Mechanisms and applications of laser desorption Fourier transform mass spectrometry

The combination of laser desorption (LD) and Fourier Transform Mass Spectrometry (FTMS) was investigated as a means of analyzing polar, nonvolatile molecules in this research. Chapters one and two are overviews of the FTMS field. Chapter one describes the basic principles and recent developments of the FTMS. Chapter two describes the applications of FTMS with a YAG laser. The mechanism of cationization of sucrose by sodium in LD/FTMS was investigated as a function of laser power density at a wavelength of 1064 nm. in chapter 3. A double substrate, split probe was used to separate NaCl and sucrose while maintaining coincidence with the laser beam. Gas-phase cationization is extensive a power density of 10$\sp6$ W/cm$\sp2$, whereas little evidence for this mechanism is found at 10$\sp{10}$ W/cm$\sp2$. Chapter four describes the investigation of the LD characteristics of four nucleosides at wavelengths of 266 and 1064 nm. The pyrimidine nucleosides, thymidine and uridine, give disodiated molecular ions at desorption onset at 266 nm. whereas the purine nucleosides, adenosine and guanosine, yield sodiated base fragments. Pyrimidine disodiated molecular ion formation is explained by a shift in the lactam-lactim equilibrium toward the lactim form in the T$\sb1$ state, a feature not characteristic of the purines. Gas-phase cationization is not a major means of forming cationized ions upon IR irradiation unlike the desorption of sucrose. A direct desorption mechanism is proposed instead. Chapter five describes the mixture analysis of amino acids and tripeptides by LD/FTMS. LD mass spectra of a 15-component amino acid mixture consisting of three ng. of each was obtained. The relative ion abundances are not proportional to concentration. The most important factors influencing amino acid desorption are the differences in the individual amino acid sublimation enthalphies. A five-component mixture of tripeptides of widely differing solubilities was analyzed successfully as well