Identity by UV/VIS
USP <857> <1207.2>
Absorption spectrophotometry is the measurement of an interaction between electromagnetic radiation and the molecules/atoms of a chemical substance. Techniques frequently employed in pharmaceutical analysis are Ultraviolet (UV), Visible (Vis), Infrared (IR), and Atomic Absorption (AA) spectroscopy. Spectrophotometric measurement in the visible region is often referred to as colorimetry. The spectral ranges as specified in USP <857> and <1207.2> are divided into UV (190-380nm) and Vis (380-780nm).
For many pharmaceutical substances, measurement can be made in the UV and Vis regions of the spectrum with greater accuracy and sensitivity than NIR and IR. When solutions are observe in 1cm cells, concentrations of about 10µg of the specimen per mL will produce absorbances of 0.2-0.8 in the UV or the Vis region. The UV and Vis spectra of substances generally do not have a high degree of specificity and yield very little, if any, useful chemical information. Nevertheless, they are highly suitable for quantitative assays, and for many substances, they are useful as additional means of identification.