Solid phase extraction for the confirmation of results in polar pesticides residue analysis by HPTLC

HPTLC is a convenient method for confirming the presence and identification of pesticide residues following gas chromatographic analysis of sample solutions obtained by clean-up according to the Deutsche Forschungsgemeinschaft multiresidue method S 19. For several crops, however, the polar eluates 4 and 5 obtained from the small silica gel column are abounding with co-extractives which interfere with HPTLC determination and also with GLC in some cases. They are effectively removed by solid phase extraction on a small aminopropyl cartridge, using a tertbutyl methyl ether/methanol (99 + 1) mixture as the eluant. The recoveries for 28 polar pesticides were not adversely affected.