A new polymer capable of reacting with primary amines was synthesised from allyl mercaptan, o-phthalic dialdehyde and ethylene glycol dimethacrylate by radical polymerisation. Reactive hemithioacetal formed by allyl mercaptan and dialdehyde can bind primary amino groups without additional pre-activation forming the fluorescent isoindole complex. It gives a great opportunity to monitor binding and perform loading of the amino compounds onto the reactive surface. The reactive polymer is found to be an effective matrix for immobilisation of the proteins and other amino-containing compounds in affinity chromatography and could be used for their detection in solution. (C) 2001 Elsevier Science Ltd. All rights reserved.