Fabrication and design of open microchannels for capillary electrophoresis separations and matrix-assisted laser/desorption mass spectroscopy analysis

We describe the development and performance of microchips that interface capillary electrophoresis (CE) with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The chip contains an open channel where CE is performed. The open channel functions as the CE column and is used to separate the mixture. Once separation occurs, the solvent is evaporated and the chip placed in the ionization source of a Fourier transform mass spectrometer. To perform the MALDI, a buffer will be used in the CE that will also function as matrix once the solvent is evaporated. Preliminary results will be described showing: (1) the design and construction of a new ionization source for an external source FTMS that will handle the microchip, (2) the feasibility of the CE on an open channel and (3) the feasibility of MALDI on an open channel. Two chips made of glass with groves cut on the surface have been fabricated for these experiments. The rates of evaporation of different solvent mixtures indicate that evaporation will not be a problem during the CE analysis. The rates of evaporation are considerably slower than the speed of the separation. To determine the feasibility of CE, a colored dye was placed on a 2 cm long column and high voltages attached to the two ends. Movement of a colored dye on the chip was observed under an electric field correspond to about 500 V/cm. This experiment indicates that CE can be performed on an open channel. The first experiments with MALDI of biomolecules, in this case oligosaccharides have been performed. (beta) -Cyclodextrin, a seven-membered cyclic oligosaccharide, was mixed with 3,5-dihydroxybenzoic acid (matrix) on an open channel. Striking the grove with a 337 nm beam from a N2 laser produces the mass spectrum of the compound with excellent resolution and high signal-to-noise.