Repetitive determination of copper(II) and regeneration of a chromogenic reagent using a cation-exchange column in a circulatory flow-injection system

The spectrophotometric determination of Cu(II) with 4-methyl-5-[(sulfomethyl)amino]-2-(2-thiazolylazo)benzoic acid(TAMSMB) was carried out by a cyclic flow-injection analysis. A cation -exchange column for on-line regeneration of the main reagent was incorporated in this FIA system, allowing a repetitive determination of Cu(II). A solution of 5×10−5 M TAMSMB in 0.1 M acetate buffer (pH 3.7) in a single reservoir (50 ml) was continuously circulated at a constant flow rate of 1.25 ml min−1. Into the stream, an aliquot (20 μl) of a sample containing Cu2+ was quickly injected by means of a 6-way valve. The complex formed was monitored spectrophotometrically at 585 nm in the flow system. Then, the stream passed through a cation-exchange column, which was introduced after the flow-through cell. A successful ligand-exchange reaction of Cu2+ between the TAMSMB reagent and a cation-exchanger, as well as a simultaneous regeneration of the free reagent took place. The stream then returned to the reservoir. The regeneration and recycling of the TAMSMB reagent allowed as many as 500 repetitive determinations of 1.5 mg l−1 Cu2+ solutions with the same 50 ml circulating solution.