Abstract: The permeability of conducting polymer-modified electrodes to electroactive amino-acids, the effects of deposited layer thickness, and the use of polyaniline and polypyrrole, were studied. Polyaniline was more effective than polypyrrole in supressing amino-acid oxidation (when the polymer layer was >100 mC cm-2, however, it was also less permeable to L-amino-acids than polypyrrole. Such electrodes were applied to the determination of H2O2 enzymatically produced from L-amino-acids in an L-amino-acid oxidase reactor by flow injection analysis. The amperometric response from from 0.01 to 1 mM phenylalanine, tryptophan, tyrosine and cysteine was recorded. Modification of electrodes with polyaniline may be important in reducing electrode fouling at conducting polymer electrodes where L-amino-acid oxidase is immobilized to, or entrapped within, the polymer.

Abstract: A 30 cm electrodialysis cell with a central channel separated from an upper cathode-containing channel and a lower anode-containing channel by horizontal cation- and anion-exchange membranes, respectively, was used. Electrodialysis was performed at 20 V with the sample solution passing through the central channel and 0.2 M pyrophosphate buffer solution of pH 8 passing through the other channels (each at 0.8 ml/min); arginine migrated into the cathode channel. After adjustment of the pH to 7.5 with 0.2 M citrate buffer, the solution leaving the cathode channel was injected into a carrier stream of 0.2 M phosphate buffer of pH 7.6 (2 ml/min) and passed through two glass columns (2.3 cm x 5 mm i.d.) containing catalase and L-amino-acid oxidase immobilized on controlled-pore glass beads (details given). The resulting H2O2 produced by the enzymatic oxidation of arginine was determined in a flow cell at a Pt electrode at 0.7 V vs. SCE. No details of detection limits are given. Other amino-acids, e.g., lysine, interfered with the method, which should also be applicable to the determination of other L-amino-acids in such mixtures under appropriate electrodialysis conditions.