Effect of surfactants on the diffusion coefficients of proteins, measured by analytical SPLITT fractionation (ASF) in the diffusion mode.

This work reports further studies of protein transport parameters in the new technique called analytical SPLITT fractionation. The SPLITT fractionation channel mimics a dialysis-like separation utilizing differential transport across an ultra-thin lamina flowing through a channel. The flowing stream is split into two sub-streams at the channel outlet, between which the protein is distributed. The cell is capable of rapidly measuring diffusion coefficients of proteins, based on their differential transport across the channel thickness, which affects the distribution between the two outlet sub-streams. The sub-stream next to the sample introduction port is more enriched than the sub-stream at the counter port when the diffusion coefficients is small. The smaller the diffusion coefficient, the higher the degree of retrieval of the protein at the sample side outlet. The entire process is realized within a short time, and a quantitative treatment of the signals of the two sub-streams yields a retrieval factor which is used for the determination of the diffusion coefficient. The conditions under which the selectivity of the diffusion SPLITT cell is optimal were examined. Analytical SPLITT fractionation has proven successful, using a number of proteins under various conditions. Results showed that the technique can detect subtle changes in proteins diffusion coefficients, and confirm that addition of small concentrations of surfactants does not change their transport parameters significantly.