Miniaturized flow cells

Micro reaction systems may help to overcome or at least reduce some of the above-mentioned limitations [69]. Electrochemical micro reactors with miniature flow cells where electrodes approach to micrometer distances should have much improved field homogeneity. As a second result of confined space processing, the addition of a conducting salt may be substantially reduced. In addition, benefits from a uniform flow distribution and efficient heat transfer may be utilized. 

Broekaert J. A. C. Optimization of electrochemical hydride generation in a miniaturized flow cell coupled to microwave-induced plasma, atomic emission spectrometry for the determination of selenium, Fresenius Journal of Analytical Chemistry, in press. 

Berg, H. C., and Block, S. M. (1984) A miniature flow cell designed for rapid exchange of media under high-power microscope objectives./. Gen. Microbiol. 130, 2915-2920. 

Control of discrete system elements, which allows added flexibility for sampling, is important to consider. An integrated computer-controlled system was demonstrated for a microdialysis probe coupled online to a flow-though system for lactate and glucose monitoring in serum samples [30]. The system comprised a microdialysis probe and a micromachined sihcon stack along with a miniaturized flow cell and sensor array. The integrated system was computer controlled with a response time of 4 min. 

Simple FIA for lactate sensing are based on incorporation of LOD- or LDH-modified electrodes into flow injection systems. FIA based on enzyme reactors that contain LOD or LDH have also been developed for electrochemical or optical lactate sensing. Other enzyme electrodes or reactors can also be incorporated into lactate FIA systems, leading to the development of FIA systems that simultaneously detect lactate and other target molecules (Renneberg et ah, 1991). In addition, miniaturized flow cell that can be incorporated into FIA system (Nakamura et ah, 2001) and enzyme thermistor-based FIA has been developed (Chen et ah, 2011). 

A major advantage of FIA systems is the ease of combination with other flow systems. In particular, FIA systems comprising sample dilution flow systems and lactate-sensing flow systems have been developed. Moreover, miniaturized flow cells such as uTAS have been developed for lactate sensing. Future incorporation of suitable flow systems into FIA will enable the development of miniaturized FIA systems that can automatically detect lactate in multiple samples without pretreatment. 

B. Bahnev, L. van der Sneppen, A. E. Wiskerke, F. Ariese, C. Gooijer, and W. Ubachs, Miniaturized Cavity Ring-Down Detection in a Liquid Flow Cell, Anal. Chem. 2005, 77. 1188. 

Pulse polarographic studies have been described using a microcell of 0.5 mL capacity, which analyzed two 1,4-benzodiazepines, with the lowest detection limit reported to date being 10-20 ng/mL of blood [199]. Detailed construction of the cell and electrode assembly was also described (shown in Fig. 26.16). Further miniaturization of this type of three-electrode cell is not practical hence further increases in sensitivity will have to rely on electrochemical detector flow cells of microliter capacity such as those used in conjunction with liquid chromatography (see Chap. 27). 

Thacker [24] reported the design of a miniature flow fluorimeter for liquid chromatography. The body of the fluorimeter was machined from a block of aluminium and contained a low-pressure mercury lamp, an excitation filter, a quartz flow cell, an emission filter, a photomultiplier tube and a photoconducter in order to compensate for fluctuations in lamp intensity. Fluorescence was examined at a direction perpendicular to that of the excitation light. The cell was small enough for it to be attached directly to the end of the column with a minimum dead volume. 

The previously mentioned drawback of biosensing devices, i.e., the possibility to measure just one metabolite at a time, is nowadays partially overcome through the recent advances in miniaturization and the development of arrays of sensors. Each of the sensors constituting the array can consist in a different biosensor, allowing multi-analyte determinations. In some cases, if the array is located in a flow cell, it can be coupled to microdialysis sampling. Examples have been presented by several authors, even if the proposed... 

Even before the introduction of miniaturized biosensor arrays, however, some systems able to simultaneously measure glucose and lactate had been reported in the literature. One example is provided by Osborne et al. [157], who described plastic film carbon electrodes fabricated in a split-disk configuration and then modified to obtain a dual biosensor. They achieved a continuous monitoring of these metabolites by placing the dual electrode in a thin-layer radial flow cell coupled to a microdialysis probe. The stability of the sensors was sufficient for short-term in vivo experiments in which the crosstalk, i.e., the percentage of current measured by one biosensor but due to product generated by the partner biosensor, was acceptable for an in vivo application. 

The key enabler to using FTIR for BWA detection is to develop selective and robust sampling protocols coupled to a miniaturized, portable FTIR unit. To that end, we have developed front-end liquid flow cells which incorporate electric field (E-Field) concentration methods for spores onto the surface of an Attenuated Total Reflection (ATR) IR crystal. IR spectra are presented which show collection and detection results with BG spores in water. The approaches we have developed take advantage of the fact that all spores are negatively charged in neutral pH solutions. Therefore, E-Field concentration of spores directly onto an ATR sampling element enables low level concentration measurements to be possible. 

E. Verpoorte, A. Manz, H. Lndi, A. E. Bruno, F. Maystre, B. Krattiger, H. M. Widmer, B. H. Vanderschoot, and N. F. Derooij, A Silicon Flow Cell for Optical-Detection in Miniaturized Total Chemical-Analysis Systems, Sensors and Actuators B-Chemical, vol. 6, no. 1-3, pp. 66-70, Jan. 1992. 

SPR detection is highly adaptable to multiplexed configurations in miniaturized formats. The flow cells in the original Biacore systems had four measuring spots positioned within a few millimeters (Fig. 19). Prototype systems with eight parallel flow channels have also been described and applied to food analysis apphcations [64]. 

Figure 6.12. Detailed drawings of (a) The injection valve module (b) reactor module R1 comprising one mixing tee (c) reactor module R2 comprising two mixing tees and (d) reactor module R3, which, designed for titrations, comprises a gradient tube and and a mixing tee (cf. Figs. 4.62 and 4.63). The reactors, valve, and flow cell modules, as well as additional electrochemical detector modules, are interchangeably accommodated on an elastic back-plate so that the versatility of the miniaturized FIA lab system can be further expanded.

Careful consideration must be given to the design of the detector flow cell as it forms an integral part of both the chromatographic and optical systems. A compromise between the need to miniaturize the cell volume to reduce extracolumn band broadening... 

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