Instrumentation microchip

The transposition of capillary electrophoresis (CE) methods from conventional capillaries to channels on planar chip substrates is an emergent separation science that has attracted widespread attention from analysts in many fields. Owing to the miniaturization of the separation format, CE-like separations on a chip typically offer shorter analysis times and lower reagent consumption augmented by the potential for portability of analytical instrumentation. Microchip (p-chip) electrophoresis substrates boast optically flat surfaces, short diffusion distances, low Reynolds numbers, and high surface (or interface)-to-volume ratios. By exploiting these physical advantages of the chip over conventional capillaries, efficient p-chip electrophoresis systems can accomplish multiple complicated tasks that may not be realized by a conventional CE system alone. 

Two types of conductivity detectors exist the contact conductivity detector, where the electrodes are in direct contact with the electrolyte, and the contactless coupled conductivity detector (C D also called oscillometric detector). With this detector, two stainless-steel tubes that act as electrodes are mounted on a capillary at a certain distance from each other. By applying an oscillation frequency, a capacitive transition occurs between the actuator electrode and the liquid inside the capillary. After having passed the detection gap between the electrodes, a second capacitive transition between the electrolyte and the pickup electrode occurs (see Figures 7 and 8 which is an example of separation of cations). In different reviews, Zemann and Kuban and Hauser discuss the advantages of this technique which include rather simple mechanical parts and electronics, and Kuban et al. compared several C D detectors. This technique has also been used as a detector for analysis by microchip CE. C" D detectors are available to be mounted on existing CE instruments. 

The present chapter will review instrumental aspects for successful coupling of CE with MS, regarding interfaces, ionization sources, and analyzers. Practical considerations concerning different CE modes such as CZE, NACE, MEKC, and CEC coupled with MS will also be discussed and illustrated with a focus on recent pharmaceutical applications. Additionally, quantitative CE-MS will be presented and various methodologies used to achieve sensitive and repeatable analysis will be discussed. Finally, the final section of this chapter will give an overview on new devices (i.e., microchips), hyphenated to MS, in terms of fabrication methods, microchip designs, MS interfacing, and applications. 

EC detection is a promising alternative for capillary electrophoresis microchips due to its inherent characteristics, allowing a proper miniaturisation of the devices and compatibility with the fabrication processes, in case of an integrated detection. Moreover, the low cost associated permit the employment of disposable elements. As the EC event occurs on the surface of electrodes and the decrease in size usually results in new advantages (see Chapter 32), the possibilities of incorporating EC detectors are broad. The simplicity of the required instrumentation, portable in many cases, suit well with the scaling-down trend. Moreover, as the sample volume in conventional micro-channel devices is less than 1 nL, a very highly sensitive detector should be constructed to analyse even modest concentrations of sample solutions. Since sensitivity is one of the accepted characteristics of EC detection EC-CE microchips approach to the ideal analytical devices. 

Fig. 34.6. Electropherograms for (a) pAP and (b) AsA using a polymer-microchip with an end-channel Au wire detector inadequately (A) and properly (B) aligned. Conditions Vsep = +2000V injection 5s at +2000V Ec] = +0.8V (vs. Ag/AgCl), running buffer 50 mM Tris-Gly pH 9.0. Copyright (2006) from Instrumentation Science and Technology by Ref. [159]. Reproduced by permission of Taylor Francis Group, LLC., http //www.taylorandfrancis.com.

This chapter demonstrated that microchip electrophoresis reached maturity and is appropriate for analysis of nitrated explosives. However, to create easy-to-operate field portable instruments for pre-blast explosive analysis would require incorporation of world-to-chip interface, which would be able to continuously sample from the environment. Significant progress towards this goal was made and integrated on-chip devices which allow microfluidic chips to sample from virtually any liquid reservoir were demonstrated [25,31]. 

Immusoft is a software that has been developed to perform computer-driven assays in our microchips. This software has a user-friendly graphical user interface, and it enables control of the pump, the valves and the electrochemical detection system, as well as the development of specific assay protocols, the running of simultaneous or sequential experiments in eight parallel microchannels, the automatic read-out of the results and the processing of the obtained data. These different functions are managed by way of three main menus, named Method, Analysis and Results, and the software also comprises two additional items dedicated to the setting of the computing parameters and to the maintenance of the instrumentation. 

Semiconductors (Microchips)/Integrated Circuits/Components, Manufacturing Instrument Manufacturing, including Measurement, Control, Test Navigational Computers Electronics. Distribution Computer Telecommunications Equipment Distribution... 

Electrochemical detection offers also great promise for CZE microchips, and for other chip-based analytical microsystems (e.g., Lab-on-a-Chip) discussed in Section 6.3 (77-83). Particularly attractive for such microfluidic devices are the high sensitivity of electrochemical detection, its inherent miniaturization of both the detector and control instrumentation, low cost, low power demands, and compatibility with micromachining technologies. Various detector configurations, based on different capillary/working-electrode... 

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