Parallel FIA Systems

When a parallel FIA system is designed, two conditions must be fulfilled. First, as the channels can be interchanged only when the carrier stream does not move, and because the sample zone always has to be 

After the geometrical identity of both channels and the reproducibility of the stopped-flow manipulation have been established in this way, the conditions of an assay were simulated by alternately storing sample zones (of dye solution) in the channels with the aim of demonstrating which residence time may actually be obtained if a certain sampling frequency of, say, 120 samples/h should be maintained. For this purpose, however, the timing sequence of the electronic timer and the sample injector had to be altered. 

When we examine the time distribution of the recorded signal (Fig. 4.18c), it is apparent that the peak width at its base in this system is approximately twice as long as the time interval between the sample injection and the moment when the signal starts to rise. In a simple stopped-flow system this time distribution does not present a problem because a new cycle is initiated only when the next sample is injected. The timer for a two-channel parallel stop analysis must, however, run in a fixed go-stop-go cycle, because while one sample zone is being injected (or flushed out) the other is stored, and if the length of the storage period is not always the same, the analyzer will not yield reproducible results-unless, of 

When the procedure described above was first published [153], the following reservations were made as to the concept of parallel FIA (a) the method has been tried only by dispersion experiments with a dye and not with any chemistry (b) it is much more complicated than all other FIA approaches, which is against the spirit of the overall simplicity of FIA designs and (c) too much room has been allocated to the desription of the parallel method, which has not yet been applied to any practical assay. Therefore, many may prefer an air-segmented continuous-flow system as a practical alternative for T s 1-10 min. Yet the description of 

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