BINDING CHARACTERISTICS OF VARIOUS NEUROCHEMICALS TO GLASSY-CARBON

The determination of acetylcholine and choline using liquid chromatogr aphy with electrochemical detection using the approach of Potter et al . [J. Neurochem., 41 (1983) 188] normally requires isolation of the de sired species before an analysis of tissue samples can be undertaken d ue to coeluting interferences afforded by other neutrochemicals. We ha ve recently shown that this problem can be overcome by the use of a gl assy carbon precolumn to effectively trap the interfering species [Ika rashi et al., J. Chromatogr., 575 (1992) 29]. We now report on the nat ure and mechanism of this adsorption onto glassy carbon for norepineph rine, dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, homovanilli c acid and 5-hydroxyindoleacetic acid. For both the acidic and basic c ompounds which comprise this group, distinct Langmuir adsorption proce sses appear to be involved for both the neutral and ionic forms of the individual compounds. Using various data fitting approaches, we have attempted to derive appropriate adsorption constants for the two forms of each compound. Theoretical predictions employing these derived con stants provided results which match reasonably well with the observed adsorption data in most cases.