The spectrometer is an established spectroscopic technique SPEC instrument that's used to measure the chemical identity and structure of materials in various industries and laboratories, including pharmaceuticals, fine chemicals, minerals, and food. Spectrophotometry, at its core, involves measuring how much light a substance absorbs by passing a light beam through a sample and quantifying the. A spectrometer is a scientific instrument used to analyze the composition of matter through the interaction of light with a sample. Absorption results from the vibration and rotation of the molecules.