Which formula is an expression of the Beer-Lambert law routinely applied to spectrophotometric analysis?

Which formula is an expression of the Beer-Lambert law routinely applied to spectrophotometric analysis?

• A. Au X (Cs/As) = Cu
• B. Cu X (Cs/As) = Au
• C. As X (Cs/Cu) = Au
• D. A = 2 - log %T

Answer: (A)

Absorbance is proportional to concentration for a given path length and wavelength, so the ratio of absorbances for two solutions equals the ratio of their concentrations: Au/As = Cu/Cs. Rearranging gives Cu = (Au × Cs) / As, which is the same as Au × (Cs/As) = Cu. This form is routinely used in spectrophotometry to determine an unknown concentration from a standard, because it directly utilizes the measured absorbances of the unknown and the standard along with the standard’s known concentration. The alternative A = 2 − log %T is another way to express the Beer-Lambert relationship in terms of percent transmittance, but the ratio form above is the standard method for calculating unknown concentrations from a known standard.

Absorbance is proportional to concentration for a given path length and wavelength, so the ratio of absorbances for two solutions equals the ratio of their concentrations: Au/As = Cu/Cs. Rearranging gives Cu = (Au × Cs) / As, which is the same as Au × (Cs/As) = Cu. This form is routinely used in spectrophotometry to determine an unknown concentration from a standard, because it directly utilizes the measured absorbances of the unknown and the standard along with the standard’s known concentration. The alternative A = 2 − log %T is another way to express the Beer-Lambert relationship in terms of percent transmittance, but the ratio form above is the standard method for calculating unknown concentrations from a known standard.