Am&ha Chtmica Acta, 285 (1994) 193-208 Elsevier Science B.V., Amsterdam 193 Expert system for the voltammetric determination of trace metals Part IV. Methods for speciation of chromium and arsenic M. Esteban and C. Ariiio Departament de Quhica AnaKtica, Vniversitat de Barcelona, Av. Diagonal 647,08028 Barcelona (Spain) I. Ruislnchez, M.S. Larrechi and F.X. Rius Departament de Quimica, Vniversitat Rovira i Vvgili (Tarragona), PI. Imperial Thraco I, 43005 Tarragona (Spin) (Received 8th February 1993; revised manuscript received 20th April 1993) Abstract A previously described expert system for the voltammetric determination of Cu, Zn, Cd, Pb, In, Ni, Co, Tl, Hg, V and Se (optionally also Te) is enlarged and improved by including methods for speciation of chromium and arsenic. Voltammetric procedures for the quantification of Cr(III), CrWI), A&II) and As(V) are considered, Cr(III) and As(V) being determined by the difference between total chromium and Cr(VI), and total arsenic and As(III) respectively. The techniques implemented are differential pulse polarography, differential pulse anodic stripping voltammetry, differential pulse cathodic stripping voltammetty and differential pulse adsorptive stripping voltamme- try, using mercury drop electrodes and a rotating gold electrode. The expert system is developed using KES (knowledge engineering system). Keywords: Voltammetry; Arsenic; Chromium; Expert system; Metal speciation; Cbemometrics; Trace metals In previous papers [1,2], a knowledge-based expert system for the voltammetric determination of several trace metals was described. Elements considered were Cu, Zn, Cd, Pb, In, Ni, Co, Tl, Hg, V and Se (optionally also Te). The tech- niques implemented were differential pulse po- larography (DPP), differential pulse anodic strip- ping voltammetry (DPASV), differential pulse ca- thodic stripping voltammetry (DPCSV) and dif- ferential pulse adsorptive stripping voltammetry (DPAdSV), using mainly mercury drop electrodes (SMDE and HMDE). Correspondence to: M. Esteban, Departament de Quimica Analitica, Facultat de Quimica, Universitat de Barcelona, Av. Diagonal 647,08028 Barcelona (Spain). The expert system is designed for those users who have some knowledge in electrochemical analysis but cannot be considered as specialists. Furthermore, it can be a valuable tool for teach- ing electroanalytical methods and for showing applicability of expert systems. In this paper, an enhancement of the previ- ously described expert system is reported, which is devoted to the speciation of chromium and arsenic. Chromium is an important ecotoxic trace metal which can be present, in natural waters, in two oxidation states: the reactive and toxic Cr(V1) and the relatively inert Cr011). Cr(VI) is present at various concentration levels, 0.1-0.5 pg l-l, in ocean waters [3], to 200 I.cg I-’ in some poluted ground waters [4]. 0003-2670/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDI 0003-2670(93)E0459-K