Models for dispersion in flow injection analysis. Part 1. Basic requirements and study of factors affecting dispersion

The various approaches adopted for accounting for dispersion behaviour in flow injection analysis are examined and the advantages of a modelling approach are discussed. The variation of the dispersion coefficient as a function of (a) flow-rate, (b) tube length, (c) tube inner diameter and (d) method of injection obtained under typical flow injection conditions are studied and discussed. Explanations for some of the effects observed are presented in terms of molecular diffusion and convective flow patterns. The advantages of “time” injection over the more usual “slug” injection are clearly demonstrated and the use of the single well stirred tank model to describe the relationship between volume injected and dispersion coefficient under conditions of time injection are examined. The applications of this model to describing the entire curve shape for slug injection and of the potentially more versatile two-tank model are briefly introduced.