The performance of a quadrupole mass filter operated in the RF-only mode has been investigated. A discussion of both the formal and qualitative theories of quadrupole mass analyzers is given. Data is presented which demonstrates that the transmission properties of such devices deviate markedly from those which would be predicted from the Mathieu stability diagram. The transmission efficiency of ionic species, through an RF-only quadrupole, is shown to depend primarily on three factors. The first of these is the formal stability of the ion trajectory as summarized by the coordinates of the particle in a, q space. The second factor is the acceptance aperture of the quadruople in combination with the emittance of the ion source. The final factor is shown to be spacial focusing conditions which arise due to the nature of the frequency components that are contained within the trajectory of an ion as it traverses the quadrupole electrode structure. The theory of such spacial focusing conditions is reported. The measurement of naturally occurring isotope abundance ratios is used to demonstrate the magnitude of errors which may result due to the nonideal transmission properties of the RF-only quadrupole. Suggestions are provided to minimize such mass discrimination effects. Additional experiments dealing with the quadrupole notch filter are described. Performance of a unique voltage tuned quadrupole notch filter is demonstrated. The theory, design, and construction details of such a device are reported.

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Electrospray (ES)-based ambient ionization techniques have been rapidly developed and became indispensable tools for direct sample analysis using mass spectrometry. In this study, it was found that with the use of porous substrate, analytes present in complex samples could be detected by directly introducing untreated sample on porous tips. Moreover, the specific feature, micro-channels of the porous tips, allows efficient sample loading and facilitates electrospray ionization (ESI), which is beneficial for the direct sample analysis. Systematic study on the influences of the physical and chemical factors of various porous materials (polyester, polyethylene and wood) on the detection sensitivity and ionization efficiency was firstly investigated. It was found that the chemical interaction between the porous materials and analytes could significantly affect the detection sensitivity for analytes. Hydrophobic spraying tips showed better detection sensitivity for polar analytes while better detection for non-polar analytes was obtained when hydrophilic spraying tip was used. Moreover, the electrostatic properties of spraying tips could also affect the detection sensitivity for analytes. Hydrophobic materials (i.e., polyethylene and polyester) which tend to form negative charge on the surface could facilitate the ionization of analytes in negative ion mode. With a clear understanding of the effect of porous spraying materials on detection sensitivity, tip spray ionization mass spectrometric method was developed and successfully applied to direct analysis of pharmaceutical, forensic, clinical and food samples. Rotary sample stages compatible to the ion source of two commercial mass spectrometers were designed and constructed for the automation of tip spray ionization mass spectrometry, which allowed the analysis of 12 samples in less than 15 minutes. In addition, instead of using porous substrates for the sample deposition, the developed technique was further applied to the direct chemical analysis of American ginseng tissue, demonstrating the feasibility of performing direct analysis on raw herbs in solid state. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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Modified Si wafers and nanoparticles (5-50 nm) have been developed and explored to assist laser desorption ionization mass spectrometry (LDI-MS) for small molecule analysis. DIOS (desorption/ionization on silicon) plates were prepared according to published protocols. DIOS was tested and compared with the optimized silicon nanoparticles derivatized by penterfluorophenylchlorosilane (PFP). SPALDI (Si nanoparticle assisted LDI) requires less laser flux than common MALDI and DIOS thus provides significant less background and higher ionization efficiency. It has higher surface homogeneity, relative salt tolerance and high selectivity which may origin from analyte dependent pre-charging. Surface characterization has been investigated. And different analytes including drugs, peptides, pesticides and acids in both biological and environmental samples have been applied by positive or negative ionization mode. Detection limits, down to the low femtomole per microliter levels have been achieved for propafenone and verapamil. SPALDI is an easily applicable practical tool at a potential low cost.

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