Diffusion in Liquid Systems. I. A Simple and Fast Method of Measuring Diffusion Constants

Abstract

A simple and fast method of measuring diffusion constants based on the hydrodynamic continuity equation for laminar flow in small diameter tubing rather than the classical Pick's second law is proposed. The apparatus for measuring the diffusion constants consists mainly of a constant volume pump, a sample injection port, a 168 m long × 1/16, in. o.d. × 0.020 i.d. stainless steel tube coiled into a 1.5-ft diameter coil, uv and differential refractometer detectors, a volume counter, and a recorder. The diffusion constant D was calculated from the variance of the residence time distribution of the solute in the tubing. The values of D obtained from the intercept (Q/DL = 0) of a plot of D vs. Q/DL (Q being the flow rate and L the tubing length) gave limiting values of D which agree reasonably well with diffusion constants measured by the free diffusion cells method reported in literature. © 1972, American Chemical Society. All rights reserved.