Semiconductor laser-induced fluorescence detection in picoliter volume flow cells

A visible semiconductor laser-induced fluorescence detection system for ultratrace chemical analysis of nanoliter-to-picoliter samples is optimized and characterized in detail. With low-power semiconductor lasers emitting at 675 and 639 nm for excitation, the best limit of detection is 8000 molecules for a model fluorescent compound (1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide) in an ethanol solution. Fused silica capillaries with inner diameters between 250 and 11 microm were employed as picoliter volume flow cells, which permits the use of the system in miniaturized separation techniques such as packed and open tubular liquid chromatography and capillary electrophoresis.