Micro volume control

The bead injection system was designed to operate in the sequential injection mode. It is possible to carry out bead injection analysis in a low-cost flow injection system with a unidirectional pump and without a computer, mainly for applications where samples and reagents are abundant and when there is no need for micro-volume control. To this end, it is necessary to use a flow cell able to achieve bead retention, accommodation of chemical reactions and detection [87,88]. 

Several techniques for miniaturization of simple chemical and medical analysis systems are described. Miniaturization of total analysis systems realizes a small sample volume, a fast response and reduction of reagents. These features are useful in chemical and medical analysis. During the last decade many micro flow control devices, as well as the micro chemical sensors fabricated by three dimensional microfabrication technologies based on photofabrication, termed micromachining, have been developed. Miniaturized total analysis systems (pTAS) have been studied and some prototypes developed. In microfabricated systems, microfluidics , which represent the behavior of fluids in small sized channels, are considered and are very important in the design of micro elements used in pTAS. In this chapter microfluidics applied flow devices, micro flow control devices of active and passive microvalves, mechanical and non-mechanical micropumps and micro flow sensors fabricated by micromachining are reviewed. 

Micro flow control devices open new possibilities for the miniaturization of conventional chemical and biochemical analysis systems. The micro total analysis system (pTAS) including microfabricated detectors (e.g. silicon based chemical sensors, optical sensors), micro flow control devices and control/detec-tion circuits is a practical micro electro mechanical system (MEMS). pTAS realize very small necessary sample volume, fast response and the reduction of reagents which is very useful in chemical and medical analysis. Two approaches of monolithic and hybrid integration of these devices have been studied. Monolithic and hybrid types of flow injection analysis (FIA) systems were already demonstrated [4, 5]. The combination of the partly integrated components and discrete components is useful in many cases [6]. To fabricate such systems, bonding and assembling methods play very important roles [7]. 

The dissociation constant, p Tg, controls the pH effect of the retention of ionizable compounds. Dissociation constants are measured by titration, and micro-volume flow titration has been developed. Dissociation constants can also be predicted from the atomic partial charge. An extended study of dissociation constants has been carried out, and a new method was proposed similar to a modified Hammett s equation. The dissociation constants used in this book were predicted by this new method from the atomic partial charge. ... 

The focus of the examples given in this chapter is clearly on micro reactors for chemical processing in contrast to p-TAS or Lab-Chip systems for bioanalytical applications. In the latter microfluidic systems, the fluidic requirements are somehow different from those in micro reactors. Typically, throughput plays only a minor role in p-TAS systems, in contrast to micro reactors, where often the goal is to achieve a maximum molar flux per unit volume of a specific product. Moreover, flow control plays a much greater role in p-TAS systems than in micro reactors. In... 

The small reaction volumes in micro reactors and the large specific surface areas created are beneficial for coping with the problems caused by the release of the large heats, as mentioned above [37, 38]. Delicate temperature control is what is expected for micro-reactor operation isothermal processing is said to be achiev-... 

The above-mentioned targets refer to general advantages of micro reactors [42, 80, 100, 114, 119]. Enhanced transfer and better controlled residence time improve conversion and selectivity. The tools have small internal volumes, allowing one to generate flexibly a multitude of samples in serial or parallel fashion. Synthesis can be combined with a multi-step procedure. The economy of micro-reactor processes has not really been analyzed so far however, it is clear that as laboratory tools they allow in a number of cases technical expenditure, personnel and costs to be reduced. 

Following the above-mentioned motivation, precise control over temperatare can be exerted in micro reactors [9,10]. Also, parallel or fast serial screening, handling small volumes distributed over compactly arranged reaction flow-through chambers, can be achieved in micro reactors. 

P Ij The liquid volume flow to the micro reactor is controlled by an HPLC pump [38]. The gas flow was set by mass flow controllers. Temperature was monitored by resistance thermometers. 

---