Marcela Zanetti Corazza

Grafting 3-mercaptopropyl trimethoxysilane on multi-walled carbon nanotubes surface for improving on-line cadmium(II) preconcentration from water samples.

In the present study, the performance of multi-walled carbon nanotubes (MWCNTs) grafted with 3-mercaptopropyltrimethoxysilane (3-MPTMS), used as a solid phase extractor for Cd(2+) preconcentration in a flow injection system coupled to flame atomic absorption spectrometry (FAAS), was evaluated. The procedure involved the preconcentration of 20.0 mL of Cd(2+) solution at pH 7.5 (0.1 mol L(-1) buffer phosphate) through 70 mg of 3-MPTMS-grafted MWCNTs packed into a minicolumn at 6.0 mL min(-1). The elution step was carried out with 1.0 mol L(-1) HCl. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to estimate the extent of the MWCNT chemical modification. The 3-MPTMS-grafted MWCNTs provided a 1.68 times improvement in the sensitivity of the Cd(2+) FAAS determination compared to the unsilanized oxidized MWCNTs. The following parameters were obtained: preconcentration factor of 31.5, consumptive index of 0.635 mL, sample throughput of 14 h(-1), and concentration efficiency of 9.46 min(-1). The analytical curve was constructed in the range of 1.0-60.0 μg L(-1) (r=0.9988), and the detection and quantification limits were found to be 0.15 μg L(-1) and 0.62 μg L(-1), respectively. Different types of water samples and cigarette sample were successfully analyzed, and the results were compared using electrothermal atomic absorption spectrometry (ETAAS) as reference technique. In addition, the accuracy of proposed method was also checked by analysis of certified reference material NIST SRM 1573a (tomato leaves) and standard reference material NIST SRM 1643e (trace elements in natural waters).

Preparation of new ion-selective cross-linked poly(vinylimidazole-co-ethylene glycol dimethacrylate) using a double-imprinting process for the preconcentration of Pb2+ ions

A new ion-selective cross-linked poly(vinylimidazole-co-ethylene glycol dimethacrylate) prepared via a double-imprinting process was developed for the recognition and preconcentration of Pb(2+) from water samples. The sorbent was characterized by FT-IR, SEM, TGA and textural data. The maximum dynamic sorption capacity of Pb(2+) was 42.04 mg Pb(2+) g(-1) of the double-imprinted polymer. The sorption kinetics data were described by a pseudo-second-order model. The double-imprinted polymer exhibited a higher sorption efficiency of Pb(2+) than the blank polymer (non-imprinted polymer). The preconcentration procedure involved the loading of a Pb(2+) solution at pH 7.25 through 40.0 mg of the double-imprinted polymer packed in a mini-column at 5.0 mL min(-1). The selective efficiency of proposed method for the Pb(2+) preconcentration was assured by competitive sorption using different proportions of Pb(2+)/cations and Pb(2+)/anions. An analytical curve was obtained in the range 0.0-300.0 μg L(-1) (r=0.999) and a limit of detection of 2.46 μg L(-1) was obtained. The preconcentration factor was found to be 21, the consumptive index 0.95 mL and the concentration efficiency 5.25 min(-1). The preconcentration method was successfully applied to the Pb(2+) ions determination in different kinds of water samples with high recovery values (91.3-108.9%).

Preconcentration of Nickel(II) by a Mini-Flow System with a Novel Ternary Oxide Solid Phase and Flame Atomic Absorption Spectrometry

ABSTRACT A SiO2/Al2O3/Sb2O5 mixed 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/Sb2O5 packed 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−1 were 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).

Double-Imprinted Cross-Linked Poly(Acrylamide-co-Ethylene Glycol Dimethacrylate) as a Novel Sorbent for the On-Line Preconcentration and Determination of Copper(II) by Flame Atomic Absorption Spectrometry

An on-line preconcentration system was coupled to flame atomic absorption spectrometry (FAAS) for the determination of copper(II) in water using poly(acrylamide-co-ethylene glycol dimethacrylate) synthesized via a hierarchical double-imprinting process. The on-line preconcentration procedure was based on loading the sample into a minicolumn packed with the synthesized material, followed by elution with 1.8 mol L−1 HNO3. To achieve the highest performance, the method was optimized by 25-1 fractional and 22 full factorial designs. Under the optimum conditions, the following analytical parameters were obtained: detection limit of 0.48 µ gL−1, quantification limit of 1.61 µgL−1, preconcentration factor of 31.0, consumption index of 0.58 mL, preconcentration efficiency of 8.63 min−1, and sample throughput of 15 h−1. The precision of the method was evaluated as the relative standard deviation (n=10) of 10.0 and 150.0 µgL−1 copper(II), yielding values of 3.27% and 1.97%, respectively. The analytical efficacy of the proposed method was justified by successful determination of copper(II) in water. The synergistic effects of copper(II) and cetyl trimethylammonium bromide, employed as templates, improved the preconcentration, thus improving the method without the double imprinting effect.