Abstract
A method for adapting widely used CE conditions for the separation of fluorescently labeled carbohydrates to permit online ESI-MS detection is presented. Reverse polarity separations were performed in bare fused-silica capillaries with an acidic BGE. Under these conditions, negatively charged 8-aminopyrene 1,3,6-trisulfonate-labeled carbohydrates migrate forward against the EOF, which is towards the capillary inlet. Therefore, the CE-MS interface must simultaneously back-fill the capillary, in order to maintain the CE circuit, and provide a stable forward flow at the sprayer tip to support the electrospray process. This was achieved using a junction-at-the-tip interface, which provides a flow of solution to the junction formed by the capillary terminus and the inner wall of the emitter needle tip. Because the flow rate required for this arrangement is much less than in conventional sheath flow interfaces, dilution of the analytes is minimized. Optimized separation conditions permit baseline resolution of glucose oligomers containing up to 15 glucose units, while longer oligomers, up to 33 glucose units, were observed as resolved peaks in the negative ion mode mass spectrum.
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