SH/T 0255-1992 Determination of water in additives and additive-containing lubricating oils (coulometric method)

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Card type: Test method

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

• Standard number: SH/T 0255-92
• Chinese full title: Determination of water in additives and additive-containing lubricating oils (coulometric method)
• English name: not provided in the available source
• Supersession relationship: supersedes SY 2508-83
• Other: marked "〔2wei" year confirmed〕" requires confirmation against the source standard (source-text extraction), the year number is suspected to be confirmed in 20XX, unclear in the source text
• 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 method for determining water content in petroleum additives, additive-containing lubricating oils, and lubricating oils by the coulometric method.
• This standard applies to petroleum additives, additive-containing lubricating oils, and lubricating oils.
• Non-applicable scope: not provided in the available source.

3. Method principle

A certain amount of dehydrated solvent (benzene or toluene) is mixed with the sample and subjected to azeotropic distillation; the distillate is used as the electrolyte with a mixed solution of Karl Fischer reagent, methanol, and chloroform in a certain proportion, and its water content is determined by the coulometric method.

When water is present in the distillate, iodine oxidizes sulfur dioxide, and the following chemical reaction occurs (the source uses structural formulas, source-text extraction has considerable noise, only recognizable text is recorded here):

• I₂ + SO₂ + 3 K… + H₂O → 2(…)HI + (…) (pyridine/iodide structural formula, requires confirmation against the source standard (source-text extraction))
• The generated pyridine sulfate then reacts with methanol to form stable methylpyridinium sulfate (source structural formula, requires confirmation against the source standard (source-text extraction))
• The consumed iodine is replenished by oxidation of iodide ions in the solution at the anode: 2I⁻ − 2e⁻ → I₂
• By measuring the quantity of electricity required to replenish the consumed iodine, according to Faraday's law of electrolysis, the water content in the sample can be determined.

4. Reagents and materials (purity / preparation)

• 4.1 Anhydrous methanol: analytical reagent.
• 4.2 Pyridine: analytical reagent.
• 4.3 Iodine: analytical reagent.
• 4.4 Benzene: use after dehydration with 5A molecular sieve or other molecular sieves capable of dehydration.
• 4.5 Molecular sieve: 5A or other types of molecular sieves suitable for dehydration.
• 4.6 Sulfur dioxide: sulfur dioxide from an industrial cylinder or generated by placing a certain amount of anhydrous sodium sulfite in a 2L round-bottom flask and adding sulfuric acid dropwise. It must be dehydrated with sulfuric acid before use.
• 4.7 Chloroform: analytical reagent.
• 4.8 Preparation of Karl Fischer reagent (Karl Fischer reagent):
  • Solution A: Dissolve 50g iodine in 80mL pyridine, shaking continuously to dissolve all the iodine, then add 260mL anhydrous methanol; at this point an orange crystalline substance should appear in the solution.
  • Solution B: Add 40mL pyridine to 40mL liquid sulfur dioxide or an equivalent amount of gaseous sulfur dioxide; at this point the solution is pale yellow.
  • In a cooling bath, slowly add Solution B to Solution A; at this point the crystalline substance in Solution A slowly dissolves, yielding a brown Karl Fischer reagent. After the solution cools, tighten the stopper and store in a desiccator; it can be used only after stabilizing for 24h.
• 4.9 Preparation of electrolyte: mix uniformly in the ratio of methanol to pyridine by volume of 2:1 and chloroform to methanol by volume of 1:1, and store in a stoppered brown bottle.

5. Instruments and equipment

• 3.1 Coulometer: a coulometer capable of supplying a constant electrolysis current of at least 10mA or more and a detection device, such as the YS-2V coulometer produced by Jiangsu Electroanalytical Instrument Factory or other types of instruments.
• 3.2 Electrolysis cell: see Figure 1a, Figure 1b.
• 3.3 Semi-micro distillation apparatus: see Figure 2.
• 3.4 Syringes: 1, 2, 5, 30mL.
• 3.5 Microsyringes: 0.5, 1.0μL (source "I.O1.Lo" requires confirmation against the source standard (source-text extraction)).
• 3.6 Alcohol lamp or small electric furnace.

Electrolysis cell structure (according to the text labels in Figure 1a and Figure 1b):

• Standard ground joint No. 1—14, connected to the indicator electrode;
• Standard ground joint No. 2—10, connected to the drying tube;
• Standard ground joint No. 3—14, connected to the anode electrode;
• Standard ground joint No. 4—10, sample inlet covered with a rubber cap (a penicillin injection vial stopper may be used as a substitute);
• Standard ground joint No. 5—19, connected to the cathode electrode; below the opening a glass tube No. 19 is welded, the lower opening of the tube is welded with glass rod φ3 into a mesh cage shape, and the cathode glass sleeve is placed inside it;
• One platinum sheet electrode (indicator electrode); platinum sheet electrode (electrolysis electrode); drying tube.

6. Recommended operating conditions

• Electrolysis current: at least 10mA or more (see 3.1).
• Azeotropic distillation rate: 30–50 drops per minute (see 6.2).
• Distillation endpoint: after 95% of benzene has distilled out (i.e., no more distillate drops out), remove the distillate receiving bottle and immediately cover and weigh it (see 6.2).
• Endpoint stability: electrolyze to the predetermined endpoint; if the endpoint can remain stable for 1min at this time, the current value can be calibrated and the sample can be introduced (see 6.1).
• Selection range of sample amount and benzene amount (source table, some values in source-text extraction require confirmation against the source standard):

Note: The source table above is severely damaged at source-text extraction; only the water content ranges can be recognized, and the values for sample amount and benzene amount cannot be reliably recognized, so they are all marked "requires confirmation against the source standard (source-text extraction)".

7. Sampling and sample preparation

• 6.2 Azeotropic distillation: after shaking the oil sample thoroughly to make it uniform, take a certain amount of sample and dehydrated benzene as specified in the table below into a micro distillation flask, quickly assemble the micro distillation apparatus, and carry out azeotropic distillation.
• 6.3 Before sample introduction, first rinse the syringe five to seven times with the sample to be analyzed, then take 1mL of the sample to be analyzed and quickly inject it into the electrolysis cell through the rubber stopper at the sample inlet of the electrolysis cell.
• Other sampling and sample preparation details: not provided in the available source.

8. Analytical procedure

• 5.1 Place a stirring bar in the pre-dried anode chamber of the electrolysis cell, then add 50–60mL electrolyte to the anode chamber, then add Karl Fischer reagent until the electrolyte is reddish brown; take 2mL of this electrolyte and add it to the cathode chamber, cover the titration cell cap, and apply vacuum grease to all ground joints to prevent moisture absorption, keeping the electrolysis cell sealed and ready for use.
• 5.2 Adjust the instrument according to the coulometer instruction manual.
• 5.3 Connect the wires of the electrolysis cell to the coulometer properly.
• 6.1 Use a syringe to inject an appropriate amount of water-containing methanol into the electrolysis cell so that the electrolyte contains a trace amount of water, and the recorder indication approaches the zero position; then electrolyze to the predetermined endpoint. If the endpoint can remain stable for 1min at this time, the current value can be calibrated and the sample can be introduced.
• 6.2 Azeotropic distillation: after shaking the oil sample thoroughly to make it uniform, take a certain amount of sample and dehydrated benzene as specified in the table below into a micro distillation flask, quickly assemble the micro distillation apparatus, and carry out azeotropic distillation at a distillation rate of 30–50 drops per minute; after 95% of benzene has distilled out (i.e., no more distillate drops out), remove the distillate receiving bottle and immediately cover and weigh it.
• 6.3 Before sample introduction, first rinse the syringe five to seven times with the sample to be analyzed, then take 1mL of the sample to be analyzed and quickly inject it into the electrolysis cell through the rubber stopper at the sample inlet of the electrolysis cell.
• 6.4 Calculate the result after electrolysis is completed.
• 6.5 Carry out a blank test and determination of the blank value by this method without adding the analytical sample.

9. Qualitative and quantitative determination and calculation formula

The water content of the sample X (ppm) is calculated according to the following formula:

X = I × t × 1000 / (10722 × m)

Where:

• I— electrolysis current, mA;
• t— electrolysis time, s;
• m— mass of the sample, g;
• 10722— quantity of electricity consumed for electrolysis of 1mg water (mC/mg).

(The source formula source-text extraction is "X = I " t x 1000 / 10722m", arranged as above according to context; symbols require confirmation against the source standard (source-text extraction).)

10. Precision

Repeatability: for the same operator, the difference between two repeated determination results shall not exceed the following values.

(In the source table, ") 100" requires confirmation against the source standard (source-text extraction); according to context it should be "> 100".)

11. Report

not provided in the available source.

12. Normative references

not provided in the available source (the main text does not list a normative reference document list).

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 Q&A