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

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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.
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[@SaeedGullMengal-i9l]

Waki mam nice method bahot best samjaya apne

[@AlmizaAmin]

what is decreasing for wht we used negative sign

[@prakashchowdhury8783]

Nice

[@vijaykumarroy639]

Definition is not beer lambert law it's only beer law

[@solutionpharmacy]

Yes that is beers law...please watch the diagram explanation carefully for understanding the beers lambert law..