††††††††††† The monochromator is included as an important device of the optical system of an atomic absorption spectrophotometer.The function of this device in atomic absorption is to separate the spectral line of interest from others spectral lines with different wavelengths emitted by the hollow-cathode lamp.The desired spectral line is chosen with the preferred wavelength and bandwidth by an appropriate monochromatorís setting named grating.A grating is a reflective surface, scored either mechanically or holographically with parallel grooves that can be designed for different wavelength regions.Generally, most of the instruments are equipped with two gratings with the goal to cover a wavelength range from 189 to 851 nm which is used in atomic absorption. A typical monochromator design is shown below. It consists of the diffraction grating (dispersing element), slits, and spherical mirrors.