A novel approach to determine residual aldehyde content in conjugated polysaccharides with 3-methyl-2-benzothiazolinonehydrazon (MBTH) by colorimetric method, automation, and HP-SEC

Polysaccharide activation by periodate oxidation to form aldehydes, followed by conjugation with proteins via reductive amination is a general procedure to make polysaccharide-protein conjugate vaccines. Controlling the level of residue aldehyde content after conjugation is critical to ensure vaccine product stability. Herein, to support conjugation process optimization, we developed a 3-methyl-2-benzothiazolone hydrazone (MBTH) chemistry-based colorimetric method, which can measure low-level residual aldehyde polysaccharide-protein conjugate in high throughput 96-well plate format. This mechanism of detection works in two steps. First, MBTH reacts with the aldehyde group to form azine. Then the excess MBTH was oxidized by ferric ammonium sulfate in sulfamic acid to form a reactive cation, which reacts further with azine to form formazan, a characteristic blue chromophore at 610 nm, for colorimetric detection. The method performance, including detection limit, linearity range, matrix effect, kinetics, and color stability was systematically studied. For samples with severe matrix interference, a supplemental size exclusion chromatography (SEC) method was also developed as an alternative method.