Determination of amino acids and proteins by dual-electrode detection in a flow system

Abstract

A new analytical procedure using a serial dual-electrode detector was developed for amino acid and protein analysis. Bromine was generated at die upstream electrode and detected by the downstream electrode. Amino acids and proteins present in the samples were shown to lower the downstream current but had no apparent effect on me upstream current. The potential of both electrodes, the flow rate of the mobile electrolyte, and the dispersion of the samples were optimized to give satisfactory linear working ranges for seven amino acids (10-6-10-3 M) and total proteins (10-7-10-3 M). The working range can be extended up to 10-1 M amino acid and 10-2 M protein by using a more anodic upstream potential. Direct determination without preconcentration can thus be performed on all the real food samples analyzed. This method has been applied to the flow injection analysis of total proteins in food, with results comparable to those obtained using the established AOAC procedure. The dual-electrode detector provides a suitable method for detecting analytes after HPLC separation. Compared to the traditional method with UV detection, the dual-electrode detector is shown to provide a better selectivity for the detection of ribonuclease and catalase in food.