(06) Beer Lambert`s Law Derivation and Deviation | UV Spectroscopy | Instrumental Method of Analysis

Download the "Solution Pharmacy" Mobile App to Get All Uploaded Notes, Model Question Papers, Answer Papers, Online Tests and other GPAT Materials - https://play.google.com/store/apps/de...

The Beer-Lambert Law, also known as Beer's Law, describes the relationship between the absorption of light by a sample, the concentration of the absorbing species in the sample, the path length of the sample, and the intensity of incident light. This law is fundamental in UV-visible spectroscopy and is expressed as:

A = ε⋅c⋅L

Where:
A is the Absorbance (or Optical Density) of the sample.
ε is the Molar Absorptivity (also known as the molar extinction coefficient), measured in L·mol⁻¹·cm⁻¹. It represents the ability of a substance to absorb light at a particular wavelength.
c is the Concentration of the absorbing species in moles per liter (mol/L).
L is the Path Length of the sample in centimeters (cm), which refers to the distance the light travels through the sample.

Derivation:
The Beer-Lambert Law can be derived from the basic principles of light attenuation through a medium. It considers the relationship between the intensity of incident light (and the intensity of transmitted light (I) through the sample, which is related to the concentration of the absorbing species.

A=ε⋅c⋅L

Deviations from Beer-Lambert Law:
1. While the Beer-Lambert Law holds true under specific conditions (such as dilute solutions and monochromatic light), several factors can lead to deviations from its linear behavior:

2. Non-linearity at High Concentrations: At high concentrations, interactions between molecules (such as aggregation, self-association, or chemical reactions) may occur, leading to deviations from linearity due to deviations from ideal behavior.

3. Instrument Limitations: Deviations can arise from limitations in the instrument, such as stray light, instrumental noise, or non-uniformity of the sample.

4. Wavelength Dependency: In some cases, absorption may not be solely wavelength-dependent, especially for complex molecules or mixtures, leading to deviations from Beer-Lambert Law.

5. Solvent Effects: Changes in solvent polarity, viscosity, or interactions with the solute can lead to deviations, especially when solvent properties significantly affect the absorbing species.

6. Chemical Equilibria and Structural Changes: Chemical equilibria or structural changes in the absorbing species can affect absorptivity, causing deviations from linearity.

7. While the Beer-Lambert Law serves as a valuable tool for quantitative analysis in many cases, it's essential to be aware of these potential deviations and understand the limitations in order to accurately interpret spectroscopic data.

Get in touch with the solution by just clicking the following links-

Facebook Group-   / solutionpharamcy  
Mobile App - https://play.google.com/store/apps/de...
New Channel (Pharmacy Dictionary)    / @pharmacydictionary  
E-Mail for official and other work - [email protected]
#solutionpharmacy #Pharmacologyclass #Pharmacognosyvideos #GPAT