SH/T 0582-1994 Determination of sodium content in lubricating oils and additives (atomic absorption spectrometry)

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Card type: Test method

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

• Standard number: SH/T 0582-94
• Chinese full title: Determination of sodium content in lubricating oils and additives (atomic absorption spectrometry)
• English name: not provided in the available source
• Replacement relationship: not provided in the available source (the source states "confirmed in 2004")
• Approval/implementation: approved by China Petrochemical Corporation in 1994-03-10, implemented in 1994-10-01

2. Scope of application and non-applicability

• Applicable: determination of sodium content in unused and used lubricating oils and additives.
• Not applicable: not provided in the available source.

3. Method principle

The sample is ashed and then dissolved with hydrochloric acid to prepare a sample solution containing hydrochloric acid. The absorbance of sodium atoms at the wavelength 589.0 nm is measured by atomic absorption spectrometry. According to the principle of matrix matching, an aqueous sodium chloride solution is used as the standard solution to determine the sodium content in the sample.

4. Reagents and materials (purity / preparation)

• 4.2.1 Deionized water: distilled water further subjected to secondary deionization treatment with cation exchange resin (hydrogen form), in which the sodium content shall be such that it does not affect the determination.
• 4.2.2 Quantitative filter paper: diameter 9 cm.
• 4.2.3 Air: compressed air purified to be free of oil and water.
• 4.2.4 Acetylene gas: purity of 99.9% or above.
• 5.1 Hydrochloric acid: guaranteed reagent grade. Prepare a 1:1 (volume ratio) hydrochloric acid solution.
• 5.2 Sodium chloride: spectroscopically pure.
• 6.1 Sodium standard stock solution: weigh sodium chloride 2.5420 g (accurate to 0.1 mg) that has been dried at 105℃, 2 h and brought to constant mass, dissolve it in deionized water, transfer and dilute to a 1000 mL volumetric flask to prepare a standard stock solution with a sodium content of 1 mg/mL, and store it in a polyethylene plastic bottle.
• 6.3.1 Standard solution series: use a pipette to draw an appropriate amount of the sodium standard stock solution from clause 6.1 into a volumetric flask, dilute with deionized water so that each standard solution contains one-tenth of the total volume of that solution of hydrochloric acid, and their sodium contents are respectively 0, 1, 2, 3, 4, 5, 6, 7 μg/mL (or corresponding concentrations diluted 10 times) standard solution series. Note: This standard solution series need not be prepared on the same day and can be used for 8 weeks; matrix matching shall be carried out when necessary.

5. Instruments and equipment

• 4.1.1 Atomic absorption spectrophotometer: various models of commercial instruments equipped with an air/acetylene flame atomizer.
• 4.1.2 Sodium hollow cathode lamp.
• 4.1.3 Balance: sensitivity 0.01 g and 0.0001 g.
• 4.1.4 Quartz beaker (or quartz crucible): 50 mL.
• 4.1.5 High-temperature furnace: capable of being controlled at 550℃±25℃.
• 4.1.6 Electric furnace: 1 kW (adjustable).
• 4.1.7 Pipettes: 0.5, 1, 2, 5, 10 mL.
• 4.1.8 Volumetric flasks: 10, 25, 50, 100, 200, 1000 mL.
• 4.1.9 Polyethylene plastic bottles: 250, 1000 mL.
• 4.1.10 Polyethylene plastic wash bottles: 500 mL.

6. Recommended operating conditions

Table 1 Instrument operating conditions (element: Na)

Note: The conditions in Table 1 are for reference only; the conditions for different types of instruments are not completely the same. Flame emission may be used instead of absorption measurement.

7. Sampling and sample preparation

• 7 Sampling: the sample shall be thoroughly stirred uniformly (heated to about 50℃ if necessary); if the sample contains water and impurities, it shall be dehydrated and filtered, and then a representative test sample shall be taken for analytical testing.
• 8.1 In a clean and dry quartz beaker (or quartz crucible), weigh the test sample as recommended in Table 2. For additive samples with high sodium content, weigh onto a "I"-shaped quantitative filter paper of about 15 mm×25 mm and then place it in a quartz beaker (or quartz crucible).

Table 2 Sample amount

Note: Depending on the sensitivity of the instrument and the sample situation, the sample amount may be changed, but the weighing precision must be ensured. (In Table 2, the sample amount column source-text extraction is seriously misaligned, requires confirmation against the source standard (source-text extraction))

8. Analytical procedure

• 8.2 Carry out ashing treatment according to the method of GB/T 508, but the ashing temperature is 550℃±25℃; after ignition for 2 h, take it out and cool to room temperature. If the sample is difficult to ash completely, add dropwise a few drops of hydrochloric acid solution (5.1) in the quartz beaker (or quartz crucible) to wet the residue to aid ashing, evaporate to dryness, and then continue ignition at 550℃±25℃ for 15 min. If ashing is still not complete after the above treatment, the ashing aid and ignition may be repeated.
• 8.3 Dissolve the ash with 10 mL hydrochloric acid solution (5.1). If insoluble matter remains after multiple dissolutions, it shall be filtered to remove the residue.
• 8.4 Transfer the above solution to a 25 (or 50) mL volumetric flask, dilute with deionized water, and respectively add hydrochloric acid solution (5.1) 5 (or 10) mL. Prepare the sample solution (or a sample solution diluted 10 times). Note: When dilution or addition of relevant reagents is required, maintain matrix matching with the standard sample.
• 8.5 Without adding sample, prepare the corresponding blank solution according to the procedures of clauses 8.3～8.4.
• 8.6 Under the instrument operating conditions (see Table 1), after zeroing with deionized water, proceed as follows:
  • 8.6.1 Measure the absorbance of the blank solution (or zero the instrument).
  • 8.6.2 From low content to high content, measure the absorbance of the 6.3.1 standard solution series in sequence.
  • 8.6.3 Measure the absorbance of the sample solution (8.4). If it is not within the absorbance range of 8.6.2, re-prepare the sample solution until the requirement is met.
  • 8.6.4 Repeat step 8.6.2.
  • 8.6.5 Repeat step 8.6.3, with two consecutive measurements.
  • 8.6.6 From high content to low content, measure the absorbance of the 6.3.1 standard solution series in sequence.
  • 8.6.7 Measure the absorbance of the blank solution (or zero the instrument).
  • 8.6.8 Repeat steps 8.6.1～8.6.7. Use the average of the two absorbance measurements as the measured absorbance value for each standard solution and sample solution. Note: For samples with high sodium content exceeding the measurement range, measurement can be carried out by reducing the sample amount, increasing the dilution volume, and shortening the absorption path length, etc.
  • 8.6.9 Plot the calibration curve using the measured absorbance values of the standard solution series (6.3.1) as the ordinate and the corresponding concentrations as the abscissa.
• 8.7 According to the measured absorbance value of the sample solution, find the corresponding sample solution concentration Cx (μg/mL) from the calibration curve. Instruments with direct concentration readout can directly read the Cx value.
• 6.3.2 Instrument adjustment and absorbance measurement:
  • 6.3.2.1 Adjust the instrument according to the conditions in Table 1.
  • 6.3.2.2 Measure absorbance: zero with deionized water, and measure the absorbance of each concentration solution of the 6.3.1 standard solution series in sequence (with the burner rotated or not rotated), from low content to high content, and then from high content to low content. Measure the absorbance of each standard solution twice, and take the average as the measured value.
• 6.3.3 Plot the standard calibration curve: use the concentration values of each standard solution as the abscissa and their corresponding absorbances as the ordinate. Plot the sodium standard calibration curve to check the linearity of the standard calibration curve and the condition of the instrument, etc.

9. Qualitative and quantitative determination and calculation formulas

• 9.1 According to the Cx value of clause 8.7, the sodium content X%(m/m) in the sample is calculated according to formula (1): X = Cx × V / (m × 10⁴) …… (1) Where: m— mass of the sample, g; Cx— concentration of the sample solution, μg/mL; V— dilution volume, mL.
• 9.2 If the measured value is in the linear portion of the calibration curve, the sodium content X%(m/m) in the sample is calculated according to formula (2): X = (Ax × Cs × V) / (As × m × 10⁴) …… (2) Where: m— mass of the sample, g; V— dilution volume, mL; Ax— absorbance of the sample solution; As— absorbance of the standard solution higher than Ax and closest to Ax; Cs— concentration of the standard solution corresponding to As, μg/mL.

10. Precision

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

• 10.1 Repeatability: the difference between two results obtained by repeated determination by the same operator shall not be greater than the repeatability specified in Table 3.
• 10.2 Reproducibility: the difference between two results each provided by different laboratories shall not be greater than the reproducibility specification in Table 3.

Table 3 Precision %(m/m)

11. Report

Take the arithmetic mean of two results from duplicate determinations (X) as the determination result.

12. Normative references

• GB/T 508 Determination of ash in petroleum products

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