Single Zone Yielding a Double Peak

Since the formation of double peaks recently has become recognized as a source of new information, it is important to discuss the mechanisms by means of which doublet peaks are formed from a single injected zone. The formation of double peaks may be due to physical dispersion processes alone or to a combination of the dispersion process and the chemical processes that form a detectable species. 

As a result of the injection process, humped peaks formed by the dispersion process alone can be observed in a single-line FIA system under conditions of laminar flow provided that the reduced time t = Dm//(0.5rf) is close to 0.04, where Dm is the diffusion coefficient (cm /s), d is the diameter of the tube, and t is the time. This observation for FIA was first described by Vanderslice et al. [142], who also recently computed and depicted in an elegant way the microstructure of flow boluses under lam- 

Double peaks formed by a combination of the dispersion process and ensuing chemical reactions forming the detectable species have been observed frequently, and the reason for double-peak formation is the lack of reagent in the center of the injected sample zone [153, Fig. 6.6, p. 137]. This inevitably happens in any FIA system whenever the combination of the original sample concentration Cs and that of the reagent C% and their dispersion coefficients becomes 

In the simplest case the sequence throughout the zone is superstoichiometry, equivalence, substoichiometry, equivalence, and superstoichiometry (Fig. 2.24). Obviously, if the species would react in several 

Stoichiometric ratios n 1), the preceding regions would coexist in the dispersing zone in several sequences and the detected zone will show a corresponding number of maxima, minima, and their combinations. 

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