Beer's Law

 Beer examined the relationship between absorption and the concentration of coloured solutions.

log base(10) (Io/IT) = A

The extinction coefficient, which is equal to  the absorbance of a 1% solution, at a path length of 1 cm:

epselon e = A(1% w/v , 1 cm)

When both the equations combined we will get

e × l is equal to the slope of the calibration curve (absorbance vs. concentration): 

A= e*c*l

Where: e = extinction coefficient ((concentration units)-1cm-1) c = concentration (concentration units) l =

 

path length (usually 1 cm)

There are many other names/conventions for A, such as E (extinction), and OD (optical density).

Beer’s law must always be tried for each substance being measured in order to see if there is a linear 

relation between A and the concentration of the drug in solution.