SH/T 0583-1994 Determination of Relative Molecular Mass of Hydrocarbons (Thermoelectric Measurement of Vapor Pressure Method)

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

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

• Standard number: SH/T 0583-94 (confirmed in 2004)
• Chinese name: Determination of Relative Molecular Mass of Hydrocarbons (Thermoelectric Measurement of Vapor Pressure Method)
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Reference adoption: ASTM D 2503-92 "Determination of Relative Molecular Mass (Molecular Weight) of Hydrocarbons (Thermoelectric Measurement of Vapor Pressure Method)"
• Drafting unit: Refinery of Shanghai Gaoqiao Petrochemical Company; proposed by: Shanghai Gaoqiao Petrochemical Company; centralized by: Research Institute of Petroleum Processing
• Main drafters: Deng Shuming, Tao Wenchen, Zhang Jinfang
• Approval/implementation: approved by China Petrochemical Corporation 1994-03-10, implemented on 1994-10-01

2. Scope of application and non-applicability

• Applicable to petroleum fractions with an initial boiling point not lower than 220℃ and a relative molecular mass within 300.
• Not applicable: not provided in the available source (only the precision note states that the precision for petroleum fractions with a relative molecular mass above 800 has not been determined).

3. Method principle

Dissolve a certain mass of sample in a suitable certain amount of solvent, and separately place 1 drops of the sample solution and 1 drops of the solvent onto two thermistors in a sealed chamber saturated with solvent vapor. Because the saturated vapor pressure of the sample solution is lower than the saturated vapor pressure of the solvent, solvent molecules in the saturated vapor phase will condense on the sample solution drops, releasing heat of condensation, and thus a temperature difference is produced between the two drops. By measuring the temperature change and comparing it with a previously prepared standard curve, the relative molecular mass of the sample can be calculated.

4. Reagents and materials (purity / preparation)

• 5.1 Solvent: must be able to completely dissolve the sample and have no association, condensation, or dissociation effect on the sample. Solvents suitable for hydrocarbons and petroleum fractions:
  • 5.1.1 Benzene: analytical reagent. Note: benzene is toxic, carcinogenic, flammable, and its vapor can be absorbed through the skin; use with adequate ventilation.
  • 5.1.2 Trichloromethane (chloroform): analytical reagent. Note: chloroform is toxic and fatal if swallowed; use with adequate ventilation.
  • 5.1.3 1,1,1- Trichloroethane: analytical reagent. Note: toxic; use with adequate ventilation.
  • 5.1.4 n-Hexane: analytical reagent. Note: flammable, vapor can flash, harmful if inhaled; keep away from heat sources and open flames during use.
  • Note: When different solvents are used to determine the same sample, the measured relative molecular masses differ slightly. In case of dispute, the result determined with benzene as solvent shall prevail.
• 5.2 Standard samples: use chromatographically pure substances with known accurate relative molecular masses as standard samples. Standard samples that have been used successfully include: biphenyl phthalide (210.2), n-triacontane (422.8), n-octadecane (254.5), squalane (422.8), n-tetracosane (338.7).
  • Requires confirmation (source-text extraction): the original text "biphenyl phthalide" and "squalane" are suspected to be source-text extraction noise; the names of the reference materials require confirmation against the source standard.

5. Instruments and equipment

• 4.1 Vapor pressure osmometer (VPO instrument): sensitivity per division not greater than 1×10⁻⁶℃ (original text "1 x 10-0`C" requires confirmation against the source standard (source-text extraction)), sample chamber constant-temperature stability ±0.001℃/h.
• 4.2 Volumetric flask: 25 mL.
• 4.3 Syringe: needle with spring, 1 mL.

6. Recommended operating conditions

• Sample chamber temperature: 37℃ (6.3).
• Stabilization time: 2～3 h (6.3).
• Bridge voltage: adjust until the potentiometer for the bridge input voltage indicates the maximum value 100% (6.5).
• Zero point change: should be within 0.5% of full scale (6.5, 6.8).
• Equilibrium criterion: read ΔV once every 1 min until the difference between two readings does not exceed 1 mV (6.6).
• Standard solution concentration range: 0.01～0.1 mol/L, at least six kinds (6.1).

7. Sampling and sample preparation

• 7.1 Weigh a certain mass of sample in a 25 mL volumetric flask, weighing to 0.1 mg, and dilute to the mark with the selected solvent.
• Recommended sample amount:
  • Relative molecular mass <200: 0.3 g
  • 200～500: 0.3～0.6 g
  • 500～700: 0.6～0.9 g
  • 700～1000: 0.9～1.3 g

8. Analytical procedure

• 6.1 Completely dissolve the standard sample in the selected solvent to prepare standard solutions with an amount-of-substance concentration in the range 0.01～0.1 mol/L, at least six kinds.
• 6.2 Remove the upper system of the sample cell, take out the solvent cup, and rinse the solvent cup with the selected solvent. Place a dedicated vapor wick in a clean, dry solvent cup and add about 20 mL of solvent. Put the solvent cup back into the sample cell slot so that the opening of the vapor wick is in line with the observation window. Reinstall the upper system of the sample cell.
• 6.3 Turn on the power, turn on the voltage stabilizer and the instrument heating switch, and adjust the ten-turn helical potentiometer so that the sample chamber stabilizes at 37℃ temperature for 2～3 h.
• 6.4 Use at least eight clean, dry syringes; two of them each take about 1 mL of solvent and place them into holes No. 1 and No. 2 of the injection chamber; the remaining syringes take about 1 mL each of the 6.1 standard solutions in batches, and place them in batches into holes No. 3, No. 4, No. 5, and No. 6 for preheating in order of increasing concentration.
• 6.5 Turn on the switch of the general-purpose electronic temperature measuring instrument. Use about 4 drops of solvent from holes No. 1 and No. 2 to rinse the two thermistors respectively, then suspend 1 drops of liquid of similar size on each. After the instrument stabilizes, set the sensitivity range to the highest range and adjust the zero point. Press the "%" advance button and adjust the bridge voltage so that the potentiometer for the bridge input voltage indicates the maximum value 100%. Repeatedly check the zero point until the zero point change is within 0.5% of full scale.
• 6.6 Use 3～4 drops of the standard solution from hole No. 3 to rinse the sample thermistor, then suspend 1 drops of the standard solution on the sample thermistor, suspend 1 drops of the solvent from hole No. 1 on the reference thermistor, start timing, and read the ΔV value. Read once every 1 min until the difference between two readings does not exceed 1 mV, which is considered to have reached equilibrium. Record the time to reach equilibrium; this is the equilibrium time of this solvent in subsequent experiments. Record the ΔV value at the time equilibrium is reached, to the nearest 1 mV.
• 6.7 According to the same method as in clause 6.6, test the standard solutions in the remaining holes in sequence, and record the ΔV value at the time each standard solution reaches equilibrium.
• 6.8 After testing each concentration of standard solution, immediately rinse the sample thermistor with the solvent from hole No. 2, suspend 1 drops of solvent, and then check the instrument zero point. The zero point change should be within 0.5% of full scale.
• 6.9 On rectangular coordinate paper, plot the standard curve with the amount-of-substance concentration of the standard solution (mol/L) as the abscissa and the corresponding ΔV value for each concentration as the ordinate. Note: the standard curve determined with the same batch number of the same solvent should be repeated. If the batch number changes, the standard curve should be redetermined.
• 7.2 Use two syringes to take about 1 mL of solvent and place them into holes No. 1 and No. 2; use other syringes to take about 1 mL of sample solution and place them into the other holes; adjust the instrument zero point and bridge voltage according to the same method as in clause 6.5.
• 7.3 Use 3～4 drops of the sample solution from clause 7.2 to rinse the sample thermistor, suspend 1 drops of sample solution on the sample thermistor, suspend 1 drops of the solvent from hole No. 1 on the reference thermistor, and record the ΔV value at the equilibrium time determined in clause 6.6, to the nearest 0.1 mV. When testing a group of samples, repeatedly check the instrument zero point.
• 7.4 From the ΔV value at the time the sample solution reaches equilibrium, find the corresponding amount-of-substance concentration (mol/L) value from the standard curve obtained in clause 6.9.

9. Qualitative and quantitative determination and calculation formula

The relative molecular mass of the sample Mr (calculated as the molar mass of the molecule) is calculated according to the following formula:

Mr = c / c₁

Where:

• c —— concentration of the sample solution, g/L;
• c₁ —— amount-of-substance concentration found from clause 7.4, mol/L.

(The original formula was typeset as a fraction; source-text extraction appears as "c one c l - - M r", restored according to context as Mr = c / c₁, requires confirmation against the source standard (source-text extraction).)

10. Precision

• The precision of this standard is based on test results using benzene as solvent.
• Judge the reliability of test results according to the following provisions (95% confidence level).
• Repeatability: the difference between two results obtained by the same operator using the same instrument on the same sample for repeated determinations shall not exceed the value listed in the table below.
• Reproducibility: the difference between two results obtained by different operators in different laboratories on the same sample shall not exceed the value listed in the table below.

Precision specification table:

Note: This standard does not determine the precision for petroleum fractions with a relative molecular mass above 800.

(The values in the original precision table source-text extraction are severely disordered and cannot be reliably restored, so they are marked as requiring confirmation against the source standard.)

11. Report

Take the arithmetic mean of the two results of repeated determinations as the average relative molecular mass of the sample, rounded to an integer.

12. Referenced documents

• ASTM D 2503-92 "Determination of Relative Molecular Mass (Molecular Weight) of Hydrocarbons (Thermoelectric Measurement of Vapor Pressure Method)" (reference adoption)
• Other referenced documents: not provided in the available source

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 for questions and answers