Computer Program for Solving a Spectrophotornetric Three-Component Mixture The spectrophotometric analysis of a binary mixture has been a classic experiment used for years in quantitative analysis and instrumental analysis courses, and this experimental procedure can be found in r number of texts and laboratory manuals.' Several examples of these experiments are mixtures of permanganate-dichromate, titanium-vanadium as their peroxide complexes and imn(I1)-iron(ll1) as their 1,lO-phenanthraline complexes. Several years ago, we were interested in extending this procedure to a three-component mixture as an experiment for our instrumental analysis class. We were interested in utilizing the ultraviolet spectrophotametric method for analyzing a mixture of o-, rn-, and p-cresals in isooctane, which is a procedure in the laboratory manual by Guilbault and H a ~ g i s . ~ As these authors point out, the mathematical solution of this system using three simultaneous equations is time-consuming. Thus, we have written a computer program in Basictoenable thestudents toeasily and quickly calculate their results. Our program is written for use with our Tektronix 4051 equipment, but can be used with any other type of computer system utilizing the Basic language. This program is written specifically for the purpose of solving three simultaneous equations that are associated with the three-cumponent spectraphotometric experiment, but is also adaptable to any set of three solvable simultaneous linear equations. In the laboratory, the procedure used is the same as for a binary mixture. Absorbance measurements are run on each component a t three wavelengths (all three wavelengths for the three species are the same), when in standard solution. These absorbance values are used to calculate, from Beer's law, the molar absorptivities of each species a t eaeh wavelength. To use the program, these standard absorbances, along with the standards' concentrations, are entered in a certain order. Also required are theabsorbances of the unknown, which contains a mixture of these same three components, at each of the three wavelengths. By using matrix algebra, the program then solves for the concentration of each component in the unknown mixture. The unknown concentrations will be in the same units as those of the standards, which must all have the same units. If the molar absorptivities are already known, each is entered, corresponding to the absorbances of the standards, and the concentration of eaeh eomoonent entered as a value of one. The yrint
