Blood analysis, continuous flow system

The discrete systems of automatic analysis developed so far have not, in general, solved the problem of deproteinization in a way as satisfactory as the dialysis step adopted in the continuous-flow system. An earlier version of the Robot Chemist included a module in which precipitation of proteins followed by filtration was carried out, and the Mecolab system can incorporate a centrifugation step, following which a sample of supernatant can be automatically aspirated, but both these approaches are relatively cumbersome. Consequently attention has been directed to the development of analytical methods for blood serum or plasma that do not involve a deproteinization stage, but although alternative methods not involving the removal of protein may be feasible for many estimations, the responsibility for confirming the validity of such alternative procedures remains with the analyst. 

Yoon et al. [48] proposed a liquid junction free polymer membrane-based reference electrode system for blood analysis under flowing conditions. They used silicmi wafers as well as ceramic substrate to fabricate ion selective sensors with an integrated reference electrode. The silver chloride layer was coated with a membrane based on aromatic polyurethane (PU 40 membrane) with equimolar amounts of both cathodic and anodic lipophilic additives (TDMACl and KTpCIPB) to reduce the electrical resistance (see Chaps. 12 and 13). The ceramic-based sensors were fabricated by screen-printing methods. Both reference electrodes showed a rather stable potential in various electrolyte solutions with different pH values and different concentrations of clinically relevant ions, providing that the ionic strength of the solution is over 0.01 M. The integrated ISE cartridge based on the ceramic chip could be used continuously for a week. 

The first application of on-line dialysis to a flow system seems to be that made by Skeggs [ 1 ] in his pioneering work on segmented continuous flow analysis. The first report on using on-line dialysis in a non-segmented flow system was that made by Kadish and Hall [2], whereas Hansen and Ruzicka [3] were the first to report such applications in FIA. Despite its early implementation in HA, apyplications of on-line dialysis in this field have been rather few compared to other separation techniques, and mostly dedicated to the analysis of blood serum. This may be due to the fact that dialysis is a slow separation procedure compared to the speed of most FI procedures, and the dialysis efficiencies are usually quite low. 

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