1 Introduction

There is no doubt that combining planar chromatography, particularly HPTLC, with spectrophotometric and other chromatographic techniques extends the capabilities of analysis substantially. These techniques seek to maximise the information that can be obtained from a separation on a plate. HPLC, MS (mass spectrometry), FTIR (Fourier transform infrared spectroscopy), and Raman spectroscopy have all been coupled effectively with HPTLC. However, in practice there is the cost factor to consider, and one has to balance the extended analysis capability with the extra expense involved.

There are a number of special features of TLC/HPTLC that give it an advantage over other chromatographic methods when it comes to coupling with other analytical techniques. In TLC, the separation, development and detection are not a continuous process. This is a unique advantage as many TLC plates can be run simultaneously and the separation evaluated qualitatively before detection. However, it also enables the chromatographer to concentrate on the analytes of interest without having to wait for further elution. The presence of unknowns is also more likely to be detected and their structure identified as the whole chromatogram is contained between the origin and the solvent front. Another special feature is the ability of TLC to "store" a separation. After development of the chromatogram, the separated components of the sample remain on the sorbent layer. If these components are stable, the chromatogram can be stored for some time until a decision has been reached as to which coupling technique is required. Normally only very slow diffusion...