Development Of Microwave Plasma Atmospheric Pressure Desorption/Ionization Source For Mass Spectrometry

Mass spectrometry has recently undergone a contemporary revolution with the introduction of a new group of ambient desorption/ionization (D1) sources known collectively as direct ionization techniques. To date, more than20ionization techniques have been developed and they are widely used in the field of food, medicine, environment, in vivo analysis, metabolomics, proteomics and bio-tissue mass spectrometry imaging, etc. The techniques show very important influences and the practical values. In this study, an ambient ionization technique with the independent intellectual property rights was developed based on microwave plasma, and the mass spectrometric applications of this technique were done, the main contents are as follows:(1) The microwave plasma atmospheric pressure desorption/ionization (MWPAPDI) source was developed based on the microwave plasma torch (MPT), then by coupled it with a mass spectrometer (Consair TOF MS), the direct analysis methods for the various samples of solid phase, liquid phase and gaseous phase were developed. These methods do not need sample pretreatment and the samples can be analyzed directly.(2) From the MWPAPDI, the conditions and the mechanisms for the generation of the two important primary ions H3O+and NH4+with their water clusters were studied. The results shows that the flowing rate and the temperature of the drying nitrogen from the mass spectrometer have important effects on these primary ions and the corresponding product ions [M+H]+and [M+NH4]+. While the momentum of the particles in the plasma and the plasma temperature are the important factors to influence the microwave plasma desorption process.(3) The rules of dissociation and ionization for the alkanes were studied by MWPAPDI through the two sample introduction ways:the atmospheric pressure-volatizing sampling and the traditional central tube sampling. The results show that the straight-chain alkanes are more easily to dissociate by losing—CH2—then the generated fragment ions will recombine to prolong the carbon chain lengths. The end products are the new alkanes by losing or adding n (—CH2—)(nis not fixed) from the original alkanes through the central tube sampling. For the straight-chain alkanes through the atmospheric pressure-volatizing sampling, their molecules are more easily to be kept intact, and when the number of carbon atoms is equal to or more than4, the straight-chain alkanes can form the product ions of [M+13]+. Based on this rule, a novel direct analysis method for quick-identification of saturated straight-chain alkanes with similar physical properties was proposed.(4) The reactions of the aromatic compounds in the microwave plasma were investigated through the atmospheric pressure-volatizing sampling and the central tube sampling. It was found that the complex and various reactions, such as reduction, oxidation and protonation, etc., could occur in either sampling ways. The atmosphereic components, such as oxygen and nitrogen, also participate in the reactions. For the reduction reactions, the hydrogenated products with different deduction degree can be obtained. These processes are facilitated by the microwave plasma and require no additional catalysts.(5) Based on the analysis for medicines by MWPAPDI-MS, a rapid qualitative detection method for one or more active pharmaceutical ingredients (APIs) in medicines with different forms (tablets, ointments, and capsules) was developed. This method is simple without the need for chemical reagents and sample pretreatments. It also has high throughput that the analysis speed can reach360samples per hour with manual sampling. In this method, the fragment ion signals exist in the full-scan spectra, these information can assist to identify the APIs.(6) The miniaturization was made for the current MWPAPDI source. The new miniature source is more easily to operate and the power consumption reduces. While the abilities for the desorption/ionization of this miniature source are still adequately kept and shown by the observation of the application experiments.