VOLTAMMETRIC DETERMINATION OF METHYL PARATHION, ORTHO, META AND PARA NITROPHENOL WITH A CARBON PASTE ELECTRODE MODIFIED WITH C-18

The determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C18. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s-1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml-1 for ONP, 5 ng ml-1 for MNP, 4.3 ng ml-1 for PNP and 7.9 ng ml-1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.