Measurement of optical density

Optical density or absorbance gives an idea about the light absorbing characteristics of a solution. The amount of light absorbed by coloured solutions is obeying Beer-Lambert laws. Optical density is usually measured by using two instruments namely calorimeter and spectrophotometer. The main components of a calaorimeter are a light source (tungsten lamp), filters (to obtain monochromatic light), cuvette (glass tube to fill the solution), photocell (for the collection of transmitted light and transferring it into electrical impulse) and a galvanometer (for the measurement of electrical impulse). Calorimeter is capable of analyzing only coloured solutions. Spectrophotometer is an advanced calorimeter where monochromatic light source is obtained by the usage of a prism or grating. It is a sophisticated instrument with additional components like amplifiers, stabilized power supply and digital display system. Spectrophotometer can be used for both coloured and colourless solutions. Both calorimeter and spectrophotometer are used by biomedical engineers to quantitatively analyze biomolecules and other chemical present in a biological sample solution.