The orgallophosphorus insecticide, (O,O-dimethyl S-(I,2-dicarboethoxyethyl) dithiophosphate), known as malathion, malathon, mercaptothion, carbofos, or carbetox, is polarographically inactive, and is, therefore, determined polarographically by indirect methods 1-3.
Since malathion shifts the half-wave potential, El, of some substances such as maleic and fumaric acids, oxygen and hydrogen peroxide, JURA concluded that there is adsorption of malathion which forms a film on the dropping mercury electrode sur-face1. NANGNIOT using a cathode-ray polarograph of linear tension-sweep in aqueous methano~HC1 medium, obtained 3 adsorption peaks for malathion and considered that this confirmed the adsorbability of malathion on tile dropping mercury electrode 4, ~.
According to present knowledge of the effects produced on polarographic curves by adsorbed electro-inactive substances 6-s, malathion should behave as a typical surface-active substance and as such should suppress the polarographic maxima of the first kind 9. It was decided to study the effect of malathion on such a polarographic maximum and to investigate the use of the expected effect for analytical purposes.
Since it is known 5 that malathion hydrolyses very easily at all pH-values other than 5.261% its effect on the maximum was investigated in non-aqueous conditions. Using a solvent-supporting electrolyte system of ammonium trimethylphenyl chloride in benzene-methanol, we found that in non-aqueous conditions malathion does not suppress the benzoyl peroxide maximum unless there is a short contact with a medium permitting hydrolysis of malathion. We studied, therefore, the relation between the degree of suppression, the initial malathion concentration, and the watercontact time with and without atmospheric contact.
APPARATUS AND MATERIALS
A Heyrovsks~ LP-6o type polarograph with an electronic recording system was used. A dropping mercury electrode (DME) served as cathode and the reference electrode consisted of mercury of the bottom of a Novak-type electrolysis vessel. The capillary constants found in doubly-distilled water at o V gave mt= o.o116 g. The composition of tile solvent-supporting electrolyte system was 2% ammoniumtrimethylphenyl chloride in benzene-methanol (I : 3). The maximum-producing depolarizer was o.5 % benzoyl peroxide in the given solvent-supporting electrolyte system. The avail-