Flow-injection responses of diffusion processes and chemical reactions

The technique of flow-injection analysis (FIA), now 25 years old, offers unique analytical methods that are fast, reliable and consume an absolute minimum of chemicals. These advantages together with its inherent feasibility for automation warrant the future application of FIA as an attractive tool of automated analytical chemistry. The need for an even lower consumption of chemicals and for computer analysis has motivated a study of the FIA peak itself, i.e., a theoretical model that provides detailed knowledge of the FIA profile was developed. It was shown that the flow in a FIA manifold may be characterised by a diffusion coefficient that depends on the flow rate, denoted as the kinematic diffusion coefficient. The description was applied to systems involving species of chromium, both in the case of simple diffusion and in the case of chemical reaction. It is suggested that the description may be used in the resolution of FIA profiles to obtain information about the content of interferences, in the study of chemical reaction kinetics and to measure absolute concentrations within the FIA-detector cell.