Fluorescent Indicators

Detection is a special problem which must be considered when beginning a separation. Since most compounds are colourless, this might require considerable time to find the best reagents to spray on to a plate to visualize the components found in the sample. Such spray visualization might need a series of reagents to reveal the different species found in a complex mixture, such as with drugs of abuse.

One method used since the early days of TLC has been incorporation of a fluorescent indicator in the layer. A few per cent by weight of an inorganic salt such as manganese-activated zinc silicate, zinc cadmium sulfide, and others can be used. When visualizing a compound that can absorb the particular wavelength of light used to activate the fluorescent indicator, it will appear as a dark spot against the background fluorescence of the plate. This fluorescent indicator is often activated with either 254 or 366 nm wavelength light. It then fluoresces green, light blue or off-white. Other colours may be seen, too, but these are usually found when an organic fluorescent indicator is used. These latter indicators are often sprayed on after the plate is developed and dried, since they can move with many mobile phases that might be used for developing the plate.

The wavelength of the activation is usually stated after the F designation used by many manufacturers. One other item that might be important regarding fluorescent indicators is the fact that some might not be stable if exposed to strong acids like hydrochloric or sulfuric (i.e. mineral acids). Such strong acids can change the crystal structure of the inorganic salts and make them nonfluorescent. Usually this does not present problems since the fluorescent detection is tried as soon as the plate is dried, and before any other reagents are sprayed on to it for further detection of other types of compounds - ones that would not fluoresce or quench.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment