1. Separation and Purification Sciences Div.3M United Kingdom PLC, 3M Centre Bracknell RG12 8HT U.K.
2. Dept. of Biochemical EngineeringUniversity College London London WC1E 6BT U.K.
3. Separation and Purification Sciences Div.3M Centre St. Paul MN 55144
4. Dept. of Biochemical EngineeringUniversity College London London WC1E 6BT UK