Sensitivity enhancement in near-field photothermal-lens detection in capillary electrophoresis using laser-induced online precipitation.

This paper reports simultaneous photoinduced precipitation-based online preconcentration of target analytes at the inner walls in capillary zone electrophoresis (CZE) and surface-enhanced near-field crossed-beam photothermal-lens detection of the preconcentrated analytes. A simple technique using online readjustment of the optical scheme of the thermal-lens detector in the course of the separation for gaining optimum sensitivity for both water-soluble and precipitated analytes is proposed. It provides a considerable decrease in the limits of detection (LOD) with good concordance with the previously developed theoretical approach to this combination (D. A. Nedosekin, W. Faubel, M. A. Proskurnin, and U. Pyell, Talanta, 78, 682-690 (2009)). As a result, an enhancement of more than an order of magnitude in the limit of detection of the photoactive 4-aminoazobenzene compared to conventional thermal-lens detection in CZE is achieved while retaining very good sensitivity for unabsorbed analyte (Mordant Yellow 7). The application of the thermal-lens detector to the investigation of laser-induced reactions in flow in capillaries is discussed.