Principle of spectrophotometer

• If a pencil of light is allowed to pass through a colored solution, some amount of light will be absorbed while the rest of the light will be passed through.
• The amount of light absorbed is proportional to the nature of solution, concentration of solute and the distance of the path of light.

i.e. Amount of light absorbed ( A) = ExLxC

where,

E = extinction coefficient or nature of solute

L = Distance of the path of light

C = Concentration

Or, A α C and A α1/ transmittance (T)

i.e. absorbance is a direct measure of concentration.

• Photometer are instruments that measure the amount of light absorbed, transmitted, emitted or other wise.