A chip-based capillary electrophoresis-contactless conductivity microsystem for fast measurements of low-explosive ionic components

Abstract

A miniaturized analytical system for separating and detecting inorganic explosive residues, based on the coupling of a micromachined capillary electrophoresis (CE) chip with a contactless conductivity detector is described. The low electroosmotic flow (EOF) of the poly(methylmethacrylate) (PMMA) chip material facilitates the rapid switching between analyses of cations and anions using the same microchannel and run buffer (and without an EOF modifier), and hence offers rapid ( < 1 min) measurement of seven explosive-related cations and anions. Experimental parameters relevant to the separation and detection processes have been optimized. Addition of a 18-crown-6 ether modifier has been used for separating the peaks of co-migrating potassium and ammonium ions. The ionic-explosive microchip system combines the distinct advantages of contactless conductivity detection with the attractive features of plastic CE microchips. The new microsystem offers great promise for monitoring explosive-related ions at the sample source, with significant advantages of speed/warning, efficiency, cost, or sample size.

Contactless Conductivity Detection in Capillary Electrophoresis: A Review

“…Fast-and slow-migrating anions were separated in less than 90 seconds [84] and a fast separation of inorganic anions within 15 seconds [94] was demonstrated in PMMA chips. Four alkylated methylphosphonic acids, characterized as degradation products of chemical warfare agents, were separated in PMMA microchips in the anionic separation mode by Wang et al [96].…”

“…Several authors have demonstrated the application of devices with embedded insulated electrodes to the determination of inorganic cations [80,83,92,93]. Wang and co-workers [84,94] and Tanyanyiwa et al [35,85] demonstrated the determination of inorganic cations in glass and PMMA devices. Limits of detection of about 1 mM were reported for the determination of inorganic cations when using elevated voltages for detection [35].…”

“…The electroosmotic flow in PMMA channels is significantly reduced in comparison to fused-silica capillaries [84,94] and therefore separations of anionic compounds are possible in common electrolyte solutions even without addition of EOF modifiers. Fast-and slow-migrating anions were separated in less than 90 seconds [84] and a fast separation of inorganic anions within 15 seconds [94] was demonstrated in PMMA chips.…”

Screen‐Printed Contactless Conductivity Detector for Microchip Capillary Electrophoresis

“…The electrode pairs are screenprinted and cut into cover sheets and subsequently sealed onto channel plates thus creating an integrated separation and detection device. Such screen-printed detectors do not require manual fabrication of the electrodes from metal foils [5,15] or other tedious protocols [8, 12 -14]. The new scheme enables fast fabrication and alignment of the sensing electrodes with the channel plate and thus dramatically decreases the overall analytical device fabrication time.…”

“…Various electrode materials such as silver paint [10], platinum [8,12], platinum-iridium [13], gold [14], copper [15], and aluminum [5,6] have been used as conductivity (both contact and contactless) detector electrodes and the fabrication process has usually involved various methods ranging from sputtering of the metal [6,8,12], physical placement of the electrode close to the separation channel [7], electron beam evaporator [14], or gluing either copper [15] or aluminum layers [5] onto the cover plate. While the photolithographic methods are difficult to carry out, other normal deposition methods such as sputtering and thermal or electron beam evaporation require etching steps and hence impose limitations in dimensions of the electrodes.…”