Beer lamberts law

BEER LABMBERTS LAW DEFINITIONS AND DERIVATIONS AND DEVIATIONS AND APPLICATIONS

1. BEER-LAMBERTS- LAW (Absorption Spectroscopy ) Presented by:- D.Mahendra.M.pharm (PA&QA)

2. I N TRODU C TIO N BEERS LAW LAMBERTS LAW DEVIATIONS ABSORPTION LAWS 2

3. BEERS LAW 3 When a beam of monochromatic radiation is passed through a solution of an absorbing substance, the rate of decrease of intensity of radiation with thickness of the absorbing solution is proportional to the intensity of incident radiation as well as the concentration of the solution. - di / dt  I c - di / dt = K’I c   I = Intensity of incident radiation passing through a thickness of “ t “ of the medium. di = decrease in intensity of radiation   - di / dt = rate of decrease of intensity of radiation with thickness of the absorbing medium.   K’ c = molar absorption coefficient. = Concentration of the solution in moles/litre .

4. LAMBERTS LAW 4 Lamberts law – when a beam of monochromatic radiation passes through a homogenous absorbing medium, the rate of decrease of intensity of radiation with the thickness of the absorbing medium is proportional to the intensity of incident radiation. - di / dt  I - di / dt = KI I = Intensity of incident radiation passing through a thickness of “ t “ of the medium. di = decrease in intensity of radiation - di / dt = rate of decrease of intensity of radiation with thickness of the absorbing medium. K = propionate constant or absorption coefficient.

5. Let, I o be the intensity of the incident radiation I be the intensity of the radiation after passing through the medium. The intensity of the absorbed radiation can be given as I abs I abs = I o - I 5 - a ’ cx I = I o 10 , where a = extinction coefficient of the absorbing medium. a , = k ’ / 2.303

6. Deviations of Absorption laws Absorption Vs Concentration Straight line Positive deviation 6 Negative deviation Concentration A b s or b ance

7. DEVIATIONS : 7 When a non linear curve is obtained, the system is said to undergo deviation. The two types of deviations are positive and negative deviations. Positive deviation results in when a small change in concentration produces a greater change in absorbance. Negative deviation results when a large change in concentration produces smaller change in absorbance.

8. Instrumental deviations – stray radiation, improper slit width, fluctuations in single beam and monochromatic light is not used. Physiochemical changes in solutions factors like association, dissociation, ionization (change in pH), faulty development of colour (incompletion of reaction). Reasons 8

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