In a spectrophotometric analysis, the relationship between the concentration of a solution and its absorbance can be described by the Beer-Lambert Law, also known as Beer's Law. According to Beer's Law, the absorbance of a solution is directly proportional to the concentration of the absorbing species and the path length of the light through the solution.
Mathematically, Beer's Law is expressed as:
A = εcl
Where: A is the absorbance of the solution, ε is the molar absorptivity (also known as the molar absorption coefficient), which is a constant characteristic of the absorbing species and the wavelength of light being used, c is the concentration of the absorbing species in moles per liter (Molarity), and l is the path length of the light through the solution in centimeters.
The law assumes that the solution is dilute and that the absorbing species does not undergo any chemical or physical changes upon absorption of light. It is important to note that Beer's Law is typically valid within a certain concentration range, beyond which deviations may occur due to factors such as intermolecular interactions, self-absorption, or instrumental limitations.
In practice, spectrophotometric analysis involves measuring the absorbance of a series of standard solutions with known concentrations and constructing a calibration curve. This curve can then be used to determine the concentration of an unknown sample by measuring its absorbance and applying Beer's Law.