Beer-Lambert Law Lecture 2 PDF

BEER’S LAW AND THE RELATIONSHIP BETWEEN ABSORBANCE, CONCENTRATION, AND TRANSMITTANCE Lecture 2 Dr Najwa Al Jahdhami Topics to be covered.Beer’s law in terms of absorbance, concentration, and transmittance.Application o...

BEER’S LAW AND THE RELATIONSHIP BETWEEN ABSORBANCE, CONCENTRATION, AND TRANSMITTANCE Lecture 2 Dr Najwa Al Jahdhami Topics to be covered.Beer’s law in terms of absorbance, concentration, and transmittance.Application of Beer’s law in quantitative calculation.Conditions that may result in reactions deviation from Beer’s law Beer-Lambert Law is a linear relationship between the absorbance and the concentration, molar absorption coefficient and optical coefficient of.a solution …Cont The molar absorption coefficient (ᵋ) is a sample dependent property and is a measure of how strong an absorber the sample is at a.particular wavelength of light The concentration (C) is simply the moles L-1 (M) of the sample.dissolved in the solution the length (l) is the length of the cuvette used for the absorbance.measurement and is typically 1 cm …Cont The Beer-Lambert law states that there is a linear relationship between the concentration and the absorbance of the solution, which enables the concentration of a solution to be calculated by.measuring its absorbance Application of Beer Lamberts Law with Spectrophotometers No assay gives a linear response between absorbance and concentration for all concentrations, going from small to large, because sooner or later, some reactant becomes limiting and less.color is formed All procedures require one to determine whether spectrophotometric response is linear for usual concentrations to be measured and to.determine the limits of linearity Spectrophotometric Calculation spectrophotometric procedures, the absorbance of an unknown concentration of a particular constituent is compared with that of a known concentration (a standard), which is reacted in the same way to produce a :colored solution. The following relation holds Au/AS= Cu/Cs.A is absorbance, while C is concertation.The subscript u is given for the unknown, while s for the standard Transmittance When light strikes a cuvette that contains a colored sample, some of the light is.absorbed by the solution ; the rest is transmitted through the sample to the detector The ratio of the amount of transmitted light divided by the amount of incident light is ”known as “Transmittance Transmittance = It / Io :However, it is more commonly expressed as a percentage transmittance T% = 100 X It / Io …Cont The absorbance, A, of the solution is related to the transmittance and :incident and transmitted intensities through the following relations :The above formula can be converted from T to %T A= log 1/T x 100% so, A= log 100/ % T.…Cont :Solving the previous slide equation A = log 100% - log % T OR A = 2.00 – log %T …Cont The absorbance has a logarithmic relationship to the transmittance; with an absorbance of 0 corresponding to a transmittance of 100% …Cont Conditions that can deviate from Beer’s law Elevated concentration of analyte exceeds the reagent reaction.1 capacity Transmitted light is not a single wavelength (monochromatic).2.Interference by solvent absorbance.3.Presence of stray light.4.Cuvette imperfection.5