Abstract: A weakly chemiluminescent (CL) emission has been observed during the decomposition of hydrogen peroxide catalyzed by copper(II) in basic aqueous solution. On adding an appropriate amount of amino acid solution into the mixed solution of hydrogen peroxide and copper(II), a strong CL emission was recorded. This CL emission depends on the kind of amino acid. The CL emissions for tryptophan and phenylalanine were fast, but for other amino acids, they were relatively slow. In the presence of a low concentration of carbonate in the basic solution, the CL emission was enhanced for ail amino acids. This CL system was developed for the determination of amino acids with a flow injection system. The detection limits of tryptophan and phenylalanine were 4.5 x 10^-6 and 1.1 x 10^-5 MI respectively. After the liquid chromatographic separation of tryptophan and phenylalanine by means of an ODS-80Ts column (5 µm, 250 mm x 4.6 mm i.d.) with water as eluent, the present CL system was used as a post-column detector for these two amino acids in tablets without any special labeling treatment.

Abstract: A biosensor for the analysis of D-amino acids is described. Carbon paste (graphite/paraffin oil) was chemically modified with immobilized D-amino acid oxidase and either horse-radish peroxidase or fungal peroxidase from Arthromyces ramosus. The two enzymes dissolved in buffer, together with an amine containing oligomer or polymer, were adsorbed on dry graphite. Prior to immobilization, the graphite was heat treated at 700°C for 15 s to promote an efficient electron transfer between graphite and the peroxidase. The mixture was dried before addition of the pasting liquid. The sensor is based on the fact that the hydrogen peroxide produced by the action of D-amino acid oxidase is electrocatalytically reduced through the action of the peroxidase. The amine containing compound acted as a stabilizer and activator of the enzymes in the paste. The enzyme electrode was investigated as a sensor for D-phenylalanine and hydrogen peroxide in a flow-through electrochemical cell connected to a single line flow injection system. The influences on the response by different additives to the paste and pH are reported. Linear calibration curves were obtained between 0.1 and 1.4 mM for D-phenylalanine and 5 and 1000 µM for hydrogen peroxide at an applied potential of -50 mV vs. Ag/AgCl. The sensor was also active for the following D-amino acids: D-alanine, D-valine, D-leucine, D-isoleucine, D-serine, D-aspartic acid, D-glutamic acid, D-lysine, D-histidine, D-arginine, D-tryptophan, D-methionine, and D-proline.