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 various pH values (5.9-11). Determination of free amino groups was performed on lyophilized microcapsules by means of a back titration method using trinitrobenzenesulfonic acid (TNBS). Increasing reaction pH was shown to result in a progressive decrease of microcapsule free amino groups. 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 prepared from pH 9, whose -NH2 content did not exceed 110 mumol/g dry weight. These results were compared with previous findings concerning the involvement of hydroxy and carboxy groups of HSA microcapsules as a function of pH, that had been obtained from FT-IR spectroscopic studies.