1 Introduction

Once development of the chromatogram is complete, usually some kind of visualisation of the chromatographic zones is required as most compounds are not visibly coloured. Many compounds will absorb UV light or exhibit fluorescence when excited by UV or visible light, but most require visualisation using an appropriate spraying or dipping reagent. Due to the inert nature of the sorbents commonly used in TLC layers, chemical reactions can be carried out on the plate without the sorbent layer being affected. A wide variety of chemical reagents have been used to good effect for chromatographic zone detection. Even quite aggressive reagents, like hydrochloric or sulfuric acid solutions, can usually be tolerated. The list of visualisation reagents for TLC is large, reflecting the versatility of detection techniques. A number of excellent publications exist in which the formulations for both spraying and dipping reagents have been collated from the chromatography literature. ^{[1] [3]} Some reagents are termed universal reagents as they are used to visualise a wide range of compounds of differing molecular structures. Included in this group of reagents are acid solutions and vapours, ammonia vapour, fluorescein, dichlorofluorescein, and iodine. Some reagents can be used in destructive techniques. They cause a breakdown of the compounds of interest leaving behind a visible deposit on the chromatographic layer. Conversely there are nondestructive techniques that allow detection of compounds in the chromatographic zones without the layer or zones being chemically altered. Included in nondestructive techniques are visible and UV light, and...