absorbancia

Absorbancia, or absorbance, is a measure of the amount of light at a specific wavelength that a sample absorbs. It is defined by the equation A = log10(I0/I), where I0 is the incident light intensity and I is the transmitted light intensity. Because A = −log10(T) with T = I/I0, absorbance is a dimensionless quantity, though it is commonly reported with units of absorbance units (AU) or simply as A.

In practice, absorbance is measured with a spectrophotometer, which uses a light source, a wavelength selector, and a detector to quantify how much light passes through a sample placed in a cuvette, typically with a 1 cm path length. The measurement depends on light at a selected wavelength and is calibrated against a blank to zero the instrument.

The Beer-Lambert law relates absorbance to concentration: A = εlc, where ε is the molar absorptivity (L·mol⁻¹·cm⁻¹), l is the path length in centimeters, and c is the solute concentration in moles per liter. This relation describes a linear relationship between A and c within a certain range, forming the basis for quantitative analyses through calibration curves.

Applications span chemistry, biology, and environmental analysis, including determination of nucleic acid and protein concentrations, enzyme assays, and many colorimetric tests. Limitations include deviations from linearity at high absorbance, scattering by suspended particles, and the need for monochromatic light and well-prepared blanks. Proper use requires well-characterized standards and adherence to the instrument’s linear range.