RESUMO
The preparation, characterization and analytical applications of gold electrodes modified with omega-mercapto alkyl/aryl sulfonates are described. The devices resulted effective for the determination of free and labile Pb(II) in water samples by anodic stripping voltammetry (E(dep) = -600 mV) and in particular 2-mercaptobenzimidazole-5-sulfonate (MBIS) offered the best performances with detection limit of 0.4 microg L(-1). Quantitative stripping of Pb from the electrode surface during the anodic scan, is obtained using sodium citrate buffer (pH = 9.0) as supporting electrolyte. Natural waters were analysed by standard addition method with good recoveries (mean percentage = 97%); no fouling effects due to humic acids or other organic constituents were observed in the reported conditions.
RESUMO
Absence of gradients and Nernstian equilibrium stripping (AGNES) is a recently developed electroanalytical technique specifically designed for the direct determination of free concentrations of metal ions. AGNES is applied here to the determination of free Zn concentration in a river water sample. The method has been validated with synthetic solutions of low ionic strengths containing Zn and 2,6-pyridinedicarboxylic acid and then applied to synthetic river waters and to a natural sample collected from Besòs River in Montcada i Reixac (Catalonia, North-Eastern Spain). In the river sample, an average free Zn concentration of 12.8(4) nM was obtained, while the total dissolved Zn concentration was 0.51(8) microM. To control and maintain pH and pCO(2) constant during AGNES measurements, a novel device for N(2)/CO(2) mixed purging has been developed.
RESUMO
The preparation and application of a humic acids modified gold electrode (HA-CME) have been described. Derivatization of HAs as beta-thioesters caused their partial fragmentation and, thus, a consequent separation by size exclusion chromatography (SEC) was necessary. The CME prepared with functionalized HAs having an average MW of 52000 demonstrated to be effective for trace As(III) determination (LOQ = 0.3 microg L(-1)). This CME has been characterized both by electrochemical techniques and atomic force microscopy (AFM). The HA-CME provided reliable measurements in natural waters at different salinity with no need of desalting the sample. Total inorganic arsenic could be determined after reduction of As(V) with SO2. Under these conditions, organic arsenic species were not mineralized and did not interfere.
