GB/T 40394-2021 PDF in English
GB/T 40394-2021 (GB/T40394-2021, GBT 40394-2021, GBT40394-2021)
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Determination of trace trimethylamine in methanol for industrial use -- Gas chromatography mass spectrometry
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Standards related to (historical): GB/T 40394-2021
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GB/T 40394-2021: PDF in English (GBT 40394-2021) GB/T 40394-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.080.60
CCS G 16
Determination of trace trimethylamine in methanol for
industrial use - Gas chromatography-mass spectrometry
ISSUED ON: AUGUST 20, 2021
IMPLEMENTED ON: MARCH 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Method summary ... 4
5 Reagents and materials ... 5
6 Instruments and equipment ... 6
7 Sample ... 6
8 Analysis steps ... 6
9 Result calculation ... 8
10 Precision ... 8
11 Test report ... 9
Appendix A (Informative) Reference gas chromatography-mass spectrometry
working conditions for the determination of trace trimethylamine in methanol for
industrial use ... 10
Appendix B (Informative) Reference chromatogram mass spectrum ... 11
Determination of trace trimethylamine in methanol for
industrial use - Gas chromatography-mass spectrometry
Warning – This document is not intended to explain all safety issues related to
its use; the user is responsible for taking appropriate safety and health
measures, which shall also comply with the relevant national regulations.
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
7.1 Sampling
Sampling shall comply with the provisions of GB/T 6680; sampling safety shall
comply with the provisions of GB/T 3723.
7.2 Sample pretreatment
7.2.1 Before sampling, add 1 mL ~ 2 mL of concentrated hydrochloric acid to a clean
1 000 mL sampling bottle (see 6.5).
7.2.2 Before analysis, add 100 mL of hydrochloric acid solution (see 5.7) to 100 mL
of sample (see 7.2.1); pipette 5.00 mL into the headspace bottle (see 6.4); add 5 mL
of saturated sodium hydroxide solution (see 5.10); gland seal to be tested.
8 Analysis steps
8.1 Drawing of the standard working curve
8.1.1 Set the instrument parameters with reference to Table A.1 - Reference gas
chromatography-mass spectrometry working conditions for the determination of
trace trimethylamine in methanol for industrial use - in Appendix A.
8.1.2 Pipette 5.0 mL of the series trimethylamine standard working solutions (see
5.12) into the headspace bottle in turn; add 5 mL of saturated sodium hydroxide
solution; then, inject them into the gas chromatography-mass spectrometer through
the headspace sampling device in turn for measurement. Take the mass concentration
of trimethylamine as the abscissa and the peak height or peak area of the quantitative
ion with a mass-to-charge ratio (m/z) of 58 as the ordinate, to draw the standard
working curve, as shown in Formula (1).
Where:
Ai – the peak area of trimethylamine in the standard solution i;
a – slope of the linear equation;
ρi – trimethylamine content in the standard solution i, in micrograms per liter (μg/L);
b – intercept of the linear equation.
8.2 Sample determination
8.2.1 Qualitative analysis
Under the same gas chromatography-mass spectrometry working conditions as
drawing the standard working curve (see 8.1.1), scan the trimethylamine standard
solution (see 5.12) and the sample to be tested (see 7.2.2) in the selected ion mode
(SIM) respectively. See Appendix B for a reference gas chromatograph mass
spectrum.
Use the retention time (RT) of trimethylamine in the sample, the relative abundance
of the auxiliary qualifier ions with the mass-to-charge ratios (m/z) of 42, 58, 59 to
double-qualify. The deviation BETWEEN the relative abundance of the auxiliary
qualifier ions of trimethylamine in the sample AND the relative abundance of the
auxiliary qualifier ions of trimethylamine in the standard solution shall be controlled
within 20%.
8.2.2 Quantitative analysis
Under the same gas chromatography-mass spectrometry working conditions as
drawing the standard working curve (see 8.1.1), inject the sample to be tested (see
7.2.2) into the gas chromatography-mass spectrometer for determination through the
headspace sampling device. Measure the samples to be tested twice in parallel.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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