GB/T 38234-2019 Determination of fatty acid methyl esters in aviation turbine fuel by gas chromatography-mass spectrometry

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Card type: Test method

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

• Standard number: GB/T 38234—2019
• Chinese full title: Determination of fatty acid methyl esters in aviation turbine fuel by gas chromatography-mass spectrometry
• English title: Determination of fatty acid methyl esters (FAME) in aviation turbine fuel - Gas chromatography-mass spectrometry
• Replacement relationship: not provided in the available source (the foreword does not mention a replaced standard)
• Publication/implementation: published on 2019-10-18, implemented on 2020-05-01
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280)
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, Sinopec Shanghai Research Institute of Petrochemical Technology, PetroChina Petrochemical Research Institute
• Main drafters: Wang Wei, Li Chengwei, Shi Dejun

2. Scope of application and non-applicability

• This standard specifies a test method for the qualitative and quantitative determination of fatty acid methyl esters in aviation turbine fuel by gas chromatography-mass spectrometry.
• It is applicable to the determination of various fatty acid methyl esters derived from biodiesel in aviation turbine fuel (see Table 1), with a total fatty acid methyl ester content determination range of 4.5 mg/kg~140 mg/kg.
• Note 1: Aviation turbine fuel (as well as aviation turbine fuel contaminated by diesel or biodiesel) may contain some relatively high molecular weight hydrocarbon components, and these components will mask the peaks of trace fatty acid methyl esters. Low-carbon-number fatty acid methyl esters, such as fatty acid methyl esters obtained from coconut oil, will be interfered with by some heavy components in aviation turbine fuel and cannot be quantitatively determined at low content.
• Note 2: This standard mainly examines several fatty acid methyl esters listed in Table 1; the mass fraction of these fatty acid methyl esters in common biodiesel is generally above 95%. In addition, methyl heptadecanoate may exist in animal fats such as dairy products and egg yolk lecithin, so it is also included.

Table 1 Fatty acid methyl esters examined in this standard

3. Method principle

After mixing the aviation turbine fuel sample with the internal standard, introduce it into a gas chromatograph-mass spectrometer (GC-MS), then separate it through a polar capillary column to separate the small amount of polar fatty acid methyl ester compounds from the nonpolar hydrocarbon compounds that are the main components of aviation turbine fuel. In order to remove background interference generated by heavy components in the sample, selected ion monitoring (SIM) is required. In selected ion monitoring, the ions detected are all characteristic ions of fatty acid methyl ester components and are not characteristic ions of hydrocarbon compound background peaks. Prepare a series of fatty acid methyl ester standard solutions of different concentrations, with n-dodecane as the solvent for the standard solutions, and use GC-MS to obtain the working curve of the standard solutions. Combining the working curve of the standard solutions and the test results of the actual sample, the content of the fatty acid methyl esters to be determined in the aviation turbine fuel is finally obtained.

4. Reagents and materials (purity / preparation)

• 5.1 The various fatty acid methyl esters described in Table 1, with a purity of 99% or above, used to prepare calibration solutions of fatty acid methyl esters. Note: These fatty acid methyl esters may be reagents packaged separately or mixed standard reagents of multiple fatty acid methyl esters.
• 5.2 Helium: the carrier gas for the chromatographic column is helium, with a purity greater than 99.99%.
• 5.3 n-Dodecane: purity greater than 99%.
• 5.4 Dichloromethane: analytical reagent. Warning—toxic; harmful if ingested or absorbed through the skin.
• 5.5 Deuterated methyl heptadecanoate-d3 (original text is “deuterated methyl heptadecanoate-dss”, requires confirmation against the source standard (source-text extraction)): more than 98% (atomic ratio) of the hydrogen atoms are deuterated.

Preparation:

• 7.1.1 1000 mg/L Preparation of deuterated methyl heptadecanoate-d3 internal standard solution
  • 7.1.1.1 Place the 100 mL volumetric flask on an analytical balance, use a dropper to add 100 mg±0.5 mg of deuterated methyl heptadecanoate-d3 (5.5), then add 100 mL n-dodecane (5.3) to obtain a 1000 mg/L solution.
  • 7.1.1.2 When not in use, transfer the 1000 mg/L internal standard solution to a sealed glass container and store it in a refrigerator under the condition of 4°C±2°C; the internal standard solution must be used within three months. Before use, check whether there is phase separation or discoloration, shake vigorously and then let stand to remove air bubbles. If precipitation, phase separation, or discoloration is found in the internal standard solution, discard the standard sample.
• 7.1.2 1000 mg/kg Preparation of fatty acid methyl ester stock solution
  • 7.1.2.1 Place the 250 mL Erlenmeyer flask (4.4) on an analytical balance, pipette a certain amount of fatty acid methyl esters (5.1), and dissolve in n-dodecane to obtain a fatty acid methyl ester stock solution, in which the concentration of each individual fatty acid methyl ester is 1000 mg/kg.
  • 7.1.2.2 When not in use, transfer the 1000 mg/kg fatty acid methyl ester stock solution to a sealed glass container and store it in a refrigerator under the condition of 4°C±2°C; the fatty acid methyl ester stock solution must be used within three months. Before use, check whether there is phase separation or discoloration, shake vigorously and then let stand to remove air bubbles. If precipitation, phase separation, or discoloration is found in the fatty acid methyl ester stock solution, discard the standard sample.
• 7.1.3 1000 mg/kg Calculation of fatty acid methyl ester content in the fatty acid methyl ester stock solution: calculate according to formula (1): Cr,1000 = mY/mT ×100 (original text source-text extraction is “Cr:1000 = "Y X100 / 12T”, requires confirmation against the source standard (source-text extraction)). Where: Cr,1000——1000 mg/kg content of each fatty acid methyl ester (Y) in the fatty acid methyl ester stock solution, in mg/kg; mY—— mass of each fatty acid methyl ester (Y), in g; mT—— total mass of the fatty acid methyl ester stock solution, in g.
• 7.1.4 100 mg/kg Preparation of fatty acid methyl ester stock solution: take 1000 μL (original text is “1000 ML”, requires confirmation against the source standard (source-text extraction)) of the fatty acid methyl ester stock solution (7.1.2) into a 10 mL volumetric flask, dilute to 10 mL with n-dodecane to obtain a 100 mg/kg fatty acid methyl ester stock solution. Calculate according to formula (2): Cr,100 = Cx,1000/10 (original text source-text extraction is “Cr., 100 = Cx.1 00g / 10”, requires confirmation against the source standard (source-text extraction)). Where: Cx,100——100 mg/kg content of each fatty acid methyl ester (Y) in the fatty acid methyl ester stock solution, in mg/kg.
• 7.1.5 Preparation of fatty acid methyl ester standard solutions: use n-dodecane as solvent to prepare standard solutions containing six fatty acid methyl esters C16:0, C17:0, C18:0, C18:1, C18:2, C18:3, in which the content of each fatty acid methyl ester is 0 mg/kg, 2 mg/kg, 4 mg/kg, 6 mg/kg, 8 mg/kg, 10 mg/kg, 20 mg/kg, 40 mg/kg, 60 mg/kg, 80 mg/kg, 100 mg/kg. The preparation process can be carried out directly in chromatographic vials; dilute 100 mg/kg fatty acid methyl ester stock solution (7.1.4) by volume to obtain the solutions shown in Table 2. After preparation is complete, use a glass syringe to add 10 μL internal standard solution (7.1.1) to each chromatographic vial, seal the chromatographic vials and shake well.

Table 2 Preparation of standard solutions from 100 mg/kg fatty acid methyl ester stock solution by volume dilution to 0 mg/kg~100 mg/kg

Note: In Table 2, the order of the two columns “100 mg/kg fatty acid methyl ester mother liquor volume” and “n-dodecane volume” is suspected to be misplaced in source-text extraction; the above table has been organized according to the logic of the total 1000 μL, requires confirmation against the source standard (source-text extraction).

• Calculate the exact content of each fatty acid methyl ester (Y) in the final standard solution according to formula (3): Cr = Cx,100 × VY,100 / 1000 (the source text source-text extraction is “Cr = Cx.100 XV: .100 / 1000”, requires confirmation against the source standard (source-text extraction)). Where: Cr—— the content of each fatty acid methyl ester (Y) in the standard solution, in mg/kg; VY,100—— the volume value of the added 100 mg/kg fatty acid methyl ester mother liquor (see Table 2), in μL. Note: The calculation process for preparing the standard sample is suitable for using a spreadsheet; it is recommended to generate a suitable spreadsheet.

5. Apparatus and Equipment

• 4.1 Gas chromatograph-mass spectrometer: equipped with an electron impact (EI) ionization source, preferably capable of simultaneous selected ion monitoring (SIM) and full scan (SCAN) data acquisition modes, equipped with a split/splitless or cold on-column injector. The total ion current chromatogram (TIC) obtained by full scan can be used for qualitative identification of each fatty acid methyl ester sample.
  • Note 1: It is more appropriate to use an injection liner packed with glass wool.
  • Note 2: If the instrument cannot simultaneously run selected ion monitoring and full scan modes, but qualitative identification of each fatty acid methyl ester monomer is required through spectral library matching, it is recommended to test each sample twice, once using selected ion monitoring mode and once using full scan mode. The instrument sensitivity must ensure that each fatty acid methyl ester monomer can be detected in n-dodecane solution at 0.5 mg/kg, with a signal-to-noise ratio of at least 10:1. The instrument also needs to be equipped with data acquisition and analysis software and be able to accurately measure the integrated area of each peak.
  • Note 3: Selected ion monitoring mode is used for quantitative testing, while the total ion current chromatogram data obtained in full scan mode is used for qualitative identification of each fatty acid methyl ester monomer.
• 4.2 Chromatographic column: This standard recommends the following two strongly polar chromatographic columns, with a stationary phase of bonded/cross-linked polyethylene glycol (PEG-20M). Column 1: 30 m (column length) × 0.25 mm (inner diameter) × 0.25 μm (film thickness); Column 2: 50 m~60 m (column length) × 0.2 mm (inner diameter) × 0.4 μm (film thickness). Note: HP INNOWAX type chromatographic columns can meet the usage requirements of this standard.
• 4.3 Analytical balance: readability 0.0001 g.
• 4.4 Glass stoppered conical flask: capacity 250 mL.
• 4.5 Volumetric flask: 10 mL, 100 mL.
• 4.6 Dropper.
• 4.7 Pipette: adjustable scale range 10 μL–100 μL and 100 μL–1000 μL (the source text is “10wL–100 pL and 100 ML–1 000 in L”, requires confirmation against the source standard (source-text extraction)).
• 4.8 Chromatographic vial: 1.5 mL~2 mL, crimp cap or screw cap.
• 4.9 Pipette: 1 mL.
• 4.10 Glass syringe: 10 μL (the source text is “10wL”, requires confirmation against the source standard (source-text extraction)).

6. Recommended Operating Conditions

• 7.2.1 Gas chromatograph-mass spectrometer settings: the carrier gas helium flow rate through the column is 0.6 mL/min.
  • Column 1: Column oven temperature program: initial temperature 120°C, hold for 3 min; ramp at a rate of 3°C/min to 240°C, and hold for 5 min; total run time 48 min.
  • Column 2: Column oven temperature program: initial temperature 150°C, hold for 5 min; ramp at a rate of 12°C/min to 200°C, and hold for 17 min; ramp at a rate of 3°C/min to 252°C, and hold for 6.5 min; total run time 50 min.
  • Sample injection volume is 1 μL, using a splitless injector, inlet temperature 260°C.
  • Ion source: electron impact ionization source (EI), ionization energy 70 eV, ion source temperature 220°C, quadrupole temperature 150°C, GC-MS interface temperature 260°C.
  • Using simultaneous full scan and selected ion monitoring acquisition mode, full scan mass scan range 50 u~350 u.
  • Autosampler syringe cleaning solvent: dichloromethane (5.4).
  • Solvent delay time 20 min.
  • In the test sequence, high-content standard solution samples and blank n-dodecane solvent are alternated to eliminate carryover from high-content samples.
  • Note 1: In most cases, the above settings can give satisfactory results. If necessary, the column oven temperature program or column model can be optimized so that various fatty acid methyl esters and deuterated internal standards can achieve complete separation.
  • Note 2: In some fatty acid methyl ester raw materials, C18:1 has two peaks, and they are separated from each other by less than 0.5 min. These two peaks are assigned as cis and trans isomers, and the peak areas of these two peaks are summed together and regarded as one sample peak.
• 7.2.2 Selected ion monitoring settings: When using column 1 and the corresponding column oven temperature program, the retention times and characteristic ions of the fatty acid methyl ester standard samples are shown in Table 3; a typical selected ion monitoring (SIM) chromatogram is shown in Appendix A.

Table 3 Retention Times and Characteristic Ions of Each Fatty Acid Methyl Ester Standard and Internal Standard

7. Sampling and Test Sample Preparation

• 6.1 Unless otherwise specified, sampling shall be carried out in accordance with GB/T 4756 or GB/T 27867.
• 6.2 Use dark glass bottles or metal containers lined with epoxy resin and equipped with inert sealing caps to store aviation turbine fuel. Used containers may be used, but it should be ensured that these containers have only been in contact with aviation turbine fuel having a fatty acid methyl ester content of less than 5 mg/kg. Rinse the sampling container and sealing cap at least 3 times with the sample to be sampled. Each rinse shall use an amount of sample equivalent to 10%~20% of the container volume. Each rinse shall close the container, shake for at least 5 min, and then pour out the sample.
  • Note 1: Chapter 6 of ASTM D4306 provides a check procedure for determining whether a test sample container is suitable; this procedure can be used to detect the effect of trace impurities on the container.
  • Note 2: It is more convenient to use new sampling containers, because it is extremely difficult to remove trace fatty acid methyl esters remaining from previous samples.
• 9.1 Use a pipette to add 1 mL of the aviation turbine fuel test sample to be tested into a chromatographic vial, use a glass syringe to add 10 μL of internal standard solution, cap and seal, and shake well.

8. Analytical Procedure

• 9.2 Place the standard solution, the test sample with internal standard added, and the n-dodecane blank sample into the autosampler, and perform injection testing according to the settings in 7.2.1 and 7.2.2. After testing the standard solution, the test sample can be tested directly. If there are more than 5 test samples in each batch, then after every 5 samples tested, a 2 mg/kg standard solution must be run as a quality control sample to check the stability of the detector.
• 9.3 After analyzing 25 samples, the entire standard solution series needs to be rerun; if the deviation between the ratio of the peak area of C18:0 (8.2.1) to the peak area of the internal standard in the quality control sample and the initial standard solution test result exceeds 5%, then the data of the previously tested 5 samples must be discarded, and the entire standard solution series must be retested.
• 8.1 Qualitative identification of each fatty acid methyl ester in the standard solution: Use the fatty acid methyl ester standard sample (7.1.2) of 1000 mg/kg to obtain a total ion current chromatogram in full scan mode; based on the retention time and mass spectrum of each peak, qualitative identification of various fatty acid methyl esters in the standard solution can be carried out.
• 8.2 Quantitative calibration curve
  • 8.2.1 Analyze each fatty acid methyl ester in the standard solution under the selected ion monitoring conditions determined according to 7.2.2, obtain the peak areas of these fatty acid methyl esters and the internal standard, and calculate the ratio of each fatty acid methyl ester component to the internal standard peak area according to formula (4) (A): A = AFAME/AIS. Where: AFAME—— peak area of the measured fatty acid methyl ester component; AIS—— peak area of the measured internal standard. Note: Many instruments' built-in software includes functions for internal standard calibration and content calculation. Using this function can automatically calculate the calibration curve and results, replacing formula (4).
  • 8.2.2 This standard uses two calibration curve segments, where the calibration curve range for each fatty acid methyl ester is 0 mg/kg–10 mg/kg (standard sample contents 0 mg/kg, 2 mg/kg, 4 mg/kg, 6 mg/kg, 8 mg/kg, 10 mg/kg) and 0 mg/kg–100 mg/kg (standard sample contents 0 mg/kg, 20 mg/kg, 40 mg/kg, 60 mg/kg, 80 mg/kg, 100 mg/kg). Draw calibration curves for the two ranges respectively; the ordinate of the calibration curve is the peak area ratio (A) [see formula (4)], and the abscissa is the content of each fatty acid methyl ester component. The calibration curve is required to pass through zero and ensure linearity for each component. The correlation coefficient of each fatty acid methyl ester calibration curve should be greater than 0.985. If this requirement is not met, the entire standard solution series needs to be retested. When testing samples, also test the fatty acid methyl ester standard solution simultaneously to correct instrument drift. Note: In practice, the correlation coefficient can reach above 0.995.
  • 8.2.3 The quantitative calibration curve for each fatty acid methyl ester component should satisfy formula (5): A = k × CFAME. Where: k—— slope of the quantitative calibration curve; CFAME—— content of each fatty acid methyl ester component in the standard solution, unit mg/kg.

9. Qualitative and Quantitative and Calculation Formulas

• 10.1 Calculation of each fatty acid methyl ester content: After qualitatively identifying each fatty acid methyl ester peak, determine the peak area of each compound and the internal standard peak area from the selected ion chromatogram. Calculate the content of each fatty acid methyl ester component at different contents according to formula (6) and the quantitative calibration curve of the standard solution (CFAME,S): CFAME,S = A × ρsol/ρs (original source-text extraction is "CFAME,S= A / X Pa0 / Ps", requires confirmation against the source standard (source-text extraction)). Where: CFAME,S—— content of each fatty acid methyl ester component in the sample, unit mg/kg; ρsol—— density of n-dodecane solvent (measured using method SH/T 0604), unit g/cm³; ρs—— density of aviation turbine fuel sample (measured using method SH/T 0604), unit g/cm³. Note: When calculating the final result, the density difference between aviation turbine fuel and n-dodecane needs to be considered. The gas chromatograph injector injects a fixed volume of sample each time, and the density of the aviation turbine fuel sample differs somewhat from the standard solution solvent n-dodecane; therefore, when calculating the sample content based on the quantitative calibration curve of the standard solution, the density difference between the two needs to be considered.
• 10.2 Calculation of total fatty acid methyl ester content: The total fatty acid methyl ester content is the sum of the contents of the 6 fatty acid methyl esters in Table 1. Calculate the total fatty acid methyl ester content in the sample according to formula (7) (CFAME,T): CFAME,T = ΣCFAME,S. Where: CFAME,T—— total fatty acid methyl ester content in the sample, unit mg/kg.
• 10.3 Expression of results: The test result is the total fatty acid methyl ester content in the sample (10.2), accurate to 0.1 mg/kg. If the source of the fatty acid methyl esters needs to be determined, the content of each fatty acid methyl ester component (10.1) may also be given.

10. Precision

• 11.1 Overview: The precision data given in 11.2 and 11.3 were obtained according to IP 367. All data come from an interlaboratory collaborative test conducted in 2009, with the number of test instruments and test personnel each being 12, and the number of aviation turbine fuel samples being 16. Judge the reliability of test results according to the following provisions (95% confidence level).
  • Note 1: In the interlaboratory collaborative test, two samples containing no fatty acid methyl esters were also included in the test samples. No bias occurred in the oxidative desulfurization-treated and hydrotreated fuel samples tested in the collaborative test.
  • Note 2: During data analysis, the data for 3 samples with nominal values of 0 mg/kg and 1 mg/kg and other outlier data were discarded, and finally more than 20% of the data were discarded.
  • Note 3: In the interlaboratory collaborative test, 3 oxidative desulfurization-treated samples were also included, with nominal values of 0 mg/kg, 30 mg/kg, and 100 mg/kg, respectively. No bias occurred in the testing of oxidative desulfurization-treated and hydrotreated fuel samples.
• 11.2 Repeatability (r): The difference between two repeat test results obtained by the same operator using the same instrument on the same sample shall not exceed the value of formula (8). r = 0.163 2 (X1 + 3). Where: X1—— average of two repeat determination results, unit mg/kg.
• 11.3 Reproducibility (R): The difference between two single, independent test results obtained by different operators in different laboratories using different instruments on the same sample shall not exceed the value of formula (9). R = 0.257 9 (X2 + 3). Where: X2—— average of two single, independent determination results, unit mg/kg.
• 11.4 Typical precision values are detailed in Table 4.

Table 4 Typical values of repeatability (r) and reproducibility (R)

Note: In Table 4, the content column source-text extraction clearly gives only 5.0, 10.0, 140.0; the content values for the remaining rows are not provided in the available source. The above table is annotated by row count recursion, requires confirmation against the source standard (source-text extraction).

11. Report

The test report shall include at least the following information:

• a) State this standard;
• b) Type and number of the sample to be tested;
• c) Test results (see 10.3);
• d) Any deviation from the test procedure;
• e) Test date.

12. Referenced Documents

• GB/T 4756 Manual sampling of petroleum liquids
• GB/T 27867 Automatic sampling of petroleum liquids in pipelines
• SH/T 0604 Determination of density of crude oil and petroleum products (U-shaped vibrating tube method)
• References:
  • [1] ASTM D4306, Standard practice for aviation fuel sample containers for tests affected by trace contamination.
  • [2] IP 367, Petroleum products—Determination and application of precision data in relation to methods of test.

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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