Deviation from Beer’s Law

Deviation from Beer’s Law

Instrumental deviations

•       Fluctuation in the electric power.

•       Stray radiation that can strike the detector without passing through the sample.(-ve)

•       The use of polychromatic light.

•       Reflection loss error resulting from an inaccurate response of detector.

How to Minimize the instrumental deviation

•       Use constant power supply.

•       Using narrow bands of radiation.

•       Restricting absorbance measurements varies from about 0.2 to 1.

•       Painting the cell compartment with black paint.

Chemical Deviations.

Deviations from beer's law appear when the absorbing species undergoes:

Association-dissociation reactions

Acid-base reactions

Polymerization reactions

Complexation reactions

Reactions with solvent

To minimize chemical deviations

•       Adjust the pH by using buffer solutions.

•       Adding a large excess of complexing agent.

•       Ionic strength adjustment.

•       Preparation of a calibration graph over the measurement range.

•       By choosing wavelength for the analysis at which all of the absorbing species have the same absorbitivity .