Colorimetric determination of reactive amino groups of a solid support using Traut’s and Ellman’s reagents

A simple colorimetric method has been developed for the quantitative determination of reactive amino groups of a solid support. The method calls for the use of a reagent that reacts specifically and facilely with amino groups and concurrently introduces free sulfhydryl groups. The latter can then be titrated colorimetrically by using the well-known Ellman’s reagent. Thus, an excess of 2-iminothiolane (Traut’s reagent) was reacted with amine-carrying solid supports. After removing unreacted 2-iminothiolane and keeping the resultant solid-phase sulfhydryl groups in a reduced state by using dithiothreitol, the solid supports, after being thoroughly washed, were then reacted with 5,5′-dithiobis-(2-nitrobenzoic acid) to quantify the sulfhydryl groups that were generated from reacting solid-phase amino groups with Traut’s reagents.