysis electrode, carefully remove them, and keep the electrolyte level 3 mm～6 mm above the platinum electrode.
  • 10.3.2 Connect the titration cell to the instrument according to the instructions.
  • 10.3.3 Adjust the gas flow rate and set the furnace temperature and instrument parameters according to the instructions. The recommended instrument operating conditions are shown in Table 2.
  • 10.3.4 If a boat injection system is used, before analyzing samples, first send an empty sample boat into the pyrolysis furnace and burn it for about 20 min to ensure that there are no impurities on the sample boat that affect the analysis results.
• 11 Calibration and standardization
  • 11.1 Set the operating parameters for internal calibration with reference to the instrument manufacturer's recommendations.
  • 11.2 Before analysis, rinse the microsyringe repeatedly with the test sample. If there are bubbles in the syringe, rinse the syringe again to ensure there are no bubbles before drawing the test sample.
  • 11.3 The injection volume can be determined by the volume method or the mass method. The injection volume should not exceed 80% of the syringe volume.
    • 11.3.1 Volume method: Fill the syringe with the test sample to the required mark, pull back the plunger of the syringe, and draw in a segment of air so that the lowest liquid level rises to the 10% mark, and record the liquid volume in the syringe. After injection, pull the syringe back again so that the lowest liquid level rises to the 10% mark, and record the liquid volume in the syringe. The difference between the two volume readings is the injection volume of the test sample. Note: A fully automatic injector may be used instead of the manual injection step.
    • 11.3.2 Mass method: According to the method described in 11.3.1, draw the test sample into the syringe to the required volume, weigh the mass of the syringe before and after injecting the test sample, and the difference is the mass of the test sample. The mass of the syringe needs to be weighed with a balance of sensitivity 0.01 mg.
    • 11.3.3 After sampling with the syringe, the test sample should be quickly and quantitatively injected into the instrument. Two injection modes may be used: boat injection and syringe injection.
      • 11.3.3.1 Boat injection system: Slowly and quantitatively inject the test sample from the syringe into the sample boat containing quartz wool, and the last drop of the test sample must also be injected onto the sample boat. Withdraw the syringe and immediately start the analysis. Before analysis, the instrument baseline remains stable. When the sample boat approaches the pyrolysis furnace, the test sample vaporizes and the baseline changes. After the test sample vaporizes and burns, the baseline stabilizes again. Then pull the sample boat from the furnace back to the position before injection. After the sample boat is pulled back, it should stay for at least 2 min before the next injection operation, so that the sample boat is completely cooled (Note 1～Note 3). If carbon deposit is observed at the outlet of the pyrolysis tube, the injection speed of the sample boat must be slowed down or the sample amount reduced. If carbon deposit is observed in the sample boat after the analysis is completed, the residence time of the sample boat in the center of the pyrolysis furnace should be extended.
        • Note 1: To ensure complete combustion of the test sample, the injection speed may be slowed down or the residence time of the sample boat in the furnace increased.
        • Note 2: The length of residence time required for complete combustion depends on the matrix of the test sample. Generally, a residence time of 2 min is sufficient. Increasing the residence time when necessary can ensure complete combustion of the test sample.
        • Note 3: The degree of cooling required for the sample boat is related to the volatility of the test sample. For volatile samples, using the cooling device in 7.10.1.1 to cool the sample boat or extending the cooling time of the sample boat can minimize the volatilization of the sample.
      • 11.3.3.2 Syringe injection system: Carefully insert the entire syringe needle into the inlet of the pyrolysis tube, and place the syringe on the injector. The residual test sample in the syringe needle vaporizes and burns at high temperature, causing the baseline to change. After the baseline stabilizes again, immediately start the injection analysis. When the instrument returns to a stable baseline again, withdraw the syringe. If carbon deposit is observed at the outlet of the pyrolysis tube, the syringe injection speed must be slowed down or the sample amount reduced. Note: To avoid overloading the combustion capacity of the system, it is recommended that the syringe injection speed be between 0.5 μL/s～1.0 μL/s.
  • 11.4 The instrument may be calibrated by one of the following two methods.
    • 11.4.1 Single-point calibration: According to the method described in 11.2～11.3.3, determine the total sulfur content of the standard solution and the blank, and measure each sample twice. Take the average of the two results and calibrate the instrument according to the manufacturer's instructions. Use a standard solution with a total sulfur content similar to that of the unknown sample to determine the total sulfur content in the unknown sample. Check the system performance with a standard solution at least once a day (see Chapter 12).
    • 11.4.2 Standard curve calibration: According to the method described in 11.2～11.3.3, determine at least 3 standard solutions of different concentrations and a blank solution, and measure each sample 2 times. Take the average of the 2 results and calibrate the instrument according to the manufacturer's instructions. Establish a first-order or second-order linear standard curve, and use this standard curve to determine the total sulfur content in the unknown sample. Check the system performance with a standard solution at least once a day (see Chapter 12).
  • 11.5 Select a standard sample with an expected total sulfur content similar to that of the test sample, perform a calibration test, and take the average of two measurement results. The difference between the two measurement results should not exceed the repeatability requirement in 16.1.2. Calculate the recovery rate r (%) according to formula (5).
  • 11.6 Since only part of the sulfur entering the pyrolysis tube is converted to sulfur dioxide and another part is converted to sulfur trioxide, and sulfur trioxide does not react with the titrant, a sulfur standard substance similar in type and boiling range to the test sample should be selected to ensure the accuracy of the determination. Under the above operating conditions, the recovery rate should be above 75%; otherwise, the operator should check various operating parameters or prepare the electrolyte again. If the equipment is operating normally, the recovery rate is expected to be between 75% and 90%.
  • 11.7 Removal and recalibration: Remove carbon deposits generated on components according to the instrument manufacturer's instructions. After removal and adjustment, reinstall the instrument and perform a leak check. Before analyzing samples again, the instrument needs to be recalibrated according to the procedure in clause 11.4.
• 12 Quality assurance and control
  • 12.1 After each calibration, quality control (QC) sample analysis is required. During use, analyze at least one QC sample each time. The purpose of analyzing the QC sample is to verify instrument performance and determine the accuracy of the test process. If there are many samples, the frequency of determination of the QC sample needs to be increased. For samples with sulfur content lower than 2.0 mg/kg, the frequency of determination of the QC sample is even more in need of increase, and after all samples have been tested, one more QC sample should be additionally tested; if the deviation of the QC sample is found to be relatively large, then all samples need to be re-determined.
  • 12.2 If the laboratory has already established a QC procedure, it may be used to determine the reliability of the measurement results.
  • 12.3 If the laboratory has not established a QC procedure, Annex A may be referenced for QC evaluation.
• 13 Test procedure
  • 13.1 Obtain the test sample in accordance with Chapter 9. The total sulfur content of the test sample should be similar to the total sulfur content of the standard solution. If necessary, the test sample may be diluted by mass dilution or volume dilution to meet the concentration range requirements.
  • 13.2 Rinse the syringe several times with the test sample. Using the method described in 11.2 to 11.3, determine the total sulfur content of the test sample.
  • 13.3 Inspect the pyrolysis tube and other components in the gas flow path to ensure complete oxidative combustion of the test sample.
  • 13.4 Repeat the determination of each test sample 2 times, and calculate the average response value. Determine the density of the test sample at room temperature when it is tested in accordance with the method of GB/T 1884, GB/T 29617, or SH/T 0604.

9. Qualitative and quantitative determination and calculation formulas

• 14.1 The total sulfur content in the test sample Cs, the sample calculation is as shown in formula (6) or formula (7), in units of milligrams per kilogram (mg/kg). The derivation process of formula (6) and formula (7) is given in Annex B.

Formula (6): Cs, sample = ms, sample × 1000 / (M sample × K) (the original text source-text extraction is "m5. with M ×1000 / M inw XK", requires confirmation against the source standard (source-text extraction))

Formula (7): Cs, sample = ms × 1000 / M sample (the original text source-text extraction is "msX1000 / Cs.unFamSPum", requires confirmation against the source standard (source-text extraction))

Where:

• ms, sample — the measured mass of sulfur in the test sample, in units of micrograms (μg);

• K — mass dilution coefficient, i.e., the ratio of the mass of the test sample to the total mass of the test sample plus solvent, in units of grams per gram (g/g);

• M sample — the mass of the test sample, obtained by the gravimetric method or calculated from the injection volume and density, V×ρ, in units of milligrams (mg);

• V — injection volume, obtained by the volumetric method or calculated from mass and density, M/ρ, in units of microliters (μL);

• ρ test sample — the density of the test sample, determined at room temperature when the test sample is tested in accordance with the method of GB/T 1884, GB/T 29617, or SH/T 0604, in units of grams per milliliter (g/mL);

• 1000 — conversion factor, the coefficient when converting from μg/mg to mg/kg.

• 10.2.1 The concentration of the stock solution (Ca) is calculated according to formula (3) (the original text source-text extraction is "mgXwsX10m×10° / 100", requires confirmation against the source standard (source-text extraction)). Where: m₀—mass of the solute, in units of grams (g); —mass fraction of sulfur in the solute, %; —mass fraction of the solute, %; 10⁶—conversion factor, the coefficient when converting from g/mL to mg/L; 100— the volume of the volumetric flask, in units of milliliters (mL). (The original text source-text extraction symbols are incomplete, requires confirmation against the source standard (source-text extraction))

• 10.2.2 The sulfur concentration in standard solutions of different concentrations (Cs) is calculated according to formula (4): Cs = Ca × V / 100 (the original text source-text extraction is "Cs=CaX Ka / 100", requires confirmation against the source standard (source-text extraction)). Where: Ca— the concentration of sulfur in the stock solution, in units of milligrams per liter (mg/L); V— the volume of the stock solution pipetted, in units of milliliters (mL); 100— the volume of the volumetric flask, in units of milliliters (mL).

• 11.5 Recovery r (%) is calculated according to formula (5): r = c / c₀ × 100 (the original text source-text extraction is "C, ×100 / 「=", requires confirmation against the source standard (source-text extraction)). Where: c—— the average value of the total sulfur content determination in the standard sample, in units of milligrams per liter (mg/L); c₀—the theoretical value of the total sulfur content in the standard sample, in units of milligrams per liter (mg/L).

• 15 Expression of results: take the arithmetic mean of the determination results as the determination result, in units of mg/kg. When the determination result is greater than or equal to 10.0 mg/kg, the result is retained to 1 mg/kg; when the determination result is less than 10.0 mg/kg, the result is retained to 0.1 mg/kg.

• Annex B (informative) Derivation of the formulas in Chapter 14: The derivation of some calculation formulas in Chapter 14 of B.1.1 is based on the displacement of the electric charge of triiodide ions consumed by the reaction in the titration cell (reaction formula I₃⁻ + 2e⁻ → 3I⁻, the reaction equation is garbled in the source transcription; verify the displayed interpretation against the original standard). The difference in the reactant (triiodide ions) between the start and when the current is interrupted at the titration endpoint is proportional to the net charge transferred Q. B.1.2 In most cases, a constant current is applied, so the product of the current i and the time required to reach the endpoint t is the quantity of charge Q, that is, the iodine produced in equilibrium with the reactant; that is, Q=i·t, therefore, the equivalent number of the reactant is equal to Q/F, where F is the Faraday constant, with a value of 96500 C/mol. B.1.3 The calculation process for the total sulfur content in the test sample Cs, sample (in units of mg/kg) and mass ms (in units of μg) is shown in formula (B.1) to formula (B.5). B.1.4 Derivation using a disk integrator: A in formula (B.5) is expressed as cm², however, A can also be expressed as count. Because 1 cm²=1000 counts, therefore, A(cm²)=counts×10⁻³. Therefore, replacing A(cm²) with counts×10⁻³, formula (B.5) becomes formula (B.8), and formula (B.6) becomes formula (B.9) to formula (B.10). Note: count— full-scale drift value on the integrator × 100. (Annex B formula source-text extraction noise is severe, specific coefficients require confirmation against the source standard (source-text extraction))

10. Precision

• 16.1.1 Overview: Through determination by 6 laboratories of 17 samples of different types (such as: motor gasoline, diesel, jet fuel, distillate oil and other light petroleum products) with total sulfur content between 0.5 mg/kg and 1000 mg/kg, the total sulfur content determination results are statistically calculated in accordance with the requirements of GB/T 6683 to obtain the precision of this document (95% confidence level).
• 16.1.2 Repeatability: The difference between 2 determination results obtained by the same operator, using the same instrument, under the same operating conditions, on the same test sample shall not exceed the value obtained by formula (8).
  • Formula (8): r = 0.096 X^0.703 (the original text source-text extraction is "r=0.096X9703", requires confirmation against the source standard (source-text extraction))
  • Where: X—2 the average value of the test results of the runs, in units of milligrams per kilogram (mg/kg).
• 16.1.3 Reproducibility: The difference between 2 single and independent test results obtained in different laboratories, by different operators, using different instruments, on the same test sample shall not exceed the value obtained by formula (9).
  • Formula (9): R = 0.549 X^0.804 (the original text source-text extraction is "R=0.549X2.804", requires confirmation against the source standard (source-text extraction))
  • Where: X—2 the average value of the test results of the runs, in units of milligrams per kilogram (mg/kg).
• 16.1.4 Typical precision values are detailed in Table 3.

Table 3 Typical values of repeatability (r) and reproducibility (R)

• 16.2 Bias: The test results obtained from analyzing standard reference materials are within the repeatability range of this document. Standard materials were analyzed, and the difference between the obtained test results and the given values of the standard materials is within the reproducibility range of this document.

11. Report

not provided in the available source (the main text does not have a dedicated "Report" chapter; the requirements for expression of results are given in Chapter 15).

12. Reference documents

Normative reference documents (Chapter 2):

• GB/T 1884 Standard test method for density of crude petroleum and liquid petroleum products by laboratory determination (hydrometer method)
• GB/T 4756 Standard practice for manual sampling of petroleum liquids
• GB/T 6682—2008 Specifications and test methods for water for analytical laboratory use
• GB/T 27867 Standard practice for automatic sampling of petroleum liquids in pipelines
• GB/T 29617 Standard test method for density, relative density, and API specific gravity of liquids by digital density meter
• SH/T 0604 Standard test method for density of crude petroleum and petroleum products (U type vibrating tube method)

References:

• [1] GB/T 6683 Standard practice for determining precision data for test methods of petroleum products
• [2] NB/SH/T 0843 Standard practice for statistical techniques for evaluation of analytical testing systems in the petrochemical industry
• [3] ASTM MNL7 Manual on Presentation of Data and Control Chart Analysis

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick reference for questions and answers