Determination of free amino group content of serum albumin microcapsules using trinitrobenzenesulfonic acid: effect of variations in polycondensation pH

Abstract

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 -NH 2 content: those obtained at low pH values (8 and < 8) which contained more than 400 μmol g dry weight, and those prepared from pH 9, whose -NH 2 content did not exceed 110 μmol 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.