Surface Desorption Atmospheric Pressure Chemical Ionization: Mechanism And The Applications In The Analysis Of Food And Pharmaceutical Samples

Recently, the research of ambient ionization techniques and the development ofrapid, in-situ, real-time, online and/or low-loss analytical methods are of increasinginterest. Surface desorption atmospheric pressure chemical ionization mass spectrometry(DAPCI-MS), being rapidly developed in recent years, is an ambient ionizationtechnique for direct analysis of complex samples without pretreatment. The DAPCIsource can desorbs/ionize the surface without using of high pressure gas and toxicsolvent, can directly analyze the powder samples, and is much easier for miniaturization.In this study, the mechanism of DAPCI is experimentally investigated and the newmethods based on the DAPCI-MS are established for the direct analysis of food, drugsand clinical samples.Based on the brief overview of the mass spectrometer structure, the commonionization technique and the development of DAPCI, the main contents of this thesis areas follows:1. For the studying of the mechanism of DAPCI, the desorption area on theanalyzing surface under no sheath gas DAPCI source has been determined(diameter=140μm), the primary ions of DAPCI source produced using different solventhave been experimentally investigated, and the ions chemical behavior of polar,non-polar, weekly polar substances have been described. These results demonstrated thatthe DAPCI worked on these three steps: producing primary ions, desorbing the surfaceand ionizing the analyzer by the ion/molecular reaction between primary ions and theanalyzer. The study is important for the depth understanding the mechanism of DAPCIsource and promoting the application of DAPCI in the field of imaging massspectrometry, gas phase molecular/ion chemistry and non-polar or weekly polarsubstances detection. 2. This paper has characterized the performance (LA-DAPCI) and optimized theparameter setting of liquid-assisted DAPCI (LA-DAPCI) and demonstrated that theLA-DAPCI has both primary ions and primary solvent droplets. This part of the study isbenefit on mechanism researching and applications of DAPCI technique.3. The edible oils of different quality, sea cucumbers of different areas but the samegenus, human kidney stones of different causes, the Liuwei Dihuang Wan of differentmanufactures and processing technology, and the amoxicillin of different manufacturersand raw materials have been analyzed by DAPCI-MS. The trend compounds in thiscomplex samples are directly identified by tandem mass spectrometry with no orminimal pretreatment. The results showed that the high-throughput mass spectrometryanalysis of the above complex samples can be finished by DAPCI-MS. The relativestandard deviation (RSD) of the measurement of edible oils was7.18%, with ananalytical speed of16seconds per sample. Moreover, based on the data of mass spectralfingerprints, the mathematic models are built by the chemometrics method, such asprincipal component analysis (PCA) and neural network (NN). These results show thatthe technology of DAPCI-MS is a powerful tool in the application of food safety andmedical healthy.