An electrooxidative technique to fast fabricate copper phosphate electrodes capable of integrating high performance liquid chromatography for the label-free detection of fish freshness

A simple and fast one-step electrooxidative method has been developed to monolithically produce a copper phosphate (Cu3(PO4)2) compound on a disposable copper tape, which can be integrated with high performance liquid chromatography (HPLC) for the estimation of fish freshness. The Cu3(PO4)2 compound of flake-like nanostructures was formed by applying a first anodic peak potential at the copper tape for 10 min in a 1 M sodium dihydrogen phosphate (NaH2PO4) (pH 5.0) solution. The Cu3(PO4)2 electrodes can detect the oxidative reaction of histidine and histamine in 20 mM NaH2PO4 solutions with pH 5.0-8.5. When integrating the electrodes with a flow injection system, the linear range and the calculated detection limit of histamine were respectively 2.5-250 ppm and 0.15 ppm. The electrodes integrated to HPLC can specifically detect the histamine concentrations in fish samples in the pH 7.5 NaH2PO4 solution, achieving an accuracy rate of 95.3% and a recovery rate of 101.1%.