A Miniaturized Precolumn for On-Line Trace Enrichment and Direct Plasma Injection in Narrow-Bore Liquid Chromatography

A precolumn for on-line trace enrichment in narrow-bore liquid chromatography has been designed and some critical parameters like precolumn length, inlet capillary I.D. and flow-rate have been studied. The precolumn allows direct injection of plasma and serum samples without any previous clean-up. Due to the trace enrichment, concentration sensitivity is improved 50-fold when 100 μl samples are applied as compared to standard micro-loop injections of 0.5 μl. The applicability of the system has been demonstrated by the analysis of the anti-cancer drug etoposide (VP-16) in human plasma with comparable or even better results than those obtained with conventional-size systems.