NB/SH/T 0903-2015 Determination of methanol content in fatty acid methyl esters — Gas chromatography

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Card type: Test method

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

• Standard number: NB/SH/T 0903—2015 (the cover source-text extraction shows "NB/SHVT 0903—2015", suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction))
• Chinese title: Determination of methanol content in fatty acid methyl esters — Gas chromatography
• English title: Standard test method for determination of methanol content in fatty acid methyl esters by gas chromatography
• Replacement relationship: This standard is first published; it uses the redrafting method to modify and adopt EN 14110:2003 "Fat and oil derivatives — Fatty acid methyl esters — Determination of methanol content"
• Main differences from EN 14110:2003: modified the standard title; added two chromatographic columns and chromatographic conditions, condition B and condition C; in clause 3.3, added acetone as internal standard when using condition C; moved the original annex B chromatogram to Figure 1 in the main text, and added Figure 2 and Figure 3; deleted annex B
• Publication/implementation: published on 2015-10-27, implemented on 2016-03-01
• Issuing authority: National Energy Administration
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafters: Li Changxiu, Kong Cuiping

2. Scope of application and non-applicability

• Applicable to: determination of methanol content in fatty acid methyl esters used as biodiesel and domestic heating oil
• Determination range: methanol mass fraction 0.01%~0.5%
• Not applicable to: determination of methanol content in fatty acid methyl ester mixtures containing other low-boiling components

3. Method principle

• 2.1 The test sample is heated in a sealed bottle to 80 ℃, causing the methanol molecules contained therein to escape from the liquid phase into the gas phase. When the methanol component reaches dynamic equilibrium between the gas and liquid phases, a certain amount of the gas phase portion is introduced into the gas chromatography system, and the methanol content is detected using a flame ionization detector. In general, methanol is the only peak in the chromatogram.
• 2.2 The methanol content may be quantified by the external standard method (method B), or by adding an internal standard before heating the test sample and quantifying according to the calculated internal standard correction factor (method A). When manual injection is used, the internal standard method (method A) shall be used.

4. Reagents and materials (purity / preparation)

• 3.1 Unless otherwise specified, all reagents shall be of analytical grade.
• 3.2 Methanol: purity higher than 99.5%.
• 3.3 2- propanol: purity higher than 99.5%, used in quantification method A as internal standard.
• 3.4 Acetone: purity higher than 99.5%, used in quantification method A as internal standard.
• 3.5 Fatty acid methyl ester reference sample: methanol mass fraction lower than 0.001%. Note: It may be purchased directly, or prepared as follows: take fatty acid methyl esters with a total fatty acid methyl ester mass fraction not lower than 96.5%, wash three to five times with distilled water in a separatory funnel, then heat to 90 ℃ under reduced pressure and stirring to evaporate off water.
• 3.6 Carrier gas: nitrogen, helium or hydrogen, purity higher than 99%.
• Preparation of calibration solutions (Chapter 6):
  • 6.1 Calibration solution A (methanol mass fraction 0.5%): add 25 mL fatty acid methyl ester reference sample to a 25 mL volumetric flask, add about 112 mg (142 μL) methanol to the liquid phase with a microsyringe, accurately weigh the masses of fatty acid methyl ester and methanol respectively, to the nearest 0.1 mg, and shake vigorously to ensure uniform mixing.
  • 6.2 Calibration solution B (methanol mass fraction 0.1%): accurately pipette 5 mL calibration solution A into a 25 mL volumetric flask, carefully add fatty acid methyl ester reference sample to the mark.
  • 6.3 Calibration solution C (methanol mass fraction 0.01%): accurately pipette 1 mL calibration solution B into a 10 mL volumetric flask, carefully add fatty acid methyl ester reference sample to the mark.

5. Instruments and equipment

• 4.1 Headspace sample vial: capacity 20 mL.
• 4.2 Metal bottle cap with inert septum (such as polytetrafluoroethylene or fluororubber).
• 4.3 Microsyringe: 10 μL, graduation value 0.1 μL (the original text source-text extraction is "10wL, graduation value 0.1wL", requires confirmation against the source standard (source-text extraction)).
• 4.4 Gas syringe: 500 μL or 1000 μL, equipped with a locking valve (for manual injection) (the original text source-text extraction is "500wL. or 1000wL", requires confirmation against the source standard (source-text extraction)).
• 4.5 Crimping pliers and opening pliers.
• 4.6 Pipettes: 1 mL, 2 mL, 5 mL.
• 4.7 Volumetric flasks: 10 mL and 25 mL.
• 4.8 Gas chromatograph: equipped with a capillary column, split/splitless inlet (may be equipped with an automatic headspace sampling system), flame ionization detector, and chromatographic signal recording and integration system.
• 4.9 Capillary column: the column should elute a symmetrical methanol peak; the stationary phase may be methylpolysiloxane (such as DB1, SE30) or polyethylene glycol (such as DBWAX, CAR-BO..., the original text here source-text extraction is truncated, requires confirmation against the source standard (source-text extraction)). When using a methylpolysiloxane stationary phase, a film thickness of not less than 0.5 μm is recommended. For some biodiesel samples that have been stored for a long time or have complex components, a column with strong retention for oxygen-containing compounds, such as a CP-Lowox column, may be used to improve the separation of methanol from other components. Note: those equipped with the above stationary phase (the original text source-text extraction is truncated, requires confirmation against the source standard (source-text extraction)) Chromosorb 101 packed columns may also be used. Other types of chromatographic columns that can achieve the same separation effect may also be used.
• 4.10 Automatic headspace equipment: the repeatability of the automatic headspace equipment shall be not lower than 1%, depending on experimental conditions such as equilibration temperature, heating time, and headspace sampling volume. If necessary, the repeatability of the headspace system may be checked by repeatedly analyzing the same sample. Note: It is recommended to use automatic headspace equipment; in addition to its good repeatability, it also allows automatic and rapid analysis using the external standard method. Manual injection may also be used, but extra care is required when manually taking the gas phase portion from the sample vial and injecting it into the chromatography system.
• 4.11 Analytical balance: readability 0.1 mg.
• 4.12 Constant-temperature oven (the original text source-text extraction is "[garbled oven specification]-6 or 8042", suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction)).
• 4.13 not provided in the available source (the content after original number 4.13, source-text extraction, is missing, requires confirmation against the source standard (source-text extraction)).

6. Recommended operating conditions

• 5.1 Select appropriate chromatographic operating conditions according to the column characteristics and carrier gas type to ensure that the chromatographic peaks of methanol and 2- propanol (or acetone) (the original text here source-text extraction is truncated, requires confirmation against the source standard (source-text extraction)).
• 5.1.1 Condition A (the original table source-text extraction is severely incomplete, only part of the content can be identified, requires confirmation against the source standard (source-text extraction)):
  • Chromatographic column: OV-1, film thickness 3 μm
  • Inlet temperature: 150 ℃
  • Column oven temperature: 50 ℃
  • Carrier gas: hydrogen, nitrogen or helium
  • Detector: flame ionization detector (FID)
  • Detector temperature: 250 ℃
  • Gas flow rates: H2: 35; air: 400; N2: 35 (unit mL/min, the original text source-text extraction is "[unreadable gas label]:35; air:400;N:35", requires confirmation against the source standard (source-text extraction))
  • Headspace sampling conditions: sample equilibration temperature 80 ℃; sample equilibration time 30 min (the original text source-text extraction is "30", requires confirmation against the source standard (source-text extraction)); injection volume 500~1000 μL
• 5.1.2 Condition B (the original table source-text extraction is severely incomplete, requires confirmation against the source standard (source-text extraction)):
  • Column inlet pressure/k (the original text source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • Split flow/(mL/min) (the original text source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • Detector temperature/℃: 250
  • Gas flow rates: H2: 35; air: 400; N2: 35
  • Headspace sampling conditions: sample equilibration temperature 80 ℃; injection volume 500~1000 μL
• 5.1.3 Condition C:
  • Chromatographic column: CP-Lowox, column length 10 m (the original text source-text extraction is "column length 10mg", requires confirmation against the source standard (source-text extraction)), inner diameter 0.5 mm (the original text source-text extraction is "inner diameter 0.5[unreadable character] mm", requires confirmation against the source standard (source-text extraction)), film thickness 10 μm (the original text source-text extraction is "10/wm", requires confirmation against the source standard (source-text extraction))
  • Inlet temperature: 200 ℃
  • Column oven temperature: 150 ℃
  • Carrier gas: hydrogen, nitrogen or helium
  • Column inlet pressure/k (the original text source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • Split flow/(mL/min) (the original text source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
  • Detector: flame ionization detector (FID)
  • Detector temperature: 250 ℃
  • Gas flow rate: H2: 35; air: 400; N2: 35
  • Headspace sampling conditions: sample equilibration temperature 80 ℃; injection volume 500~1000 μL
• 5.2 Operation: install and operate the gas chromatograph according to the product instructions.
• Typical chromatograms: Figure 1 (conditions A), Figure 2 (conditions B), Figure 3 (conditions C), the original figure caption information source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction).

7. Sampling and test sample preparation

• No independent sampling and test sample preparation chapter is provided in the available source. The test sample preparation conditions should be completely consistent with the test conditions of the calibration solutions (see 7.1.2, 7.2.2).

8. Analytical procedure

• Two quantitative methods are optional; detailed descriptions of the internal standard method and the external standard method are given in clause 7.1 and clause 7.2, respectively.
• 7.1 Method A— internal standard method: only when the number of samples to be tested is small and there is no automatic headspace equipment, this quantitative method is preferentially selected. For manual injection, see the note after clause 4.10.
  • 7.1.1 Internal standard calibration
    • 7.1.1.1 Add 5 g±0.01 g of calibration solution A, B or C to three headspace sample vials respectively, and use a microsyringe to add 5 μL 2- propanol or acetone to the liquid phase. Immediately press the cap tightly and shake vigorously to mix evenly.
    • 7.1.1.2 At intervals of 10 min, place the internal standard solution sample vial in a constant-temperature water bath, and leave it for 45 min.
    • 7.1.1.3 In a constant-temperature oven, preheat the gas syringe (4.4) to 60 ℃. Take 500 μL or 1000 μL of the gas phase (headspace) of the above solution for chromatographic analysis.
    • 7.1.1.4 Calculate the correction factor F of each calibration solution according to formula (1); the value of F should be rounded to two decimal places.
    • 7.1.1.5 For the F values determined with three calibration solutions, the coefficient of variation should be less than 15%; if it exceeds this, the source of test error should be checked, and calibration should be restarted from Chapter 6. The average value of the correction factors of the three calibration solutions (approximately 0.7 when using 2- propanol) is used for the following calibration calculation of 7.1.2.
  • 7.1.2 Analysis and calculation by the internal standard method: the preparation of the test sample and the analysis conditions should be completely consistent with the test conditions of the calibration solutions in 7.1.1. Calculate the mass fraction of methanol in the test sample Cm according to formula (2), and round to two decimal places.
• 7.2 Method B— external standard method: when automatic headspace equipment is equipped and a large number of samples are analyzed, this method is usually preferentially selected. If there is no automatic headspace equipment and only manual injection can be used, the external standard method is not recommended.
  • 7.2.1 External standard calibration
    • 7.2.1.1 Add 2 mL calibration solution A, B or C to the headspace sample vial respectively, immediately cover the sample vial cap, and shake well. Then place the sample vial in the headspace sampler and perform sample analysis according to the product instructions.
    • 7.2.1.2 Use linear regression for calibration calculation, with methanol content as the independent variable and peak area as the dependent variable to draw the standard curve. From the obtained slope d and y-axis intercept e, the regression equation can be transformed into formula (3).
    • 7.2.1.3 If the correlation coefficient of the standard curve equation is less than 0.95, the source of test error should be checked, and calibration should be restarted from Chapter 6.
  • 7.2.2 Analysis and calculation by the external standard method: the preparation of the test sample and the test conditions should be completely consistent with the test conditions of the calibration solutions in 7.2.1. Calculate the mass fraction of methanol in the test sample Cm according to formula (3), and round to two decimal places.

9. Qualitative and quantitative determination and calculation formulas

• Formula (1) correction factor F: F = (C_i × S_m) / (C_m × S_i) Where: C_i— mass fraction of 2- propanol or acetone in the calibration solution, % (when 5 μL 2- propanol is added to 5.0 g standard solution, C_i = 0.0785%); C_m— mass fraction of methanol in the calibration solution, %; S_i—2- peak area of propanol or acetone; S_m— peak area of methanol.
• Formula (2) mass fraction of methanol in the test sample by the internal standard method Cm: Cm = (F × S_m × C_i) / S_i Where: F— correction factor obtained according to 7.1.1; S_m— peak area of methanol; C_i— mass fraction of 2- propanol or acetone in the test sample, % (when 5 μL 2- propanol is added to 5.0 g sample, C_i = 0.0785%); S_i—2- peak area of propanol or acetone.
• Formula (3) external standard method: Cm = a + b × S_m Where: Cm— mass fraction of methanol, %; a— coefficient obtained from (-e/d); b— coefficient obtained from (1/d); S_m— peak area of methanol; d— slope of the standard curve; e— y-axis intercept of the standard curve.
• Rounding of results: round to two decimal places.

10. Precision

• The precision data of Method A and Method B were both obtained from interlaboratory tests organized in 1999 (see Appendix A). The test data show that for methanol mass fractions in the range of 0.01%~0.20%, there is no significant difference between Method A and Method B (manual injection operation or automatic headspace injection operation). Judge the reliability of test results according to the following provisions (95% confidence level).
• 8.1 Repeatability r: for two results obtained by the same operator, using the same instrument, the same method, and continuous repeated determination of the same test sample, the difference should not exceed the value obtained by formula (4): r = 0.056X + 0.001 Where: X— average value of the two results of repeated determination.
• 8.2 Reproducibility R: for two single and independent results obtained by different operators, using different instruments, the same method, and separate determination of the same test sample, the difference should not exceed the value obtained by formula (5) (the original formula (5) source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction)). Where: X— average value of the results of two independent determinations.
• Appendix A (informative appendix) Interlaboratory test results: this test involves the analysis results of 5 test samples by 10 laboratories in European countries. The test samples include: sample 1— fatty acid methyl esters prepared from a mixture of rapeseed oil and sunflower oil (25:75); sample 2— fatty acid methyl esters prepared from sunflower oil; sample 3— fatty acid methyl esters prepared from rapeseed oil; sample 4— fatty acid methyl esters prepared from rapeseed oil (the original source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction)); sample 5— fatty acid methyl esters prepared from rapeseed oil (the original source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction)). The results were processed according to EN ISO 4259. The table data in Appendix A source-text extraction is severely incomplete, requires confirmation against the source standard (source-text extraction).

11. Report

The report should state:

• complete description of the test sample information;
• the sampling method used;
• the method procedure used and the number of this standard;
• operating details not listed in the standard, and other factors that may affect the analysis results;
• the determination results, if a repeatability test was performed (the original text here source-text extraction is truncated, requires confirmation against the source standard (source-text extraction)).

12. Normative references

• GB/T 1.1—2009 (this standard was drafted according to the rules given therein)
• EN 14110:2003 (modified adoption)
• EN ISO 4259, Petroleum products — Determination and application of precision data in relation to methods of test (ISO 4259:1992/Cor 1:1993) (reference document)

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