Sequential determinations by confluent reagent introduction in the sample loop: system characteristics and applications Original Research Article

A flow diagram was proposed in order to create two different regions in the sample zone. This was attained by introducing a volume of the reagent in a confluence point positioned in the sample loop. The two regions generated allowed the determination of two analytes in the sample zone. The feasibility of the system was demonstrated for the spectrophotometric determination of Fe(II) and total iron, i.e. Fe(II+III), in pharmaceutical products. In the proposed flow diagram, the reducing reagent, ascorbic acid, was introduced in the middle of the sample loop and 1,10-phenanthroline was introduced by confluence before the flow cell. The flow conditions to proportionate signal resolution were critically evaluated. The analytical frequency attained was 40 h−1 (i.e. 80 determinations per hour since two species are sequentially measured in the same sample zone). The accuracy was checked by comparing with a standard batch procedure and a paired t-test showed that all results obtained for pharmaceutical products are at the 95% confidence level agreement.