Djenaine De Souza

Voltametria de onda quadrada. Primeira parte: aspectos teóricos

The theoretical aspects of square wave voltammetry were discussed. Reversible, irreversible and quase-reversible electrode reactions were analyzed and the correlations between parameters like frequency, period, square wave potential and amplitude were showed. In this way, diagnostic relationships allow to characterize the electrode process. The analytical applications were discussed in base of the increment in the analytical response (current) due to the characteristics of the developed equations and the unique mode of collecting the electrode response, i.e., the direct and reverse signals. Finally, recent advances in the basic theory, as the applications to the hydrodynamic electrode and the ultramicroelectrode were also analyzed, and the multiple pulses square wave voltammetry was also introduced.

Multiple square wave voltammetry for analytical determination of paraquat in natural water‚ food‚ and beverages using microelectrodes

This paper reports on the use of multiple square wave voltammetry (MSWV) for analytical determination of paraquat herbicide at gold microelectrode (Au-ME) in different samples of natural water, food, and beverages. In this work, the MSWV consisted in a sequence of four pairs of potential pulse in the same step and the interval potential evaluated was of the 0.0V at -1.2V versus Ag/AgCl 3.0 mol L(-1). The paraquat herbicide presented two reduction peaks, in -0.69V and -0.99V, with profile of the redox process totally reversible, and the use of multiple pulses allowed a detection of nanomolar levels after the optimization of experimental and voltammetric conditions. Analytical curves were constructed for pulse potential frequency of 250 s(-1), pulse amplitude of 50 mV, scan increment of 2 mV and pulse number of 8 pulses in a same step. The two reduction peaks showed that the peak currents were found to be directly proportional to the pesticide concentration in the range comprised between 5.0 x 10(-7)mol L(-1) and 1.04 x 10(-5)mol L(-1). With this, it was possible to determine detection limits (DL), which resulted in 0.044 microgL(-1) (0.044 ppb) and 0.146 microg L(-1) (0.146 ppb), respectively, for peak 1 and peak 2. DL results, obtained using MSWV, were 2-3 orders of magnitude lower (10(-2) to 10(-3)) less than those observed for traditional square wave voltammetry or published in literature, clearly pointing to the advantages arising from the possibility of using a MSWV for analytical purposes in contaminated matrices. In addition, the proposed methodology was applied in different samples of natural water, food and beverages without pre-treatment or pre-concentration step, where a recovery measurement indicated that the methodology could be employed to analyze paraquat in such matrices.

Voltametria de onda quadrada. Segunda parte: aplicações

The aim of this work is to discuss some selected applications of square wave voltammetry published in the last five years. The applications focused here cover several electroanalytical fields such as: determination of pesticides; molecules with biological activity; metals and other environmental pollutants. Special attention is given to the work developed in the Grupo de Materiais Eletroquimicos e Metodos Eletroanaliticos - IQSC - USP concerning the utilization of square wave voltammetry, with different kinds of electrodes, for the determination of pesticides in natural waters and active principles in pharmaceutical formulations. The new methodology is simple, fast and sensitive when compared with the traditional ones such as chromatography and spectrophotometry. The satisfactory results obtained provide alternative procedures for the quality control of drugs and the monitoring of pesticides in natural environments.

Utilização de técnicas eletroanalíticas na determinação de pesticidas em alimentos

The aim of this work is to discuss selected applications of electroanalytical techniques for the detection of pesticides in foods and beverages, published in the last ten years. The applications involved different working electrodes for the electroanalytical determination of pesticides, namely amperometric biosensors, cholinesterase-based biosensors, polymer-modified electrodes, ultramicroelectrodes and hanging mercury drop electrodes. They were used for several voltammetric and amperometric techniques in different analytical procedures for the detection and quantification of different classes of pesticides in different food matrices.

UTILIZAÇÃO DA MÚLTIPLA VOLTAMETRIA DE ONDA QUADRADA NA DETERMINAÇÃO ELETROANALÍTICA DE COMPOSTOS ORGÂNICOS E INORGÂNICOS

This paper reports the development of multiple square wave voltammetry and the possibilities of its use for electroanalytical determinations of organic and inorganic compounds with the improvement of the signal-to-noise ratios and detection limits 2-3 orders of magnitude lower than those obtained with conventional square wave voltammetry. The theoretical aspects and analytical applications were demonstrated as an increased analytical response (current) and application of different pulse modes for different redox processes. Preliminary results obtained for several redox systems using different electrode surfaces are shown, demonstrating also that MSWV represents an excellent alternative for the determination of ultra-traces of organic and inorganic compounds.