A SENSITIVE METHOD FOR MEASURING DIFFUSION COEFFICIENTS IN AGAROSE GELS OF ELECTROLYTE SOLUTIONS

A transient-state method for measuring diffusion coefficients in agarose gels is described. Assuming agarose affects results only by increasing the length of the diffusion path and calibrating the diffusion apparatus against known diffusion coefficients, 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 diffusion coefficients of NaCl, Na+ in NaCl, and BaCl2 with literature values. The lowest concentrations studied at which the method yielded free-solution values of diffusion coefficients were C = 0.05 M for DNaCl, C = 0.01 M for DNa, and C = 0.5 M for DBaCl2. 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 <0.2% of the mean.