SH/T 0242-1992 Determination of lead content in light petroleum products (atomic absorption spectrometry)

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Card type: Test method

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

• Standard number: SH/T 0242-92
• Chinese full name: Determination of lead content in light petroleum products (atomic absorption spectrometry)
• English name: not provided in the available source
• Replacement relationship: replaces SY 2242-85
• Other: confirmed in 2004
• Approval/implementation: approved by China Petrochemical Corporation in 1992-05-20, implemented in 1992-05-20

2. Scope of application and non-applicability

• This standard specifies a method for determining lead content in samples by atomic absorption spectrometry.
• Applicable to light petroleum products such as naphtha and unleaded gasoline.
• The lowest measurable lead concentration for a treated 500g sample is 1ng/g (10ppb). (In the original text, source-text extraction here is "long/g(lOppb)a", suspected to be "1ng/g (10ppb)", requires confirmation against the source standard (source-text extraction))
• Not applicable: not provided in the available source.

3. Method principle

Lead in the sample is extracted with iodine monochloride. The extract is boiled and cooled to room temperature; then excess potassium iodide is added, forming a lead iodide complex, and the iodine produced is reduced with ascorbic acid. Finally, the iodine complex is back-extracted with methyl isobutyl ketone and determined with an air-acetylene flame atomic absorption spectrophotometer.

4. Reagents and materials (purity / preparation)

• 5.1 Lead nitrate: purity higher than 99.8%.
• 5.2 Deionized water: single-distilled water treated with cation and anion exchange resins. Hereinafter referred to as water.
• 5.3 Nitric acid: guaranteed reagent grade.
• 5.4 Hydrochloric acid: guaranteed reagent grade.
• 5.5 Potassium iodide: analytical reagent grade.
• 5.6 Potassium iodate: analytical reagent grade.
• 5.7 Iodine monochloride solution (about 0.5M): weigh 55.5g potassium iodide into a 250mL beaker, transfer with water to a 1L glass-stoppered volumetric flask, add about 400mL water, then add 445mL hydrochloric acid, shake to dissolve, and cool to room temperature. Slowly add 37.5g potassium iodate while shaking and cooling with running tap water until the iodine initially formed redissolves, giving a clear orange-red solution; after cooling to room temperature, dilute to 1L with water.
  • Note: Rubber stoppers must not be used for containers holding iodine monochloride. Under certain conditions, iodine monochloride can react with ammonium ions to form nitrogen triiodide, which is very explosive. Therefore, iodine monochloride must absolutely be kept from contact with ammonia or ammonium salts.
• 5.8 250g/L Ascorbic acid solution: dissolve 25g ascorbic acid in water and dilute to 100mL.
• 5.9 332g/L (2.0M) Potassium iodide solution: dissolve 33.2g potassium iodide in water and dilute to 100mL. Store in a dark bottle; storage time must not exceed 2d.
• 5.10 Methyl isobutyl ketone (MIBK) reagent: analytical reagent grade.
• 5.11 Lead standard solution: dry lead nitrate in an oven at 105℃ for 1h, remove and immediately place in a desiccator to cool to room temperature, accurately weigh 1.5984g, dissolve with about 300mL 3% (V/V) nitric acid solution, then dilute to 1L with water, and store in a polyethylene plastic bottle. The lead concentration of this solution is 1mg/mL.
• 5.12 Anhydrous ethanol: analytical reagent grade.

5. Instruments and equipment

• 4.1 Atomic absorption spectrophotometer: single-slot burner (slot length 100mm) capable of providing the necessary air flow to ensure the sensitivity specified in 6.2.
• 4.2 Lead hollow cathode lamp.
• 4.3 Oscillator.
• 4.4 Electric furnace: power 1.5kW (adjustable).
• 4.5 Polyethylene plastic bottle: 1000mL.
• 4.6 Graduated cylinder: 50, 100, 500, 1000mL.
• 4.7 Pipette: 0.5, 1, 5, 10mL.
• 4.8 Measuring cup: 10, 50mL.
• 4.9 Separatory funnel: 250, 1000mL.
• 4.10 Glass beaker: 10, 50, 100, 250mL.
• 4.11 Volumetric flask: 10, 25, 100, 250, 500, 1000mL.
• 4.12 Hard glass sampling bottle: 2000mL.
• Note: All glassware should, before use, be shaken and washed with chromic acid cleaning solution for 5min, then washed three times with water, then shaken and washed with hot nitric acid at a volume ratio of 1:1 for 5min, and finally rinsed three times with deionized water.

6. Recommended operating conditions

• 6.2 Determine atomic absorption measurement conditions: the operator shall, according to the instrument used in this laboratory and with reference to the following conditions, select the optimum operating conditions to ensure that the instrument measurement sensitivity reaches an absorbance of 0.02 or more for the 1μg/mL methyl isobutyl ketone test solution.
• 6.2.1 Analytical line wavelength: 283.3nm.
• 6.2.2 Working curve range: 0.5 to 4.0μg/mL.
• 6.2.3 Lamp current: 5 to 10mA.
• 6.2.4 Burner head height: make the light beam pass through the atomization zone of the flame.
• 6.2.5 Air-to-acetylene flow ratio is 8:4 (lean flame); after methyl isobutyl ketone is aspirated, make it a stoichiometric flame.

7. Sampling and sample preparation

• 6.1 Sampling: clean and dry the hard glass sampling bottle according to the glassware washing method. If sampling from a process unit, first open the sampling port and discharge an amount equal to three to five times the dead-leg oil, then directly take the sample into the sampling bottle and immediately cap it. If sampling from an oil tank, follow GB/T 4756; the sample taken should be analyzed and determined within 24h.
• 6.3 Prepare lead standard series solutions:
  • Use a pipette to accurately transfer 5mL of lead standard aqueous solution with concentration 1mg/mL into a dry 500mL volumetric flask, add 1 small drops of nitric acid, add about 100mL anhydrous ethanol; dilute to the mark with methyl isobutyl ketone, mix well, and store in a polyethylene plastic bottle. The solution should be clear and transparent. The lead concentration is 10μg/mL. Storage time must not exceed 15d.
  • Use a pipette to accurately take 10μg/mL lead standard solution 1.25, 2.5, 5.0, 10.0mL, and place them respectively into four different 25mL dry volumetric flasks. Then dilute to the mark with methyl isobutyl ketone; the solutions should be clear and transparent. The concentrations of this lead standard series solution are 0.5, 1.0, 2.0, 4.0μg/mL.

8. Analytical procedure

• 7.1 According to GB/T 1884, accurately determine the sample density.
• 7.2 Take about 500g of sample into a 1000mL separatory funnel, add 10mL±0.2mL iodine monochloride solution, stopper, shake on an oscillator for 5min, and let stand to separate. Collect the lower aqueous extract in a 100mL beaker, shake and wash the oil layer three times with 10mL water each time for about 3min, and combine each washing liquid into the 100mL beaker.
• 7.3 Heat the above extract on an electric furnace to boiling. Remove the beaker, cool to room temperature, transfer to a 250mL separatory funnel, add 10mL potassium iodide solution and shake well, then add 10mL ascorbic acid solution, dilute to 100mL with water, and shake well.
• 7.4 Use a pipette to accurately add 10mL methyl isobutyl ketone, shake on an oscillator for 3min, let stand for about 2min until the two phases separate, discard the aqueous phase, and transfer the organic phase to a 10mL dry volumetric flask as the sample solution. This sample solution must be measured within 8h.
• 7.5 Under the selected measurement conditions, aspirate methyl isobutyl ketone into the flame, zero the instrument, immediately measure the lead standard series solutions, then immediately measure the blank solution and sample solution. Plot the working curve with the absorbance of the standard series solutions as the ordinate and the corresponding concentration as the abscissa. Then, based on the absorbance of the blank solution and sample solution, find the concentrations of the blank solution and sample solution from the working curve. If "direct concentration reading" is used, the concentration can be measured directly.
• 7.6 A blank test must be carried out for each sample determination; the blank test follows the sample test procedure except that no sample is added. The blank measurement value should not be greater than 0.2μg/mL.

9. Qualitative and quantitative determination and calculation formula

The lead content of the sample X [ng/g (ppb)] is calculated according to the following formula:

X = (C - C₀) × V₁ × 10³ / (V × ρ₂₀)

Where:

• C—— lead concentration of the sample solution, μg/mL;
• C₀ — blank lead concentration, μg/mL;
• V₁ — volume of methyl isobutyl ketone used for back-extraction, mL;
• V—— sample volume, mL;
• ρ₂₀ — sample density, g/mL.

(Note: The original formula source-text extraction contains noise; the symbols have been inferred and organized from context, requires confirmation against the source standard (source-text extraction).)

10. Precision

Judge the reliability of test results according to the following provisions (95% confidence level).

• 9.1 Repeatability: the difference between two results obtained by the same operator in repeated determinations shall not exceed the value in the table below.
• 9.2 Reproducibility: the difference between two results submitted by different laboratories shall not exceed the value in the table below.

(Note: The original table source-text extraction contains noise; the units and meanings of "7" and "11" require confirmation against the source standard (source-text extraction).)

11. Report

Take the arithmetic mean of two repeated determination results as the determination result of this standard.

12. Referenced documents

• GB/T 1884 Standard test method for density of crude petroleum and liquid petroleum products (hydrometer method)
• GB/T 4756 Standard practice for manual sampling of petroleum liquids

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