Portugaliae
Electrochimica Acta

The large and systematic change in cell potential (AE ) resulting from the addition of 0-l%m/m acetic acid to a mixture of ethyl or methyl acetates -20%v/v ethanol, or methanol, containing 1x10 -13 tetraethylammonium fluoride (TEAP) as background electrolyte, using fluoride electrode and calomel reference electrode filled with lithium chloride .provides a new graphical method for the rapid determination of acetic acid in ethyl or methyl acetates. Reading obtained by direct potentiometry show good reproducibility. The method is characterized by accuracy and simplicity of operation and compares favorably with the gas chromatographic method.

The interfacial region between a glassy carbon electrode and tetrabutylammonium electrolytes (halide, perchlorate and tetrafluoro - borate) in N,N-dimethylformamide has been studied using impedance techniques at varying electrolyte concentration (0.01M -í 0.20M) in the potential range 0.0 -> -2.0V vs . SCE. The spectra ca n be divided into a concentration independent low frequency part «100Hz) which is the same f o r all these electrolytes and a high frequency part depending on electrolyte and its concentration but not dc potential. Comparison is made with spectra obtained in aqueous solution. The results are discussed in terms of the physical properties of the solvent, electrolyte, glassy carbon, and the structure of the interfacial region. The low frequency feature is ascribed to electrolyte/electrode interaction s and electrode porosit, and the high frequency feature to processes involving the electrolyte anion. Keywords: glassy carbon electrode, electrode/electrolyte interface, DMF, impedance, tetrabutylammonium salts.

A general study on current reversal chronopotentiometry at spherical electrodes (as are the hanging mercury drop electrode or the static mercury drop electrode) is carried out. The effects of amalgam formation, insolubility of reaction product a n d electrode curvature on the potential l time function s are presented. The value of the ratio o f/t 2 (where f is the transition time in the reverse step and t 2 is the previous electrolysis time) can be used as diagnostic criterion to detect amalgamation or insoluble product formation. Methods to determine kinetic parameters and the formal standard potential of the electroactive couple in all the possible behaviors of the reduced species are proposed.

A simple differential pulse polarographic (DPP) method has been developed for the determination of Pipemidic acid. The Britton Robinson (BR) buffer of DH 2.07 was used as supporting electrolyte. The peak potential occurs at -809 V (SCE). The differential pulse polarographic peak height varies linearly with the concentration of pipemidic acid over the range—8.26 x 10B- — 7.41 x 10-5 M. The precision of the proposed method is excellent with relative standard deviation around 0.83% at a concentration of 6.54 x 10-6 M. Keywords: Pipemidic acid , differential pulse polarographic analysis.