SH/T 0409-1992 Determination of aromatic hydrocarbon content in liquid paraffin (ultraviolet spectrophotometry)

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Card type: Test method

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

• Standard number: SH/T 0409-92
• Chinese full name: Determination of aromatic hydrocarbon content in liquid paraffin (ultraviolet spectrophotometry)
• English name: not provided in the available source
• Replacement relationship: replaces ZB-F42 013-89 (the source writes "replaces ZB- F42 013- 89", requires confirmation against the source standard (source-text extraction))
• Reference adoption: current analytical method UOP 495-75 of the American UOP company (Molex ultraviolet spectrophotometric determination of aromatic hydrocarbon content in normal paraffin products)
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20

2. Scope of application and non-applicability

• Applicable to the determination of aromatic hydrocarbon content in liquid paraffin.
• Determination range of aromatic hydrocarbon content: 3 ppm(m/m) to 5%(m/m).
• The determination result is the average value of alkylbenzenes and naphthalenes.
• Not applicable: not provided in the available source.

3. Method principle

The sample is placed in a 1 cm quartz cuvette, and the maximum absorbance near 285 nm and 270 nm is measured. (In the source, "285mn" and "270mn" are source-text extraction noise and should be nm)

4. Reagents and materials (purity / preparation)

• 4.1 isooctane: with water as reference, the absorbance at 360–230 nm should be 0.000 (the source's "360-230 two places" requires confirmation against the source standard (source-text extraction)).
• 4.2 water: deionized water or distilled water.

5. Instruments and equipment

• 5.1 ultraviolet-visible spectrophotometer: double-beam scanning recording, wavelength range 195–800 nm, wavelength accuracy 0.5 nm, wavelength reproducibility 0.02 nm (the source's "0.02nmo" requires confirmation against the source standard (source-text extraction)).
• 5.2 cuvettes: paired quartz cuvettes, path length 1 cm.
• 5.3 volumetric flasks: 25 mL.

6. Recommended operating conditions

• Cuvette path length: 1 cm quartz cuvette.
• Reference liquid: isooctane.
• Measurement wavelengths: near 270 nm and near 285 nm.
• Absorbance control range: when diluting the sample, the maximum absorbance at the specified wavelength is preferably between 0.4–1.5.
• Other conditions: not provided in the available source.

7. Sampling and sample preparation

• Whether the sample needs dilution depends on the aromatic hydrocarbon content in the sample.
• If the aromatic hydrocarbon content is above 0.1%(m/m), the sample needs appropriate dilution.
• The sample amount is preferably such that the maximum absorbance at the specified wavelength is between 0.4–1.5.
• Weigh about 0.3–0.5 g of sample (accurate to 0.2 mg) into a 25 mL volumetric flask, and dilute to the mark with isooctane.

8. Analytical procedure

• 6.2 Calibration test: instead of directly calibrating the spectrophotometer with known naphthalene compounds, take the average absorptivity of C10–C13 naphthalenes at the wavelength 285 nm as 33.7 L/g·cm, and near 270 nm as 30.0 L/g·cm (see Appendix A). Similarly, take the average absorptivity of common C10–C16 alkylbenzenes near 270 nm as 3.01 L/g·cm (see Appendix B). (In the source, "C,. one C13 prohibited type", "30.OUg " cm", "C,. one C1 6", "3.011/g-cm" are source-text extraction noise, requires confirmation against the source standard (source-text extraction))
• 6.3 Determination, divided into two cases:
  • 6.3.1 When the alkylbenzene content in the sample is lower than 650 ppm(m/m) and the naphthalene content is lower than 50 ppm(m/m), the naphthalene content can be ignored during determination, and its interference with the determination of alkylbenzenes is not considered. The sample does not need dilution. With isooctane as the reference liquid, directly read the maximum absorbance of the sample near 270 nm, and calculate the aromatic hydrocarbon content according to formula (1).
  • 6.3.2 When the aromatic hydrocarbon content in the sample is above 0.1%(m/m), measure the absorbance of naphthalenes at 285 nm, calculate the naphthalene content, measure the alkylbenzene content near 270 nm, and correct the interference of naphthalenes with the determination of alkylbenzenes according to formula (3). The sample needs to be diluted with isooctane, and isooctane is used as the reference liquid for determination.
• In both cases above, a quartz cuvette of 1 cm thickness is used to hold the reference liquid and the sample.

9. Qualitative and quantitative determination and calculation formulas

• 7.1 Undiluted sample: the alkylbenzene content W1 (ppm) is calculated according to formula (1):
  • W1 = A270 × 10^6 / (a′ · b · c)
  • Where: A270—270 is the maximum absorbance on the baseline near the wavelength nm; 10^6— is the constant directly converted to ppm(m/m); a′—average absorptivity (or calibration coefficient) of alkylbenzenes, 3.01 L/g·cm; b— is the cuvette path length, cm; c— is the approximate density of the undiluted sample (mass concentration of the sample in the cuvette), g/L.
  • Calculation example: W1 = 0.20 × 10^6 / (3.01 × 1 × 750) = 17.7 ≈ 18 (Figure 1 ultraviolet spectrum of 18 ppm(m/m) alkylbenzenes in molecular sieve liquid paraffin)
• 7.2 Diluted sample: use a 1 cm cuvette and record the spectrum of the diluted sample. When the aromatic hydrocarbon content is relatively high, naphthalenes interfere with the determination of alkylbenzenes, and this interference needs to be calibrated.
  • Note 1): the mass concentration of the sample in the cuvette is the approximate density of the undiluted sample (g/L).
  • 7.2.1 The naphthalene content W2 (ppm) is first directly calculated according to formula (2):
    • W2 = A285 × 10^6 / (a″ · b · c)
    • Where: A285—285 is the absorbance on the baseline at wavelength nm; 10^6— is the constant directly converted to ppm(m/m); a″—average absorptivity (or calibration coefficient) of naphthalenes, 33.7 L/g·cm; b— is the cuvette path length, cm; c— is the mass concentration of the sample in the cuvette, g/L.
  • 7.2.2 Then calibrate the interference of naphthalene near 270 nm, and the alkylbenzene content W2(%) is calculated according to formula (3):
    • W2 = (A270 − 0.89 A285) × 100 / (a′ · b · c)
    • Where: A270—270 is the maximum absorbance on the baseline near the wavelength nm; 0.89— is a constant, the ratio of absorptivities is a285/a270 = 30.0/33.7 = 0.89 (the source's "[unreadable characters]=[unreadable characters]。.89" requires confirmation against the source standard (source-text extraction)); 100— is the constant for conversion to percentage content; a′—average absorptivity (or calibration coefficient) of alkylbenzenes, 3.01 L/g·cm; b— is the cuvette path length, cm; c— is the mass concentration of the sample in the cuvette, g/L.
  • 7.2.3 Total aromatic hydrocarbons are the sum of the naphthalene content and the alkylbenzene content.
  • Calculation example: diluted sample, see Figure 2.
    • W2 = 0.35 × 10^6 / (33.7 × 1 × 13.5) = 770 (the source's "[unreadable character]5x1[unreadable characters]=770" requires confirmation against the source standard (source-text extraction))
    • W2 = (0.71 − 0.89 × 0.35) × 100 / (3.01 × 1 × 13) = 0.981
    • Total aromatic hydrocarbons = W1 + W2 = 0.077 + 0.981 = 1% (the source's "[unreadable character]，[unreadable character]W,2" and "1[unreadable character]" require confirmation against the source standard (source-text extraction))
• 7.3 Report the aromatic hydrocarbon content in the sample as a mass ratio (%, ppm), and the result should be taken to two decimal places.

10. Precision

For the same operator, in the same laboratory, using the same instrument, according to the procedure specified in the method, within a relatively short time interval, the allowable difference between determination results for the same sample: when the aromatic hydrocarbon content of the sample is 1%(m/m), the allowable difference is not greater than 0.32%.

11. Report

Report the aromatic hydrocarbon content in the sample as a mass ratio (%, ppm), and the result should be taken to two decimal places.

12. Referenced documents

• Appendix A: data published by API research project 44 (supplementary document)—table of absorptivities of naphthalenes (near 285 nm and 270 nm)
• Appendix B: data published by API research project 44 (supplementary document)—table of absorptivities of alkylbenzenes, etc. (near 270 nm)
• Reference: American UOP company UOP 495-75 (Molex ultraviolet spectrophotometric determination of aromatic hydrocarbon content in normal paraffin 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