Separation of proteins using sandwich membranes

The effect of sandwich configurations of paired ultrafiltration membranes on the transmission and rejection of proteins were evaluated using various sandwich arrangements. Data is presented for the fractionation of BSA and myoglobin, and for that of lysozyme and myoglobin. Two membranes were sandwiched together in several different configurations without spacer. The sandwich configurations were known as SS-sandwich, BS-sandwich, BB-sandwich and SB-sandwich, where S indicates that the skin layer faces the feed and B indicates that the support layer faces towards the feed. The result of single membrane transmission was compared with the transmission of the various sandwich arrangements. Interestingly not having a skin layer on top and in contact with the feed (as in BS and BB sandwich configurations) was useful for enhancing protein transmission whilst SS and SB configurations can be used to increase protein rejection. For the separation of lysozyme and myoglobin, a selectivity value of 9 was found for S, SS and SB configurations The effect of sandwich membranes varies not only with MWCO but also, to a small extent, with different types of membrane material. For example, the transmission of both proteins using single membranes is comparatively higher than the sandwich membrane for RC and PES membranes, but this was not found to be so for YM membranes.

The experimental data obtained in this study show that the transmissions of proteins through the sandwich membranes are not only sensitive to the physicochemical condition of the experiment but also dependents on the various sandwich configurations examined in this study. The various sandwich configurations affect the transmission behaviour of BSA and myoglobin more strongly than the transmission of lysozyme. The orientation of the top membrane in the sandwich had a controlling influence. On the other hand, the filtration behaviour of the proteins was only slightly affected when the orientation of the bottom membrane in the sandwich was varied. The filtration behaviour of proteins with sandwiches membranes were also a strong function of pH and buffer solutions. The “soft” and “hard” characteristic of the proteins is also believed to influence their transmission behaviour. Lysozyme, which is a “hard” protein, shows different filtration behaviour than the “soft” proteins, myoglobin and BSA. For binary protein solutions, different protein mixtures behave differently with different sandwiches configurations. For the separation of lysozyme and myoglobin, a selectivity value of 9 was found for S, SS and SB configurations.