Determination of Trimethylamine in Aquatic Products by Headspace-Gas Chromatography-Tandem Mass Spectrometry

The 10 g of aquatic product sample was taken, and 20 mL of 5% (volume fraction, the same below) trichloroacetic acid solution was added. The mixture was homogenized for 1 min, and centrifuged for 5 min. The supernatant was passed through the defatted cotton, and the filtrate was collected. The residue was extracted with 15, 10 mL of 5% trichloroacetic acid solution, respectively. All the filtrate was combined, and diluted to 50 mL with 5% trichloroacetic acid solution. An aliquot (2.0 mL) was placed into a 20 mL-headspace vial, which was sealed with a cap. Then 5 mL of 10% (mass fraction) sodium hydroxide solution was injected from the edge of the cap with a syringe. After equilibrating at 45 ℃ for 40 min, the resulting gas was introduced into a gas chromatograph-tandem mass spectrometer. Trimethylamine was separated on HP-INNOWAX capillary column under programmed temperature conditions, ionized with an electron bombardment ion source, and scanned in multiple reaction monitoring mode. The characteristic ion pairs at mass to charge ratio (m/z) of 58/42 was used for quantitative analysis by the external standard method, and m/z 59/43 and m/z 58/30 were used for qualitative analysis. It was shown that linear relationship between the peak area of quantitative ion pair and mass concentration of trimethylamine was kept in the range of 0.2-50 mg·L⁻¹, with detection limit (3S/N) of 0.3 mg·kg⁻¹. The recovery at the addition level of 5, 25, 100 mg·kg⁻¹ was found in the range of 88.3%-94.0%, with RSDs (n=6) of the determined values in the range of 1.1%-3.7%. The proposed method was used for the analysis of fish meat samples, and trimethylamine was not detected. The above sample was stored at −18, 4 ℃ for 7 d, giving the detection amounts of trimethylamine of 0.4, 195 mg·kg⁻¹, which might be related to the microbial decomposition of fish meat into trimethylamine during storage.