SH/T 0077-1991 Determination of Iron Content in Lubricating Oils (Atomic Absorption Spectrometry)

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Card type: Test method

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

• Standard number: SH/T 0077-91
• Full title: Determination of Iron Content in Lubricating Oils (Atomic Absorption Spectrometry)
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Other: This standard includes two methods, namely Part One Ashing Method and Part Two Direct Method. This standard refers to and adopts the Federal Republic of Germany national standard DIN 51397 TIT2(80) "Determination of Iron Content in Lubricating Oils by Atomic Absorption Spectrometry". Approved by China Petrochemical Corporation 1991-11-26, implemented on 1992-12-01, confirmed in (2001) year.

2. Scope of application and non-applicability

Part One Ashing Method (Chapter 1)

• This standard specifies a method for the determination of iron content in lubricating oils by atomic absorption spectrometry after ashing the sample.
• It is applicable to the determination of iron content in unused and used lubricating oils, with a concentration range of: 10～200 mg/kg.
• This standard is also applicable to the determination of iron content in additives.

Part Two Direct Method (Chapter 12)

• This standard specifies a method for the determination of iron content in lubricating oils by atomic absorption spectrometry after diluting the sample with a solvent.
• It is applicable to the determination of iron content in unused and used lubricating oils, with a concentration range of 10～200 mg/kg.

Not applicable: not provided in the available source.

3. Method principle

Part One Ashing Method (Chapter 3 Method summary) After the sample is ashed and dissolved in hydrochloric acid, a sample solution containing hydrochloric acid is prepared. The absorbance of iron atoms at wavelength 248.3 nm is measured by atomic absorption spectrometry. Using a hydrochloric acid solution of ferric oxide as the reference solution, the iron content in the sample is determined.

Part Two Direct Method (Chapter 14 Method summary) The sample is diluted with an organic solvent in a certain proportion and directly sprayed into the flame of an atomic absorption spectrometer to measure the absorbance. The absorbance of the sample is compared with the absorbance of the reference solution to determine the iron content in the sample.

4. Reagents and materials (purity / preparation)

Part One Ashing Method

Materials (4.2):

• 4.2.1 Deionized water: distilled water further subjected to secondary deionization treatment with a cation exchange resin (hydrogen form). Its iron content shall be such that it does not affect the determination.
• 4.2.2 Quantitative filter paper: diameter 9 cm.
• 4.2.3 Copper wire mesh: aperture 0.05 mm.
• 4.2.4 Air: compressed air purified to be free of oil and water.
• 4.2.5 Acetylene gas: purity 99.9%.

Reagents (Chapter 5):

• 5.1 Ferric oxide: high purity.
• 5.2 Hydrochloric acid: guaranteed reagent [36%～38%(m/m)]. Prepare a 1:1 (by volume ratio) solution.
• 5.3 Ammonium nitrate: analytical reagent. Prepare a 100 g/L solution. (The original text source-text extraction writes "ammonium amine", requires confirmation against the source standard (source-text extraction))

Preparation of iron standard stock solution (6.1): Weigh dried ferric oxide 1.4296 g (accurate to 0.1 mg), dissolve with 1:1 (by volume ratio) hydrochloric acid solution 20 mL, transfer to a 1000 mL volumetric flask, dilute to the mark with deionized water, and mix well. Prepare an iron standard stock solution with an iron content of 1 mg/mL, and store it in a narrow-mouth polyethylene plastic bottle.

Preparation of standard solutions (6.4.1): Use a pipette to draw an appropriate amount of the iron standard stock solution from clause 6.1 into a volumetric flask, dilute with deionized water so that the hydrochloric acid concentration in each standard working solution is 10%(V/V). Prepare standard solutions with concentrations of: 0, 1, 2, 3, 4, 5, 10, 20 μg/mL. Note: This standard solution need not be prepared on the same day and can be used for several weeks.

Part Two Direct Method

Materials (15.2):

• 15.2.1 Air: purified to be free of oil and water.
• 15.2.2 Acetylene gas: purity 99.9%.
• 15.2.3 Paint industry solvent naphtha: complies with the provisions in SH 0005.
• 15.2.4 White oil: complies with the provisions of number 15 in SH 0007. (The original text source-text extraction writes "symbol", requires confirmation against the source standard (source-text extraction))
• 15.2.5 Copper wire mesh: aperture 0.05 mm.

Reagents (Chapter 16):

• 16.1 Organic iron standard: analytical reagent, with known iron content.
• 16.2 2- ethylhexanoic acid: chemical reagent.
• 16.3 Toluene: analytical reagent.

Blank solution (17.1): Paint industry solvent naphtha is the blank solution.

Preparation of iron standard stock solution (17.2): Weigh an appropriate amount of the organic iron standard into a 100 mL beaker (accurate to 0.1 mg), add 3 mL toluene, 7 mL 2- ethylhexanoic acid and 20 g white oil, stir and dissolve under warm conditions (maximum 50℃), after cooling to 15～20℃, make up to 100 g with white oil, and store in a narrow-mouth bottle. This solution is an iron standard stock solution of 200 mg/kg. Note: The iron standard stock solution can be stored for three months.

Preparation of standard working solutions (18.1): Use a pipette to accurately take an appropriate amount of the iron standard stock solution into a 25 mL volumetric flask, add an appropriate amount of white oil, and dilute with the blank solution to reach the concentrations given in Table 2. Table 2 concentrations: serial numbers 1～5, concentrations 1, 2, 3, 4, 5 mg/kg (the original unit source-text extraction writes "f[unreadable unit character].L", requires confirmation against the source standard (source-text extraction)). Note: ① The standard working solutions must be prepared on the day of the test; ② An appropriate amount of white oil is added to the standard working solutions so that the viscosity of the standard working solutions and the sample solution are basically consistent. If the sample amount is 1.5 g, the amount of white oil added is 2.0 g.

5. Instruments and equipment

Part One Ashing Method (4.1)

• 4.1.1 Atomic absorption spectrophotometer: various models of commercial instruments equipped with an air-acetylene flame atomizer.
• 4.1.2 Iron hollow cathode lamp.
• 4.1.3 Balance: sensitivity 0.1 mg.
• 4.1.4 Porcelain crucible or quartz beaker: 50 mL.
• 4.1.5 High-temperature furnace: 0～1000℃.
• 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, 1000 mL.
• 4.1.9 Narrow-mouth polyethylene plastic bottles: 250, 1000 mL.
• 4.1.10 Polyethylene plastic wash bottle: 500 mL.

Part Two Direct Method (15.1)

• 15.1.1 Atomic absorption spectrophotometer: wavelength range 190～900 nm, any atomic absorption spectrophotometer capable of measuring the analytical line of iron within the absorbance range of 0.1～0.5 can be used.
• 15.1.2 Iron hollow cathode lamp.
• 15.1.3 Volumetric flasks: 25 mL.
• 15.1.4 Pipettes: 0.5, 1, 2, 5 mL.
• 15.1.5 Beakers: 100 mL.
• 15.1.6 Balance: sensitivity 0.1 mg.
• 15.1.7 Narrow-mouth bottle: brown, 250 mL.
• 15.1.8 Stirring motor: 1400～1500 r/min.

6. Recommended operating conditions

Part One Ashing Method Table 1 Instrument operating conditions

Note: The conditions in Table 1 are for reference only; the conditions for different instrument models are not exactly the same. (The original table header part source-text extraction has much noise; the values are based on the original text, requires confirmation against the source standard (source-text extraction))

Part Two Direct Method Table 3 Instrument operating conditions

Note: The performance of different instrument models varies; the above conditions are for reference only. (The original table header part source-text extraction has much noise; the values are based on the original text, requires confirmation against the source standard (source-text extraction))

7. Sampling and sample preparation

Part One Ashing Method (Chapter 7 Sampling) After the sample is thoroughly stirred evenly (if necessary, heated to about 60℃), take a representative test sample for analysis and testing.

Preparation work (6.2, 6.3):

• 6.2 Clean porcelain crucibles and glassware with hydrochloric acid and deionized water.
• 6.3 Filter the test sample with copper wire mesh to remove solid particles with a diameter greater than 0.05 mm.

Part Two Direct Method (18.2 Preparation of sample solution)

• 18.2.1 Warm the sample to about 60℃, stir evenly with a stirring motor, and pass through a copper wire mesh to remove solid particles with a diameter greater than 0.05 mm.
• 18.2.2 Weigh 1～3 g sample (accurate to 0.1 mg) into a 25 mL volumetric flask, dilute to the mark with blank solution, mix well and set aside for measurement.

8. Analysis procedure

Part One Ashing Method (Chapter 8 Test procedure)

• 8.1 In a clean, dry porcelain crucible (or quartz beaker), weigh a test portion of 2～5 g (to the nearest 0.1 mg).
• 8.2 According to the method of GB/T 508, perform ignition and ashing at 775℃±25℃. If the test portion is difficult to ash completely, then after the porcelain crucible (or quartz beaker) has cooled, add dropwise a few drops of 100 g/L ammonium nitrate to moisten the residue, and after it has evaporated, continue ignition.
• 8.3 Dissolve the ash with 10 mL 1:1 (by volume ratio) hydrochloric acid solution. If the ash cannot be completely dissolved, the amount of hydrochloric acid solution should be increased and dissolution repeated multiple times. If insoluble matter remains after multiple dissolutions, it should be filtered to remove the residue.
• 8.4 Transfer the above solution to a 25, 50 or 100 mL volumetric flask, dilute with deionized water and make the hydrochloric acid concentration therein 10%(V/V). Prepare the test solution, to be measured.
• 8.5 Without adding a test portion, follow the steps of clause 8.3 and clause 8.4 to prepare a corresponding blank solution.
• 8.6 Under optimized instrument conditions, zero with deionized water, and measure in sequence:
  • 8.6.1 Measure the absorbance of the blank solution (or zero).
  • 8.6.2 Measure the absorbance of the standard working solution with the lowest iron content.
  • 8.6.3 Measure the absorbance of the standard working solution with medium iron content.
  • 8.6.4 Measure the absorbance of the standard working solution with the highest iron content.
  • 8.6.5 Measure the absorbance of the test solution, continuously measuring twice.
  • 8.6.6 Measure the absorbance of the standard working solution with the highest iron content.
  • 8.6.7 Measure the absorbance of the standard working solution with medium iron content.
  • 8.6.8 Measure the absorbance of the standard working solution with the lowest iron content.
  • 8.6.9 Measure the absorbance of the blank solution (or zero).
  • 8.6.10 Repeat the steps of clauses 8.6.1～8.6.9. Take the average of the two absorbance measurements as the measured value.
• Note: For lubricating oils and additive test portions that exceed the measurement range, measurement can be carried out by methods such as reducing the sample amount, increasing the dilution volume, and shortening the optical path length.
• 8.7 Based on the measured absorbance value of the test solution, find the corresponding test solution concentration Cx(μg/mL) from the working curve (a direct-reading concentration instrument can directly read the Cx value).

Working curve plotting (6.4.2, 6.4.3):

• 6.4.2.1 Adjust the instrument according to the conditions in Table 1.
• 6.4.2.2 Measure absorbance: zero with deionized water, and sequentially measure the absorbance of each concentration solution of the standard solutions in clause 6.4.1. From low content to high content, then from high content to low content, measure the absorbance of each standard working solution twice. Take the average as the measured value.
• 6.4.3 Plot the working curve: use the concentration values of each standard working solution as the abscissa and the corresponding absorbance as the ordinate. Plot the working curve for iron.

Part Two Direct Method (18.3 Measure Absorbance)

• 18.3.1 Adjust the instrument according to the conditions in Table 3.
• 18.3.2 Zero with the blank solution.
• 18.3.3 Measure the standard working solution with the lowest iron content.
• 18.3.4 Measure the standard working solution with medium iron content.
• 18.3.5 Measure the standard working solution with the highest iron content.
• 18.3.6 Measure the absorbance of the test solution, continuously measuring twice.
• 18.3.7 Measure the standard working solution with the highest iron content.
• 18.3.8 Measure the standard working solution with medium iron content.
• 18.3.9 Measure the standard working solution with the lowest iron content.
• 18.3.10 Zero with the blank.
• 18.3.11 Repeat the steps of 18.3.3～18.3.10, and take the average of the two absorbance measurements as the measured value.
• Note: ① For high-content test portions that exceed the measurement range, measurement can be carried out by methods such as changing the optical path length, reducing the sample amount, or dilution; ② During the interval between measurements of the reference solution and the test solution, continuously spray the blank solution to maintain constant measurement conditions.

9. Qualitative and Quantitative and Calculation Formulas

Part One Ashing Method (Chapter 9 Calculation)

9.1 The iron content in the test portion X (mg/kg) is calculated according to formula (1):

X = Cx · V / m

Where:

• m — mass of test portion, g;
• Cx — concentration of test solution, μg/mL;
• V — dilution volume, mL.

(The original formula (1)source-text extraction is displayed as “[unreadable formula symbol] Cx”, the formula form requires confirmation against the source standard (source-text extraction))

9.2 If the measured value is in the linear portion of the working curve (that is, when the absorbance of the test solution is less than the absorbance of the 10 μg/mL standard working solution), the iron content in the test portion X (mg/kg) is calculated according to formula (2):

X = (Ax / As) · Cs · V / m

Where:

• m — mass of test portion, g;
• V — dilution volume, mL;
• Ax — absorbance of the test solution;
• As — absorbance of the standard working solution closest to Ax;
• Cs — concentration of the standard working solution corresponding to As, μg/mL.

(The original formula (2)source-text extraction is displayed as “[unreadable formula symbol], Ax AF·”, the formula form requires confirmation against the source standard (source-text extraction))

Part Two Direct Method (Chapter 19 Calculation)

The iron content in the test portion X (mg/kg) is calculated according to formula (3):

X = (Ax · C · f · 25) / (As · m)

Where:

• Ax — average absorbance of iron in the test solution;
• As — average absorbance of the standard working solution with iron concentration similar to that in the test portion;
• C — concentration of the standard working solution corresponding to As, mg/kg;
• f — dilution factor;
• m — mass of the test portion, g;
• 25 — volume of the test solution, mL.

(The original formula (3)source-text extraction is displayed as “X [unreadable formula symbol] Ax·C·f x 25 / A,·m”, the formula form requires confirmation against the source standard (source-text extraction))

10. Precision

Part One Ashing Method (Chapter 10) Judge the reliability of test results according to the following provisions (95% confidence level).

• 10.1 Repeatability: The difference between two results of repeated measurements by the same operator shall not exceed 10% of the arithmetic mean.
• 10.2 Reproducibility: The difference between two results submitted by different laboratories shall not exceed 30% of the arithmetic mean.

Part Two Direct Method (Chapter 20) Judge the reliability of test results according to the following provisions (95% confidence level).

• 20.1 Repeatability: The difference between two results of repeated measurements by the same operator shall not exceed 10% of their arithmetic mean.
• 20.2 Reproducibility: The difference between two results submitted by different laboratories shall not exceed 30% of their arithmetic mean.

11. Report

Part One Ashing Method (Chapter 11) Take the arithmetic mean of two results of repeated measurements as the measurement result, and round to an integer.

Part Two Direct Method (Chapter 21) Take the arithmetic mean of two results of repeated measurements as the measurement result, and round to an integer.

12. Reference Documents

Part One Ashing Method (Chapter 2 Reference Standards)

• GB/T 508 Determination of Ash in Petroleum Products

Part Two Direct Method (Chapter 13 Reference Standards)

• SH 0005 Solvent Naphtha for Paint Industry
• SH 0007 White Oil for Cosmetics

Additional Notes:

• This standard is technically administered by the Research Institute of Petroleum Processing.
• This standard was drafted by the Refinery of Shanghai Gaoqiao Petrochemical Company and Dalian Petrochemical Company.
• The main drafters of this standard are Chen Changqun and Jiang Bo.
• This standard refers to and adopts the Federal Republic of Germany national standard DIN 51397 TIT2(80) “Determination of Iron Content in Lubricating Oils by Atomic Absorption Spectrometry”.

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