Design, construction and development of a laser desorption ionization/laser ablation time-of-flight mass spectrometer for chemical analysis with and without surface plasmon resonance.

摘要

Theoretical modeling of the Wiley-McLaren double-focusing field system (two acceleration fields) provided the critical dimensions for the design and construction of a time-of-flight mass spectrometer (TOFMS) for this research. For optimum resolution, the distances within the acceleration fields, s (0.26 cm) and d (2.60 cm) were determined for a drift tube length D of 42.2 cm. Arcing occurred frequently using our laser desorption ionization (LDI)/laser ablation (LA) technique; five different configurations were designed and evaluated. The third configuration was determined to be the most useful for LDI/LA-TOFMS experiments.;The LDI/LA technique was tested for molecular mass and structural reactivity analysis. This LDI/LA technique was successfully applied to dithizone, 1,4,8,11-tetraazocyclotetradecane, dicyclohexyl-18-crown-6 ether, [5]-helicene dendrimer, gramicidin S, substance P, mellitin, PAHs, fullerenes/derivatives, thia fatty esters/acids, and a variety of related compounds. One advantage of the present LDI/LA technique, over conventional ones is that the sample does not need to have appreciable spectral absorption at the laser wavelength.;The physical process that occurred during our LDI/LA technique was elucidated with internal standardization and ion association using gramicidin S. The LDI/LA mechanism generating the [M + Ag]+ cation was thought to be electronic-excitation (at low laser fluences) that evolved into a thermal one (at high laser fluences), depending on the silver film thickness.;The five configurations were also evaluated for incorporating surface plasmon resonance (SPR) into our LDI/LA technique to ultimately construct a novel SPR-LDI/LA-TOFMS instrument. They indicated that silver surface plasmons have a SPR angle thetar of 44° and an energy of 3.7 eV for a thin silver film thickness of 40 nm. The SPR-LDI/LA technique demonstrated that a lower minimum laser fluence for the production of the silver cluster cations [Agn]+ was required at theta r. SPR was thus confirmed to assist in the electronic-excitation desorption during LDI/LA of a thin silver film with or without deposited samples. The capability to perform SPR-LDI/LA on a molecular weight of 1141 Da from a thin silver film represents a new milestone beyond previous achievements. (Abstract shortened by UMI.)