Detection with 365-nm UV Light

Nonselective detections can be performed in short- and long-wave UV hght. For this, UV lamps of the appropriate excitation wavelengths are necessary, and these are supplied in various forms by, e.g., CAMAG, DESAGA and Merck. Darkrooms are very suitable locations for UV lamps combined with documentation equipment, as the eval- 

Practical Tip for working with UV lamps dark glasses must always be worn to prevent eye damage. 

The assessment of the additional zones is very risky if the substance imder investigation shows different absorption behavior from that of the impurities. Figrue 70a shows how this difference can be recognized on the TLC plate. Here, two pharmaceutical substances were applied pointwise and bandwise in amoimts of 400 pg and 8 pg. After the development, strong fluorescence quenching of the second substance can be seen in short-wave UV light, while this is much weaker for the first substance, so that the 8-pg amoimt only appears as a trace. After derivatization with iodine, no difference between the intensities of the spots of the two substances can be detected (Fig. 73b). 

Practical Tip for documentation with 254-nm UV light 35-mm cameras or video equipment is used to produce the required images, which are in black-and-white because these give better contrast of the spot with the background. Tlie color of the fluorescence indicator cannot therefore be seen on these images, so that no conclusions can be drawn about the precoated layers used. 

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