Rapid diffusion coefficient measurements using analytical SPLITT fractionation: application to proteins.

This work reports a new technique for the rapid measurement of diffusion coefficients using a special flow cell called a SPLITT cell. Such SPLITT cells, designed for continuous SPLITT fractionation, utilize differential transport across a thin (approximately 100 microns) ribbonlike lamina flowing through the cell. The liquid stream in the cell is split into two substreams at the outlet. The relative concentration in the two outlet substreams of a dilute component introduced into one of two inlet substreams is mathematically related to the appropriate transport coefficient, in this case the diffusion coefficient D. Thus D can be calculated from measured values of relative outlet concentrations. This approach has been tested using a number of dilute protein solutions. The results at different stream-splitting ratios are reasonably self-consistent and agree with most literature values for D within 5%. This approach provides a simple, rapid, and predictable means for determining the diffusion coefficients of proteins and other substances.