<title>Sensitive capillary-based on-column detection method by laser wave mixing</title>

Abstract

Laser wave-mixing spectroscopy is presented as a simple, sensitive, on-column detection method for capillary electrophoresis. The use of a single focusing lens to focus and mix two input beams significantly simplifies the optical alignment requirement of this nonlinear laser method. High signal collection efficiency allows excellent detection sensitivity for both fluorescing and non-fluorescing analytes, since the signal is a sharp coherent beam. This laser detection method can be conveniently interfaced to capillary-based separation systems since it offers small detector probe volumes, efficient use of short excitation or absorption path lengths, efficient use of low laser power levels available from small, compact, inexpensive laser sources, and inherently narrower peak widths (i.e., squared Gaussian). Potential applications include sensitive detection of biomolecules, either labeled or in their native fonns, using appropriate excitation wavelengths. Furthermore, laser wave-mixing detection can be used also in the indirect detection mode where the solvent or the buffer system yields a baseline signal, and nonabsorbing analytes can be measured indirectly in the form of negative peaks.