Continuous sample recirculation in an opened-loop multicommutated flow system Original Research Article

A continuous circulating multicommutated flow system based on an opened-loop configuration is proposed. The sample is inserted into the flow system and continuously recirculated until a suitable dilution level is attained, which is permanently surveyed by including the detector in the circular reactor. A continuous removal of the highly dispersed front and trailing zones of the sample plug improves dilution efficiency. The chromogenic reagent used as carrier solution is permanently renewed, which contributes to a constant renewal of the reaction zone increasing the reaction rate by reducing its dependence on the dispersion at the sample/reagent interface. The developed methodology was tested in the determination of chloride in parenteral solutions by the formation of the iron (III) thiocyanate complex with expansion of the linear range of determination up to 10 000 mg l−1. Results were reproducible (RSD <1.8%) and in agreement with those obtained by the conventional procedure.