NB/SH/T 0827-2010 Determination of sulfur-containing compounds in light petroleum distillates by gas chromatography and sulfur selective detection

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

• Standard number: NB/SH/T 0827—2010
• Chinese name: Determination of sulfur-containing compounds in light petroleum distillates by gas chromatography and sulfur selective detection
• English name: Standard test method for sulfur compounds in light petroleum liquids by gas chromatography and sulfur selective detection
• Replacement relationship: This standard is first published (original text: This standard is first published)
• Correspondence: Corresponds to ASTM D5623-94 (2004), degree of consistency is non-equivalent
• Publication/implementation: 2010-05-01 published, 2010-10-01 implemented
• Publishing unit: National Energy Administration
• Responsible organization: Sinopec Research Institute of Petroleum Processing
• Drafting unit: Sinopec Research Institute of Petroleum Processing
• Main drafters: Yang Yongtan, Wang Zheng

Main differences from ASTM D5623-94 (2004) (listed in the original text):

• Some referenced standards adopt the corresponding national standards or industry standards of our country.
• ASTM uses a 30m × 0.32mm × 4μm chromatographic column, this standard replaces it with a 50m × 0.2mm × 0.5μm chromatographic column.
• The initial temperature of ASTM is 10°C, the initial temperature of this standard is 35°C.
• The programmed temperature ramp rate of ASTM is 10°C/min, the programmed temperature ramp rate of this standard is 2°C/min.
• This standard adjusts the split ratio.
• ASTM uses constant pressure mode, this standard uses constant flow mode.
• The retention times in Table 1 of ASTM are given under the condition of hydrogen as carrier gas, the retention times in Table 1 of this standard are given under the condition of nitrogen as carrier gas, and the retention times of several common sulfur-containing compounds are supplemented.
• In the test procedure of ASTM, only a sulfur chemiluminescence detector is used, this standard may use a sulfur chemiluminescence detector and an atomic emission spectrometer detector.
• ASTM recommends diphenyl disulfide, 3- chlorothiophene, 2- bromothiophene or other suitable sulfur-containing compounds as internal standard compounds, this standard recommends dibenzothiophene or other suitable sulfur-containing compounds as internal standard compounds.

2. Scope of application and non-applicability

• 1.1 This standard specifies a method for the determination of various volatile sulfur-containing compounds in light petroleum distillates. It is applicable to petroleum distillates, motor gasoline (including gasoline containing oxygen-containing compounds) and other petroleum fractions with a final boiling point not greater than 230°C at atmospheric pressure.
• The determinable mass fraction range varies depending on the sample type and the instrument used; in most cases, it is applicable to samples with a sulfur mass fraction of individual sulfur-containing compounds in the range of 0.1mg/kg ~ 100mg/kg.
• 1.2 This standard is not intended to identify all individual sulfur-containing compounds. Within the determination range specified by the method, the detector should respond linearly to sulfur and all individual sulfur-containing compounds should have an equimolar response to sulfur, and both unidentified and identified individual sulfur-containing compounds can be quantitatively determined. The mass fractions of many reactive sulfur-containing compounds, such as hydrogen sulfide and methanethiol, will change during sampling and analysis. The total sulfur mass fraction of a sample can be estimated by summing the measured sulfur mass fractions of individual sulfur-containing compounds, but this standard is not the preferred method for determining the total sulfur mass fraction.
• 1.3 This standard uses International System of Units (SI) units.
• 1.4 This standard is not intended to address certain hazardous materials, operations, equipment, and all safety issues related thereto. Users should establish appropriate safety and protective measures before using the standard, and ensure that there are operable management systems.
• Not applicable: This standard is not suitable for the determination of sulfur-containing compounds in liquefied petroleum gas (see 7.1).

3. Method principle

• 3.1 The sample is analyzed by gas chromatography equipped with a sulfur selective detector, and an appropriate internal standard compound or external standard compound is selected for calibration. It is assumed that all sulfur-containing compounds have the same molar response to sulfur.
• 3.2 After the sulfur-containing compounds elute from the gas chromatographic column, they can be quantitatively detected by a sulfur selective detector that responds linearly and equimolarly to sulfur. The sulfur selective detector may be a sulfur chemiluminescence detector or an atomic emission spectrometer detector.
• 4 Significance and application: Gas chromatography equipped with a sulfur selective detector provides a method for rapid qualitative and quantitative determination of sulfur-containing compounds in various petroleum fractions and petroleum products. These oils often contain various types and contents of sulfur-containing compounds. Many sulfur-containing compounds have odors, are corrosive to equipment, and can easily cause poisoning of catalysts in petroleum processing. For controlling the sulfur-containing compounds in finished oils, giving the type distribution of sulfur-containing compounds in various petroleum fractions is more practically significant than only obtaining total sulfur information.

4. Reagents and materials (purity / preparation)

• 6.1 All chemical reagents used in the test are of analytical grade. If reagents of other purities can ensure that the accuracy of the determination results is not reduced, they may be used.
• 6.1.1 Solvent: such as isooctane (2,2,4- trimethylpentane), used to prepare test mixtures and internal standard compound stock solutions. Warning: Isooctane is flammable. Inhalation of its vapor or contact with skin should be avoided as much as possible.
• 6.1.2 Dilution solvent: such as toluene, used to prepare test mixtures. Warning: Toluene is flammable and toxic by inhalation. Inhalation of its vapor or contact with skin should be avoided as much as possible.
• 6.1.3 Carrier gas: high-purity nitrogen or helium. It is recommended to further purify the carrier gas with molecular sieves or other suitable removal agents to remove water and hydrocarbon compounds from the carrier gas. Sufficient gas pressure must be available to ensure a constant carrier gas flow rate. Warning: Nitrogen or helium is a high-pressure compressed gas.
• 6.1.4 Detector gases: hydrogen, air, and oxygen can be used as detector gases, and these gases should not contain contaminants that interfere with the determination (especially they must not contain sulfur-containing compounds). Warning: Hydrogen is easily combustible under high pressure. High-pressure air and oxygen support combustion.
• 6.1.5 External standard method: The sulfur-containing compounds and matrix selected for the external standard method can represent the matrix and sulfur-containing compounds of the sample to be analyzed. SH/T 0253 may be used to determine sulfur content to calibrate the determination results of this standard. The determination procedure of the internal standard method can also be used for the external standard method. The matrix should have no effect on the peak or area determination of the calibration sample selected for the external standard method. For the preparation of the selected standard sample, see ASTM D4307. If the system meets the requirements of 8.3 system evaluation, only one external standard compound is needed for quantification. The external standard substance contains at least sulfur-containing compounds with contents similar to those in the sample to be tested (within one order of magnitude).
• 6.1.6 Internal standard compound: Any sulfur-containing compound that is easily distinguished from the sulfur-containing compounds in the petroleum fraction and is not contained in the sample to be analyzed can be used as an internal standard compound. In this standard, considering the possible analysis of sulfur compounds in heavier fractions, dibenzothiophene is selected as the internal standard compound. The purity of dibenzothiophene should be higher than 99%. When the purity is unknown or questionable, use an appropriate method to analyze the dibenzothiophene content in the sample, and use this as the accurate internal standard purity value. Warning: Sulfur-containing compounds are flammable. Inhalation of their vapor or contact with skin should be avoided as much as possible.
• 6.1.6.1 Preparation of internal standard compound stock solution: Add about 0.1g ~ 1g of internal standard compound, calculated as sulfur, to 1kg of isooctane solution containing 10% toluene to prepare the internal standard compound stock solution.
• 6.1.7 Sulfur-containing compound standard solution: purity should be higher than 99%. Prepare standard samples of all sulfur-containing compounds of interest. When the purity is unknown or questionable, use an appropriate method to determine the content of the sulfur-containing compound, and use this as the accurate purity for quantification. Warning: Sulfur-containing compounds are flammable. Inhalation of their vapor or contact with skin should be avoided.
• 6.1.8 Test mixture: Prepare a stock solution of sulfur-containing compounds according to ASTM D4307. The stock solution should contain possible volatile sulfur-containing compounds in the sample, such as dimethyl sulfide (~0.1g/kg), 2- propyl mercaptan (~0.1g/kg), thiophene (~10g/kg), 3- methylthiophene (~10g/kg) and benzothiophene (~10g/kg). Dilute the stock solution 1000 times with an isooctane solution containing 10% toluene. Although 2- propyl mercaptan is unstable upon long-term storage, the asymmetry of the mercaptan peak can still be used to characterize the activity of the gas chromatographic system.

5. Instruments and equipment

• 5.1 Chromatograph: Any gas chromatograph with the following characteristics may be used.
  • 5.1.1 Programmed temperature system: The chromatograph should have linear programmed temperature capability over the temperature range required to completely separate the sulfur-containing compounds to be tested. The programmed temperature ramp rate must be repeatable to ensure that the retention time repeatability throughout the analysis is within 0.05min.
  • 5.1.2 Injection system: The injection system should have a temperature control system to ensure continuous operation at an injection temperature up to the maximum operating temperature of the chromatographic column. The injection method uses a syringe, and the repeatability of the injection volume must be ensured.
  • 5.1.3 Carrier gas and detector: Stable carrier gas and detector gas flow rates are very important for obtaining the best analytical column efficiency. It is best to use a pressure regulator or mass flow controller to ensure that the flow error is controlled within 1%.
  • 5.1.4 Detector: The detector has the following characteristics: (a) linear range > 10⁴; (b) minimum detection limit of 5pg/s; (c) equimolar response to sulfur; (d) no quenching phenomenon for co-eluting hydrocarbon compounds, and no interference with the determination of sulfur-containing compounds.
• 5.2 Chromatographic column: The chromatographic column should have the ability to completely separate the sulfur-containing compounds to be tested. The chromatographic column used and typical chromatographic conditions are shown in 5.2.1, and Table 1 lists the retention times of some sulfur-containing compounds. The chromatographic column used should be resistant to high temperatures and have low column bleed at high temperatures to ensure that the detector response is not reduced.
• 5.3 Data acquisition system
  • 5.3.1 Recorder: Integrator or chromatographic workstation. mV or equivalent recorder, with a full-scale response time of 2s or less, suitable for controlling the detector signal.
  • 5.3.2 Integrator or chromatographic workstation: It is recommended to use an electronic integration device or computer to measure the detector response. The device and software must have the following characteristics: (a) display chromatograms; (b) display chromatographic peak area values; (c) qualitative identification by retention time or (and) relative retention time; (d) calculate and use response factors; (e) quantify by internal standard method and external standard method and give results.

6. Recommended operating conditions

• 5.2.1 Typical chromatographic conditions:
  • 5.2.1.1 Chromatographic column: Use a 50m × 0.2mm × 0.5μm polydimethylsiloxane (PONA) chromatographic column.
  • 5.2.1.2 Injection volume: between 0.1μl ~ 2.0μl.
  • 5.2.1.3 Inlet: temperature 275°C; split ratio: 100:1.
  • 5.2.1.4 Column temperature: initial temperature 35°C, 2°C/min raised to 180°C, held for 10min. If internal standard method is used for quantification, initial temperature 35°C, 2°C/min raised to 180°C, 10°C/min raised to 250°C, held for 10min. (This paragraph in the source source-text extraction has noise, the temperature ramp rate and hold time wording requires confirmation against the source standard (source-text extraction))
  • 5.2.1.5 Carrier gas: nitrogen.
  • 5.2.1.6 Detector: sulfur chemiluminescence detector or atomic emission spectroscopy detector.
• Table 1 Retention times of common sulfur-containing compounds (chromatographic conditions see 5.2.1): hydrogen sulfide 4.10; carbonyl sulfide 4.16; methanethiol 4.81; ethanethiol 5.20; dimethyl sulfide 6.07; carbon disulfide 6.90; 2-propanethiol 7.xx (requires confirmation against the source standard (source-text extraction)); 2-methyl-2-propanethiol 9.97; 1-propanethiol 10.29 (requires confirmation against the source standard (source-text extraction)); methyl ethyl sulfide 10.79; 2-butanethiol 10.95; thiophene 12.56; 2-methyl-1-propanethiol 14.75; diethyl sulfide 16.85; 1-butanethiol 16.84 (requires confirmation against the source standard (source-text extraction)); 2-methylthiophene 18.xx (requires confirmation against the source standard (source-text extraction)); 3-methylthiophene 21.89; tetrahydrothiophene 56.28; 2-methyltetrahydrothiophene 56.84; ethylthiophene 57.32; dimethylthiophene 58.73; dimethylthiophene (second item) requires confirmation against the source standard (source-text extraction); methylbenzothiophene requires confirmation against the source standard (source-text extraction). Note: chromatographic conditions see 5.2.1. (In Table 1 some retention time values source-text extraction have severe noise, marked as requires confirmation against the source standard (source-text extraction))

7. Sampling and specimen preparation

• 7.1 Use a suitable sampling method for sampling. This standard is not suitable for the determination of sulfur-containing compounds in liquefied petroleum gas. Sampling of volatile liquids to be tested shall be carried out in accordance with GB/T 4756. There shall be a sufficient amount of sample (for the internal standard method, there shall be 10g ~ 20g of sample) for multiple analyses. Samples and sulfur-containing compound standard samples shall be stored at 7°C ~ 15°C. Containers holding samples or standard samples shall not be opened at temperatures higher than 15°C.
• 9.2 Preparation of specimen in internal standard method quantification: In a container that can be made up to volume, add an appropriate amount of internal standard compound dissolved in isooctane or other solvent, then add an appropriate amount of the sample to be tested, and dilute to the mark with solvent. The mass fraction of the internal standard compound, calculated as sulfur, in the specimen shall be half of the maximum mass fraction of a single component in the original sample; the mass fraction of the internal standard compound calculated as sulfur from 1mg/kg ~ 50mg/kg is suitable for most samples.

8. Analysis procedure

• 8.1 Chromatograph: Start the chromatograph according to the chromatograph manufacturer's instructions; the operating conditions of the chromatograph and detector are given in 5.2.1.
• 8.2 Detector: Start the detector according to the manufacturer's instructions; after equilibration for a certain time (5min ~ 10min), adjust the detector output signal or integrator input signal to zero. Adjust the signal to match the signal noise and baseline drift.
• 8.3 System evaluation: The compatibility of trace reactive sulfur-containing compounds with the injection system shall be evaluated, using the system test mixture in 6.1.8 as the test sample, injecting (0.1μl ~ 2.0μl) and analyzing. All sulfur-containing compound peaks shall be symmetrical and have equimolar response. The relative response factor of each sulfur-containing compound in the mixture is calculated according to formula (1):
  • Rᵢ = (w₀ᵢ × Aᵣ) / (wᵣ × A₀ᵢ) … (1)
  • Where: Rᵢ — relative response factor of the sulfur-containing compound being tested; w₀ᵢ — mass fraction of the sulfur-containing compound calculated as sulfur, mg/kg; Aᵣ — relative peak area of the sulfur-containing compound; wᵣ — mass fraction of the reference sulfur-containing compound calculated as sulfur, mg/kg; A₀ᵢ — relative peak area of the reference sulfur-containing compound.
  • The deviation of the response factor of each sulfur-containing compound shall be within ±10%; if the deviation of the response factor exceeds ±10% or the peak shape is asymmetric, it indicates that there is a problem with the chromatographic system or detector, and the instrument must be calibrated to ensure suitable selectivity, sensitivity, linearity, or system integrity. If necessary, optimize the chromatographic system according to the manufacturer's instructions.
• 9.1 The operating conditions of the instruments and chromatograph used are given in 5.2.1. Table 1 shows the retention times of common sulfur-containing compounds in gasoline samples under the operating conditions shown in 5.2.1; if conditions permit, the retention times of the main sulfur-containing compounds can be determined experimentally. Figure 1 is a chromatogram of sulfur-containing compounds in a typical gasoline sample (Figure 1 Note: operating conditions see 5.2.1, chromatographic column: 50m × 0.2mm × 0.5μm of PONA column, column temperature: initial temperature 35°C, 2°C/min raised to 180°C, held for 10min. Figure 1 peak identification: 1—ethanethiol; 2—dimethyl sulfide; 3—carbon disulfide; 4—2-propyl mercaptan; 5—2-methyl-2-propyl mercaptan; 6—1-propyl mercaptan; 7—methyl ethyl sulfide; 8—thiophene; 9—dimethyl disulfide; 10—2-methylthiophene; 11—3-methylthiophene; 12—C₂-thiophene; 13—C₃-thiophene; 14—benzothiophene; 15—methylbenzothiophene; 16—C₂-benzothiophene. Figure 1 typical gasoline sample contains about sulfur 570mg/kg)
• 9.3 External standard method specimen analysis: Calibrate the instrument at least once a day or as needed. During calibration, the injection volume of the external standard method quantification standard must be kept exactly the same as the injection volume of the specimen to be tested.
• 9.4 Chromatographic analysis: Introduce a representative specimen into the chromatograph; when using the internal standard method for quantification, the specimen must contain an accurate amount of the internal standard compound. The injection amount of the specimen and standard sample must not overload the detector (forming a flat-topped peak); the injection amount is generally suitable between 0.1μl ~ 2.0μl. Obtain chromatographic data with a recorder, integrator, or chromatographic workstation, and inspect the chromatogram and data to avoid errors.

9. Qualitative and quantitative determination and calculation formulas

• 10.1 Mass fraction of sulfur-containing compounds calculated as sulfur: After qualitatively identifying each sulfur-containing compound in the gasoline sample, measure the relative peak area of each sulfur-containing compound obtained.
• 10.1.1 Determination of the mass fraction of sulfur-containing compounds calculated as sulfur by the internal standard method: Compare the relative peak area of each sulfur-containing compound with the relative peak area of the internal standard compound. Calculate the mass fraction of each sulfur-containing compound calculated as sulfur according to formula (2):
  • w₀ᵢ = (w₀ᵢₛ × mᵢₛ × Aᵢ) / (mₛ × Aᵢₛ) … (2)
  • Where: w₀ᵢ — mass fraction of the sulfur-containing compound to be tested calculated as sulfur, mg/kg; w₀ᵢₛ — mass fraction of the internal standard compound calculated as sulfur in the stock solution, mg/kg; mᵢₛ — mass of the stock solution added to the specimen, g; Aᵢ — relative peak area of the sulfur-containing compound; mₛ — mass of the specimen, g; Aᵢₛ — relative peak area of the internal standard compound.
• 10.1.2 Determination of the mass fraction of sulfur-containing compounds calculated as sulfur by the external standard method: Select a suitable external standard compound for quantification according to 6.1.5. The sulfur-containing compound and matrix used for external standard method quantification can represent the sample being analyzed. Compare the relative peak area of each sulfur-containing compound with the relative peak area of the external standard compound. Calculate the mass fraction of each sulfur-containing compound calculated as sulfur according to formula (3):
  • w₀ᵢ = (w₀ₑ × Dₑ × Aᵢ) / (Dₛ × Aₑ) … (3)
  • Where: w₀ᵢ — mass fraction of the sulfur-containing compound to be tested calculated as sulfur, mg/kg; w₀ₑ — mass fraction of the external standard compound calculated as sulfur, mg/kg; Dₑ — density of the external standard compound matrix, kg/m³; Aᵢ — relative peak area of the sulfur-containing compound to be tested; Dₛ — density of the gasoline sample to be tested, kg/m³; Aₑ — relative peak area of the external standard compound.
• 10.2 Report the mass fraction of each sulfur-containing compound calculated as sulfur (retain one decimal place, unit mg/kg).
• 10.3 Mass fraction of total sulfur in the specimen: The mass fractions calculated as sulfur of all known and unknown sulfur-containing compounds in the specimen are summed according to formula (4) to obtain the total sulfur mass fraction.
  • w_sulfur = Σ w₀ᵢ … (4)
  • Where: w_sulfur—— total sulfur mass fraction of the specimen, mg/kg.
• 10.4 Report the total sulfur mass fraction of sulfur-containing compounds in the specimen (retain one decimal place, unit mg/kg).
• 10.5 Mass fraction of sulfur-containing compounds calculated as compounds: What is given in 10.1 is the mass fraction of sulfur-containing compounds calculated as sulfur. Sometimes the mass fraction of sulfur-containing compounds calculated as compounds is of more interest. It can be calculated according to formula (5):
  • w_c = (w₀ᵢ × M) / (S × 32.07) … (5)
  • Where: w_c—— mass fraction of the sulfur-containing compound calculated as the compound, mg/kg; w₀ᵢ — mass fraction of the sulfur-containing compound calculated as sulfur, mg/kg; M—— molar mass of the sulfur-containing compound, g/mol; S—— number of sulfur atoms; 32.07—— atomic weight of sulfur. (Formula (5) source-text extraction has relatively heavy noise, the meanings of the symbols require confirmation against the source standard (source-text extraction))

10. Precision

• 11.1 Precision: Judge the reliability of the specimen determination results according to the following provisions (95% confidence level).
• Repeatability: The difference between two test results obtained by the same operator in the same laboratory on the same specimen shall not exceed the numerical ranges in Table 2 and Table 3.
• Table 2 Internal standard method determination repeatability (unit is mg/kg): sulfur determination range 1 ~ 100, repeatability 0.11 × 2x (x is the average of two replicate determination results); sulfur determination range 10 ~ 200, repeatability 0.12 × 2x. (source-text extraction noise, formula form requires confirmation against the source standard (source-text extraction))
• Table 3 External standard method determination repeatability (unit is mg/kg): sulfur determination range 1 ~ 28 (requires confirmation against the source standard (source-text extraction)), repeatability 0.31 × 10 (requires confirmation against the source standard (source-text extraction)); sulfur determination range 10 ~ 200, repeatability 0.24 × 10 (requires confirmation against the source standard (source-text extraction)). (x is the average of two replicate determination results)
• Reproducibility: different operators in different laboratories, using different instruments, the difference between two test results obtained on the same sample shall not exceed the numerical ranges of Table 4 and Table 5.
• Table 4 Internal standard method determination reproducibility (unit is mg/kg): sulfur determination range 1 ~ 100, reproducibility 0.42 × 2x; sulfur determination range 10 ~ 200, reproducibility 0.33 × 10 (requires confirmation against the source standard (source-text extraction)). (x is the average of two determination results)
• Table 5 External standard method determination reproducibility (unit is mg/kg): sulfur determination range 1 ~ 100, reproducibility 0.53 × 2x; sulfur determination range 10 ~ 200, reproducibility 0.52 (requires confirmation against the source standard (source-text extraction)). (x is the average of two determination results)
• 11.2 Bias: there is no certified reference material with an accepted method bias, therefore the bias of this method has not been determined.

11. Report

• 10.2 Report the mass fraction of each sulfur-containing compound, calculated as sulfur (retain one decimal place, unit is mg/kg).
• 10.4 Report the total sulfur mass fraction of sulfur-containing compounds in the sample (retain one decimal place, unit is mg/kg).
• Other report format requirements: not provided in the available source.

12. Normative references

• GB/T 4756 Petroleum liquids — Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 11140 Determination of sulfur content in petroleum products (X ray spectrometric method)
• SH/T 0253 Determination of total sulfur content in light petroleum products (coulometric method)
• ASTM D4307 Preparation method of liquid samples for analytical standards
• ASTM D5623-94 (2004) (corresponding standard, not equivalent)

13. Source and verification

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