Capillary-based microanalytical systems

Abstract

Miniaturization is a trend common to science and technology. Miniaturization into the capillary domain has been the most prevalent approach for improving chromatographic techniques. The advantages of moving from conventional size columns into the capillary domain include higher efficiencies, better mass limits of detection, low reagent consumption, and a small sample requirement.

Optical absorption detection is the most common detection mode in capillary-based separation systems such as capillary liquid chromatography (LC) or capillary electrophoresis (CE). A simple, versatile, and inexpensive design for an on-column optical absorbance detector has been investigated. Detector performance is comparable to commercial detectors in both the ultraviolet and visible regions. The component cost for the detector, including data processing electronics, is only a fraction of the cost of commercial instruments.

Miniaturization of both separation columns and ancillary components for capillary-based systems has made field portable liquid chromatographs feasible. A fully computer controlled, field portable capillary scale suppressed conductometric ion chromatograph (IC) that fits In a standard size briefcase has been fabricated. The system uses a capillary scale electrodialytic sodium hydroxide generator on the high-pressure side of a syringe pump to provide isocratic or gradient operation with excellent eluent purity. The system provides detection limits in the sub- to low parts per billion range, with mass limits of detection >100 times better than standard IC systems. Further, this capillary ion chromatograph has been coupled to a wet effluent parallel plate diffusion denuder for the determination of soluble lonogenic atmospheric trace gases. This resulting gas phase analyzer requires low reagent volumes for operation while providing limits of detection in the low parts per trillion range for sampled gases.