Research and development topics in analytical chemistry

Abstract

Unsegmented continuous-flow analysis or flow injection analysis (FIA) has been developed during the last 4 years as an automatic method of analysis that is simple, accurate and rapid, typical sampling rates being 120 per h o ~r . l -~ In all such systems, a stream of reagent or other carrier flows through a small-bore tube, the flow-rate being maintained by a constant-pressure or a constant-volume pump. At a point along the length of the tube an injection mechanism allows the sample to be injected into the stream and as the sample bolus passes down the tube it may react with reagent in the stream or undergo other reactions with the stream solution. Situated downstream from the injection point is a sensor that measures the extent of these reactions.As the sample is injected directly into the carrier stream it follows that there is an interfacial region between the sample plug and the carrier and that during the course of mixing concentration gradients are established across the interface if the initial concentrations in the carrier and sample are different. Thus, if we have a system in which the sample solution is a mixture of metal ions at a given pH and the carrier is at a different pH and is a solution of a reagent that reacts with the metal ions, we would expect a well defined sequence of colour-forming reactions to take place across the interfacial region as the reagent and metal ions reacted and the pH ~h a n g e d . ~ c