Bioanalytical system high-performance

Fig. 18b.1. Electrochemical cells and representative cell configurations, (a) Schematic diagram of a cell-potentiostat system, (b) Typical laboratory cell with Hg-drop electrode and drop knocker, (c) Voltammetric cell as detector at the end of a high-performance liquid chromatographic column, (d) A two-electrode (graphite) chip cell for biosensor development, (e) Three-electrode chip cells on a ceramic substrate for bioanalytical work.

Miniaturisation and automatisation of analytical and bioanalytical systems have had a great development in the last decade. The final goal of miniaturised devices is represented by micro-total analysis systems (g-TAS), also called lab-on-a-chip (LOC). These devices bring advantages in terms of mass production, low cost and disposability as well as speed, high performance, portability and low energy requirements. 

The above example demonstrates the power of utilizing modeling tools when designing microstructures for high-performance bioanalytical systems. Trivial design errors are easily avoided and preliminary optimization of a microfluidic structure may thus be accomplished in silico, prior to extensive and expensive processing rounds in the microfabrication laboratories. 

The pharmacokinetic performance of a drug influences the construction of a formulation. This has nowadays led to a dominance of drug delivery systems that provide a controlled or modified release of the drugs, defined as extended or delayed release. Release-controlling polymers are used to build up a barrier that prevents immediate release of a compound. In this way high peak plasma concentrations of drugs are avoided and usually only one dose per day is necessary. The characteristic properties of the formula are evaluated in in vivo tests where blood samples are analyzed often by extremely sensitive bioanalytical methods. 

Precision of peak areas or heights is important because they are used for calculating amounts during quantification. It is also the most important performance criterion for an LC injection system. Precision should be determined using a minimum of five rephcate chromatograms. For bioanalytical samples, precision is studied at least at low, medium, and high concentrations. This is repeated on separate days to calculate intraday and interday precision. 

Th for the precursor ion indicates interferences sufficiently serious that it is not clear where the analyte peak boundaries should be set in order to measure peak area in contrast, use of a peak width of 0.2 Th gave a much cleaner, well defined peak (Figure 6.12). This example is taken from an extensive examination (Jemal 2003a) of the performance of this enhanced resolution quadrupole system in the context of high throughput bioanalytical assays. While the increased selectivity was clearly established, it was also found that the enhanced resolution mode of operation requires considerably more attention... 

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