ABSTRACT
Paper and thin-layer chromatography (TLC) along with several additional variants are generally referred to as planar chromatography. Planar chromatographic methods can be traced back to the mid-1800s with a variant of paper chromatography (capillary analysis). Approximately 40% of the methods in the United States Pharmacopeia and over 80% of the chromatographic methods described in the Japanese and Chinese pharmacopoeias are based on planar chromatography. Significant advances have been made in instrumental preparative planar chromatography with the introduction of centrifugally accelerated layer chromatography. The primary distinction of overpressurized TLC from the other techniques is that the mobile phase is pumped into the sorbent. This is accomplished by covering the chromatographic plate with a plastic membrane held in place by external pressure. Planar techniques can tolerate application of either solutions or suspensions. In addition, the solvent used to dissolve the sample need not be compatible with the TLC mobile phase as is the case for high-performance liquid chromatography methods.
