Electrochemical and optical detectors for capillary and chip separations

Abstract

In separations in capillaries or on chips, the most predominant detectors outside of the field of proteomics are electrochemical (EC) and optical. These detectors operate in the μM to pM range on nL peak volumes with ms time resolution. The driving forces for improvement are different for the two classes of detectors.With EC detectors, there are two limitations that the field is trying to overcome. One is the everpresent surface of the electrode which, while often advantageous for its catalytic or adsorptive properties, is also frequently responsible for changes in sensitivity over time. The other is the decoupling of the electrical systems that operate electrokinetic separations from the system operating the detector.With optical detectors, there are similarly a small number of important limitations. One is the need to bring the portability (size, weight and power requirements) of the detection system into the range of EC detectors. The other is broadening and simplifying the applications of fluorescence detection, as it almost always involves derivatization.Limitations aside, the ability to make detector electrodes and focused laser beams of the order of 1 μm in size, and the rapid time response of both detectors has vaulted capillary and chip separations to the forefront of small sample, fast, low mass-detection limit analysis.

Recent developments in CE and CEC of peptides

“…nanoliter detection cell volume with millisecond time resolution. The earlier developed special detection cell constructions with increased optical path and thus enhanced sensitivity (Zshaped cell, buble cell, or sleeve cell), and some new designs of the UV-absorption detector for capillary and chip separations are described in the recent reviews on optical detection schemes [160,161].…”

18 Coupling CE and microchip-based devices with mass spectrometry

“…It is simpler to establish a voltage drop across microchannels than pressure drops that would require miniaturized valves and pumps. Furthermore, microchips often include integrated detection methods such as optical and EC detectors, 333 and can also be hyphenated to MS. Although there are many efforts invested in developing miniaturized and multiplexed MS, 3342338 the main drawback of this coupling presently is that MS cannot be miniaturized and integrated to the microchip.…”

Detection of Copper Ion with Laser-Induced Fluorescence in a Capillary Electrophoresis Microchip

“…Different optical methods were also employed in microchips to detect metal ions, including absorbance (Malcik et al 2005;Du et al 2005), reflectance (Caglar et al 2006), chemiluminescence (Liu et al 2003), photodiode array detection (Collins and Lu 2001), and colorimetric methods (Deng and Collins 2003). Currently, the most sensitive optical detection method is based on Laser-induced Fluorescence (LIF) (Xu, Li, and Weber 2007). The optical arrangement of detection devices plays an important role for sensitivity and detection limit Fu et al 2006).…”