Development and Application of New Thermal Dissociation Atmospheric Chemical Ionization for Rapid Mass Spectrometric Analysis under Ambient Conditions

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.