UVabsorbanssin

UVabsorbanssi, or ultraviolet absorbance, is a measure of how strongly a sample absorbs ultraviolet light. It is commonly determined with a UV–visible spectrophotometer and is reported as absorbance, denoted A. The value is dimensionless and depends on the instrument settings, path length, and solvent.

The quantitative basis is the Beer-Lambert law: A = εlc, where ε is the molar absorptivity (a property of the absorbing species, in L mol−1 cm−1), l is the optical path length through the sample (in cm), and c is the concentration of the absorbing species (in mol L−1). In practice, measurements are often made with a cuvette of 1 cm path length, and a blank containing the solvent is used to correct for background absorbance. The law holds within a linear range of concentrations; outside this range, the relationship may deviate due to stray light, scattering, or detector limitations.

Common applications include quantitative analysis and purity assessment. Nucleic acids exhibit strong absorbance near 260 nm, while proteins absorb near 280 nm due to aromatic amino acids. The ratio A260/A280 serves as a rough indicator of sample purity, with typical values around 1.8–2.0 for pure DNA and ~2.0 for pure RNA. UV absorbance is also used to monitor reaction progress, determine solvent or reagent concentrations, and assess sample quality alongside calibration curves.

Practical considerations include ensuring a clear, non-scattering sample, choosing an appropriate wavelength (often at or near the absorption maximum), and staying within the instrument’s linear range (approximately A 0.1–1.0 for many setups). Solvent absorption, cuvette quality, and internal filter effects can influence measurements and must be controlled.