Separation of a mixture of eighteen pesticides by two-dimensional thin-layer chromatography on a cyanopropyl-bonded polar stationary phase

Eighteen pesticides have been separated by two-dimensional thin-layer chromatography on a moderate polarity CN-modifled silica gel. CN-silica is widely used as a adsorbent in both normal- and reversed-phase chromatography. Large selectivity differences are obtained by combination of both NP and RP modes on cyanopropyl-bonded polar adsorbents. The greatest spread of points was obtained by combining nonaqueous normal-phase mobile phases (tetrahydrofuran or ethyl acetate in n-heptane) and aqueous reversed phases (a polar solvent (methanol or acetonitrile) in water), both on thin layers of cyanopropyl-bonded polar adsorbent. Correlations of R, values in NP and RP systems were used for practical separation of a mixture of eighteen pesticides by 2D TLC on this adsorbent. Plates were scanned and videoscanned to show the real pictures of the 2D TLC separation.