Amperometric determination of underivatized amino acids at a nickel-modified gold electrode by anion-exchange chromatography

A nickel-based composite electrode obtained by anodic electrodeposition of nickel (III) oxyhydroxide film on the gold electrode substrate was characte rized as an amperometric sensor and successfully applied to the determinati on of underivatised amino acids in flow-through systems. The electrodeposit ion of nickel oxyhydroxide films was obtained by cycling a gold electrode b etween 0.0 V and +1.0 V vs. a saturated calomel electrode in a 80 mu M Ni2 solution buffered at pH 10 with NaHCO3/Na2CO3. The resulting Au-Ni composi te electrode exhibits good stability in alkaline medium and can be used as an amperometric sensor of underivatised amino acids at a fixed applied pote ntial (+0.55 V vs. Ag/AgCl). The detection limits (S/N=3) for all investiga ted compounds ranged between 5 and 30 pmol injected, while the linear range s spanned over two or three orders of magnitude. The contents of several fr ee amino acids in two sample cheeses from different brands were evaluated b y calibration graphs. (C) 2000 Elsevier Science B.V. All rights reserved.