T/PCA 005-2024 Determination of bromomethane in coffee by headspace/gas chromatography-mass spectrometry

Scope

Main Technical Content: 1. Scope: This document specifies the headspace/gas chromatography-mass spectrometry method for the determination of methyl bromide residues in raw coffee. This document is applicable to the determination of methyl bromide residues in raw coffee. 2. Normative References 3. Terms and Definitions 4. Principle: The sample is placed in a sealed headspace vial and equilibrated at 70°C for 30 minutes. Methyl bromide reaches a dynamic equilibrium between the gas and solid phases. The gas in the headspace vial is extracted and injected into a gas chromatograph-mass spectrometer for detection, with quantification performed using an external standard method. 5. Reagents and Materials: Unless otherwise specified, only analytical-grade reagents are used in the analysis, and all test water must meet the requirements of GB/T 6682 for Class I water. 5.1 Reagents: - Methanol (CH3OH, CAS No. 67-56-1): Chromatograph-grade. - Methyl bromide (CH3Br, CAS No. 74-83-9): Purity ≥99%, or standard material certified and granted a standard substance certificate by the national authority. - Standard solution preparation: - Methyl bromide standard stock solution (100.0 μg/mL): Accurately transfer an appropriate amount of methyl bromide standard solution to a 10 mL vial, make up to volume with methanol, mix well, and transfer the standard solution to a brown glass container. Store at -18°C and protected from light for 3 months. - Methyl bromide standard working solution: Accurately transfer 200 μL, 400 μL, 600 μL, 800 μL, and 1000 μL of the 100.0 μg/mL methyl bromide standard stock solution to a 10 mL vial, make up to volume with methanol, and mix well to obtain standard working solutions with concentrations of 2 μg/mL, 4 μg/mL, 6 μg/mL, 8 μg/mL, and 10 μg/mL. These solutions can be stored at 18°C for one week. 6. Instrumentation and Equipment 6.1 Gas chromatograph-mass spectrometer with headspace device. 6.2 Electronic balance (accurate to

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