Extraction properties of modified silica gel for metal analysis by energy dispersive X-ray fluorescence

Batch-wise liquid-solid extraction using chemically modified silica was studied as a separation method for non-essential heavy-metals, such as cadmium, lead and mercury, with subsequent X-ray fluorescence analysis. Silicas modified with zirconium phosphate (SiZrP) and propyl imidazol (SiIm) were prepared for use as a solid extractor. The silica modified with imidazol groups showed a high selectivity for Hg2- and a wide linear response range (0.5 - 50 mg L-1) with a preconcentration factor of 107, but did not adsorb significant amounts of lead and cadmium. For the SiZrP system the preconcentration factors for all studied metal ions were between 43 and 47, with lower selectivity. The sensitivity depends on the characteristic emission line of each element. The linear response ranges were 0.5 to 10 mg L-1 for cadmium, 0.5 to 50 mg L-1 for lead and 0.5 to 116 mg L-1 for mercury. The stability presented by the materials were excellent, allowing reuse after regeneration in an acid media.33102005202

Adsorption parameters of Cd(II), Pb(II), and Hg(II) on zirconium(IV) phosphate chemically grafted onto silica gel surface

Adsorption properties of metallic ions not essential for human metabolism, such as cadmium, lead, and mercury, on silica chemically modified with zirconium(IV) phosphate, SiZrP, were investigated using batch systems. The immobilization procedure was efficient and the functionalization degree was 2.82% for zirconium (0.31 mol g(-1)) and 2.54% for PO43-(0.27 mol g(-1)). These results indicate that phosphate reacted with zirconium in a 1:1 ratio. The equilibrium is reached very quickly( 15 min), indicating that the adsortion sites are well exposed, The best adsorption parameters were evaluated using 50 mL of aqueous phase at pH 4.5, an adsorption time of 15 min, and 0.2000 g of adsorbent. From adsorption isotherms obtained for the metals ions and distribution coefficients the affinity of SiZrP for the metal ions studied increases in the order Cd(II) < Pb(II) < Hg(II). Twice as much lead was adsorbed by the SiZrP surface (Nf = 10.0 mu mol g(-1))as cadmium (Nf = 5.0 mu mol g(-1)). For mercury, the capacity was greater; nevertheless an adsorption plateau was not observed. (C) 1998 Academic Press.200112112

Optimization of metal extraction conditions by modified silicas using a factorial design

The extraction properties and the selectivity of silica modified with zirconium phosphate (SiZrP) and propylimidazol (SiIm) for cadmium, lead and mercury were evaluated. The optimization of these parameters was carried out by a complete 2(3) factorial design (consisting of two levels and three factors), using the intensity of energy dispersive X-ray fluorescence (EDXRF) as response factor. SiZrP adsorbed the three metallic species, while SiIm adsorbed mercury selectively. This difference was assigned to the particular adsorption process involved in each instance. The interaction factor between pH and silica type was significant, suggesting that an unidimensional study could not have optimized the system. Using small amounts of the adsorbent matrices (0.2 g) resulted in better sensitivity, as well as an important saving of chemicals.15876176

Multivariate calibrations for the SR-TXRF determination of trace concentrations of lead and arsenic in the presence of bromine

A synchrotron radiation source and total reflection x-ray fluorescence (SR-TXRF) spectrometry were used for the determination of lead and arsenic in aqueous samples. To overcome the serious spectral interference between the two species and the overlap of another interfering element (bromine), a partial least-squares regression (PLSR) method was used. The calibration models PLSR2 and PLSR1 were based on the x-ray fluorescence emission signals (9.550-13.663 keV) for a set of 26 different mixtures containing the elements of interest, lead and arsenic, as well as bromine. The results obtained by PLSR1 and PLSR2 were compared with those obtained by the conventional univariate methodology. In the latter case, the areas of the secondary emission lines (L beta for lead and K beta for arsenic) were used to elaborate the analytical curves. The capacity of all optimized models was verified using five synthetic samples (external validation). Subsequently the best model was used to determine lead and arsenic recovery capacities when these metals are retained on two ion-exchange resins (Dowex 50-X8 and Dowex 1-X8). The best multivariate model (PLSR1) allowed the determination of lead and arsenic with root mean square errors of prediction (RMSEPs) of 0.03 and 0.24 mg l(-1), respectively. The reduction of this parameter, with respect to the values obtained by conventional univariate methodology (0.26-0.03 mg l(-1) for lead and 0.30-0.24 mg l(-1) for arsenic), indicates that the proposed multivariate methodology really overcomes the problems associated with spectral interferences and minimizes the influence of an interfering agent (bromine). Copyright (c) 2005 John Wiley & Sons, Ltd.351798

Sorption and Preconcentration of the Herbicides Atrazine, Simazine, and Ametryne on Montmorillonite

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)This paper describes the treatment of montmorillonite (MT), with K+ (MTK), Na+ (MTNa), and Ca2+ (MTCa) to explore the use of these minerals for the extraction and preconcentration of the herbicides atrazine, simazine, and ametryne from aqueous medium. In the sorption process, the three materials exhibited good performance; ametryne was totally sorbed. For atrazine and simazine, MTK showed a removal between 90% (atrazine) and higher than 99% (simazine). The recoveries employing solutions at initial concentrations of 100 mu gL1 of each herbicide showed results of 90% (simazine) and 94% (atrazine), whereas for 10 mu gL1, the results of 73% (simazine) and 81% (atrazine) were obtained. On the other hand, ametryne showed poor recovery values (25 to 40%), probably due to a stronger interaction with MTK, lowering the recovery values. Based on the results for atrazine and simazine, MTK presented good features to be used as sorbent phase and for preconcentration, being easily prepared with low cost, demanding low amounts to be used for this purpose, providing fast sorption of atrazine and simazine, and with appropriate recoveries.463439451Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPES [PROCAD 0082/05-8