GB/T 38203-2019 Determination of fatty acid methyl ester content in aviation turbine fuel by high performance liquid chromatography with evaporative light scattering detector

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Card type: Test method

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

• Standard number: GB/T 38203—2019

• Chinese name: Determination of fatty acid methyl ester content in aviation turbine fuel by high performance liquid chromatography with evaporative light scattering detector

• English name: Determination of fatty acid methyl esters (FAME) in aviation turbine fuel—HPLC evaporative light scattering detector method

• Replacement relationship: not provided in the available source (the foreword only describes drafting rules and custodianship, and does not mention a replaced standard)

• Drafting rules: drafted in accordance with GB/T 1.1—2009

• Proposed and custodied by: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC280)

• Drafting organization: Sinopec Research Institute of Petroleum Processing

• Publication/implementation: published on 2019-10-18, implemented on 2020-05-01

• ICS: 75.160.20; Chinese standard classification number: E31

2. Scope of application and non-applicability

• Applicable: determination of fatty acid methyl ester content in aviation turbine fuel using high performance liquid chromatography with evaporative light scattering detector; applicable to samples with fatty acid methyl ester content in the range 3.0 mg/kg to 140 mg/kg.
• Not applicable/note: fatty acid methyl esters obtained from coconut oil have relatively strong volatility and are not suitable for determination using this standard (note to Chapter 1).
• Warning: personnel using this standard should have formal laboratory work experience; this standard does not point out all possible safety issues, and users are responsible for taking appropriate safety and health measures and complying with the conditions specified in relevant national laws and regulations.

3. Method principle

By using high performance liquid chromatography equipped with a normal-phase silica gel column, the fatty acid methyl esters in the aviation turbine fuel sample are separated from the hydrocarbon matrix, and different components are detected with an evaporative light scattering detector. The qualitative and quantitative analysis of the fatty acid methyl ester components is carried out by comparison with the same standard mixed standard. If the fatty acid methyl ester content in the test sample exceeds the range of the calibration curve, dilute with jet fuel containing no fatty acid methyl esters. (Chapter 3)

4. Reagents and materials (purity / preparation)

• General (5.1): unless otherwise specified, reagents of analytical grade or above should be used.
• 5.2 GLC-10 ester mixed standard: 100 mg ampoule-packed fatty acid methyl ester mixed standard, which is a mixture of five fatty acid methyl ester components: C16:0, C18:0, C18:1, C18:2, and C18:3, each accounting for 20% of the total (mass fraction), and the purity of each single component determined by gas chromatography is not less than 99%. It may be prepared by mixing individual esters of minimum purity 99% (methyl palmitate C16:0, methyl stearate C18:0, methyl oleate C18:1, methyl linoleate C18:2, methyl linolenate C18:3) at 20% each (mass fraction). If sampling from an opened container, the purity of each individual ester should be re-determined by gas chromatography.
• 5.3 2- methylpentane: grade HPLC.
• 5.4 n-dodecane: analytical grade.
• 5.5 pentane: grade HPLC.
• 5.6 ethyl acetate: grade HPLC.
• 5.7 jet fuel: obtained from petroleum fractions, meeting the requirements of Table 1 in GB 6537—2018, and containing no fatty acid methyl esters. Used to prepare calibration solutions (7.1.5), quality control samples (8.3), and as a blank sample. When determined using this standard, no peak should appear in the fatty acid methyl ester region in the high performance liquid chromatography chromatogram. Note: kerosene fractions produced by hydro-upgrading processes other than esters and fatty acids may be selected.
• 5.8 fatty acid methyl ester: purity greater than 95% or concentration determined by NB/SH/T 0831. Note: used to prepare quality control samples, and may be extracted from oilseeds other than coconut oil.
• 5.9 nitrogen: purity not less than 99.999% (volume fraction).
• Mobile phase preparation (7.2.3): accurately measure 10 mL ethyl acetate (5.6) with a pipette into a 1000 mL volumetric flask, dilute to volume with 2- methylpentane (5.3) or pentane (5.5), and mix thoroughly. Note: in addition to the above mobile phase, other reagents with performance meeting the requirements (satisfying 7.2.5) may be used as the mobile phase.
• Basic standard solution (7.1.2 to 7.1.4): quantitatively transfer all of the GLC-10 mixed standard to a 100 mL volumetric flask, rinse the ampoule with about 10 mL n-dodecane and transfer the rinse liquid, repeat the rinsing at least five times, mix, and dilute to the mark with n-dodecane. After dilution to volume, the mass concentration of the fatty acid methyl ester mixture is 1000 mg/L, and each component is 200 mg/L. Store at 4℃±2℃ when not in use temporarily or when used within three months.
• Series of calibration standard solutions (7.1.5, Table 2): use an automatic pipette to transfer the basic standard solution to a 50 mL volumetric flask, dilute to volume with jet fuel containing no fatty acid methyl esters, and prepare a series of calibration standard solutions from 0.5 mg/L to 5.0 mg/L.

Table 2 Preparation of calibration standard solutions

5. Instruments and equipment

• 4.1 High performance liquid chromatograph (HPLC): equipped with an evaporative light scattering detector, with a maximum allowable injection volume of the sample valve system of 200 μL. The chromatograph should meet the operating condition requirements. Note: it may be equipped with a column oven to control the operating temperature at 35℃.
• 4.2 Evaporative light scattering detector (ELSD): the sensitivity should be high enough to ensure that, under specific operating conditions, the peak height obtained for the ester mixed standard at a single-component mass concentration of 0.5 mg/L GLC-10 is at least three times the noise. Note: some ELSD have relatively large noise effects, and it is advisable to use a split switching valve before the detector to purge hydrocarbons and prevent them from entering the detector, switching the valve to connect to the detector about 2 min before the fatty acid methyl esters elute.
• 4.3 Chromatographic data acquisition system.
• 4.4 High performance liquid chromatography silica gel column: see Table 1.
• 4.5 Volumetric flasks: volumes of 10 mL, 50 mL, 100 mL, 1000 mL.
• 4.6 Automatic pipette: capable of transferring 100 μL to 1000 μL and 1000 μL to 5000 μL solutions.
• 4.7 Pipette: 10 mL.
• 4.8 Balance: precision of 0.0001 g.

Table 1 Recommended silica gel columns and operating conditions

6. Recommended operating conditions

• Column temperature: 35℃ (4.1 note, 7.2.1, Table A.1)
• Mobile phase flow rate: 1.0 mL/min (7.2.4, Table A.1)
• Elution mode: isocratic elution (constant-composition solvent elution method) (7.2.1)
• Injection volume: 80 μL (Table A.1)
• ELSD Evaporation temperature: 20℃ (Table A.1)
• ELSD Drift temperature: 30℃ (Table A.1)
• Nitrogen flow rate: 1.2 L/min (Table A.1)
• Detector preparation (7.2.2): turn on ELSD according to the instrument instructions, connect the nitrogen gas, and set the nitrogen flow rate (or pressure) and evaporation temperature; the mobile phase should not be pumped into the detector before the detector reaches the set operating conditions.
• System stabilization (7.2.4): after ELSD reaches the set operating conditions, set the pump flow rate to 1.0 mL/min and wait for the system to stabilize.
• Resolution check (7.2.5): inject the L5 calibration solution and check whether all fatty acid methyl ester components are separated one by one from the jet fuel peak (see Figure A.1). The peak area of C16:0 should be at least 50% of the peak area of C18:0; lower the evaporator-drift tube temperature to increase the response of C16:0 relative to C18:0, while ensuring that it is not interfered with by the later-eluting jet fuel peak. If C16:0 and C18:0 are not yet separated, adjust the chromatographic operating conditions (such as mobile phase and column length) or separately inject fatty acid methyl ester samples individually to determine the relative response factors of C16:0 and C18:0. Note: the drift tube temperature is the most important parameter and should be as low as possible to obtain the maximum response value for fatty acid methyl esters, but it must also be high enough to volatilize most components in the jet fuel sample.
• Sensitivity check (7.2.6): inject the L1 calibration solution, and the peak height of the fatty acid methyl ester components (0.5 mg/L) should be at least three times the noise level under these operating conditions.

7. Sampling and test sample preparation

• 6.1 Unless otherwise required, sampling shall be carried out in accordance with the requirements of GB/T 4756 or GB/T 27867, and the sampling amount shall be at least 60 mL.
• 6.2 Use equipment dedicated to aviation turbine fuel for sampling; sampling equipment must not be mixed with other oils or additives. Requirements to avoid sample contamination: gloves should remain clean before sampling and should not cause cross-contamination of the sample; flush the sampling line before sampling to ensure the sample will not be contaminated by previous samples.
• 6.3 Use an amber glass bottle or a lidded metal container with an epoxy resin lining. Note: ASTM D4306-12b Chapter 6 provides guidelines for judging the suitability of containers used for test samples affected by trace contamination.
• 6.4 The container used shall be confirmed to be used only for aviation turbine fuel, and its fatty acid methyl ester content shall be less than 5 mg/kg. Note: Considering that it is difficult to thoroughly remove trace fatty acid methyl esters from previously stored samples, it is advisable to use new containers.
• 6.5 Rinse the container and stopper at least three times with the sample to be tested. The amount of sample used for each rinse shall be 10%～20% of the container volume. For each rinse, tightly close the stopper, shake the container for at least 5 s, and then drain the sample completely.
• Sample dilution (9.2): If the fatty acid methyl ester components in the sample exceed the test range of the calibration curve, dilute with jet fuel (5.7) until the content of each component falls within the range of the calibration standard curve. Accurately weigh a 10 mL volumetric flask using a balance, to the nearest 0.0001 g, add a certain amount of sample and weigh again, record the sample mass to the nearest 0.0001 g, add jet fuel, mix, and make up to volume.

8. Analysis Procedure

• 9.1 If conditions permit, the sample should be injected directly onto the chromatographic column (see 9.2).
• 9.2 When outside the calibration curve range, dilute as described in Section 7.
• 9.3 Set up the sequence in the chromatography operating system, analyzing standard samples first and then test samples. The run sequence should include a standard sample every six injections to ensure the instrument is operating normally. For each batch of samples, run the QC sample (Chapter 8) and a blank sample (5.7).
• 9.4 Run the sequence (9.3), record the peak area of each fatty acid methyl ester component in the standard and test samples. Check the baseline and perform manual integration if necessary.
• 9.5 Ensure that the correct standard sample concentrations are entered into the calibration table of the chromatography data processing system, and establish a calibration curve for each component of the fatty acid methyl esters (C16:0, C18:0, C18:1, C18:2 and C18:3). See Figure A.2 for an example.
• 9.6 C16:0 and C18:0 may elute at the same time; in this case, the concentrations of C16:0 and C18:0 may be added together and a combined calibration curve established. The curve may use quadratic or cubic data fitting, forced through the origin, with a correlation coefficient not less than 0.995.
• Quality control (QC) sample preparation (Chapter 8):
  • 8.1 Using a balance, weigh 50 mg±1 mg of fatty acid methyl esters (5.8) into a 100 mL volumetric flask, add n-dodecane, and shake to mix until completely dissolved.
  • 8.2 Make up to the mark with n-dodecane, cap the volumetric flask, and shake to mix evenly.
  • 8.3 Using an automatic pipette, transfer 0.4 mL of this solution to a 50 mL volumetric flask, add jet fuel (5.7), make up to the mark, and shake to mix evenly.
  • 8.4 If not used temporarily or if used within three months, store the QC sample below 4℃±2℃.

9. Qualitative and Quantitative Analysis and Calculation Formulas

• Qualitative and quantitative analysis: The qualitative and quantitative analysis of fatty acid methyl ester components is carried out by comparison with the same standard mixed standard (Chapter 3); establish a calibration curve for each component (9.5).
• Calculation (10.1): Calculate the mass concentration of each fatty acid methyl ester component in the aviation turbine fuel to be tested and the QC sample via the standard curve, in units of mg/L. Sum the mass concentrations of each component (C16:0＋C18:0＋C18:1＋C18:2＋C18:3), and convert the result from mg/L to mg/kg according to formula (1). If the density is unknown, it must be determined; the determination method shall be selected from GB/T 1884 (use GB/T 1885 for calibration) or SH/T 0604.

Formula (1): C = x / ρ

Where:

• C—— content of fatty acid methyl esters, in milligrams per kilogram (mg/kg);

• x—— mass concentration of fatty acid methyl esters, in milligrams per liter (mg/L);

• ρ—— density of the sample, in kilograms per liter (kg/L).

• 10.2 If the sample was diluted to bring the fatty acid methyl ester component concentrations within the calibration curve range, corresponding conversion shall be performed.

• Expression of results (Chapter 11): Report the total fatty acid methyl ester content in the sample, with the result accurate to 0.1 mg/kg.

10. Precision

• 12.1 Overview: Judge the reliability of test results according to the following provisions (95% confidence level).
• 12.2 Repeatability (r): The difference between two test results obtained consecutively by the same laboratory, the same operator, using the same instrument, according to the same method, on the same test sample shall not exceed the value calculated by formula (2).

Formula (2): r = 0.1251(X₁＋4)

Where: X₁——the average of two replicate determination results, in units of mg/kg.

• 12.3 Reproducibility (R): The difference between two single, independent test results obtained by different laboratories, different operators, using different instruments, on the same test sample shall not exceed the value calculated by formula (3).

Formula (3): R = 0.2022(X₂＋4)

Where: X₂——the average of two single, independent determination results, in units of mg/kg.

Table 3 Typical values of repeatability (r) and reproducibility (R)

11. Report

The test report shall include the following information (Chapter 13):

• a) Type and identification of the tested product;
• b) Number of this standard;
• c) Determination results (Chapter 11);
• d) Any deviations from the test procedure described in this standard;
• e) Test personnel;
• f) Test date.

12. Normative References

Normative references (Chapter 2):

• GB/T 1884 Standard test method for density of crude petroleum and liquid petroleum products (hydrometer method)
• GB/T 1885 Petroleum measurement tables
• GB/T 4756 Standard practice for manual sampling of petroleum liquids
• GB 6537—2018 3 Jet fuel
• GB/T 27867 Standard practice for automatic sampling of petroleum liquids by pipeline
• NB/SH/T 0831 Determination of fatty acid methyl esters and linolenic acid methyl ester content in biodiesel—Gas chromatography
• SH/T 0604 Determination of density of crude petroleum and petroleum products (U-shaped vibrating tube method)

References:

• [1] ASTM D4306-12b Standard practice for aviation fuel sample containers for tests affected by trace contamination.

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.

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