In vivo monitoring of amine neurotransmitters using microdialysis with on-line capillary electrophoresis

Microdialysis sampling was coupled via a flow-gated interface on-line to ca pillary electrophoresis with laser-induced fluorescence (LIF) detection for in vivo monitoring of neuroactive amino acids and amines. In the instrumen t, analytes are derivatized precolumn with o-phthaldehyde and beta -mercapt oethanol to form fluorescent isoindole products. The instrument was improve d over previous designs by incorporating a sheath-flow cuvette for reduced background in LIF detection which improved sensitivity by 15-fold. The meth odology was improved by utilizing a voltage ramped injection which allowed generation of 500 000 theoretical plates with 20 s separations. Resolution of the isoindole derivatives was further improved by addition of hydroxypro pyl-modified beta -cyclodextrin to the electrophoresis buffer. The new inst rumentation and methods allow resolution and detection of glutamate, gamma -aminobutyric acid, glycine, aspartate, serine, taurine, glutamine and dopa mine (if levels are elevated) collected from in vivo sampling probes every 20 s. The technique is suited to continuous monitoring for dynamic measurem ents of these compounds in vivo.