The monochromator contains an entrance slit, a dispersive element (usually a diffraction gratin or a prism) and an exit slit. Typically the widths of the entrance and exit slits are fixed for a given instrument. A source of light passed through the entrance slit and splits into. Two types of UV-VIS Spectrophotometers are available: the single monochromator type and the double monochromator type. But why are two types available? This explains the. In this volume, we will describe the monochromator, an important part of the spectrophotometer that was explained in UV TALK LETTER Vol. 2 "The Structure of a Spectrophotometer". The name is from Greek mono- 'single'; chroma 'colour' and Latin -ator 'denoting an agent'.