ABSTRACT
In spectrophotometry the sample is irradiated and the extent to which the incident light is absorbed is measured; in fluorimetry, the sample is irradiated and the resulting activated emission, at a different wavelength, is measured. The pH of samples used for measurement can dramatically affect the absorption spectrum, and this property should also be utilized in the development of a spectrophotometric method. It has been stated that direct measurement of the UV-visible absorption spectrum is of little help as a qualitative test for drugs in biological fluids because these spectra are very similar for compounds having the same chromophores. A variety of aromatic aldehydes has been used as spray reagents for paper and thin-layer chromatography, including anisaldehyde, and vanillin. In contrast to spectrometry, in fluorimetry, the final measurement is not of transmitted light but of emitted light at right angles to incident light, and hence the analyst is looking for the difference between zero and small values of emitted light.
