SH/T 0224-1992 Determination of nitrogen content in petroleum additives (Kjeldahl method)

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Card type: Test method

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

• Standard number: SH/T 0224-92 (confirmed in 2004)
• Chinese title: Determination of nitrogen content in petroleum additives (Kjeldahl method)
• English title: not provided in the available source
• Replacement relationship: replaces ZB E60 002-86
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20

2. Scope of application and non-applicability

• Applicable to petroleum additives.
• The metal elements calcium, barium, zinc, and magnesium, and the non-metal elements sulfur, phosphorus, oxygen, chlorine, etc., do not interfere with the determination.
• The determination range is 0.01%～2%(m/m).
• Non-applicable scope: not provided in the available source.

3. Method principle

The sample is digested in sulfuric acid with mercury as a catalyst. After all nitrogen in the sample has been converted to ammonium sulfate, an excess of sodium hydroxide solution is added for distillation, and the ammonia generated by the reaction is absorbed in boric acid. The ammonia absorbed in boric acid is titrated with a standard hydrochloric acid titrant solution, and the nitrogen content in the sample is calculated from the volume of standard hydrochloric acid titrant solution consumed in the titration.

4. Reagents and materials (purity / preparation)

Unless otherwise specified with special requirements, the reagents used in this standard are all analytical grade reagents, and the water is distilled water.

• 4.1 Sulfuric acid.
• 4.2 Potassium sulfate.
• 4.3 Mercury.
• 4.4 Sodium hydroxide: prepare as a 350 g/L solution. It must be placed in a glass bottle whose inner wall is coated with paraffin wax.
• 4.5 Zinc granules.
• 4.6 Sucrose: guaranteed reagent grade.
• 4.7 Other reagents: sodium sulfide, sulfosalicylic acid, boric acid, hydrochloric acid, methyl red, bromocresol green, anhydrous sodium carbonate, etc.
• 5.1 Sulfuric acid digestion mixture: 400 mL sulfuric acid plus 10 g sulfosalicylic acid.
• 5.2 Sodium sulfide solution: 40 g sodium sulfide dissolved in 500 mL water.
• 5.3 Boric acid solution: 50 g boric acid added to 1 L water, heated and boiled, then after cooling take the supernatant liquid.
• 5.4 Mixed indicator solution: 3 parts 1 g/L bromocresol green ethanol indicator solution plus 1 parts 2 g/L methyl red ethanol indicator solution, mixed uniformly.
• 5.5 Preparation and standardization of standard hydrochloric acid titrant solution
  • 5.5.1 c(HCl)=0.1 mol/L standard hydrochloric acid titrant solution: take 9 mL hydrochloric acid and dilute with water to 1 L.
  • 5.5.2 c(HCl)=0.02 mol/L standard hydrochloric acid titrant solution: take 2 mL hydrochloric acid and dilute with water to 1 L.
  • 5.5.3 Use anhydrous sodium carbonate as the primary standard reagent to standardize the concentration of the above standard hydrochloric acid titrant solution, and use the mixed indicator solution to determine the endpoint of the standardization.

5. Apparatus and equipment

• 3.1 Kjeldahl distillation flask: 1000 mL.
• 3.2 Kjeldahl digestion and distillation apparatus.
• 3.3 Glass beads: diameter about 5 mm.

6. Recommended operating conditions

• 6.1 Weigh a certain amount of sample into a Kjeldahl flask according to Table 1.

Table 1

Note: Table 1 source-text extraction has severe noise, and the row correspondence requires confirmation against the source standard (source-text extraction).

• 6.2 Slowly add the sulfuric acid digestion mixture required by Table 2 into the Kjeldahl flask while rotating it. If it is found that sample is adhering to the neck of the flask, allow the sulfuric acid digestion mixture to flow through this area as much as possible, then shake the Kjeldahl flask thoroughly so that the sample and the sulfuric acid digestion mixture are mixed uniformly.

Table 2

• 6.3 Turn on ventilation, place the Kjeldahl flask on the digestion rack of the electric furnace plate, first heat at low temperature for digestion, and after a large amount of white fumes emerges, cool slightly, then add 20 g potassium sulfate, about 1.4 g mercury, and 2～3 small glass beads.
• 6.4 Adjust the voltage of the electric furnace, slightly raise the temperature of the digestion liquid, and shake the Kjeldahl flask thoroughly once about every 20 min so that the sample is carbonized uniformly. This carbonization process takes about 1 h.
• 6.5 After carbonization is complete, gradually raise the electric furnace temperature, and within about 10 min bring the contents of the Kjeldahl flask to boiling, then control the boiling rate so that the sulfuric acid vapor condenses exactly at one third of the flask neck. After the sulfuric acid digestion mixture changes from turbid to colorless or transparent, continue digestion for 1 h. The entire process takes about 3 h.
• 6.6 Stop heating, but continue ventilation until sulfur trioxide gas has completely disappeared, then stop ventilation, and allow the contents of the Kjeldahl flask to cool naturally to room temperature.
• 6.7 Add about 100 mL water to the Kjeldahl flask, and shake the Kjeldahl flask so that all salt lumps in the flask dissolve. If there are insoluble salt lumps, warm slightly to dissolve them completely. Then add about 200 mL water.
• 6.8 Take another Kjeldahl flask, add about 300 mL water, place it in the lower part of the distillation apparatus, and connect the other parts of the distillation apparatus properly. Heat the distilled water in the Kjeldahl flask to boiling for 30 min to completely remove alkaline liquid in the apparatus.
• 6.9 Add 25 mL boric acid solution and 5 drops of mixed indicator solution to a 300 mL Erlenmeyer flask, and make sure the outlet at the lower part of the condenser is exactly fully immersed below the liquid surface.
• 6.10 Add 2～3 zinc granules and 25 mL sodium sulfide solution to the cooled and diluted Kjeldahl flask, shake the Kjeldahl flask to mix uniformly, then tilt the Kjeldahl flask and slowly add 150 mL 350 g/L sodium hydroxide solution so that an alkaline lower layer is formed.
• 6.11 Connect the above Kjeldahl flask to the rinsed distillation apparatus, and shake the Kjeldahl flask so that the alkaline lower layer and the upper layer are fully mixed. Then begin distillation, collect the distillate to about 110 mL, lower the Erlenmeyer flask so that the lower part of the condenser leaves the liquid surface, rinse the lower part of the condenser with water, and distill again for 1～2 min.
• 6.12 Adjust with water until the total volume of liquid in the Erlenmeyer flask is about 150 mL, and titrate with standard hydrochloric acid titrant solution until the solution appears light purple.
• 6.13 Carry out a blank test in the same way but using 1 g sucrose instead of the sample.

7. Sampling and sample preparation

• 6.1 Weigh a certain amount of sample into a Kjeldahl flask according to Table 1.
• The sample may be weighed directly into the bottom of the Kjeldahl flask by the difference method, or weighed using a glass plate or small porcelain crucible and then placed into the bottom of the Kjeldahl flask. However, regardless of which weighing method is used, care must be taken not to contaminate the neck of the Kjeldahl flask when placing the sample.

8. Analysis procedure

See Section 6 Recommended operating conditions (6.1～6.13).

9. Qualitative and quantitative determination and calculation formula

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

X = [(V₁ − V₀) × c(HCl) × 0.01401] / m × 100

Where:

• V₁ —— volume of standard hydrochloric acid titrant solution consumed by the sample, mL;
• V₀ —— volume of standard hydrochloric acid titrant solution consumed by the blank, mL;
• c(HCl) —— actual concentration of the standard hydrochloric acid titrant solution, mol/L;
• m —— sample weight, g;
• 0.01401 —— mass of nitrogen in grams equivalent to 1.00 mL standard hydrochloric acid titrant solution [c(HCl)=1.000 mol/L].

10. Precision

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

• 8.1 Repeatability: the difference between two results obtained by the same operator in repeated determinations shall not exceed the value listed in Table 3.
• 8.2 Reproducibility: the difference between test results obtained by two different laboratories shall not exceed the value listed in Table 3.

Table 3 Precision %(m/m)

Note: Table 3 some values source-text extraction have relatively severe noise, and the row intervals require confirmation against the source standard (source-text extraction).

11. Report

Take the arithmetic mean of two results from repeated determinations as the determination result. If it is less than 1%(m/m), take two significant figures; if it is equal to or greater than 1%(m/m), take three significant figures.

12. 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