The content of Hib polysaccharide (PS) in Hib-conjugate vaccines is usally determinened by measuring its ribose using colorimetric orcinol assay. However, the MSD vaccine contains a large quantity of lactose, a stabilizer, which makes the assay impossible. The results obtained from ongoing experiments showed that the amount of Hib PS in the MSD's vaccine could be measured on a Dionex carbohydrate analyzer as follows. The PS in the conjugate vaccine was first depolymerized in strong alkali into its single repeating unit, 80% in yield when Hib PS was used. The repeating unit of the PS in a sample was then separated from the large lactose peak by a carbohydrate column. Optimum conditions for the quantitation of the PS in the vaccine will be established.
