Increased Detection Sensitivity in Fully Off-Line OPLC by Bilateral Band Compression

A new process, bilateral band compression has been used to increase the sensitivity of detection of minor components of a mixture. After band-shaped sample application, fully off-line OPLC separation, and drying, the separated bands were compressed bilaterally, in parallel, perpendicular to the direction of development, by use of a strong eluent and capillary driven chromatography. To introduce the eluent on to the layer for band compression a simple manual tool equipped with parallel foam strips was constructed. A mixture of xanthine standards (caffeine 0.998 mg mL(-1), theophylline 1 mu g mL(-1), and theobromine 1 mu g mL(-1)) and black tea leaf extract were used to test the efficiency of detection after bilateral band compression. After band compression 20 ng theophylline and theobromine could be detected by densitometry in the xanthine standard mixture at a loading of 20 mu g/10 mm whereas they were not visible in the original, uncompressed chromatogram.