The capsular saccharide of serogroup A Neisseria meningitidis (MenA) is a homopolymer of α(1-6)-linked N-acetyl-mannosamine-6-phosphate. It is included as an immunogen in vaccines, either as free saccharide or conjugated to a carrier protein.
The European Pharmacopoeia recommends that quantitative determination of the MenA saccharide should be based on calorimetric determination of its phosphorus. Reference 1 discloses an alternative method for the quantitative determination of MenA saccharide by: trifluoracetic acid (TFA) hydrolysis (2 M at 80° C. for 3 h); followed by chromatographic separation and quantification of the liberated mannosamine-6-phosphate from the area of the peak obtained using an IonPac AS11 column coupled to the sensitive pulsed amperometric detector ED40. The highly selective nature of this method circumvents interference problems associated with the calorimetric phosphorus assay.
The MenA saccharide may be lyophilised, in which case stabilisers such as sucrose may be combined with the MenA saccharide. Such stabilisers will be present at much higher levels than the MenA saccharide itself Sucrose can interfere with the analysis of mannosamine-6-phosphate monosaccharides. Thus there is a need for an assay method for MenA that can function against a background of lyophilisation stabilisers such as sucrose.