Composite materials based on hybrid mesoporous solids for flow-through determination of ultratrace levels of Cd(ii)

Abstract

In this work we present a solid phase extraction (SPE) flow-through system coupled to graphite furnace atomic absorption spectrometry (GFAAS) for the determination of Cd(II) at ultratrace levels. The flow system holds a minicolumn which was filled, one at a time, with three different lab-made materials: (a) mesoporous silica functionalized with 3-aminopropyl groups from 3-aminopropyl triethoxysilane (HMS); (b) HMS with a resin, Amberlite IR120; and (c) HMS-Amberlite IR120 and polyvinyl alcohol (PVA). All the solids were characterized by FTIR and SEM. Batch experiments were performed in order to study the optimum adsorption pH, the adsorption kinetics and the maximum adsorption capacity. The materials were compared in terms of their aptitude for the pre-concentration of the analyte under dynamic conditions. Microvolumes of HCl were employed for the release of cadmium and its introduction into the electrothermal atomizer. The operational variables of the flow system were also tested and optimized. A comparison of the figures of merit revealed that HMS-A-PVA was the best option from an analytical point of view: limit of detection = 4.7 ng L⁻¹, limit of quantification = 16 ng L⁻¹, RSD% = 4 (n = 6, 100 ng L⁻¹), linear range: from LOQ up to 200 ng L⁻¹ and a lifetime of over 600 cycles with no obstructions to the free movement of fluids, material bleeding or changes in the analytical sensitivity. The proposed method was shown to be tolerant to several ions typically present in natural waters and was successfully applied to the determination of traces of Cd(II) in real samples. A full discussion of the main findings with emphasis on the metal ion/filling interaction is provided.