Kinetics of electrocrystallization of PbO2 on glassy carbon electrodes: influence of electrode rotation

Electrodeposition of PbO2 on glassy carbon electrodes was studied in stationary conditions and on the rotating disk electrode using chronoamperometric technique. The kinetics of electrodeposition was significantly retarded by the hydrodynamic mass transport flow. This observation is in agreement with the mechanism involving formation of soluble Pb(III) or Pb(IV) species, which may, subsequently, form PbO2. The kinetics of the nucleation and crystal growth was determined by the analysis of the initial part of the transients and of the whole curves. This process proceeds through the 3 dimensional progressive nucleation and crystal growth mechanism with an induction time. The growth rate constant is strongly affected by convection while the nucleation process and the induction time are much less influenced.Consellería de Cultura, Educación y Ciencia (project GV-2231-94)

RAPID DETERMINATION OF GLUTAMIC ACID BASED ON IMMOBILIZED ESCHERICHIA COLI AND A QUADRUPOLE MASS SPECTROMETER

Large quantities of glutamic acid are produced by the fermentation process so that rapid determination of glutamic acid is important for the control of the fermentation. Previously, we reported a microbial sensor consisting of immobilized Escherichia coli containing glutamte decarboxylase activity and a carbon dioxide gas-sensing electrode(1). The sensor has a major disadvantage of slow speed, 10 samples per hour, due to slow response of the gas-sensing electrode. We require more rapid sensors to deal with many samples from the fermentation laboratories. In stead of the gas-sensing electrode, a quadrupole mass spectrometer was employed to measure carbon dioxide gas produced from glutamic acid by the immobilized E.coli(2). The method has very high speed, more than 100 samples per hour, and has been applied to the assay of glutamic acid in the fermentation broths