Determination of the Composition of a Multi-Component Mixture by Spectrophotometric Analysis
CHEM 3281 Experiment Seven Determination Of The Composition Of A Multi-Component Mixture By Spectrophotometric Analysis Objectives: 1.Solid sample handling 2.The composition of a three-component mixture will be assayed by dissolution of the soluble components in water and measurement of their individual concentrations by visible spectrophotometry. Text Reference: Handbook of Instrumental Techniques for Analytical Chemistry, Frank Settle, editor. Prentice Hall, , Upper Saddle River, NJ 1997, Ch 25. H.H. Willard, et. al. Instrumental Methods of Analysis, 7th edition, Wadsworth Publishing Co.:Belmont, CA 1988, p. 159-172. Skoog, Holler and Nieman, Principles of Instrumental Analysis, 5th edition, Saunders College Publishing, Fort Worth, TX 1998, Ch 13 & 14D. Introduction: The Beer-Lambert law states that the log of the ratio of the power of a beam of monochromatic light incident on the sample (Io) over the power passed through the sample (I) is defined as the sample absorbance (ABS). The absorbance of a solution containing only one chromophore will be proportional to the concentration of the chromophore, C, the absorptivity, a or ε, and the optical path length, b. ABS = log (Io/I) = εbC or abC at any one wavelength ε = molar absorptivity (L/mole-cm) a = absorptivity (L/g-cm) b = path length (cm) C = concentration (moles/L or g/L) (depends on whether you are using ε or a to represent absorptivity) The absorbance of a solution containing more than one chromophore will be equal to the sum of the absorbances of each of the components at any one wavelength. ABStotal = ABS1 + ABS2 + ... ABS n
where the subscripts refer to the individual chromophoric components 1, 2 ... n. For a solution containing n components, if the optical pathlength and the molar absorptivities for each component are known, the concentration of each chromophore can be determined by measuring the total absorbance of the solution at n wavelengths (selected where a1 = a2 = ... / / an) and solving the
where the subscripts refer to the individual chromophoric components 1, 2 ... n. For a solution containing n components, if the optical pathlength and the molar absorptivities for each component are known, the concentration of each chromophore can be determined by measuring the total absorbance of the solution at n wavelengths (selected where a1 = a2 = ... / / an) and solving the