GB/T 40394-2021Determination of trace trimethylamine in methanol for industrial use—Gas chromatography-mass spectrometry (English PDF)

1 Scope

This document specifies a method for the determination of trace trimethylamine in methanol for industrial use by gas chromatography-mass spectrometry.

This document applies to the determination of trimethylamine in methanol for industrial use, where the lower limit of determination is 14 µg/L.

2 Normative references

The following documents are normatively referenced in this document and are indispensable for its application. For dated references, only the version corresponding to that date is applicable to this document; for undated references, the latest version (including all amendments) is applicable to this document.

GB/T 3723, Sampling of chemical products for industrial use - Safety in sampling

GB/T 6680, General rules for sampling liquid chemical products

GB/T 6682, Water for analytical laboratory use - Specification and test methods

GB/T 8170, Rules of rounding off for numerical values & expression and judgment of limiting values

3 Terms and definitions

No terms and definitions need to be defined in this document.

4 Method summary

By adding hydrochloric acid to the methanol sample, convert trimethylamine, which is volatile at room temperature, into trimethylamine hydrochloride; before sample injection, add sodium hydroxide to convert it into trimethylamine. Adopt headspace injection and use gas chromatography-mass spectrometry for determination. Use the trimethylamine retention time (RT) and mass-to-charge ratios (m/z), which are 42, 58, and 59, respectively, to double-qualify the qualitative ion; use the quantitative ion working curve method with a mass-to-charge ratio (m/z) of 58 for quantification.

5 Reagents and materials

Unless otherwise stated, use only guaranteed reagents in the analysis.

5.1 Water: in accordance with the stipulation for Grade-II water in GB/T 6682.

5.2 Methanol: chromatographic pure.

5.3 Helium: volume fraction not less than 99.999%, used as carrier gas.

5.4 Nitrogen: volume fraction not less than 99.999%, used as purge gas.

5.5 Trimethylamine standard solution: 0.1 mg/mL, methanol as solvent, certified reference material.

5.6 Sulfuric acid solution: 1.0 mol/L.

5.7 Hydrochloric acid solution: 0.1 mol/L.

5.8 Trimethylamine-free methanol reagent: Take 2 L of methanol (see 5.2); add 15 mL of sulfuric acid solution (see 5.6); distill; discard 100 mL of distillate before and after; take the middle distillate as a trimethylamine-free methanol reagent.

5.9 Trimethylamine-free methanol-hydrochloric acid solution: 0.05 mol/L. Mix the hydrochloric acid solution (see 5.7) with the trimethylamine-free methanol reagent (see 5.8) in a 1+1 volume ratio.

5.10 Saturated sodium hydroxide solution.

5.11 Trimethylamine standard stock solution: 4 000 µg/L. Pipette 4.00 mL of trimethylamine standard solution (see 5.5); use trimethylamine-free methanol-hydrochloric acid solution (see 5.9) to dilute it to 100 mL. It should be stored at 0 °C ~ 4 °C in a sealed place away from light, and the validity period is 1 week.

5.12 Trimethylamine standard working solution: Respectively pipette 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL, 5.00 mL to 100 mL of trimethylamine standard stock solution (see 5.11) to volumetric flasks; use 0.05 mol/L trimethylamine-free methanol-hydrochloric acid solution (see 5.9) to dilute to constant volume, to obtain trimethylamine standard working solutions with concentrations of 20 µg/L, 40 µg/L, 80 µg/L, 120 µg/L, 160 µg/L, and 200 µg/L, respectively.

6 Instruments and equipment

6.1 Gas chromatography-mass spectrometer: a gas chromatography-mass spectrometer (GC-MS) provided with temperature-programmed function, equipped with a split/splitless injection port, an electron bombardment ionization source (EI source), and a quadrupole mass detector; a data processing workstation.

6.2 Sampling device: headspace sampling device.

6.3 Chromatographic column: a quartz capillary column with basic deactivated polyethylene glycol as the matrix, 30 m in length, 0.25 mm in inner diameter, 0.25 µm in film thickness; or other equivalent chromatographic columns.

6.4 Headspace bottle: 20 mL, equipped with polytetrafluoroethylene silicone rubber gasket and sealing cap.

6.5 Sampling bottle: 1 000 mL, ground-glass stoppered flask.

6.6 Volumetric flask: 100 mL, brown glass bottle.

6.7 Pipettes: 0.5 mL, 1 mL, 2 mL, 5 mL.

7 Sample

8 Analysis steps