There is a clear need for routine methods of analysis of the ligand concentration in affinity gels. Convenient methods are required for (a) monitoring the success of syntheticgrocedures, (b) studying leakage or other deterioration during the use of the gel and (c) studying the efYect of ligand concentration on separation, which is parti-cuIarIy important in deveIoping mathematical models for affinity chromatography'. Applicable methods can be based on either hydrolysis of the gel and subsequent analysis of the ligand in the hydrolyzate, or on direct "in-gel" analysis. The hydrolytic methods have some drawbacks: the hydrolysis of sugar polymers generally results in a variety of reactive and undefined substances and causes the polymers to turn black at the temperatures needed for the hydrolysis. Accuracy will also be impaired due to the many steps in handling. In the case of labile ligands, the analytical difficulties after the hydrolysis may also be considerable.
Quantitative in-gel methods are based mainly on the potentiometric titration of rather large gel volumes', direct spectroscopic measurements in the case of suitable ligands3 or the addition of a specific reagent to a gel batch and estimation of the consumption of the reagent from the solvent after completion of the reaction-'. The last method is inaccurate for the estimation of the dilution of the reagent when added to the gel. Labelled ligands needed for radioactive methods are seldom available commercially.
we describe here an in-gel method which is based on the elution of a suitable reagent through a small column containing the gel sample. As an example, we show how aldehyde groups can be measured. In-gel methods like this avoid excessive handling of the gel. Moreover, very small samples of the gel are needed, the gel volume may be observed directly in a packed state, littIe effort is required due to the automation of the methcd and reliable results are obtained. Because the method is simple and flexible we suggest that it cou!d be adopted for routine use.