Flow injection determination of methamidophos using online photo-oxidationand fluorimetric detection

A photochemical method for the determination of methamidophos using a flow injection system is proposed. The method is based on the rapid decompositio n of methamidophos in the presence of peroxydisulphate upon irradiation wit h UV light. The phosphate generated in the photochemical process is made to react with molybdate in dilute nitric acid to form phosphomolybdic acid, w hich oxidises thiamine to thiochrome. The thiochrome can then be fluorimetr ically monitored at 440 nm with excitation at 375 nm. The method shows a li near range between 14 and 1400 ng ml(-1) with a limit of detection of 1.7 n g ml(-1). The repeatability was 0.3% expressed as relative standard deviati on (n = 10) and the reproducibility, studied on five different days, was +/ - 3%. The sample throughput was 70 injections per h. The reliability of the method for routine analysis of water and vegetable samples is demonstrated . (C) 2001 Elsevier Science B.V. All rights reserved.