Development and evaluation of the iron oxide-hydroxide based resin gel for the diffusive gradient in thin films technique

An ion-exchange resin Lewatit FO 36 was used for the preparation of a new resin gel for the diffusive gradient in thin films technique (DGT). The DGT method was optimized for the accumulation of four bioavailable arsenic species (As-III, As-V, monomethylarsonic acid, dimethylarsinic acid) in the aquatic environment. The total sorption capacity of Lewatit FO 36 resin gel was 535 mu g As disc(-1). The microwave-assisted extraction in the presence of NaCl (10 g L-1) and NaOH (10 g L-1) was used for the isolation of arsenic species from the Lewatit FO 36 resin gel. The elution efficiency of arsenic was 98.4 +/- 2.0%. Arsenic was determined by the optimized electrothermal atomic absorption spectrometry (ET-AAS) method using palladium modifier, pre-atomization cool-down step and tungsten carbides coating of graphite tube. The Lewatit FO 36 resin gel provides accurate results (c(DGT)/c(SOL) ratio 0.86-1.00) in the pH range 4 -8. No significant influence of experimental conditions was observed in the presence of chlorides (0 -0.5 mol L-1) and humic acid (0-100 mg L-1). Only a very high concentration of phosphates (10 mg L-1) caused a slight decrease in the diffusion coefficients of MMA and As-V species (8.4% and 12.4%, respectively). The presence of iron (0-1 mg L-1) caused a decrease in the diffusion coefficients, but with regard to the common concentrations of iron (less than 0.3 mg L-1), the negative effect was considered not significant for As-III and DMA in natural water. The DGT-ET-AAS method was applied for the determination of bioavailable arsenic species in the spiked river water samples and also in-situ in the water reservoir. The new resin gel was characterized by a homogeneous gel structure with excellent reproducibility (< 5% variation of results between batches) and high sorption capacity which suggests its possible long-term application (up to 286 days in the environment with the arsenic concentration of 100 mu g L-1). (C) 2019 Elsevier B.V. All rights reserved.