Figure 12.7
The automated determination of magnesium in urine using
o.o'-dihyroxyazobenzene (DAB). The final reagent concentrations
obtained are:
ethylenediamine 0.28 M HCl 0.14 M
DAB 0.07 mM KCl 0.10 Malthough delay coils may be added as required for the reaction to proceed far enough for detection.
With the carrier stream unsegmented by air bubbles, dispersion results from two processes, convective
transport and diffusional transport. The former leads to the formation of a parabolic velocity profile in
the direction of the flow. In the latter, radial diffusion is most significant which provides for mixing in
directions perpendicular to the flow. The extent of dispersion is characterized by the dispersion
coefficient D.
where C 0 is the initial concentration of the analyte and Cmax is the maximum concentration at the
detector. Values of D in the ranges <3, 3–10, and 10–15 would represent limited, medium and large
dispersions in sequence. Figure 12.8 shows a typical output trace for the enzymatic determination of
alcohol in beverages and Figure 12.9 a schematic representation for the determination of nitrate in river
water. As well as reagents in the carrier stream reactions may be effected by percolating the stream over
beads on which the reagent has been immobilized, a procedure which has been most useful in
enzymatic assays.
Flow injection analysis is a fast-developing technique with many potentialities. Particular attractions are
the relative simplicity of operation and automation, together with sample throughputs which may
exceed 100 per hour. Thus routine monitoring of process streams and pollution control are obvious
areas for application.