取10 g水产品样品,加入20 mL 5％(体积分数,下同)三氯乙酸溶液,均质1 min,离心5 min.上清液经脱脂棉过滤,收集滤液.残留物分别用15,10 mL 5％三氯乙酸溶液各提取一次,合并所有滤液,用5％三氯乙酸溶液稀释至50 mL.分取2.0 mL于20 mL顶空瓶中,压盖密封后用注射器从盖垫边缘注入5 mL 10％(质量分数)氢氧化钠溶液,在45 ℃下平衡40 min,所得气体进入气相色谱-串联质谱仪,在HP-INNOWAX毛细管色谱柱上以程序升温条件分离三甲胺,电子轰击离子源电离,多反应监测模式扫描,以所得特征离子对质荷比(m/z)58/42进行外标法定量,m/z 59/43和m/z 58/30进行定性.结果表明,三甲胺的质量浓度在0.2～50 mg·L-1内和对应的定量离子对峰面积呈线性关系,检出限(3S/N)为0.3mg·kg-1.5,25,100mg·kg-1添加水平下的回收率为88.3％～94.0％,测定值的相对标准偏差(n=6)为1.1％～3.7％.方法用于鱼肉样品的分析,未检出三甲胺.将上述样品于-18,4 ℃保存7 d后,三甲胺的检出量分别为0.4,195 mg·kg-1,可能与放置过程中鱼肉被微生物降解成三甲胺有关.
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.
trimethylamineheadspace-gas chromatography-tandem mass spectrometryaquatic product
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