3380
GARYE. SPALDING
A Sensitive Method for Measuring Diffusion Coefficients in Agarose Gels of Electrolyte Solutions1 by Gary E. Spalding UT-AEC Agricultural Research Laboratory,g Oak Ridge, Tennessee $7880 (Received April 7, 1069)
A transient-state method for measuring diffusioncoefficients in agarose gels is described. Assuming agarose affects results only by increasing the length of the diffusionpath and calibrating the diffusion apparatus against known diffusioncoefficients, the method yields free-solution values. This assumption holds as long as the system under study does not interact appreciably with agarose. The applicability and precision of the method were demonstrated by comparing measured diffusioncoefficients of NaC1, Na+ in NaC1, and BaClz with literature values. The lowest concentrations studied at which the method yielded free-solution values of diffusion coefficients were C = 0.55 1M for D N ~ CCI = , 0.01 M for D N ~and , C = 5.5 M for D B ~ c I At ~ . lower concentrations, agarose apparently interacted sufficiently with diffusing species to decrease their mobility. Where applicable, the method is very convenient and fast; 25 measurements can be made in a normal workday. The standard error of the mean of 50 determinations was generally
