The applicability of in-beam and laser desorption atmospheric pressure ionization mass spectrometry and detectors for capillary zone electrophoresis.

The applicability of in-beam and laser desorption atmospheric pressure ionization mass spectrometry (APIMS) of some explosives, polycyclic chlorinated pesticides and organophosphorus pesticides has been evaluated. Fairly simple negative ion API mass spectra of TNT, DNT and RDX are obtained. Temperature dependences of the API mass spectra of RDX and HMX are observed. In-beam and laser desorption API mass spectra of RDX and HMX are compared. The results show that the in-beam mode may be fairly adequate for the purpose of detection and identification of RDX, while the laser desorption mode may find potential application for unequivocal detection and identification of HMX at lower temperatures. Eight polycyclic chlorinated pesticides are investigated. High intensity Cl$\sb2$-isotopic peaks are observed in API mass spectra of these pesticides. This common feature may find its analytical utility for screening the presence of these pesticides in environmental matrices. Laser desorption API mass spectra of endosulfan I and II, and mirex are characterized by high intensity peaks of their unique fragment ions, which may be useful for direct detection and identification of these compounds in solid samples. The APIMS of forty organophosphorus pesticides is systematically studied. General features of their API mass spectra are summarized. The results of this basic research will facilitate the application of APIMS in real time detection and identification of organophosphorus pesticides for environmental air monitoring. Selected topics on detectors for capillary zone electrophoresis (CZE) are discussed. First, detection limits and optimum slit dimensions of on-column UV absorption detectors for CZE are estimated. The results indicate that using high intensity laser sources may improve the detection limits of this kind of detectors. Second, the possible fluid convection problem in laser irradiated on-column CZE detectors is evaluated. Theoretical analysis show that in on-column CZE detectors, fluid convection is unlikely to occur even with high intensity laser irradiation. Finally, a novel analyte zone migration velocity modulation method for CZE is proposed. The applicability of this approach in an on-column refractive index detector for CZE is demonstrated. The possible applications of this approach in other kinds of CZE detectors are presented.Ph.D.Analytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128365/2/9001645.pd