A high-efficiency sample introduction system for capillary electrophoresis analysis of amino acids from dynamic samples and static dialyzed human vitreous samples

A low-volume automated injection system for the analysis of chemically complex, amino acid samples is presented. This system utilizes submicroliter sample volumes stored on a 75-μm inner diameter capillary. A pulse of positive pressure (82 kPa) is used to load nanoliter sample volumes into an in-house fabricated interface and onto a separation capillary. Residual sample solution in the interface is immediately washed away by a continuous transverse flow through the injection interface, yielding a sharp and reproducible sample plug. By performing multiple injections of a static sample, one may average the signals to yield a signal-to-noise ratio improvement of up to 4.07-fold for 20 injections compared with a theoretical maximum of a 4.47-fold improvement. Without interruption of the applied voltage, injections performed every 150 s were used to monitor the progress of the reaction of multiple amino acids with the fluorogenic dye 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde. Analysis of dialyzed clinical vitreous samples demonstrates the resolution and quantitation of arginine, lysine, leucine, glutamine, and glutamate. Observed levels are comparable with those of nonautomated injection methods and reports by others. Figure Multiple injections of fluorescently labeled human vitreous with a detailed view of a single injection (above) and with all injections segmented and averaged for signal-to-noise ratio improvement (right)