A modified gel filtration technique producing an unusual exclusion volume of IgM: a simple way of preparing monoclonal IgM.

The vast majority of monoclonal IgM proteins is eluted just before the total volume of the column when filtered through G200 Sephadex or S200 Sephacryl gels equilibrated in a 0.005 M phosphate buffer but eluted with 0.05 M phosphate buffer containing 1.7 M NaCl. This unusual behaviour in low-ionic buffer is probably due to the poor solubility of IgM in diluted buffers. It allows a 1-step purification procedure under mild conditions and is suitable for both large and small scale preparations.