Planar chromatography (PC) like any other chromatographic technique is a multistage distribution process. It is a form of liquid chromatography in which the stationary phase is supported on a planar surface rather than a column. Separations in PC occur because of differential migration velocities through the sorbent layer in a fixed separation time. The sample zones are fixed in space at the completion of the separation, allowing off‐line monitoring. There are two planar techniques: paper chromatography and thin‐layer chromatography (TLC). In recent years, TLC has superseded paper chromatography owing to greater speed, versatility, and reproducibility. Improvements in techniques and equipment as well as the ready availability of high‐quality plates with uniform layers have extended and increased the use of TLC in clinical chemistry and other disciplines, offering quantitative as well as qualitative analysis. High‐performance thin‐layer chromatography (HPTLC), in particular, has developed to the extent that separation and quantitation can provide results that are comparable with other analytical methods such as high‐pressure liquid chromatography (HPLC). The widespread application of TLC is also due to the fact that it is simple, robust, and flexible, and has a large sample throughput. Furthermore, coupled spectroscopic methods (TLC/mass spectrometry (TLC/MS), TLC/Fourier transform infrared spectrometry (TLC/FTIR) etc.) have considerably enhanced the reproducibility of TLC.
TLC is often critically compared with column chromatography such as HPLC. This is a matter of endless dispute. Each technique has its own advantages and limitations. TLC is only inexpensive when qualitative results are needed. When reliable quantitative data are required, TLC is as expensive as column chromatography. In the authors' opinion, complementary rather than competitive chromatography offers the best solution to analytical requirements.
