SH/T 0020-1990 Determination of phosphorus content in gasoline (spectrophotometric method)

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Card type: Test method

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

• Standard number: SH/T 0020-90
• Full name: Determination of phosphorus content in gasoline (spectrophotometric method)
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Other: issued in 1990, confirmed in 2000; reference adoption of ASTM D3231-83 "Determination of phosphorus content in gasoline"
• Approval/implementation: approved by China Petrochemical Corporation 1991-03-27, implemented on 1992-04-01

2. Scope of application and non-applicability

• Applicable to the determination of phosphorus content in gasoline in the form of pentavalent phosphate esters, salts, or both coexisting.
• Determination range: 0.2～40 mg/L.
• Not applicable: not provided in the available source.

3. Method principle

In the presence of zinc oxide, the sample is decomposed by ashing; the ash residue is dissolved in sulfuric acid and reacts with ammonium molybdate and hydrazine sulfate to form a molybdenum blue complex. In a 5 cm optical path cuvette, with distilled water as reference solution, measure the absorbance at 820 nm wavelength. Since the absorbance of the molybdenum blue complex is proportional to phosphorus concentration, calculate the phosphorus content of the sample.

4. Reagents and materials (purity / preparation)

• General: All reagents are analytical grade unless otherwise specified; water is distilled water.
• 4.1 Ammonium molybdate (hazard: emits toxic gases when burning, irritates skin and eyes, harmful if swallowed).
• 4.2 Hydrazine sulfate (caution: toxic, carcinogenic reagent).
• 4.3 Molybdenum hydrazine (requires confirmation against the source standard (source-text extraction), suspected to be a typo for molybdenum hydrazine or ammonium molybdate).
• 4.4 Sulfuric acid (caution: sulfuric acid is a strong oxidant and can cause severe burns).
• 4.5 Potassium dihydrogen phosphate.
• 4.6 Zinc oxide. Note: Zinc oxide with high loose density may cause spattering; density of about 0.5 g/mL has proven satisfactory (requires confirmation against the source standard (source-text extraction)).
• 5.1 Preparation of ammonium molybdate solution: Measure 225 mL sulfuric acid, slowly add with constant stirring to a beaker containing 500 mL water placed in a cold water bath. After cooling to room temperature, add 20 g ammonium molybdate with four crystal waters, stir until completely dissolved, transfer to a 1000 mL volumetric flask, dilute to the mark with water. Note: When adding sulfuric acid to water, wear a protective face shield, rubber gloves, and a rubber apron.
• 5.2 Preparation of hydrazine sulfate solution: Measure 1000 mL water into a beaker, weigh 1.5 g hydrazine sulfate and add to dissolve. Note: This solution is unstable; store in a stoppered bottle in the dark; valid for three weeks.
• 5.3 Preparation of molybdenum hydrazine solution: Pipette 25 mL ammonium molybdate solution into a 100 mL volumetric flask containing about 50 mL water, then pipette 10 mL hydrazine sulfate solution into the volumetric flask, dilute to the mark with water. Note: This reagent is unstable and should be used within 4 h.
• 5.4 Preparation of sulfuric acid solution (1:10): Measure 100 mL sulfuric acid, add with constant stirring to a beaker cooled in a cold water bath and containing 1000 mL water.
• 5.5 Preparation of phosphorus standard stock solution: Take about 5 g potassium dihydrogen phosphate, dry in an oven at 105～110 ℃ for 3 h, weigh the dried potassium dihydrogen phosphate (4.393±0.002) g, add to a 1000 mL volumetric flask containing 150 mL sulfuric acid solution (5.4) to dissolve, after complete dissolution dilute to the mark with water. The concentration of this solution is 1.0 mg P/mL.
• 5.6 Preparation of phosphorus standard solution: Use a pipette to draw 10 mL phosphorus standard stock solution, add to a 1000 mL volumetric flask, dilute to the mark with water. The concentration of this solution is 10 μg/mL.
• 3.2 Materials: filter paper, medium-speed quantitative filter paper, diameter 9 cm.

5. Instruments and equipment

• a. Spectrophotometer: wavelength range 420～900 nm, equipped with 5 cm and 1 cm cuvettes;
• b. Pipettes: 10 mL, graduation 0.1 mL; 2 mL, graduation 0.02 mL;
• c. Constant temperature bath: equipped with a rack that allows 100 mL volumetric flasks to be immersed to the mark, capable of maintaining constant temperature (85±2) ℃; Note: If the hot water bath temperature is lower than 83 ℃, color development is incomplete;
• d. Cooling bath: equipped with a rack that allows 100 mL volumetric flasks to be immersed to the mark;
• e. Combustion dish: Gooch porcelain evaporating dish, glazed inside and outside, capacity 100 mL;
• f. Thermometer: 0～100 ℃, graduation 1 ℃;
• g. Volumetric flasks: 100, 1000 mL;
• h. High-temperature furnace;
• i. Syringe: 10 mL, equipped with a 5 cm long needle.

6. Recommended operating conditions

• Color development temperature: (85±2) ℃, maintain for 25 min.
• Measurement wavelength: near 820 nm, the maximum absorbance wavelength must not exceed 830 nm.
• Cuvette: 5 cm optical path (for high-content samples, 1 cm cuvette is allowed).
• Reference solution: distilled water.
• High-temperature furnace ashing temperature: 621～704 ℃, ash for 10 min, remove and cool, then ash again for 5 min.
• After cooling, let stand at room temperature for 8～10 min.

7. Sampling and sample preparation

• Select sample amount according to Table 1:

• Note: When it is necessary to select 10 mL sample, first add 2 mL sample to 2 g zinc oxide and ignite; after the sample cools, add 2 mL sample, and so on.
• 7.1 Place 2 g±0.2 g zinc oxide in a clean, dry combustion dish and pile into a cone shape. Note: To obtain satisfactory accuracy for determining low phosphorus content, close attention must be paid to instrument cleanliness, careful operation, and prevention of contamination; all glassware should be cleaned with acid or some means before use, but not with commercial detergents, because these compounds often contain strongly adsorbed alkaline phosphorus compounds on glass that cannot be removed by ordinary washing methods; it is best to dedicate these instruments to phosphorus determination.
• 7.2 Use a glass rod to make a deep pit in the middle of the zinc oxide pile.
• 7.3 Place the drawn sample into the zinc oxide pit, record the sample temperature, and correct to the standard value according to clause 8.2. Note: If the sample amount is 10 mL, it should be added in several portions using a syringe; insert the syringe needle tip about two-thirds into the zinc oxide pile, slowly release 2 mL sample, ignite the sample, let it burn until extinguished; after the sample cools, continue to add 2 mL sample, and so on, until the entire 10 mL sample has been added.
• 7.4 Take about 0.2 g zinc oxide anew from the reagent bottle, cover the sample, and gently tap the edge of the combustion dish to compact the zinc oxide.
• 7.5 Ignite the sample with a gas burner, allowing the sample to burn until extinguished.
• 7.6 Carry out a blank test using the same amount of zinc oxide.

8. Analysis procedure

• 7.7 Place the combustion dishes containing the sample and the blank (no sample) in a high-temperature furnace at 621～704 ℃ and ash for 10 min. Remove the combustion dishes to cool, gently tap the edge of the combustion dishes to loosen the zinc oxide, then place the combustion dishes back into the high-temperature furnace and ash for 5 min until the sample is completely burned off.
• 7.8 After the sample cools, measure 25 mL sulfuric acid solution (5.4) into each combustion dish. When adding the sulfuric acid solution, rinse the zinc oxide on the edge of the combustion dish into the dish.
• 7.9 Cover the combustion dish with a borosilicate glass dish and heat on a hot plate until the zinc oxide is completely dissolved.
• 7.10 Filter the solution through filter paper into a 100 mL volumetric flask. Wash the glass dish and combustion dish several times with water (total volume not exceeding 25 mL). Filter the washings through filter paper into the 100 mL volumetric flask.
• 7.11 Use a pipette to draw 50 mL freshly prepared molybdenum hydrazine solution, add to each volumetric flask, dilute to the 100 mL mark with water, and mix well; remove the stopper after mixing.
• 7.12 Place the 100 mL volumetric flasks into a 85 ℃±2 ℃ constant temperature bath, with the liquid level in the volumetric flasks lower than the bath liquid level, and maintain for 25 min.
• 7.13 Move the 100 mL volumetric flasks to a cooling bath, rapidly cool to room temperature, let stand at room temperature for 8～10 min, use a 5 cm optical path cuvette, with distilled water as reference solution, measure the absorbance at the wavelength of maximum absorbance; subtract the blank absorbance from each sample's absorbance, find the corresponding phosphorus content from the calibration curve, and calculate the result.
• Calibration curve plotting (5.7):
  • 5.7.1 Using a pipette, respectively take 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 mL of the phosphorus standard solution, and add them to 100 mL volumetric flasks.
  • 5.7.2 Pipette 10 mL of sulfuric acid solution (5.4) and add respectively to each of the above volumetric flasks, immediately shake to mix uniformly.
  • 5.7.3 Take freshly prepared hydrazine molybdate solution 50 mL, add to each volumetric flask, immediately shake uniformly, and dilute with water to the 100 mL mark.
  • 5.7.4 Place each volumetric flask in a constant-temperature bath so that the liquid level in the flask is immersed below the bath liquid level, and maintain at a temperature of (85±2) ℃ for 25 min.
  • 5.7.5 Move each volumetric flask to a cooling bath so that the solution cools rapidly to room temperature. Do not allow the solution temperature to fall below room temperature by 3 ℃. Note: Place a clean thermometer in one of the volumetric flasks to check the temperature of the solution.
  • 5.7.6 After the solution has cooled to room temperature, remove from the cold water bath and let stand at room temperature for 8～10 min.
  • 5.7.7 Using 2.0 mL phosphorus standard solution in a 5 cm path length cuvette, measure the maximum absorbance near 820 nm. The wavelength of maximum absorbance must not exceed 830 nm.
  • 5.7.8 After finding the wavelength of maximum absorbance, at that wavelength, using distilled water as the reference solution, respectively measure the absorbance of the blank and each standard sample.
  • 5.7.9 Subtract the blank absorbance from the absorbance of each standard sample, and plot a standard curve against the corresponding phosphorus content. Note: Must be careful to avoid contamination as much as possible. If the blank absorbance exceeds 0.04, the contamination source should be checked, and it is recommended that the results be discarded and fresh reagents and clean glassware be used again.
  • 5.7.10 For high-content samples, the use of 1 cm cuvettes is permitted.

9. Qualitative and Quantitative and Calculation Formulas

• 8.1 The phosphorus content X₁ (mg/L) of the sample at the measured temperature t ℃ is calculated according to formula (1):
  • X₁ = x / V ………………(1)
  • Where: x— phosphorus content read from the standard curve, mg; V— volume of the sample, mL.
• 8.2 The phosphorus content X₂ (mg/L) of the sample at the standard temperature (20 ℃) is calculated according to formula (2):
  • X₂ = [1 + 0.001(t - 20.0)] × X₁ ………………(2)
  • Where: t— measured temperature of the sample, ℃.

10. Precision

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

• 9.1 Repeatability: The difference between two results obtained by the same operator in repeated measurements shall not exceed the following values.

• 9.2 Reproducibility: The difference between two results obtained by two laboratories shall not exceed the following values.

11. Report

• Take the arithmetic mean of two results from repeated measurements, and correct to the standard value at 20 ℃ as the measurement result.
• Results with phosphorus content lower than 2.5 mg/L shall be reported to 0.01 mg/L; for high phosphorus content results, report to 1 mg/L.

12. Reference Documents

• ASTM D3231-83 "Determination of Phosphorus Content in Gasoline" (referenced and adopted).

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