Talanta 49 (1999) 505–510 Asynchronous merging zones system: spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products Andre ´ Fernando Oliveira, Joaquim A. No ´ brega, Orlando Fatibello-Filho * Departamento de Quı ´mica, Grupo de Quı ´mica Analı ´tica, Centro de Cie ˆncias Exatas e de Tecnologia, Uniersidade Federal de Sa ˜o Carlos, Caixa Postal 676, CEP 13.560 -970, Sa ˜o Carlos, SP, Brazil Received 2 September 1998; received in revised form 15 December 1998; accepted 29 December 1998 Abstract An asynchronous merging zones was proposed with simultaneous introduction of the sample and of the modifier reagent, ascorbic acid in the studied case, for sequential determination of Fe(II) and Fe(III) in pharmaceutical products. The sample and reagent attained a merging point at different times owing to the use of a delay reactor in the reagent channel. By inserting a large sample and controlling the dispersion in the flow system, Fe(II) and Fe(III) were sequentially measured in the front and in the rear of the sample zone, respectively. The results obtained for Fe redox speciation in pharmaceutical products are in agreement at a 95% confidence level with those obtained with a manual spectrophotometric procedure. The analytical frequency with the proposed flow analysis system was 54 samples h -1 , i.e. 108 determinations h -1 . © 1999 Elsevier Science B.V. All rights reserved. Keywords: Sequential determination; Asynchronous merging zones; Redox iron speciation 1. Introduction To increase the versatility of the flow analysis systems several strategies have been proposed for simultaneous or sequential determinations. These systems were based on diverse schemes, such as the use of various sample loops, flow splitting, combination of various detectors and multiele- mentar detection [1]. The serial insertion of sample loops separated by a large coil (1400-cm) was proposed by Fer- nandez et al. [2] and the parallel insertion of a sample loop with different residence times was evaluated by Kozuka et al. [3]. In both cases the analytes had distinct reaction rates. Cosano et al. [4] proposed an asymmetric merg- ing zones system with parallel injection of the sample and Nessler’s reagent. When the injector is in the sampling state, a large volume of sample is inserted in a loop composed by three stages, i.e. a first sample region, an enzymatic column contain- ing urease and a second sample region positioned * Corresponding author. Fax: +55-16-2608350. E-mail address: bello@dq.ufscar.br (O. Fatibello-Filho) 0039-9140/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII:S0039-9140(99)00015-6