The kinetic parameters of gold(III) sorption by unloaded polyurethane foams (PUFs) and PUFs impregnated with some onium cations e.g. tetramethylammonium perchlorate (TMA + ClO4 -), tetrabutylammonium iodide (TBA + I -), and tetraheptylammonium bromide (THA + Br -), have been determined. The retention steps were found to be fast, reached equilibrium in a few minutes and followed a first-order rate equation with an overall rate constant, k, of 0.0076 and 0.007 min -1 , respectively. The thermodynamic characteristics of gold(III) retention by the unloaded PUFs and THA + Brimmobilized PUFs have been critically studied. The negative values of DH and DS are interpreted as the exothermic and spontaneous reaction of gold(III) sorption onto unloaded PUFs and foams impregnated with THA + Br -. The cellular structure of the PUFs sorbent offer unique advantages over conventional bulk-type sorbents in the rapid, versatile effective separation and/or preconcentration of gold ions.
The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton-Robinson (BR) buffer of pH 2.6-10.3, an irreversible and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the sweep rate (nu) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (alpha) involved in the rate-determining step calculated from the linear plots of E (p,a) against ln (nu) in the pH range investigated were in the range 0.64 +/- 0.05 confirming the irreversible nature of the oxidation peak. In BR buffer of pH 7.6-8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against domperidone concentration at this peak potential was linear in the range 5.20 x 10(-6) to 2.40 x 10(-5) mol L(-1) with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 x 10(-7) and 9.1 x 10(-7) mol L(-1), respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 x 10(-6) mol L(-1) of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 +/- 3.1%), dosage form (98.35 +/- 2.9%), and in tap (97.0 +/- 3.6%) and wastewater (95.0 +/- 2.9%) samples. The method was validated by comparison with standard titrimetric and HPLC methods. Acceptable error of less than 3.3% was also achieved.
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