Biochemical Techniques and Instrumentation

2.4.5. Spacer arms

After the activation of the support matrix, a suitable spacer molecule is attached between the support and the ligand. Spacer molecule helps to prevent the hindrance between the immobilized support and the molecules to be isolated. They are important for small immobilized ligands such as an antigen and not for macromolecular ligands. Spacer arm ensures that the ligand is placed at a suitable distance from the surface of the support. Spacer arms are either attached directly to support surface or to the reactive side chain of the support matrix. Optimum length of the spacer arm is six to ten carbon atoms. Some spacer arms are purely hydrophobic consisting of methylene (CH₂) groups and others are hydrophilic consisting of carbonyl (CO) or imido (NH) groups. Several matrix supports of agarose, dextran and polyacrylamide are available with a variety of spacer arms and ligands attached for immediate use.