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 1 × 10−5 − 5 × 10−5 absorbance units (10–50 μAU). 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 ~15 μAU for the others for on-column detection through a 75 μm bore, 142 μm-diameter capillary. In actual CE experiments, the limit of detection for test solutes ranged from sub- to low-femtomole quantities.