Laser Fluorescence Detection in Microcolumn Liquid Chromatography: Application to Derivatized Carboxylic Acids

Abstract

A laser-induced fluorescence (LIF) detector is evaluated for use with high-efficiency liquid chromatography columns of capillary dimensions. This detector employs a cw helium-cadmium laser (325 nm, 5–10 mW) as the excitation source, together with a fused-silica capillary flowcell and filter/photomultiplier optical system. The flowcell, which is an integral part of the microcolumn, contributes from 0.06 nL² to 0.06 µL² variance to the chromatographic system for capillaries of 35 to 330 µm diameter, respectively. The LIF detector is capable of sensing femtogram amounts of coumarin 440, and the response is linearly related to concentration over at least eight orders of magnitude. The potential of this combination of analytical techniques is demonstrated through the analysis of multicomponent mixtures of derivatized fatty acids and prostaglandins at the pico- and subpicomole level.