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The present paper describes a new analytical method exploiting a SiO2/WO3 mixed oxide as an adsorbent synthesized via sol-gel process for the preconcentration of Ni2+. This material was characterized by energy dispersive X-ray fluorescence spectroscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, analysis of the specific surface area by Brauner, Emmett and Telle multipoint method, the average pore size and pore volume by Barrett-Joyner-Halenda method, scanning electron microscopy, and electron dispersive spectroscopy. The mixed oxide presented high surface area (710.9 m2 g−1), average pore size of 35.1 Å, and average pore volume of 0.128 cm−3 g−1. This material was used as the an adsorbent in an on-line procedure for pre-concentration of solid phase extraction, based on the adsorption of Ni2+ ions at pH 10.5 followed by elution with 1.0 mol L−1 HNO3 and determination by flame atomic absorption spectrometry. Under optimized conditions, a linear range from 10.0 to 170.0 µg L−1, an enrichment factor of 38.8-fold, and limits of detection and quantification of 4.23 µg L−1 and 14.11 µg L−1 were obtained. The precision of method, estimated as percentage of relative standard deviation of ten replicates of 30.0, 90.0 and 150.0 µg L−1 Ni2+ solutions, was lower than 4.10%. The method was employed for analysis of water samples and the accuracy was attested by addiction and recovery tests, with satisfactory recoveries (98.4–109.2%). Thus, the developed material can be successfully applied to water samples for monitoring of Ni2+ at very low levels without matrix influence. [ABSTRACT FROM AUTHOR]

A SiO2/Al2O3/Sb2O5mixed oxide was synthesized via a sol-gel method and applied to the on-line preconcentration of Ni(II) with determination by flame atomic absorption spectrometry. The mixed oxide was characterized by infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray fluorescence, thermogravimetric analysis, and the specific surface area. Analysis was performed by percolating 20.0 mL of sample at pH 7.1 through 100 mg of SiO2/Al2O3/Sb2O5packed into a mini-column at 9.5 mL min−1. Under the optimum conditions, a preconcentration factor of 77.5-fold, linear dynamic range from 5.0 to 270.0 µg L−1, and limits of detection and quantification of 0.48 and 1.61 µg L−1were obtained. The effects of several concomitant ions were evaluated and no interferences were observed. The method was employed for the analysis of water with good recoveries (92.9–100.6%) and the accuracy was verified by using a marine sediment certified reference material (MESS-3). [ABSTRACT FROM AUTHOR]

Abstract: The main purpose of the present work is to synthesize and characterize a new sorbent material, which contains manganese oxide particles finely dispersed in a silica matrix, and evaluate its ability to improve the detectability of flame atomic absorption spectrometry (FAAS) for on-line determination of trace Cd(II) in aqueous and biological samples. The surface area, pore volume and micropore size of the sorbent were found to be 232m2 g−1, 0.0303cm3 g−1 and 1.7nm, respectively. To accomplish the on-line sorbent preconcentration, 20.0mL of a pH 9.0 Cd(II) solution at a flow rate of 10.0mLmin−1 were preconcentrated onto 320mg of the SiO2/MnOx material packed into a mini-column and then eluted with 1.0molL−1 HNO3 toward the FAAS detector. The following analytical features were obtained: linear responses to Cd(II) ions in the range of 1.0–50.0μgL−1 (r=0.9968), detection limit of 0.20μgL−1, preconcentration factor of 39.4, concentration efficiency of 19.7min−1, consumptive index of 0.51mL, and analytical frequency of 20h−1. The dispersion of manganese oxide in the SiO2 matrix promoted a 2.15-fold improvement on detectability of Cd(II) ions in comparison with an analytical curve built with SiO2 as sorbent. The accuracy of the preconcentration method was verified through the analysis of natural water samples employing addition/recovery tests and GF AAS as reference technique, and analysis of certified reference materials — Lobster Hepatopancreas (TORT-2) and NIST SRM 1643e (“Trace elements in natural waters”). [Copyright &y& Elsevier]