SH/T 0181-2005 Determination of Naphthalene Hydrocarbons in Jet Fuel (Ultraviolet Spectrophotometric Method)

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Card type: Test method

1. Method number / Full title / English title / Replacement relationship

• Standard number: SH/T 0181—2005
• Chinese full title: Determination of Naphthalene Hydrocarbons in Jet Fuel (Ultraviolet Spectrophotometric Method)
• English title: Standard test method for naphthalene hydrocarbons in jet fuels by ultraviolet spectrophotometry
• Replacement relationship: replaces SH/T 0181—1992
• Adoption relationship: modified adoption of ASTM D1840-02 "Determination of Naphthalene Hydrocarbons in Aviation Turbine Fuels (Ultraviolet Spectrophotometric Method)", redrafted according to ASTM D1840-02
• Main differences from ASTM D1840-02 (listed in the original):
  • Changed "aviation turbine fuel" in the standard to "jet fuel"
  • Determined the applicable scope of test samples as jet fuel
  • Supplemented the operating essentials when measuring with a single-beam instrument
  • The silica gel used for refining spectral-grade isooctane adopts fine-pore silica gel activated at 150 ℃ for 6 h, with a particle size of 250 μm～124 μm (60 mesh～120 mesh)
• Main changes from SH/T 0181—92 (listed in the original): added restrictions on the final boiling point and naphthalene hydrocarbon content of the test sample; added explanations of relevant physical concepts involved in the measurement process; added a correction method for errors caused by optical imbalance of the absorption cell; added safety precautions during the measurement process; added a description of the sample treatment process; standardized the one-step dilution sample treatment method; revised the expression of measurement results from mass fraction to volume fraction; relaxed the range of the final absorbance measurement value from 0.3～0.7 to 0.2～0.8; changed the precision requirement for naphthalene hydrocarbon measurement results to be correlated with the naphthalene hydrocarbon content
• Publication / Implementation: published on 2005-10-10, implemented on 2006-02-01
• Issuing authority: National Development and Reform Commission of the People's Republic of China
• Secretariat: Sinopec Research Institute of Petroleum Processing
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafters: Wu Mingqing, Zhang Hong, Pan Guangcheng, Li Tao, Dong Wei, Zhang Xiaoyun
• ICS 75.160.20; E31

2. Applicable scope and non-applicability

• 1.1 This standard specifies a method for determining the content of naphthalene, acenaphthene and their alkyl derivatives (naphthalene hydrocarbons, hereinafter the same) in jet fuel by ultraviolet spectrophotometry.
• 1.2 Applicable to the determination of naphthalene hydrocarbon content not higher than 5% by volume in jet fuel with a final boiling point not higher than 315 ℃.
• 1.2 When precision is determined: the naphthalene hydrocarbon concentration range of samples used in test procedure A is 0.03%～4.25% (volume fraction); the naphthalene hydrocarbon concentration range of samples used in test procedure B is 0.08%～5.6% (volume fraction). This standard can determine the maximum content of naphthalene hydrocarbons that may be present in the sample.
• 1.3 This standard uses the International System of Units.
• 1.4 This standard involves certain hazardous materials, operations and equipment, but does not address all safety issues associated with them. Users must establish appropriate safety and protective measures and corresponding safety procedures before using this standard. For specific hazard warnings, see clauses 8.1 and 8.2.
• Non-applicability: no explicit "non-applicability" clause is provided in the available source (only limited by final boiling point, content upper limit and interference clauses).

3. Method principle

• Chapter 4 Method summary: Using the jet fuel to be tested as solute and isooctane as solvent, prepare an isooctane solution of jet fuel at a certain concentration, measure its absorbance at 285 nm, and calculate the total content of naphthalene hydrocarbons in the sample.
• Chapter 9 Calibration and standardization: There is no need to prepare an instrument working curve with a standard compound of naphthalene hydrocarbons; directly use the arithmetic mean of the absorption coefficients of mixed naphthalene hydrocarbons from C10 to C15 at 285 nm, 33.7 L/g·cm, as the absorption coefficient of the naphthalene hydrocarbons to be determined, and calculate the analysis results. The source of this average absorption coefficient is shown in Chapter 14 Table 3.
• Theoretical basis: Ultraviolet quantitative analysis is based on Beer's absorption law (3.2.3 Note), A = abc (Equation 4).

4. Reagents and materials (purity / preparation)

• 8.1 Isooctane, spectral grade.
  • Warning: Isooctane is flammable and toxic if inhaled!
  • Note: Spectral-grade isooctane can be purchased commercially or prepared from industrial-grade isooctane. Preparation method: Pack activated silica gel with a particle size of 250 μm～124 μm (60 mesh～120 mesh) and a pore size of 30 μm～15 μm (pre-activated at 150 ℃ for 6 h, cooled in a desiccator before use) into a glass column with a diameter of 40 mm～75 mm, with an effective packing height of 600 mm～1000 mm; take 4 L～5 L of industrial-grade isooctane and refine it through the silica gel column; for the refined isooctane, within the wavelength range of 240 nm～300 nm, using a 1 cm absorption cell, with distilled water as reference, measure its transmittance with an ultraviolet spectrophotometer, and collect the portion with transmittance greater than 90% as spectral-grade isooctane. Carefully seal the prepared spectral-grade isooctane in a closed glass container. When preparing spectral-grade isooctane each time, it is best to use new activated silica gel; used silica gel can also be regenerated and reused. The steps are: first wash the silica gel column with 500 mL acetone, blow dry and spread flat, dry at 400 ℃ until the color turns white; the activated silica gel must be sealed in a closed container.
• 8.2 Cleaning agent for quartz cells, volumetric flasks, and pipettes: acetone or anhydrous ethanol, requiring volatile residue less than 10 mg/kg.
  • Warning: Acetone and ethanol are flammable and toxic if inhaled!
• Other reagents: not provided in the available source (such as naphthalene standard, etc.; Chapter 9 of the original clearly states that there is no need to prepare a working curve with a standard compound).

5. Instruments and equipment

• 7.1 Spectrophotometer: When measuring the absorbance of samples in the range of 240 nm～300 nm, the slit width is required to reach 1 mm or wider (requires confirmation against the source standard (source-text extraction), the original text is "Tmm or wider"); using the mercury emission line at 253.65 nm, or the absorption spectrum of holmium oxide glass at 287.5 nm, or the absorption spectrum of holmium oxide solution at 587.5 nm (requires confirmation against the source standard (source-text extraction), the original text is "587.Frm") as the standard spectral line, calibrate the wavelength of the instrument; the wavelength accuracy of the instrument should be within ±0.1 nm; when the absorbance measured in the wavelength range 240 nm～300 nm is about 0.4, the error of the measurement result should be within ±0.5%; when the absorbance is in the range of 0.2～0.8, compared with an authoritative inspection institution, the measurement error of the absorbance of the same horizontal product (requires confirmation against the source standard (source-text extraction), suspected to be "sample") should be within ±0.5%.
  • Note: Many instrument manufacturers provide secondary standards for checking the wavelength and absorbance measurement accuracy of spectrophotometers; search among relevant national standard materials (requires confirmation against the source standard (source-text extraction), the word order is suspected to be incorrect). As long as these standards can be periodically verified in the manner recommended by the instrument supplier, they can be used to check the spectrophotometer.
• 7.2 In addition to calibration according to clause 7.1 when the instrument is used, it should also be calibrated regularly during use to ensure its performance meets the requirements of clause 7.1.
  • Note: The inspection method for spectrophotometers recommended by this standard can refer to ASTM E275. Other substitutes for the standard materials in clause 7.1 are: potassium dichromate perchloric acid solution for checking optical density accuracy (the NIST SRM 935 series introduced in ASTM E275) and a high-purity naphthalene (>99%) isooctane solution of 20 mg/L for checking wavelength accuracy. The latter has a secondary strong absorption peak at 285.7 nm, but do not use the naphthalene isooctane solution for checking optical density.
• 7.3 Quartz absorption cell: optical path 1.00 cm±0.005 cm.
• 7.4 Pipettes: 1.00 mL, 5.00 mL, 10.00 mL.
• 7.5 Lens paper.
• 7.6 Analytical balance: sensitivity 0.1 mg, when the load is 100 g, the weighing error is not greater than ±0.0002 g.
• Others: volumetric flasks (25 mL, 50 mL, 100 mL, see 10.2, 11.2); glass column (see 8.1 Note).

6. Recommended operating conditions

• Measurement wavelength: 285 nm (Chapter 4, 10.3, 12.1, 14.1)
• Reference: spectral-grade isooctane (10.3); for single-beam instruments, measure the spectral background with spectral-grade isooctane (10.3)
• Absorption cell optical path: 1.00 cm±0.005 cm (7.3)
• Absorbance reading range: 0.2～0.8 (10.3 Note, 11.2.1, Table 2)
• Dilution scheme: test procedure A (a series of dilutions, three-stage dilution) or test procedure B (100 mL one-step dilution), the user can choose (Chapter 10 Note)
• Absorption coefficient value: 33.7 L/g·cm (arithmetic mean of the absorption coefficients of mixed naphthalene hydrocarbons from C10～C15 at 285 nm) (Chapter 9, 12.1)
• Operation reference: ASTM E169 (10.1, 11.1)

7. Sampling and sample preparation

• 10.2 Prepare a three-stage dilution solution according to the following steps:
  • 10.2.1 First-stage dilution: if the sample is more volatile than isooctane, first add 10～15 mL spectroscopic-grade isooctane to a clean 25 mL volumetric flask, then weigh about 1 g of test portion (accurate to 0.0001 g) into the volumetric flask, then add spectroscopic-grade isooctane to dilute to the mark, and shake well; if the volatility of the sample is lower than that of isooctane, directly weigh about 1 g of sample into a 25 mL volumetric flask, then add spectroscopic-grade isooctane to dilute to the mark, and mix uniformly.
  • 10.2.2 Second-stage dilution: use a pipette to transfer 5.00 mL of the first-stage dilution, add it to a clean 50 mL volumetric flask, dilute to the mark with spectroscopic-grade isooctane, and shake well.
  • 10.2.3 Third-stage dilution: take 5.00 mL of the second-stage dilution, continue to treat it according to the method of 10.2.2 to obtain the third-stage dilution.
• 11.2 Test procedure B Sample preparation: weigh an appropriate amount of sample, accurate to 0.0001 g, and add it to a 100 mL volumetric flask. Dilute to the mark with spectroscopic-grade isooctane, stopper, and shake well.
  • 11.2.1 Referring to Table 2, according to the average absorptivity of naphthalene hydrocarbons 33.7, estimate the mass of sample required when the absorbance falls between 0.2～0.8. For jet fuel samples with a naphthalene hydrocarbon volume content of 0.8%～3.0%, weighing 60 mg is more suitable.
• Table 2 Estimated values of sample mass and volume required for a single dilution so that the absorbance when determining naphthalene hydrocarbons is 0.2～0.8 (assuming the sample density is 0.8 g/mL):

• Table 2 Note: Commonly used micropipettes measure an appropriate volume. If the density of the jet fuel is unknown when preparing the sample, it can be roughly regarded as 0.8 g/mL.

8. Analysis steps

• 10.1 (procedure A)/11.1 (procedure B): for the recommended operating method, refer to ASTM E169, and carefully consult the methods for the operation and cleaning of absorption cells and other glassware, instrument adjustment, and absorbance measurement.
• 10.2 Prepare a three-stage dilution solution (see Section 7).
• 10.3 Absorbance measurement: for a double-beam instrument, add spectroscopic-grade isooctane and the third-stage dilution respectively to the reference cell and sample cell of the spectrophotometer, immediately cover to prevent volatilization of the sample, check the absorption window to ensure the cleanliness of its optical surface, and then measure the absorbance of the test portion at 285 nm relative to spectroscopic-grade isooctane; for a single-beam instrument, first add spectroscopic-grade isooctane to the measurement cell, measure the spectral background, after measurement dry the measurement cell, then add the above third-stage dilution solution to the same measurement cell, and measure its absorbance at 285 nm (usually the isooctane background has already been automatically subtracted).
  • Note: To obtain the best reproducibility, the reading of the absorbance of the test portion should be between 0.2～0.8. For this purpose, when preparing the third-stage dilution, another scheme may be used instead of 10.2.3, for example, take 10 mL of the second-stage dilution and dilute to 25 mL with isooctane.
• 10.4 Absorption cell correction: for a double-beam instrument, fill the sample cell and reference cell respectively with spectroscopic-grade isooctane, measure the absorbance of the sample cell, and use this value as the correction value of the absorption cell; for a single-beam instrument, since the same absorption cell is used for sample and reference, no correction is needed.
• 11.2 Test procedure B Sample preparation (see Section 7).
• 11.3 Absorbance measurement: perform the operation as described in 10.3.
• 11.4 Correction of the absorption cell: perform the operation as described in 10.4.
• Safety note: for special hazard warnings, see clauses 8.1 and 8.2 (1.4).

9. Qualitative and quantitative determination and calculation formulas

• 12.1 The mass content of naphthalene hydrocarbons in the test portion X [% (mass fraction)] is calculated according to formula (5):
  • X = (AK / 33.7W) × 100
  • Where:
    • A—— Absorbance of the test portion after correction (absorbance reading minus absorption cell correction value);
    • K—— Cumulative volume of the diluted solution, L;
      • If serial dilution is carried out according to test procedure A, then K equals the initial volume (0.025 L) multiplied by the dilution factor. Therefore, first-stage dilution K=0.025, second-stage dilution K=0.25, third-stage dilution K=2.5. For the recommended three-stage dilution factor, K=0.625. (requires confirmation against the source standard (source-text extraction): the original text "For the recommended three-stage dilution factor, K=0.625" and the preceding statement "third-stage dilution K=2.5" are doubtful; transcribed as in the original text)
      • If the dilution is directly carried out as 100 mL according to test procedure B in Chapter 11, then K equals 0.10;
    • W—— Mass of the weighed test portion, g;
    • 33.7——C10 Average absorptivity of naphthalene hydrocarbons from C15, L/g·cm.
• 12.2 The volume content of naphthalene hydrocarbons in the test portion X2 [% (volume fraction)] is calculated according to formula (6):
  • X2 = X1 × (D/G)
  • Where:
    • X1—— Mass fraction of naphthalene hydrocarbons in the test portion, %;
    • D—— Relative density of the test portion (15 ℃/15 ℃);
    • G—— Relative density of naphthalene hydrocarbons (15 ℃/15 ℃), which is 1.00.
• 14.1 The absorptivity of various naphthalene hydrocarbons at 285 nm comes from the ultraviolet spectral collection published by the American Petroleum Institute API (see Table 3).
  • Note: 33.7 is the arithmetic mean of the absorptivities of all naphthalene hydrocarbons in Table 3; from Table 3, the reliability of this value as a determination of naphthalene hydrocarbon content can be evaluated.
• Table 3 Ultraviolet absorptivity of naphthalene hydrocarbons published in Research Project API 44 (source-text extraction has much noise, values require confirmation against the source standard (source-text extraction)):

10. Precision

• 15.1 Precision: judge the reliability of the results according to the following criteria (95% confidence level); the precision of procedure A is based on interlaboratory determinations of test portions with a naphthalene hydrocarbon volume content of 0.03%～4.25% (volume fraction); the precision of procedure B is based on interlaboratory determinations of test portions with a naphthalene hydrocarbon volume content of 0.08%～5.6% (volume fraction).
• 15.1.1 Repeatability: the difference between two results obtained by the same operator, in the same laboratory using the same instrument, according to the steps specified in the method, from repeated determinations on the same test portion shall not be greater than the value calculated according to formula (7) or formula (8).
  • Procedure A repeatability = 0.0222 × (1.00 + X) …(7)
  • Procedure B repeatability = 0.056 X^0.5 …(8)
  • Where: X—— arithmetic mean of the two repeated determination results, % (volume fraction).
• 15.1.2 Reproducibility: the difference between the results of two independent determinations on the same sample by different operators, in different laboratories, according to the steps specified in the method, shall not be greater than the value calculated according to formula (9) or formula (10).
  • Procedure A repeatability = 0.0299 × (1.00 + X) … (9) (requires confirmation against the source standard (source-text extraction): the source text labels the equation number as "Equation (9) or Equation (10)", but the number of Equation (9) does not clearly appear in the source text)
  • Procedure B repeatability = 0.094 X^0.6 … (10)
  • Where: X—— arithmetic mean of two independent determination results, % (volume fraction).
  • Note: If the instruments used do not meet the requirements of clause 7.1, it will be difficult for the precision of the test results to meet the requirements.
• 15.2 Bias: Because the composition of naphthalene hydrocarbons in samples from different sources differs, their absorption coefficients differ; therefore, the bias of this method cannot be determined.

11. Report

• 13 Report: Report the result of the volume content of naphthalene hydrocarbons in the test sample, accurate to 0.01% (volume fraction).

12. Normative references

• ASTM E 131 Terms related to molecular spectroscopy
• ASTM E 169 General technical guidelines for quantitative analysis by ultraviolet-visible spectroscopy
• ASTM E 275 Guidelines for the introduction to ultraviolet, visible, and near-infrared spectrophotometers and measurement operations
• Chapter 2 is normative references (dated / undated reference rules according to the source text).

13. Source and verification

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14. Quick Q&A reference