A new strategy for the modification of a carbon paste electrode with carrageenan hydrogel for a sensitive and selective determination of arsenic in natural waters

Abstract

An adsorptive stripping voltammetric method for the determination of As(III) and Astotal in water samples using a carrageenan modified carbon paste electrode is presented for the first time (CAR−CPE). The modified electrode was prepared in different ways: by adding CAR in solid form or as a hydrogel together with graphite and paraffin, as well as adsorbing CAR by applying a potential on an unmodified carbon paste electrode. The best results were obtained when CAR was incorporated as hydrogel (HCAR−CPE). The selection of the ratio amounts for electrode preparation was carried out applying a multivariate experimental design. Variables like amount of graphite (U1), HCAR (U2) and paraffin (U3) were optimized using a (2K+2K+C) model. The results showed that the amount of HCAR was the most significant factor, and the adequate U1:U2:U3 ratio to prepare the electrode was: 493 mg of graphite, 214 μL of paraffin and 134 μL of carrageenan as gel. The optimum parameters for the determination of As(III) were pH = 3.25 (0.01 mol L−1 H3PO4/H2PO4− solution); Eacc = −0.50 V and tacc = 30 s. The electrode presents good linear behavior concentration range from 0.50 to 6.70 μg L−1, with a limit of detection of 0.22 μg L−1. The relative standard deviation was 5.0% at the 1.5 μg L−1 As(III) level (n = 16). The method was validated by quantifying As(III) in spiked tap water from laboratory (RE: 3.0%), and it was applied for the determination of Astotal in water samples from the Loa River (North of Chile) prior reduction of As(V) with Na2S2O3 solution, obtaining 814.00 ± 0.03 μg L−1. The results of the proposed method were compared with those obtained by adsorptive stripping voltammetry with HMDE and by Inductively Coupled Plasma Mass Spectrometry (ICP−MS) techniques.