SH/T 0559-1993 Determination of alkyl nitrate content in diesel fuel (spectrophotometric method)

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Card type: Test method

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

• Method number: SH/T 0559-93 (confirmed in 2004)
• Chinese full name: Determination of alkyl nitrate content in diesel fuel (spectrophotometric method)
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Reference adoption: ASTM D4046-91 "Determination of alkyl nitrate content in diesel fuel (spectrophotometric method)"
• Approval/implementation: approved by China Petrochemical Corporation 1993-06-11, implemented on 1994-05-01

2. Scope of application and non-applicability

• Applicable to diesel fuel with alkyl nitrate content of 0.03%～0.30% (V/V).
• If the standard solution used contains the same alkyl nitrate as the sample being analyzed, this standard can determine the content of any alkyl nitrate in diesel fuel.
• Interference: other nitrate esters, nitrate radicals and nitrogen oxides interfere with the determination.

3. Method principle

The alkyl nitrate in the sample is hydrolyzed in sulfuric acid solution to generate nitric acid. The nitration reaction of m-dimethylphenol proceeds simultaneously with the generation of nitric acid. The generated nitrophenol is extracted from the reaction mixture with isooctane and reacted with sodium hydroxide to obtain a yellow sodium phenolate salt. The absorbance is measured with a spectrophotometer at wavelength 452nm±5nm. The alkyl nitrate content is calculated from the slope of the working curve [%(V/V)].

4. Reagents and materials (purity / preparation)

• 5.1 Acetic acid: analytical grade.
• 5.2 Isopropanol: analytical grade.
• 5.3 2,2,4- Trimethylpentane (isooctane): analytical grade.
• 5.4 2,4- Dimethylphenol (m-dimethylphenol): analytical grade. Note: toxic and corrosive, avoid contact with skin.
• 5.5 Sodium hydroxide: analytical grade.
• 5.6 Sulfuric acid: guaranteed reagent grade.
• 5.7 Water: meets the specifications for grade two water in GB/T 6682.
• 5.8 Alkyl nitrate: purity greater than 98%(m/m). Note: should be the same alkyl nitrate contained in the sample being analyzed.
• 6.1 Preparation of m-dimethylphenol solution: measure 4mL m-dimethylphenol, add to a 100mL volumetric flask, and dilute to the mark with acetic acid.
• 6.2 Preparation of sodium hydroxide solution: weigh 50g sodium hydroxide and dissolve in 1000mL water.
• 6.3 Preparation of sulfuric acid solution: while stirring with a glass rod, slowly add 500mL sulfuric acid to 270mL cold water.
• 6.4 Preparation of alkyl nitrate standard solution: pipette 3.0mL alkyl nitrate, add to a 100mL volumetric flask, and dilute to the mark with diesel fuel.

5. Instruments and equipment

• 4.1.1 Spectrophotometer: model 721 or similar spectrophotometer.
• 4.1.2 Cuvette: light path 1cm.
• 4.1.3 Conradson shaker: shakes 275 times per minute.
• 4.1.4 Separatory funnel: with polytetrafluoroethylene stopcock, capacity 125mL.
• 4.1.5 Volumetric flasks: 10, 100mL.
• 4.1.6 Pipettes: 1, 5, 10mL.
• 4.1.7 Microburette: 10mL.
• 4.2.1 Material: diesel fuel, additive-free.

6. Recommended operating conditions

• Measurement wavelength: 452nm±5nm.
• Cuvette light path: 1cm.
• Shaking conditions: Conradson shaker, 275 shakes per minute, shake for 30min.
• Reference: water as reference.

7. Sampling and sample preparation

• 8.1 Pipette 1.0mL sample, add to a 10mL volumetric flask, and dilute to the mark with isopropanol.
• 8.2 Pipette 1.0mL of the sample solution prepared in clause 8.1, add to a 125mL separatory funnel; pipette 1.0mL isopropanol blank solution and add to another separatory funnel.
• Note: if the blank solution is prepared with the same diesel fuel as the sample, the accuracy is higher.

8. Analysis procedure

• 7.1 Using a microburette, measure 1.0, 3.0, 5.0, 8.0 and 10.0mL alkyl nitrate standard solution (6.4) respectively into five 100mL volumetric flasks, and dilute to the mark with diesel fuel.
• 7.2 From each standard sample described in clause 7.1, pipette 1.0mL and add respectively to five 10mL volumetric flasks; then pipette 1.0mL blank diesel fuel and add to another 10mL volumetric flask; dilute each flask to the mark with isopropanol.
• 7.3 From each standard solution described in clause 7.2, pipette 1.0mL and add respectively to five 125mL separatory funnels; then pipette 1.0mL blank solution and add to another separatory funnel. The concentration of alkyl nitrate in the prepared solutions is 0.03%～0.30%(V/V).
• 7.4 Respectively pipette 1.0mL m-dimethylphenol solution (6.1) and add to each of the above separatory funnels. Shake the separatory funnels to mix evenly.
• 7.5 To each of the above separatory funnels, respectively add 40mL sulfuric acid solution (6.3). m-Dimethylphenol must be added first, then the sulfuric acid solution; otherwise the determination result will be low or negative.
• 7.6 Secure the stopper of the separatory funnel with a rubber ring and shake the separatory funnel to mix evenly. Then place the separatory funnel on a Conradson shaker and shake for 30min. Note: whether the sample fully contacts the sulfuric acid solution determines the degree of hydrolysis reaction; therefore, the shaking time and speed for samples and standard samples must be the same.
• 7.7 Add 25mL isooctane to each separatory funnel.
• 7.8 Shake the separatory funnel by hand for 1min; after standing for layer separation, discard the acid layer. Respectively add 25mL water, then shake for 1min to wash off residual acid; after layer separation, discard the aqueous layer.
• 7.9 Pipette 10.0mL sodium hydroxide solution (6.2) and add to each separatory funnel, shake the separatory funnel for 1min, then let stand for at least 10min; after the two phases separate clearly, release a few drops of the test solution from the lower part of the separatory funnel to rinse the drain tube, then place the test solution into a 1cm cuvette, use water as reference, and measure the absorbance at wavelength 452nm±5nm. Note: if the test solution does not appear yellow after adding alkali, check the pH value; if the solution is not alkaline, additional 10mL sodium hydroxide solution (6.2) may be added, and a correction calculation shall be made for the increased volume of alkali solution.
• 8.3 Operate according to the test steps in clauses 7.4～7.9. Note: if the absorbance is too high, it may be diluted with blank solution before measurement, and the calculation result shall be corrected accordingly.

9. Qualitative and quantitative determination and calculation formulas

• 7.10 The slope of the working curve K is calculated from the absorbance of each standard sample after subtracting the blank, according to formula (1):
  • K = C₀ / A₀ ………………(1)
  • Where: C₀—the sum of alkyl nitrate contents of each standard sample, %(V/V); A₀—the sum of absorbances of each standard sample after subtracting the blank.
• 8.4 The content of alkyl nitrate in the sample X[%(V/V)] is calculated from the absorbance of the sample after subtracting the blank, according to the slope of the working curve, by formula (2):
  • X = K·A ………………(2)
  • Where: A— the absorbance of the sample after subtracting the blank; K— the slope of the working curve.

10. Precision

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

• 9.1 Repeatability: the difference between two results obtained by the same operator in repeated determinations shall not exceed 0.017%(V/V).
• 9.2 Reproducibility: the difference between two results respectively submitted by different laboratories shall not exceed 0.036%(V/V).

11. Report

Take the arithmetic mean of two repeated determination results as the determination result. The number is taken to the third decimal place.

12. Referenced documents

• GB/T 6682 Water specifications and test methods for analytical laboratory use

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