摘要:
为了克服常压热解离化学电离装置(TDCI)热源控制不稳定、背景干扰较大、实验重现性相对较差等问题。文章在前期研究的基础上,分别对仪器各组成部件进行优化和改进,研制出能够根据待测物的热稳定性、极性、挥发性、熔点等性质,能够对仪器的温度、加热时间、加速电压等仪器参数连续、精确可调的新型常压热解电离源实验装置,并进行了优化和表征。与原研制的TDCI实验装置相比,新型TDCI电离装置的高压调节和温度控制的连续性和精确度以及热源的稳定性得到了极大的提高。高压调节的最小刻度从原来的1 V减小到0.1 V,温度控制系统的调控精确由原来的±5℃减小到±1℃。采用新型TDCI-MS技术,在常压和无需样品预处理的条件下,实现了实际样品可乐中痕量兴奋剂可卡因和牛奶中弱极性物质三聚氰胺的快速检测,单个样品检测时间都小于30 s,检出限低,可卡因和三聚氰胺的最低检出限分别为1.12×10-12 g/mL和2.62×10-11 g/mL,重现性好,相对标准偏差(RSD)为4.61%~9.80%,优于原TDCI电离装置的检测结果,完全满足实际样品的检测需要。由于其具有独立稳定的加热装置,与表面解吸常压电离源相比,本仪器装置更适于难挥发性化合物的快速分析。
Abstract:
In order to overcome the disadvantages of the thermal dissociation atmospheric chemical ionization source (TDCI), such as unstable thermal control, large background interferences and poor replications, an improved TDCI source has been developed in our lab for rapid chemical ionization of ambient analytes in complex matrices. Based on previous research, the operating parameters of the new TDCI source, such as the temperature of the heated capillary, heating time and capillary voltage, can be controlled automatically according to the chemical properties of the analytes such as thermal stability, polarity, volatility and melting point. In comparison with the original TDCI technique, the stability of the heat source, accuracy and continuity of the voltage and temperature control of the TDCI developed in this study were improved greatly, in which the minimum scale values of the voltage and temperature control have been reduced to 0.1 V and ±1℃, from 1 V and ±5℃, respectively. The performance of the new developed TDCI was evaluated by coupling the TDCI source to a commercial LTQ-XL mass spectrometer. Under ambient conditions without any sample pretreatment, trace amounts of a wide variety of compounds in different complex matrices, including Cocaine in cola and Melamine in milk, have been successfully detected with the improved TDCI-MS by choosing ionic liquids. The results show that the new TDCI ionization technique has a lower detection limit and better duplication than those from the original TDCI analysis. The average time for each single sample analysis was less than 30 s, the relative standard deviations of the method were in the range of 4.61% to 9.80% and the detection limits for Cocaine and Melamine were estimated to be 1.12×10-12 g/mL and 2.62×10-11 g/mL, respectively. Compared to desorption atmospheric pressure chemical ionization, the new TDCI is more suitable for non volatile compound analysis, due to its stable high voltage heating device.
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