GB/T 8020-2015 Determination of lead content in gasoline by atomic absorption spectrometry

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Card type: Test method

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

• Standard number: GB/T 8020-2015
• Chinese name: Determination of lead content in gasoline by atomic absorption spectrometry
• English name: Determination of lead in gasoline--Atomic absorption spectrometry
• Replacement relationship: replaces GB/T 8020-1987 "Determination of lead content in gasoline (atomic absorption spectrometry)"
• Adoption relationship: modified adoption using the redrafting method of ASTM D3237-12 "Standard test method for lead in gasoline (atomic absorption spectrometry)"
• Publication/implementation: published on 2015-12-31, implemented on 2016-06-01
• Custodianship: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC 280/SC 1)
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, Shenzhen Institute of Metrology and Quality Inspection
• Main drafters: Gao Ping, Mao Xinye, Huang Kaisheng, Zhao Yan, Zhang Shiyuan, Li Siyuan

2. Scope of application and non-applicability

• Applicable to the determination of total lead content in gasoline in the mass concentration range of 2.5 mg/L～25 mg/L.
• The determination results are not affected by differences in gasoline composition or different types of alkyl lead compounds.
• Method application (Chapter 4): provides a detection means for specifying the limit of trace lead in unleaded gasoline.
• Non-applicable scope: not provided in the available source.

3. Method principle

The gasoline sample is diluted with methyl isobutyl ketone (MIBK). Samples containing alkyl lead require the addition of iodine and methyltrioctylammonium chloride as stabilizers. A standard solution is prepared from lead chloride of analytical reagent grade or above, and the lead content in the sample is determined by atomic absorption spectrometry at a wavelength of 283.3 nm. With the above treatment method, all alkyl lead compounds in gasoline can give the same response. For the operating procedures of the atomic absorption spectrometer, see GB/T 15337.

4. Reagents and materials (purity / preparation)

• 6.1 Reagent purity: unless otherwise specified, all reagents used are of analytical reagent grade.
• 6.2 Water purity: unless otherwise specified, use grade two water as specified in GB/T 6682—2008.
• 6.3 Methyltrioctylammonium chloride.
• 6.4 Methyl isobutyl ketone (MIBK).
• 6.5 Lead chloride (PbCl₂, in the original text source-text extraction is written as PbCla).
• 6.6 Blank gasoline: lead content lower than mass concentration 1.32 mg/L. Note: if it is necessary to confirm whether the lead content is less than 1.32 mg/L, the sample may first be extracted and enriched and then determined with an atomic absorption spectrometer or an inductively coupled plasma emission spectrometer, or confirmed by other feasible methods. Warning—extremely flammable, harmful if inhaled, vapors may cause flash fire.
• 6.7 Methyltrioctylammonium chloride-MIBK solution with a volume fraction of 10%: dissolve 100 mL (88.0 g) of methyltrioctylammonium chloride with MIBK and dilute to 1 L.
• 6.8 Methyltrioctylammonium chloride-MIBK solution with a volume fraction of 1%: dissolve 10 mL (8.8 g) of methyltrioctylammonium chloride with MIBK and dilute to 1 L.
• 6.9 Iodine-toluene solution with a mass concentration of 30 g/L: dissolve 3.0 g of iodine with toluene and dilute to 100 mL. Warning—flammable, vapors are toxic.
• 6.10 Lead standard solution with a mass concentration of 1 321 mg/L: dissolve 0.443 3 g of lead chloride (PbCl₂) dried at 105 °C for 3 h in about 200 mL of methyltrioctylammonium chloride-MIBK solution with a volume fraction of 10%, transfer to a 250 mL volumetric flask and dilute to the mark with methyltrioctylammonium chloride-MIBK solution with a volume fraction of 10%, mix well, and transfer to a brown bottle equipped with a polytetrafluoroethylene-lined cap for storage.
• 6.11 Lead standard solution with a mass concentration of 264 mg/L: accurately pipette 50.0 mL of lead standard solution with a mass concentration of 1321 mg/L into a 250 mL volumetric flask, dilute to the mark with methyltrioctylammonium chloride-MIBK solution with a volume fraction of 1%, mix well, and transfer to a brown bottle equipped with a polytetrafluoroethylene-lined cap for storage.
• 6.12 Lead standard solutions with mass concentrations of 2.6 mg/L, 5.3 mg/L, 13.2 mg/L and 26.4 mg/L respectively: accurately pipette 1.0 mL, 2.0 mL, 5.0 mL and 10.0 mL of the solution with a mass concentration of 264 mg/L into 100 mL volumetric flasks, respectively add 5.0 mL of methyltrioctylammonium chloride-MIBK solution with a volume fraction of 1%, dilute to the mark with MIBK, mix well, and transfer to brown bottles equipped with polytetrafluoroethylene-lined caps for storage.
• 6.13 Quality control (QC) sample: select one or more stable and representative liquid petroleum products as the quality control sample to verify the effectiveness of the test process; for the specific method, see Chapter 11.

5. Instruments and equipment

• 5.1 Atomic absorption spectrometer: with scale expansion, adjustable nebulizer, and a slit burner and raw material premix chamber configured for use with an air-acetylene flame.
• 5.2 Volumetric flasks: 50 mL, 100 mL, 250 mL and 1000 mL.
• 5.3 Pipettes: 2 mL, 5 mL, 10 mL, 20 mL and 50 mL.
• 5.4 Micropipette: 100 μL pipettor or pipette (in the original text source-text extraction is written as 100wL).

6. Recommended operating conditions

• Detection wavelength: 283.3 nm.
• Flame: air-acetylene flame; adjust the mixed gas flow rate and sample transport rate to obtain a blue lean oxidizing flame (8.2.1).
• Burner head height: aspirate a lead working standard solution with a mass concentration of 26.4 mg/L, and adjust the burner head height so as to obtain the maximum instrument response; some instruments require the use of a signal amplifier so that the absorbance is between 0.150～0.170 (8.2.2).
• Calibration curve: use the blank working standard solution as the zero point of the calibration curve, aspirate the lead working standard solution, draw the calibration curve, and check the linear relationship of the calibration curve (8.2.3).

7. Sampling and sample preparation

• 7.1 Sample according to the method specified in GB/T 4756.
• 7.2 Store the collected sample in a non-lead, sealed and light-proof metal container, and keep the storage ambient temperature constant before measurement.
• Sample preparation (Chapter 9): add 30 mL MIBK to a 50 mL volumetric flask, then add 5.0 mL of gasoline sample, and mix well; add 0.10 mL (100 μL) of iodine-toluene solution with a mass concentration of 30 g/L, mix well, and let stand for 1 min to allow complete reaction; add 5.0 mL of methyltrioctylammonium chloride-MIBK solution with a volume fraction of 1%, and mix well; dilute to the mark with MIBK and mix well.

8. Analytical procedure

• 8.1 Prepare lead working standard solutions
  • 8.1.1 Use the lead standard solutions with mass concentrations of 2.6 mg/L, 5.3 mg/L, 13.2 mg/L and 26.4 mg/L in 6.12 to prepare 4 lead working standard solutions, and prepare one blank solution.
  • 8.1.2 To 5 volumetric flasks of 50 mL, respectively add 30 mL MIBK and 5.0 mL of blank gasoline, then to 3 of these volumetric flasks respectively add 5.0 mL 6.12 of lead standard solutions with mass concentrations of 2.6 mg/L, 5.3 mg/L, 13.2 mg/L and 26.4 mg/L, and do not add lead standard solution to the other one, which is used as the blank solution. (Note: the original text here states "5 volumetric flasks ... of which 3 volumetric flasks ... 4 concentrations"; the quantity statement is suspected to have source-text extraction or a clerical error in the original text, requires confirmation against the source standard (source-text extraction))
  • 8.1.3 Use a 100 μL pipettor to respectively add 0.10 mL of iodine-toluene solution with a mass concentration of 30 g/L to each volumetric flask, mix well and allow reaction for 1 min.
  • 8.1.4 Add 5.0 mL of methyltrioctylammonium chloride-MIBK solution with a volume fraction of 1% to each volumetric flask, then dilute to the mark with MIBK and mix well.
• 8.2 Instrument preparation
  • 8.2.1 Optimize the measurement conditions of the atomic absorption spectrometer, adjust the wavelength to 283.3 nm, use blank reagent (MIBK), adjust the mixed gas flow rate and sample transport rate to obtain a blue lean oxidizing flame.
  • 8.2.2 Aspirate a lead working standard solution with a mass concentration of 26.4 mg/L, and adjust the burner head height so as to obtain the maximum instrument response. Some instruments require the use of a signal amplifier so that the absorbance is between 0.150～0.170.
  • 8.2.3 Using a blank working standard solution as the zero point of the standard curve, aspirate the lead working standard solution, draw the standard curve, and check the linear relationship of the standard curve.
• 9 Test procedure
  • 9.1 Add 30 mL MIBK to a 50 mL volumetric flask, then add 5.0 mL gasoline sample, and mix uniformly.
  • 9.2 Add 0.10 mL (100 μL) iodine-toluene solution with a mass concentration of 30 g/L, mix uniformly, and let stand for 1 min to allow complete reaction.
  • 9.3 Add 5.0 mL methyltrioctylammonium chloride-MIBK solution with a volume fraction of 1%, and mix uniformly.
  • 9.4 Dilute to volume with MIBK and mix uniformly.
  • 9.5 Aspirate the sample solution and the lead working standard solution, record the absorbance, and frequently determine whether the zero point has drifted.

9. Qualitative and quantitative determination and calculation formula

• 10.1 Plot the absorbance of the lead working standard solution against mass concentration, and read the lead content of the sample from the curve.
• 10.2 If the atomic absorption spectrometer is equipped with computer software, then the computer may be used to perform the above calculation.
• This standard cancels the calculation formula X=C×10 in GB/T 8020—1987.
• Report the result to the nearest mass concentration 0.1 mg/L (Chapter 12).

10. Precision

• 13.1 Precision (judge the reliability of test results according to the following provisions, 95% confidence level)
  • 13.1.1 Repeatability r: For continuous determinations of the same sample by the same operator, in the same laboratory, using the same instrument, the difference between the two test results obtained shall not exceed 1.3 mg/L.
  • 13.1.2 Reproducibility R: For determinations of the same sample by different operators, in different laboratories, using different instruments, the difference between the two single and independent test results obtained shall not exceed 2.6 mg/L.
• 13.2 Bias: When two independent laboratories analyze the same reference material, the differences between the measurement results of the two laboratories and the standard value are both within the repeatability requirement range of this standard, with no significant bias, see Table 1.
• Table 1 Determination results of lead content in reference materials

(Note: In Table 1 of the original text, values such as 8.8, 13.0, 8.6, 13.3 are also seen, and the correspondence with the above rows and columns is suspected to have source-text extraction misalignment, requires confirmation against the source standard (source-text extraction))

11. Report

Report the lead content of the sample calculated from Chapter 10, to the nearest mass concentration 0.1 mg/L.

12. Normative references

• GB/T 4756 Petroleum liquids—Manual sampling
• GB/T 6682—2008 Specifications and test methods for water used in analytical laboratories
• GB/T 15337 General rules for atomic absorption spectrometry
• References:
  • [1] NB/SH/T 0843 Evaluation of analytical testing systems in the petrochemical industry—Statistical techniques
  • [2] ASTM D6792 Practice for Quality System in Petroleum Products and Lubricants Testing Laboratories

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 Q&A