Absorption The concept of spectrophotometry is that each chemical substance has unique characteristics that influence what wavelengths of energy it will absorb. The electromagnetic spectrum’s ultraviolet, visible, and infrared portions are used to conduct most tests. The resonant frequencies at which energy is absorbed are varied for each molecular arrangement of atoms. When the energy of various wavelengths created by a spectrophotometer is focused into a chemical sample, it is transmitted selectively. Absorption is the term for this type of energy transmission.

The human eye is only sensitive to wavelengths in the spectrum ranging from 390 nanometers (violet) to 770 nanometers (red). However, absorption happens in the UV and IR spectrums as well. Optical windows of VIS, FUV, or NIR grade are available on Spectrocell brand cells, providing good results at those wavelengths. The specs of these different window material options may be found in the accompanying charts and tables.