Application of high-performance thin-layer chromatography and automated multiple development for the identification...

The combination of high-performance thin-layer chromatography (HPTLC) with automated multiple development (AMD) allows full automation of the separation step. This provides both a separation efficiency that is considerably better than that in conventional TLC and reproducible gradient elution on the thin layer. Reliable identification of trace amounts of pesticides (e.g., 28 ppt of atrazine) in subsoil, surface and drinking water is clearly demonstrated by AMD-HPTLC using a polarity gradient based on dichloromethane. A second universal elution gradient with changed selectivity on which the substances have different relative migration distances, identification by the multi-wavelength response correlation and the option of recording UV spectra in situ constitute three independent methods for reliable and rapid verification. Using 100- instead of 200-microns HPTLC silica gel layers and reducing the running distance increments from 3 to 2 or 1 mm increase the sensitivity, the linearity and the speed of the method.