Miniaturized total analytical systems

In volumetric titrations, the titrant is added in the form of a solution. An important alternative is coulometric titration, hi this method, the titrant is generated in situ by electrolysis of the solution containing the analyte. The amoimt of charged used imtil the equivalence point has been reached is evaluated to calculate the amount of sample. Calculation is based on Faraday s law [Chap. 2, Eq. (2.36)]. Coulometric titrations are easily performed on a miniature scale. If the generator electrodes are extremely small, then mechanical stirring is not necessary. Diffusion is sufficient to transport reactants. Such microtitrator systems can be combined with an electrochemical indicator arrangement in order to establish a sensor-actuator system. Such a set-up is an example of miniaturized total analytical systems ( -TAS) which are presented in Chap. 10. Such systems are much more complex than simple chemical sensors, although in practical use this is not always transparent. 

Proceedings of the 2nd International Symposium on Miniaturized Total Analysis Systems, Analytical Methods and Instrumentation, Special Issue pTAS 96, pp. 9-15, Basel (1996). 

Lu H, Schmidt MA, Jensen KF (2001) Photochemical Reactions and On-Line UV Detection in Microfabricated Reactors. Lab Chip 1 22-28 Manz A, Harrison DJ, Verpoorte EMJ, Fettinger JC, Ludi H, Widmer HM (1991) Miniaturization of Chemical-Analysis Systems - A Look into next Century Technology or just a Fashionable Craze. Chimia 45 103-105 McCreedy T (1999) Reducing the Risks of Synthesis. Chem Ind 15 588-590 McCreedy T (2000) Fabrication Techniques and Materials Commonly Used for the Production of Microreactors and Micro Total Analytical Systems. Trac Trends Anal Chem 19 396-401... 

Ramsey, J. M., Miniature chemical measurement systems, in Widmer, E., Verpoorte, E., Banard, S. (Eds.), Proceedings of the 2nd International Symposium on Miniaturized Total Analysis Systems, Analytical Methods and Instrumentation, Special Issue pTAS 96, Basel, 1996, 24-27. 

Microfluidics and miniaturization hold great promise in terms of sample throughput advantages [100]. Miniaturization of analytical processes into microchip platforms designed for micro total analytical systems (/i-TASs) is a new and rapidly developing field. For SPE, Yu et al. [123] developed a microfabricated analytical microchip device that uses a porous monolith sorbent with two different surface chemistries. The monolithic porous polymer was prepared by in situ photoinitiated polymerization within the channels of the microfluidic device and used for on-chip SPE. The sorbent was prepared to have both hydrophobic and ionizable surface chemistries. Use of the device for sorption and desorption of various analytes was demonstrated [123]. 

Busch M, Schmidt J, Rothen SA, Leist C, Sonnleitner B, Verpoorte S (1996) Proc 2nd Int Symp Miniaturized Total Analysis Systems (TAS96), 19-22 Nov 1996, Basel, (Analytical Methods and Instrumentation, Special Issue 1996, Widmer HM, Verpoorte E, Barnard S (eds), p 120... 

Blankenstein G, Scampavia L, Branebjerg J, Larsen UD, Ruzica J, (1996) Flow switch for analyte injection and cell/particle sorting. In Proceedings 2nd international conference on miniaturized total analysis systems (pTAS 96), Basel, Switzerland, 19-22 November 1996,... 

Cullen, C.J., et al. Rapid phase space surface generation using an integrated microfabricated device reaction detection system and automated control, in Micro Total Analytical Systems 2006 The 10th International Conference on Miniaturized Systems for Chemistry and Life Sciences, 2006, Tokyo Society for Chemistry and Micro-Nano Systems. 

On the other hand, microfluidic devices for lab-on-a-chip applications are mainly used in the context of analysis and diagnostics, often integrated in soolled miniaturized total analysis systems (p-TAS) [2]. The fundamental idea of p-TAS is to integrate all analytical steps such as sampling, sample pretreatment, analyte separation and detection for qualification or quantification within one device. Depending on the complexity of the sample, a lab-on-a-chip device can be a simple sensor, a flow-injection analysis (p-FIA) or a complete analytical separation device such as a chromatographic (p-HPLC) or a capillary electrophoresis (p-CE) system [3]. 

The bulkiness of optical sensor instrumentation has prevented - so far - the use of optical chemical sensors ("optodes") in micro total analytical systems (p-TASs) This is going to change in the next future Three kinds of approaches toward optode miniaturization are presented which appear promising in context with p-TAS schemes The following are considered to hold particular promise... 

Micro Total Analysis Systems (pTAS) are chip-based micro-channel systems that serve for complete analytics. The word Total refers to the monolithic system character of the devices, integrating a multitude of miniature functional elements with minimal dead volumes. The main fields of application are related to biology, pharmacology, and analytical chemistry. Detailed applications of pTAS systems are given in Section 1.9.8. Recently, pTAS developments have strongly influenced the performance of organic syntheses by micro flow (see, e.g., [29]). By this, an overlap with the micro-reactor world was made, which probably will increase more and more. 

Recent breakthroughs in miniaturized analytical instrumentation include fully integrated lab-on-a-chip and micro total analysis systems. The former have had only moderate success as many analytical chemists have been reluctant to accept them [67]. At present, chip-based analytical systems are subject to major shortcomings such as the risk of analyte adsorption on walls and at interfaces — which is important especially in low-volume analytical systems — and optical interference at the walls of the chips hampering detection. Further research in this field is required in order to effectively circumvent these shortcomings [68]. 

---