An affordable high-performance optical absorbance detector for capillary systems

Optical absorption detection is the most common detection mode in capillary-based separation systems such as capillary liquid chromatography or capillary electrophoresis (CE). The peak-to-peak noise levels of presently available commercial absorbance detectors usable for on-column detection is of the range 1x10(-5)-5x10(-5) absorbance units (10-50 mu AU). Currently there is widespread interest in CE because of its simplicity and exceptional separation power. The most expensive item in a home-made CE set-up is the optical absorption detector. Herein we present a simple, versatile and inexpensive design for an on-column optical absorbance detector that is comparable in performance to commercial units in both ultraviolet and visible regions. The detector has been tested with Zn, Cd, and Hg lamps and a visible-light-emitting diode as the sources. Detector response is linear over several orders of magnitude. Noise levels are somewhat higher for the Hg lamp and similar to 15 mu AU for the others for on-column detection through a 75 mu m bore, 142 mu m-diameter capillary. In actual CE experiments, the limit of detection for test solutes ranged from sub- to low-femtomole quantities.