On-line laser desorption/ionization mass spectrometry
Interfaces for on-line laser desorption/ionization mass spectrometry are presented in this dissertation. An on line laser desorption interface allows samples to be introduced directly into the mass spectrometer for high-throughput applications. For this research, a linear time of flight mass spectrometer was constructed with an ionization source designed to accept various laser desorption interfaces. A ball inlet interface was used for continuous analyte deposition at atmospheric pressure and vacuum ionization. A solvent-based cleaning system and a separate capillary for MALDI matrix delivery was utilized for continuous on line sampling with the ball inlet interface. Microfluidic devices were brought into contact with the ball inlet and eluant was electrokinetically driven and deposited onto the ball inlet sampling surface. Polymer based microfluidic chips were engineered with open ended channels for on-line coupling, and peptide mixtures were separated on chip and mass detected on line. A non contact deposition method was studied using the ball inlet interface and a single droplet generator. Single droplets with 100 picoliter volume were ejected by a piezoelectric actuated droplet generator and deposited onto the ball inlet. Analyte droplets were placed onto a pre deposited matrix layer during on line analysis, and protonated molecule signal was obtained from as little as 10 fmol analyte. Two contact methods for fast sampling were studied with the ball inlet interface and a direct desorption/ionization interface. Direct contact with the ball inlet was achieved with an indented ball surface for solid, non crystalline, samples. Analytes were brought into direct contact with the ball inlet allowing deposits to settle into micromachined wells on the ball surface. The wells prevented scraping-off of the analyte by the vacuum gasket due to mechanical forces. The analysis of plant tissue, which is not suited for ball inlet sampling, was performed with the direct desorption/ionization interface.
CE, Matrix-assisted laser desorption/ionization, UV-MALDI, TOF, Time-of-flight, rotating-ball inlet, capillary electrophoresis, microfluidic chip
Networked Digital Library of Theses and Dissertations