THEORY

All modern UV-Vis measurements involve detecting and measuring the intensity ratio of the radiation at a certain wavelength in the presence or absence of the absorbing sample (transmitted radiation and incident radiation). Figure 1 shows schematics of four typically encountered optical designs: single-beam, single split-beam (where the reference detector is located within the internal optics of the system), double-beam, and reverse optic array spectrometers. Dispersion of light to achieve the desired resolution can occur before (as in the first three configurations) or after introduction of the sample, but all commercial UV-Vis instruments share the following features to perform these functions:

• Continuum source

• Monochromator or polychromator

• Sampling area

• Detector