Abstract

The determination of nitrite in homogenised egg was taken as particularly relevant for highlighting the beneficial aspects of sonoelectrochemical analysis in difficult matrices. The presence of high concentrations of protein and fat serve to foul the electrode and have traditionally prevented direct electrochemical probing of such matrices without recourse to substantial sample pre-treatment. To this end, power ultrasound (20 kHz) in combination with linear sweep techniques has been evaluated as a means of removing the need for sample manipulation beyond simple homogenisation. The electrochemical detection of nitrite was based on a nitroso-derivatisation reaction with reduction of the latter providing the analytical signal. The application of ultrasound is shown to significantly enhance the electrode response towards nitroso reduction with ultrasonically induced electrode cleaning providing a degree of signal resolution unattainable under silent conditions. The influence of electroactive egg constituents is detailed and a dual mode standard addition technique for negating such interferences is assessed. The reproducibility of the procedure is assessed with detected nitrite levels in egg found to be within MAFF limits. (C)2000 Elsevier Science B.V. All rights reserved.