GB/T 9170-1988 Determination of total nitrogen content in lubricating oils and fuel oils (improved Kjeldahl method)

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Card type: Test method

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

• Standard number: GB 9170-88 (the file name is marked as GBT-9170-1988)
• Chinese full title: Determination of total nitrogen content in lubricating oils and fuel oils (improved Kjeldahl method)
• English name: Lubricating oils and fuel oils—Determination of total nitrogen—Modified Kjeldahl method
• UDC: 665.521.5 : 662.75 : 543.06
• Replacement relationship: not provided in the available source
• Approval/implementation: approved by China Petrochemical Corporation 1988-04-22, implemented on 1989-04-01
• Reference adoption: ASTM D3228—83 "Determination of total nitrogen in lubricating oils and fuel oils by the improved Kjeldahl method"

2. Scope of application and exclusions

• Applicable to the determination of total nitrogen content in lubricating oils and fuel oils.
• Determination range: for lubricating oils, nitrogen from 0.03% to 0.1%; for fuel oils, nitrogen from 0.015% to 2.0%.
• Not applicable to certain substances containing nitrogen-oxygen bonds (NO) or nitrogen-nitrogen bonds (NN).
• It can accurately determine nitrogen in lubricating oils containing nitrogenous ashless additives.

3. Method principle

The sample is digested in sulfuric acid with potassium sulfate, mercuric oxide and copper sulfate as catalysts. After all nitrogen in the sample has been converted to ammonium sulfate, sodium sulfide is added to precipitate mercury, and then excess sodium hydroxide is added for distillation. The ammonia formed at this time is absorbed in boric acid solution, and with a mixed solution of bromocresol green and methyl red as indicator, it is titrated with standard sulfuric acid solution to determine the nitrogen content in the sample.

4. Reagents and materials (purity / preparation)

• 3.1 Unless otherwise specified, all are analytical grade reagents, and water is distilled water.
• 3.2 Sucrose: guaranteed reagent grade.
• 3.3 Sulfuric acid: density 1.81.
• 3.4 Sodium hydroxide: prepare as a 1000 g/L aqueous solution.
• 3.5 Methyl red indicator: prepare as a 0.2% ethanol solution.
• 3.6 Bromocresol green indicator: prepare as a 0.1% ethanol solution.
• 3.7 Sodium sulfide.
• 3.8 Potassium sulfate.
• 3.9 Boric acid.
• 3.10 Mercuric oxide (the reagent identity is garbled in the source transcription; its interpretation as mercuric oxide remains unverified).
• 3.11 Potassium hydrogen phthalate.
• 3.12 Copper sulfate (the reagent identity is garbled in the source transcription; its interpretation as copper sulfate remains unverified).
• 3.13 Phenolphthalein indicator: prepare as a 1% ethanol solution.
• 4.1 Boric acid solution (10 g/L): dissolve 40 g of boric acid in 1 L of boiling water.
• 4.2 Catalyst: for each sample use 9.9 g potassium sulfate, 0.41 g mercuric oxide and 0.08 g copper sulfate (the source text source-text extraction writes "9.98 potassium sulfate, 0.41 g mercuric oxide and 0.088 copper sulfate", values require confirmation against the source standard (source-text extraction)).
• 4.3 Mixed indicator: mix three parts of 0.1% bromocresol green ethanol solution with one part of 0.2% methyl red ethanol solution uniformly.
• 4.4 Sodium sulfide (40 g/L): dissolve 40 g of sodium sulfide in 90 ℃ of hot water, cool and dilute to 1 L (the source text source-text extraction writes "408/L" "408 sodium sulfide", requires confirmation against the source standard (source-text extraction)).
• 4.5 Standard sodium hydroxide solution:
  • 4.5.1 0.1 N Preparation: weigh 4.0 g of sodium hydroxide into a 100 mL beaker containing 40 mL of water, after dissolution transfer to a 1000 mL volumetric flask and dilute to the mark (the source text source-text extraction writes "4.08", requires confirmation against the source standard (source-text extraction)).
  • 4.5.2 0.01 N Preparation: take 100 mL of the above 0.1 N solution and dilute with water to 1 L.
  • 4.5.3 Standardization: weigh potassium hydrogen phthalate dried at 105 to 110 ℃ to constant mass (about 0.6 g when standardizing 0.1 N, about 0.08 g when standardizing 0.01 N), weighed to the nearest 0.0001 g, dissolve in 80 mL of water, heat to boiling, add 2 to 3 drops of 1% phenolphthalein indicator, and titrate with the sodium hydroxide solution to be standardized until a pink color appears.
  • 4.5.4 Calculation: N₁ = T × 0.2042 / V (the source text source-text extraction formula is incomplete; meanings of symbols: T is the mass of potassium hydrogen phthalate g; V is the volume of standard sodium hydroxide solution consumed mL; 0.2042 is the number of grams per milliequivalent of potassium hydrogen phthalate; the source text source-text extraction writes "0.2012", requires confirmation against the source standard (source-text extraction)).
• 4.6 Standard sulfuric acid solution:
  • 4.6.1 0.1 N Preparation: slowly add 3 mL of sulfuric acid to a beaker containing 500 mL of water, mix and cool, then transfer to a 1 L volumetric flask and dilute with water to the mark.
  • 4.6.2 0.01 N Preparation: take 100 mL of the above 0.1 N solution and add it to a 1 L volumetric flask containing 500 mL of water, and dilute with water to the mark.
  • 4.6.3 Standardization: take 20 mL of the standard sulfuric acid solution to be standardized in an Erlenmeyer flask, use phenolphthalein as indicator, and titrate with 0.1 N (or 0.01 N) standard sodium hydroxide solution until a pink color appears.
  • 4.6.4 Calculation: N₂ (or N₃) = N × V / 20 (the source text source-text extraction formula is incomplete; meanings of symbols: N is the equivalent concentration of the standard sodium hydroxide solution; V is the volume of standard sodium hydroxide solution consumed mL; 20 is the volume of the titrated solution taken mL).

5. Apparatus and equipment

• 2.1.1 Burette: 50 mL, graduation 0.1 mL.
• 2.1.2 Erlenmeyer flask: 300 mL (the flask type is unclear in the source transcription and requires verification).
• 2.1.3 Heating device: electric furnace or gas burner.
• 2.1.4 Kjeldahl digestion apparatus.
• 2.1.5 Kjeldahl flask: capacity greater than 500 mL.
• 2.2 Material: glass beads, diameter about 5 mm.
• Other equipment (mentioned in 6.9.2): a bundle of twenty capillary tubes about 20 cm long with sealed tops.
• Mercury trap (mentioned in 6.8, should be used when performing Kjeldahl nitrogen determinations in large numbers).

6. Recommended operating conditions

• Digestion: heat at low temperature for about 20 min to char the sample until bubbling stops, shaking continuously during this period; after charring, gradually raise the temperature to boiling.
• During boiling digestion, at least 15 mL of solution should be maintained in the Kjeldahl flask; if insufficient, add 5 to 15 mL of sulfuric acid.
• Boil and digest until the contents change from turbid to colorless and transparent, then digest for a further 2 h.
• Distillation: before the solution is about to boil, reduce the heating rate, boil steadily for 5 min, then boil rapidly until the liquid volume in the Erlenmeyer flask is about 130 mL.
• Reception: the total volume of liquid in the Erlenmeyer flask should be about 150 mL.
• Titration: titrate with 0.01 N standard sulfuric acid solution until the gray color just disappears and a pale purple color appears; if the consumption exceeds 50 mL, use 0.1 N standard sulfuric acid solution for the excess portion; read the burette volume to 0.05 mL.

7. Sampling and sample preparation

• 5.1 Sampling shall be carried out in accordance with GB 1756 "Method for sampling petroleum and liquid petroleum products (manual method)".
• 5.2 The sample must be fully representative.
• 6.1 Weigh 1.0 to 1.5 g of sample into a Kjeldahl flask, preventing the sample from contacting the neck of the flask, weighed to the nearest 0.1 mg, add the mixed catalyst and 2 to 3 glass beads.

8. Analytical procedure

• 6.2 Rotate the Kjeldahl flask and add 20 mL of sulfuric acid along the neck wall, shake thoroughly to mix the sample uniformly with the digestion liquid and catalyst.
• 6.3 On the Kjeldahl digestion apparatus, heat at low temperature with an electric furnace or gas burner for about 20 min to char the sample until bubbling stops, shaking continuously during this period; after charring, gradually raise the temperature until boiling.
• 6.4 During boiling digestion, maintain at least 15 mL of solution; if insufficient, add 5 to 15 mL of sulfuric acid; the amount added depends on the sulfuric acid consumed during charring; it must be added along the neck wall after the flask has cooled sufficiently and the sulfur trioxide fumes have completely disappeared. Boil and digest until the contents change from turbid to colorless and transparent, then digest for a further 2 h. After digestion is completed, the total residual volume of the solution should be approximately the same as in the blank determination.
• 6.5 Stop heating, leave the Kjeldahl flask in the fume hood until the sulfur trioxide gas has completely disappeared, then remove and cool to room temperature.
• 6.6 Add 25 mL of boric acid solution and 5 drops of mixed indicator to a 300 mL Erlenmeyer flask, place it at the outlet of the condenser, with the tip of the condenser inserted directly to the bottom of the Erlenmeyer flask.
• 6.7 Take 275 mL of distilled water, first add about 175 mL to the Kjeldahl flask, shake until all salt lumps have dissolved (if insoluble salt lumps remain, warm slightly), then add the remaining water and cool to room temperature.
• 6.8 In a fume hood, add 25 mL sodium sulfide to the Kjeldahl flask, shake well to precipitate mercury. The generated mercury sulfide must not be poured into the sewer after the experiment; it should be disposed of separately in accordance with environmental protection law requirements. When performing Kjeldahl nitrogen determination on a large scale, a mercury trap should be used.
• 6.9 Place the Kjeldahl flask in ice water and cool to about 4.5 ℃, tilt the flask without shaking, slowly add 75 mL sodium hydroxide solution (1000 g/L) to form two layers.
  • 6.9.1 Remove the Kjeldahl flask from the ice bath so that the two layers do not mix, then carefully place it on the Kjeldahl digestion apparatus.
  • 6.9.2 Immediately add a bundle of twenty capillary tubes with sealed tops, each about 20 cm long, quickly connect the Kjeldahl flask and the Kjeldahl digestion-distillation apparatus, and shake the flask to mix the contents thoroughly.
  • Note: Do not shake the acid and alkali layers in the flask before the Kjeldahl digestion-distillation apparatus is properly connected; ammonia released by premature mixing that is not absorbed by boric acid will make the determination result low.
• 6.10 Quickly heat the Kjeldahl flask to prevent the digestion liquid from cooling and causing boric acid to be sucked back into the condenser; reduce the heating rate just before the solution boils, so that it boils steadily for 5 min, to avoid the distillation rate being too fast and the ammonia concentration being too high, which would prevent boric acid from absorbing it and make the determination result low; then boil rapidly until the liquid volume in the Erlenmeyer flask is about 130 mL.
• 6.11 Lower the receiving Erlenmeyer flask, expose the lower tip of the condenser, wash the condenser tip with water, then distill for about 1 min more, stop heating, and allow to cool naturally until no more droplets flow out from the end of the condenser; at this time the total liquid volume in the Erlenmeyer flask should be about 150 mL. Before distillation, marks may be made on the Erlenmeyer flask at the 130 mL and 150 mL volume levels.
• 6.12 Titrate the solution in the receiving Erlenmeyer flask with 0.01 N sulfuric acid standard solution until the gray color of the solution just disappears and a pale purple color appears. If the titrant consumption exceeds 50 mL, the sulfuric acid standard solution used for continued titration after exceeding 50 mL should be replaced with 0.1 N solution. The burette volume should be read to 0.05 mL.
• 6.13 For each batch of samples tested, a blank determination should be carried out simultaneously; in the blank determination, take 1.0 g sucrose instead of the sample, and use 20 mL sulfuric acid during digestion.

9. Qualitative and Quantitative and Calculation Formula

The nitrogen content in the sample X [% (m/m)] is calculated according to formula (3):

X = [(V₁ − V₂) × N₂ + V₃ × N₃] × 0.01401 × 100 / m

Where (the original source-text extraction symbol is incomplete, organized according to context, requires confirmation against the source standard (source-text extraction)):

• V₁: volume of 0.01 N sulfuric acid standard solution consumed by the sample, mL;
• V₂: volume of 0.01 N sulfuric acid standard solution consumed in the blank determination, mL;
• V₃: volume of 0.1 N sulfuric acid standard solution consumed by the sample, mL;
• N₂: equivalent concentration of 0.01 N sulfuric acid standard solution;
• N₃: equivalent concentration of 0.1 N sulfuric acid standard solution;
• 0.01401: grams per milliequivalent of nitrogen (the original source-text extraction is written as “0.0110”, requires confirmation against the source standard (source-text extraction));
• 100: percentage conversion factor;
• m: sample mass, g.

10. Precision

Use the following provisions to judge the reliability of test results (95% confidence level).

• 8.1 Lubricating oil
  • 8.1.1 Repeatability: the difference between two results obtained by the same operator using the same instrument for repeated determination shall not exceed 0.01% (m/m).
  • 8.1.2 Reproducibility: the difference between results obtained by two different laboratories shall not exceed 0.02% (m/m).
• 8.2 Fuel oil
  • 8.2.1 Repeatability: the difference between two results obtained by the same operator using the same apparatus for repeated determination shall not exceed 0.066√M₁ (the repeatability formula is garbled in the source transcription; the displayed interpretation requires verification before use), where M₁ is the average of the repeated determination results.
  • 8.2.2 Reproducibility: the difference between results obtained by two different laboratories shall not exceed 0.190√M₂ (the original source-text extraction is written as “0.190vM2”, requires confirmation against the source standard (source-text extraction)), where M₂ is the average of the results obtained by two different laboratories.

11. Report

Take the arithmetic mean of two repeated determination results as the determination result. For lubricating oil, take to two significant figures; for fuel oil, if less than 1% (m/m), take to two significant figures, and if equal to or greater than 1%, take to three significant figures.

12. Reference Documents

• GB 1756 “Petroleum and Liquid Petroleum Products Sampling Method (Manual Method)”
• ASTM D3228—83 “Determination of Total Nitrogen in Lubricating Oils and Fuel Oils by Improved Kjeldahl Method” (referenced adoption)

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