Analysis of Caffeine and Related Compounds by Automated Flow Methods - Caffeine: Chemistry, Analysis, Function and Effects - page 195

11.2.1 Flow Injection Analysis
The concept of Flow Injection Analysis (FI) was originally proposed by
Ruzicka and Hansen in 1975 as an alternative approach to perform chemical
analysis under flow conditions (Ruzicka and Hansen 1975). Nowadays, FI is a
well-established and mature analytical technique with more than 12 000 FI
papers having been published in scientific journals. A simplified definition of
flow injection analysis might be, ''FI is an automated, continuous flow
approach to perform chemical analysis''. It is based on injecting a small, well-
defined volume of sample, into a continuously flowing carrier stream to which
appropriate auxiliary reagent streams can be added.
The main feature of FI that differentiates this technique from previous
Segmented Flow Analyzers (SFA) and of course from batch methodologies, is
its kinetic character. Due to precise timing and geometry, FI does not rely on
complete mixing of sample and reagent(s) (physical homogenization), nor to
completion-equilibrium of chemical reactions (chemical homogenization).
Thus, in FI it is feasible to base the principles of an analytical assay on the

d n 0 t 2 n g | 3

Figure 11.1 Representative FI manifolds of different configurations. Single- (a), two-

(b) and three-channeled (c) FI manifolds for automation of various
chemical systems. Samples (S) are injected in the carrier stream (C) and
merge downstream with suitable reagents (R/R1/R2). On-line reaction
takes place on passage through reaction coils (RC/RC1/RC2/RC3). P 5
pump; D 5 detector; W 5 waste.