“Síntese e aplicação de sílica modificada na adsorção de Cu(II), Cd(II) e As(V)” em meio aquoso: Pré-concentração em amostras de águas naturais

Abstract

This paper reports on the development of analytical methods for the determination of some toxic and potentially toxic species in ultra-trace levels in natural water samples using a less sensitive analytical technique such as flame atomic absorption spectrometry (FAAS). This technique was chosen because it is relatively simple and has a low operating cost. The solid phase extraction technique (SPE) using a new sorbent material was used to separate and preconcentrate the analyte. This study demonstrates the procedure of a new synthetic route using the technique of the co-condensation for the production of a mesoporous organofunctionalised silica with the 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole ligant and its use as a sorbent for preconcentration/analysis of metal ions speciation in water samples. The material produced was characterized by infra-red spectroscopy (FTIR), BET, 29Si and 13C nuclear magnetic resonance (NMR), among others. The adsorptive characteristics of this material were established in batch studies, where the effect of pH, adsorption kinetics and maximum adsorption capacity were studied. Multivariate optimization was used to obtain the best chemical and flow conditions in the preconcentration system, allowing the evaluation of the main and secondary interactions among the factors. By means of the analysis of the spectra obtained by FTIR, it was possible to observe C-H, C-Cl and (NH2) stretch bands from the organic fraction of the material. The surface area was 369.84 m2 g-1 with average pore diameter at 7.1 nm related to mesoporous materials. The results obtained by 29Si NMR prove the formation of the hybrid material, synthesized by co-condensation, and the 13C NMR confirms the anchoring of the ligant in the matrix. The pH 5.0 it was favors the adsorption of the ions Cu (II), the pH 3.0 it was favors the adsorption of the Cd (II) and As (V). The kinetic model of pseudo second order showed better adjustment to the experimental data, indicating chemical adsorption. The adsorption data of Cu (II), Cd (II), and As (V) were similar to those of the Langmuir model, with a maximum adsorption capacity of 0.057, 0.018 and 0.060 mmol g -1 for Cu (II), Cd(III) and As(V) , respectively, indicating that the sorption occurs in monolayer. The analytical parameters for Cu (II) were: preconcentration factor of 18.1; linear range of 10.0 - 200.0 μg L-1 (R = 0.999) and LD of 1.45 μg L-1. For Cd (II): preconcentration factor of 15.8; linear range of 2.0 - 100.0 μg L-1 (R = 0.999) and LD of 0.38 μg L-1. For As (V): preconcentration factor of 5.0; linear range of 0.25 - 2.5 μg L- 1 (R = 0.999) and LD of 0.039 μg L- 1. Accuracy was checked by addition and recovery method of the standard and/or comparative method with GFAAS or ICP OES. The recovery ranged from 97-106% Cu(II), 100-105% Cd(II), 88-103% As (V) and 96-106% As (total)). The results for Cu (II) determined with the proposed methods were concordant with those obtained with the comparative. It is concluded that the material produced can be successfully applied in the extraction / preconcentration of copper, cadmium and analysis of inorganic speciation of arsenic and low limits of detection and quantification can be obtained even using a less sensitive technique such as FAAS.