DETERMINATION OF FREE AMINO GROUP CONTENT OF SERUM-ALBUMIN MICROCAPSULES USING TRINITROBENZENESULFONIC ACID - EFFECT OF VARIATIONS IN POLYCONDENSATION PH

Microcapsules were prepared from human serum albumin (HSA) through an interfacial cross-linking process using terephthaloyl chloride at vari ous pH values (5.9-11). Determination of free amino groups was perform ed on lyophilized microcapsules by means of a back titration method us ing trinitrobenzenesulfonic acid (TNBS). Increasing reaction pH was sh own to result in a progressive decrease of microcapsule free amino gro ups. Moreover, two groups of microcapsules could be distinguished with respect to their -NH2 content: those obtained at low pH values (8 and < 8) which contained more than 400 mumol/g dry weight, and those prep ared from pH 9, whose -NH2 content did not exceed 110 mumol/g dry weig ht. These results were compared with previous findings concerning the involvement of hydroxy and carboxy groups of HSA microcapsules as a fu nction of pH, that had been obtained from FT-IR spectroscopic studies.