A multisyringe flow-based system for kinetic–catalytic determination of cobalt(II) Laura Chaparro a,b , Laura Ferrer b , Luz Leal a , Víctor Cerdà b,1 a Renewable Energy and Environmental Protection Department, Advanced Materials Research Center (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua, Chih. 31109, Mexico b Group of Analytical Chemistry, Automation and Environment, University of the Balearic Islands, Carretera de Valldemossa Km 7.5, E-07122 Palma de Mallorca, Spain article info Article history: Received 29 November 2013 Received in revised form 20 May 2014 Accepted 13 June 2014 Keywords: Cobalt(II) Kinetic–catalytic method Alizarin Multicommuted flow techniques abstract A kinetic–catalytic method for cobalt determination based on the catalytic effect of cobalt(II) on the oxidative coupling of 1,2-dihydroxyanthraquinone (alizarin) was automated exploiting multisyringe flow injection analysis (MSFIA). The proposed method was performed at pH 9.2, resulting in a discoloration process in the presence of hydrogen peroxide. The fixed-time approach was employed for analytical signal measurement. The spectrophotometric detection was used exploiting a liquid waveguide capillary cell (LWCC), of 1 m optical length at 465 nm. The optimization was carried out by a multivariate approach, reaching critical values of 124 mmol L À1 and 0.22 mol L À1 for alizarin and hydrogen peroxide, respectively, and 67 1C of reagent temperature. A sample volume of 150 mL was used allowing a sampling rate of 30 h À1 . Under optimal conditions, calibration curve was linear in the range of 1–200 mgL À1 Co, achieving a DL of 0.3 mgL À1 Co. The repeatability, expressed as relative standard deviation (RSD) was lower than 1%. The proposed analytical procedure was applied to the determination of cobalt in cobalt gluconate and different forms of vitamin B 12 , cyanocobalamin and hydroxicobalamin with successful results showing recoveries around 95%. & 2014 Published by Elsevier B.V. 1. Introduction In the context of reaction-rate based methods of analysis, catalytic methods stand out by their high sensitivity and low detection limits (and also, occasionally, increased selectivity) achieved in the determination of the catalyst concerned. Kinetic- based procedures executed by means of flow injection analysis techniques have the advantage of the precise and reproducible timing of all events so that non-equilibrium conditions can be readily exploited for quantitative assays. Kinetic discrimination and kinetic enhanced approaches can be carried out by flow techniques. In kinetic-discrimination methods, the differences in the rates of reactions of the reagent with the analyte of interest and interfering components are exploited. In kinetic enhancement, the chemical reactions involved are driven in the appropriate direction to the analyte of interest [1]. Cobalt is an essential trace element in nature and has an important role in many body functions. It is essential as a compo- nent of vitamin B 12 , and a deficiency of this vitamin can cause mild disease, neurological damage and anemia [2]. Thus, various pharmacological products involve cobalt as principal component are commercially available. However, in excess amounts it is toxic and causes pulmonary disorders, dermatitis, nausea and vomiting [3]. Hence, the quality control of cobalt concentration has to be carried out for the pharmaceutical industry in the commercialized products, since it is of great interest in nutrition researches. In order to develop a fast, sensitive and automatic method for monitoring a target analyte, flow analysis systems are excellent tools for the manipulation of solutions, allowing environmental friendly methods. The spectrophotometric technique has been employed in methods where cobalt acts as a catalyst for the oxidation of various colored substances [4–7]. Some procedures by catalytic effect have been proposed for spectrophotometric detection with flow injection analysis systems, using 4-benzylpiperidinedi- thiocarbamate [8] and tiron [7] as color developing reagents. Many 1,2-dioxy derivates of aromatic compounds (alizarin, pyrocatechin, tiron, etc.) are oxidized by hydrogen peroxide in the presence of cobalt traces. The reaction takes place in a buffer solution [9]. The reaction mechanism of alizarin dyes in combination with hydrogen peroxide in alkaline medium has been studied over a range of pH and temperature in previous work [10], in which the kinetic of oxidation between the dye and hydrogen peroxide generating bleaching of dyes is discussed in detail. One of the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta http://dx.doi.org/10.1016/j.talanta.2014.06.071 0039-9140/& 2014 Published by Elsevier B.V. E-mail address: victor.cerda@uib.es (V. Cerdà). 1 Tel.: þ34 971 173260. Please cite this article as: L. Chaparro, et al., Talanta (2014), http://dx.doi.org/10.1016/j.talanta.2014.06.071i Talanta ∎ (∎∎∎∎) ∎∎∎–∎∎∎