Quantification of free polysaccharide in meningococcal polysaccharide-diphtheria toxoid conjugate vaccines

A precipitation method using deoxycholate/HCI has been applied successfully to separate unconjugated free polysaccharide from carrier protein-bound material in meningococcal polysaccharide-diphtheria toxoid conjugate vaccines. The method effectively separated free and bound polysaccharide in conjugate vaccines prepared from Neisseria meningitidis serotypes A, C, W135 and Y. Free polysaccharide remained in the supernatant after deoxycholate treatment while protein-bound polysaccharide was fully precipitated. Testing by both colorimetric assay and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) has confirmed the selective loss of protein-bound polysaccharide in samples of conjugate vaccine or conjugate vaccine mixed with known amounts of free polysaccharide. This rapid separation method requires minimum sample handling and is specific, reproducible, and allows assessment of free polysaccharide levels in vaccines at final container concentration.