Hologram-based refractive index detector for capillary electrophoresis: separation of metal ions

Abstract

A novel refractive index detector suitable for capillary separations is presented and demonstrate& in the capillary electrophoretic separation of metal cations in 10-μm-i.d. tubes. The principle of the detector is interferometric; it features a laser diode and, as the main optical element, a holographic optical element which performs several optical functions allowing the use of capillaries with inner diameters as small as 5 μm. In contrast to the «off-axis» method, the use of holographic plates permits probing of the capillary through its center, where the optical path is larger and diffraction effects are smaller. With ani.d.=10 μm capillary the detector resolves 2 μRIU and covers a linear dynamic range of three to four decades