Repetitive determination of calcium ion and regeneration of a chromogenic reagent using chlorophosphonazo III and an ion exchanger in a circulatory flow injection system.

The spectrophotometric determination of Ca2+ with chlorophosphonazo III (CPN) has been carried out by a circulatory flow injection (FI) method. A cation-exchange mini-column for the on-line regeneration of the main reagent was incorporated in this FT system, allowing a repetitive determination of Ca2+. A solution of 4.0 x 10(-5) M CPN in a 0.05 M acetate buffer (pH 5.0) in a single reservoir (50 ml) was continuously circulated at a constant flow rate of 1.5 ml min(-1). Into the stream, an aliquot (20 microl) of a sample containing Ca2+ was quickly injected by means of a 6-way valve. The complex formed was monitored spectrophotometrically at 670 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 Ca2+ between the CPN 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 CPN reagent allowed as many as 300 repetitive determinations of 2.5 mg l(-1) Ca2+ solutions with the same 50 ml circulating solution.