RELATIONSHIP BETWEEN THE HYDROPHOBICITY AND SPECIFIC HYDROPHOBIC SURFACE-AREA OF PESTICIDES DETERMINED BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY COMPARED WITH REVERSED-PHASE THIN-LAYER CHROMATOGRAPHY

The hydrophobicity and specific hydrophobic surface area of 12 commerc ial pesticides have been determined by reversed-phase high-performance liquid chromatography (RP-HPLC) using octadecyl-bonded silica support and water-methanol mixtures as eluents. The pesticides showed regular retention behaviour, their log k' values decreased linearly with incr easing concentration of methanol in the eluent. The hydrophobicity and specific hydrophobic surface area of pesticides were significantly in tercorrelated, although the chemical structures of the pesticides were different. Principal component analysis proved that the hydrophobicit y parameters determined by RP-HPLC and reversed-phase thin-layer chrom atography are slightly different and herbicides and fungicides could n ot be distinguished according to their hydrophobicity parameters. This indicates that differences in the biological activity of these pestic ides cannot be attributed to either their hydrophobicity or specific h ydrophobic surface area alone.