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2751862 
Technical Report 
SEPARATION OF ISOMERS OF MALATHION MONOCARBOXYLIC ACID BY THIN-LAYER CHROMATOGRAPHY 
Welling, W; Blaakmeer, PT; Copier H 
1970 
HAPAB/70/01534 
Chromatog 
2 
281-3 
HAPAB A simple chromatographic technique has been developed for the separation of the alpha-and beta-monoacid isomers of malathion, O,O- dimethyl-S-(1,2-di( ethoxycarbonyl )ethyl)-phosphorodithioate. Thin- layer chromatography ( TLC ) was performed on silica gel. The plates were washed with acetone, activated for 15 min at 90C and developed with acetone ot which 0.5 vol% acetic acid was added. The developed chromatograms were dried, sptayed with a 0.5.% solution of 2,6- dibromoquinone-4-chloroimide ( DQC ) in cyclohexane and heated for 5 min at 110C. A malathion monacid sample prepared according to March et al. ( 1956 ) gave two spots with Rf values of ).39 ( alpha-isomer ) and 0.57 ( beta isomer ). About 400 mcg of an alpha- and beta-isomer iixture of malathion were applied as a band on the TLC plates. A 3-cm wide stripe was cut off to permit the compounds to be located with DQC ( reacts with the P=S bonds giving red to orangw-red spots ). The two components were concentrated and displaced with 96% ethanol in a direction perpendicular to that of separation, then scraped off. The isolated material and the silica gel powder were kept for several days in vacuo over potassium hydroxide pellets to remove as much acetic acid as possible. Each sample of isolated material was filled into a small vertical column and eluated with 50 mcl of acetone. The first drops of wluent were collected form the column and transferred by the method of Curry et al. ( 1968 ) to a 4 mg of KBr powder form which a pellet was then formed. In this way, IR spectra of the two spots with Rf values of 0.39 and 0.57 were obtained. The chromatographic separation of alpha-and beta-monacid was belieced to be produced by a pH gradient created during development and would explain why the larger pKa ( 3.74 for beta-and 3.62 for alpha-monacid ) has the higher Rf value. The described technique may be of some use in the separation of other compounds differing slightly in pKa that are otherwise difficult to separate. ANALYSIS 70/09/00, 433 1970