-spectrophotometry-

n. 1. The art of comparing, photometrically, the brightness of two spectra, wave length by wave length; the use of the spectrophotometer. [ Webster 1913 Suppl. ]

2. (Chem., Physics) the art or process of measuring the degree of absorption of light at different wavelengths by a chemical substance, by means of a spectrometer or spectrophotometer. It is a technique for chemical analysis. [ PJC ]

-- Spec`tro*pho`to*met"ric a. [Webster 1913 Suppl.]