The chromatographic broadening method of measuring diffusion coefficients, which until recently was used with gaseous mixtures, is shown to be useful for liquid mixtures. In this method, a small amount of solute (component l) is injected into a flowing stream of a solvent (component 2). From the width of the eluted peak, the diffusion coefficient is measured. The constraints due to the liquid system, as well as possible sources of errors, are discussed. It is shown that with a well-designed injection port, a small-volume detector cell, narrow tubing, and low flow rate, good diffusion data can be easily obtained. Since the method is a dynamic one, the accumulation of the data is rapid, especially if a multiple-injection technique is used. The method was utilized to measure the diffusion coefficients of several alkylbenzenes in chloroform. It was found that as the side chain of the molecule lengthens, the diffusion decreases. The effect of molecular geometry was also investigated by observing the diffusion coefficients of structural isomers. The results seem to indicate that the more branched the molecule is. the faster the diffusion. The ramifications of these findings are discussed.
Extension of the chromatographic broadening method of measuring diffusion coefficients to liquid systems. I. Diffusion coefficients of some alkylbenzenes in chloroform
Subjects: Alkylbenzenes