โ
A = e * c * l (Absorbance = Epsilon * Concentration * Path length)
Picture This (Mental Hook): Imagine light walking through a murky swamp: The deeper the swamp (Path length l) and the dirtier the water (Concentration c), the more light gets trapped (Absorbance A)! Epsilon is the unique darkness index of the swamp creature!
๐ Visual Diagram & Mental Flow:
BEER-LAMBERT LAW OF LIGHT ABSORPTION:
A = ฮต ยท c ยท l
* [A] : Absorbance (Optical Density - OD, Dimensionless!)
A = log10(I0 / I) = -log10(T)
* [ฮต] : Molar Extinction Coefficient (M^-1 ยท cm^-1)
(Aromatic amino acids: Trp at 280 nm, Tyr at 274 nm)
* [c] : Molar Concentration of solute (mol / L)
* [l] : Optical Path length of cuvette (standard = 1.0 cm)๐ The Decoded Sequence:
A
Absorbance
Directly proportional to concentration and path length in dilute solutions
260 / 280 Ratio
Purity Check
Pure DNA has A260/A280 of ~1.8; Pure RNA is ~2.0; protein contamination lowers ratio
Examiner Trap / Never Forget: Beer-Lambert law deviates at high concentrations (>0.01 M) due to electrostatic interactions between absorbing solute molecules and refractive index alterations!
