Continuous Flow Injection Analysis (FIA)

In its simplest form, Flow Injection Analysis (FIA) involves injecting a small volume (µL) of a sample solution into a moving fluid. This continuously moving carrier fluid is not segmented, and the zone formed by the repeated injection of the sample is transported to a detector to record variations in a physical or physico-chemical parameter characteristic of the sample or, more often, of one of its constituent elements.

In principle, however, continuous flow analysis differs from segmented flow analysis in that, in the latter case, the samples are separated by air bubbles and retain their identity. What's more, in segmented flow analysis, if chemical reactions are involved, the aim is to reach equilibrium before passing through the appropriate detector, which is not always the case with FIA. Continuous flow analysis also differs from liquid chromatography methods in that it does not, as a rule, involve separating the constituents of the mixture to be analyzed.

We can thus say, schematically, that the originality of continuous flow analysis and its analytical possibilities [1] is defined by the following two points:

• unsegmented flow ;

• controlled dispersion of the sample in the conveying fluid.

Although only recently developed, FIA is already widely used in analytical laboratories: in 1990, over 3,000 articles had already been published. Since then, the technique has been the subject of a great deal of work, both on its theoretical aspects and on its technological and analytical applications, and today, FIA has become a fast, simple and elegant automatic technique. More recently, so-called sequential injection analysis has emerged, derived from FIA, but with variable flow rates over time.