The electrochemical redox processes of pyridoxine hydrochloride (VB6) at a poly (methylene blue) film modified glass carbon electrode (PMBE) in a phosphate buffer solution (PBS, pH 8.0) were studied by cyclic voltammetry. The VB6 electrode reaction with quasi-reversible characteristics was diffusion-controlled at low scan rates and adsorptioncontrolled at high scan rates. The anodic peak current positive to 0.6V (vs. SCE) was found to be proportional to the concentration of VB6 in the range of 0.010 to 1.03mg

Through admittance measurements of two piezoelectric quartz crystals in parallel on one impedance analyzer and then non-linear fitting according to an equivalent circuit of two parallel Butterworth-Van Dyke circuits, we have simultaneously obtained accurate and precise impedance responses of two one-face sealed crystals to changes in solution density and viscosity, temperature, conductance, and/or electrode mass. A series of sucrose aqueous solutions, ferri-/ferrocyanide redox switching, hot water cooling, a series of NaClO4 aqueous solutions, bovine serum albumin adsorption and silver electrodeposition/stripping were selected as model systems for such purposes. Galvanostatic charging/discharging reactions at positive and negative poles in a Ni-Zn battery were synchronously monitored, with some quartz crystal microbalance (QCM) insights into the second reduction process of nickel hydroxide film. In all c ases, the crystal immersion angle effect was found to be negligible. The present method as a versatile one is highly recommended for informative two-electrode monitoring of two concurrent chemical or biological events, or for check and/or compensation of effects due to solution density, viscosity, temperature and/orconductance during QCM researches.

Electrochemical quartzcrystal microbalance (EQCM) studied revealed that the electrochemical properties of polypyrrole (PPY) in aqueous solutions are greatly dependent n the solution pH. A PPY film immersed in an aqueous KCl solution shows redox processed which involve not prevails as has been widely recognized. It has been found form comparative studies using poly (N=methylpyrrole) that protonation and deprotonation at nitrogen atoms of PPY play a key role in the observed pH-dependent electrochemicl behavior. Deprotonated PPY allows transient incorporation of hydrated cations upon reduction in weak alkaline aqueous solution. followed by alsow ejection of the incorporated cations when conventional electrolytes such as KCl and NaClO4 are used, but not in NH4Cl solution. Discussion on the catin transport in PPY is made in termas of deprotonation and protonation of nitrogen atoms of pyrrole subunits in PPY.

A simultaneous EQCM-fluorescence method has been proposed as a novel and informative tool for the study of the adsorption/desorption and oxidation for vitamin B6 (pyridoxol) at a polycrystalline Au electrode in aqueous KOH. The oxidation of pyridoxol was irreversible and accompanied by a strong electrogenerated fluorescence emission peaking at 443nm when excited at 360nm. Theadsorption and desorption of the oxidation product were found in the double layer region and were discussed by analyzing the simultaneous fluorescence and EQCM data. In addition, the voltammetrically electrogenerated fluorescence is proposed as a new and sensitive method for assay of pyridoxol with satisfactory results.

An electrochemical quartz crystal impedance system (EQCIS) was used to investigate depletion layer effects on equivalent circuit parameters of piezoelectric quartz crystal resonance in electrochemical processes of CoSO4 aqueous solutions containing 0.4mol/L ethylenediamine +0.5mol/L Na2SO4, 0.2mol/L 1,10-phenanthroline +0.5mol/L Na2SO4 and K3Fe(CN)6, or K4Fe(CN)6 aqueous solutions containing 1.0mol/L KCl in potential cycling experiments, respectively. The impedance data were analyzed according to Martin's model. For the former two systems, motional resistance R1, series resonant frequency fs, and motional inductance L1 changed reversibly with potential, and the observed values of △R1, △L1, and△fs roughly satisfied equations reflecting liquid loadingeffects, suggesting that changes in these parameters mightbe mainly governed by local variations in solution densityand viscosity near the electrode surface. For the latter two systems, reversible changes in R1 with potential coincided well with the simulated results from variations in solution density and viscosity near the electrode surface; however, besides reversible changes of △L1 and △fs with potential, rising drifts of fs and decreasing drifts of L1 were found at oxidation potentials. The drifts of fs and L1 observed are believed to result from mass changes of the gold electrode, and cyanide and chloride corrosion of the gold electrode at oxidation potentials may play an important role for the drifting phenomena. It is concluded that quantitative analyses of △R1, △L1, and △fs obtained from the EQCIS provide the possibility for differentiating the net depletion layer effect with the change in electrode mass, and the ¢R1 response may be well used for evaluating local changes in liquid loading inside the depletion layer compared with responses of △fs and △L1.