A spectrophotometric method for the estimation of amino groups on polymer supports

Abstract

A simple and sensitive method for the estimation of polymer-supported amino groups is reported. The polymer support is treated either with N-succinimidyl-4-O-(4,4′-dimethoxytrityl)-butyrate or 2,4-dinitrophenyl4-O-(4,4′-dimethoxytrityl)-butyrate and a catalytic amount of 4-dimethylaminopyridine. After removal of the excess reagent through washing, a weighed quantity of the polymer support is treated with perchloric acid to release the 4,4′-dimethoxytrityl cation from the solid support into the solution. The released 4,4′-dimethoxytrityl cation, which has a strong absorption (ε498 = 70,000/m) at 498 nm, is determined spectrophotometrically. A comparative study of these reagents with N-succinimidyl-3-(2-pyridyldithio)-propionate, 4,4′-dimethoxytrityl chloride, and sodium 2,4,6-trinitrobenzenesulfonate methods is also included.