Ultraviolet-Visible Spectrophotometry

Ultraviolet (UV) and visible spectrophotometry have been utilized in forensic toxicology for both qualitative and quantitative analysis. Lambert discovered that for monochromatic radiation, absorbance was directly proportional to the path length of the incident light through the material. Beer (1797–1850) expanded Lambert’s work by studying the relationships between concentrations of a substance in solution and found that the same linear relationship existed between concentration and absorbance as Lambert had found between thickness and absorbance. The Beer-Lambert law is the basis for quantitative analysis using UV and visible spectrophotometry. Color tests involve the reaction of a specimen, a protein-free filtrate, or an extract with a reagent or a series of reagents to produce a color or change in color. Besides color tests, another use of spectrophotometry in forensic toxicology is in the detection systems of a number of commercially available immunoassays. Many immunoassays involve the conversion of a substrate by an enzyme into a product that causes either an increase or a decrease in absorbance at a particular wavelength.