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A new universal reagent, 2- O -[2-(4,4 0 -dimethoxytrityloxyethyl)]-hydroxy acetaldehyde (DEA), has been synthesized and used for the estimation of surface-bound aminoalkyl, aminooxyalkyl, hydrazinyl, and semicarbazide functions. The reaction completes in just 10 min in the case of aminoalkylated supports and 30 min in hydrazinyl supports, whereas it takes approximately 60 min in both aminooxyalkylated and semicarbazide-modified polymer supports. DEA-treated supports, including glass slides and PP films on exposure to acid, liberates 4,4 0 -dimethoxytrityl cation, which was measured spectrophotometrically to estimate these functionalities. The method estimates accessible functional groups, useful for calculat- ing the quantity of the ligands to be immobilized.