METHOD FOR THE QUANTIFICATION OF ALGINATE IN MICROCAPSULES

Alginate is a key reagent in the preparation of microcapsules for cell transplantation. To address the question of the intracapsular alginat e concentration, a sensitive assay has been developed to quantify the alginate content of microcapsules. The method is based on the metachro matic change induced by alginate binding to the dye, 1,9-dimethyl meth ylene blue (DMMB). The assay has a high sensitivity and precision. It covers a wide concentration range enabling the measurement of alginate in dilute supernatants as well as in microcapsules. For the latter, t he membrane is initially dissolved by incubating the microcapsules in an alkaline medium. The effect of potentially interfering substances ( poly-L-lysine (PLL), citrate, chloride, sodium) and of pH has been stu died. Poly-L-lysine interfered with the assay at pH 6.5 but not at pH 13. Interference by sodium augmented with increasing sodium concentrat ion and reached a plateau at 200 mM. This problem was overcome by rout inely adjusting all samples to 500 mM sodium. The other substances tes ted had a negligible effect on the assay. The reliable measurement of alginate with this new assay will allow the optimization of the intrac apsular alginate concentration.