SH/T 0128-1992 Test method for heavy metals in paraffin wax

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Card type: Test method

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

• Standard number: SH/T 0128-92
• Full title: Test method for heavy metals in paraffin wax
• English name: not provided in the available source
• Replacement relationship: From the date of implementation of this standard, the former national standard GB 8027-87 "Test method for heavy metals in paraffin wax" is void.
• Adoption relationship: This standard is equivalent to the "Test method for heavy metals in paraffin wax" in the Japanese Pharmacopoeia.
• Technical administration / drafting: Technical administration by Fushun Research Institute of Petroleum and Petrochemicals; drafting responsibility by Fushun Research Institute of Petroleum and Petrochemicals; main drafters Zhang Qiaoge and Wang Guirong.
• Approval / implementation: Approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20.

2. Scope of application and non-applicability

• This standard specifies a test method using visual colorimetry to detect whether the amount of metal mixtures in paraffin wax that can be colored by sodium sulfide solution exceeds a limit. The limit, calculated as lead, is 10 ppm(m/m).
• This standard applies to paraffin wax, liquid paraffin, and white oil.
• Not applicable: not provided in the available source.

3. Method principle

Under the conditions of pH 3～4, dilute solutions of heavy metals such as lead, bismuth, copper, cadmium, antimony, tin, and mercury react with sodium sulfide to form yellow to brown insoluble sulfides, and the color of the solution is proportional to the heavy metal concentration. A standard solution containing a specified amount of lead and the test solution are colored with sodium sulfide, and visual colorimetry is used to determine whether the heavy metal content of the sample exceeds the limit.

4. Reagents and materials (purity / preparation)

• 3.1 Hydrochloric acid.
• 3.2 Glacial acetic acid: analytical reagent, prepared as 12%(m/m) acetic acid solution; measure 12 mL glacial acetic acid and dilute with water to 100 mL.
• 3.3 Glycerol (CH₂(OH)CH(OH)CH₂(OH)): analytical reagent.
• 3.4 Lead nitrate: analytical reagent.
• 3.5 Nitric acid: analytical reagent.
• 3.6 Sodium sulfide: analytical reagent.
• 5.1 Preparation of lead standard stock solution: accurately weigh 159.8 mg lead nitrate, dissolve it in a small amount of water and 1 mL nitric acid, transfer to a 1000 mL volumetric flask, and dilute with water to the mark. Glass containers free of soluble lead salts must be used for the preparation and storage of this solution. The solution is 1 mL containing 0.1 mg lead. This solution has a storage period of two months, and should be re-prepared when turbidity and precipitate occur.
• 5.2 Preparation of lead standard solution: take 10 mL lead standard stock solution, dilute with water to 100 mL; this solution is 1 mL containing lead 0.01 mg, and is prepared before use.
• 5.3 Preparation of sodium sulfide solution: add 5 g sodium sulfide to 10 mL distilled water, then add 30 mL glycerol, and mix thoroughly until dissolved.
  • Note: Glycerol is added as a stabilizer to prevent the sodium sulfide solution from oxidizing in air. To prevent sodium sulfide from gradually turning into yellow polysulfides and polythionates and thereby reducing its ability to form sulfides, it is best to use it within three months after preparation and store it in a cool place. If abnormal coloration occurs, the sodium sulfide solution must be re-prepared.

5. Instruments and equipment

• 4.1 Crucible: 50 mL.
• 4.2 Nessler colorimetric tube: 50 mL.
• 4.3 Graduated cylinder: 100, 50, 20 mL.
• 4.4 Pipette: 10, 2 mL.
• 4.5 Volumetric flask: 1000, 100 mL (the source text source-text extraction is written as "lomL", requires confirmation against the source standard (source-text extraction)).
• 4.6 Adjustable electric furnace.
• 4.7 Constant-temperature water bath.
• 4.8 High-temperature furnace.
• 4.9 Table balance: load capacity 200 g; sensitivity 0.2 g.
• 4.10 White steel scraper.

6. Recommended operating conditions

• pH Conditions: pH 3～4 (see method summary).
• Ashing temperature: 450～550 ℃ (see 5.4).
• Ashing time: not less than 2 h (see 5.4).
• Standing time after color development: 5 min is most suitable; after about 10 min, white turbidity begins to form due to sulfur precipitation, affecting correct observation (see note to 5.5).
• Other operating conditions: not provided in the available source.

7. Sampling and sample preparation

• 5.4 Sample treatment: take 2.0 g of the sample to be tested, place it in a crucible, place it on an asbestos board hole or on an electric furnace, slowly heat it in a fume hood until carbonization, then transfer it to a high-temperature furnace and completely ash it at 450～550 ℃; the ashing time shall be not less than 2 h. After cooling to room temperature, add 2 mL hydrochloric acid and evaporate to dryness on a water bath. Add 2 mL acetic acid solution to the residue, transfer everything to a Nessler colorimetric tube, add water to 50 mL, and use this as the test solution.
  • Note: Heating must be controlled to avoid the sample overflowing outside the crucible due to volume expansion and combustion.
• Sample amount: 2.0 g (see 5.4).
• Other sampling rules: not provided in the available source.

8. Analytical procedure

• 5.5 Take 2.0 mL lead standard solution in a 50 mL Nessler colorimetric tube, add 2 mL acetic acid solution, then add water to 50 mL, and use this as the reference solution.
• Add 1 drops of sodium sulfide solution to the test solution and the reference solution respectively, mix uniformly, and after standing for 5 min, use white paper (or a white plate) as the background, keep the two Nessler colorimetric tubes vertically side by side, remove the stoppers, and observe and compare the depth of color of the solutions from above.
• The color of the test solution must not exceed the color of the reference solution.
• Note: The most suitable standing time after color development is 5 min; after about 10 min, white turbidity begins to form due to sulfur precipitation, affecting correct observation. It is also required that the test solution and the reference solution develop color simultaneously.

9. Qualitative and quantitative determination and calculation formula

• Determination method: visual colorimetry; the color of the test solution must not exceed the color of the reference solution.
• 6 Expression of test results: if both results of duplicate determinations do not exceed the color of the reference solution, report that the heavy metal content of the sample is not greater than 10 ppm(m/m); otherwise, it is greater than 10 ppm(m/m).
• Calculation formula: not provided in the available source.

10. Precision

• The source text only specifies "both results of duplicate determinations do not exceed the color of the reference solution" as the condition for expressing results (see Section 6), and does not provide precision values such as repeatability or reproducibility.
• Specific precision indicators: not provided in the available source.

11. Report

• 6 Expression of test results: if both results of duplicate determinations do not exceed the color of the reference solution, report that the heavy metal content of the sample is not greater than 10 ppm(m/m); otherwise, it is greater than 10 ppm(m/m).
• Report format, report items, etc.: not provided in the available source.

12. Referenced documents

• The source text does not list a "Referenced documents" section.
• Historical documents involved: the former national standard GB 8027-87 "Test method for heavy metals in paraffin wax" (void from the date of implementation of this standard).
• Adoption source: "Test method for heavy metals in paraffin wax" in the Japanese Pharmacopoeia.

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