Haemophilus influenzae type B (Hib) is a major cause of bacterial meningitis in children in many countries. The capsular polysaccharide (PS) of Hib plays an important role in the virulence of the organism. The polysaccharide capsule hides cell surface components from elements of the mammalian immune system, such as antibodies and complement proteins that otherwise would activate mechanisms to kill the pathogen.

Vaccines require rigorous characterization and assays to ensure final product quality and consistency. For glycoconjugate vaccines, it is important to measure both free and total PS to ensure the quality. A large amount of unconjugated PS may suppress immunity to the antigen. Additionally, the presence of free PS is a key indicator of process consistency.

Current methods to determine PS content in vaccines such as Hib are imprecise and unreliable, especially if the vaccine contains a sugar stabilizer (e.g. lactose). Ion chromatography with pulsed amperometric detection (IC-PAD, or HPAEC-PAD) offers a simpler procedure and better sensitivity than other assays to quantify PS (here, polyribosylribitol phosphate [PRP]) in Hib vaccine.