Quantitation of free cyanide using ion exchange chromatography in Neisseria meningitidis serogroups A, C, W, Y and X conjugates used in vaccine manufacture

Polysaccharide vaccines essentially used in the prevention of bacterial infections are known to be good immunogens when conjugated to an immunogenic protein using various cyanylating agents. Analysis of residual cyanide in polysaccharide conjugate vaccines is an ardent task due to the complexity of the sample matrices and the lack of suitable methods. We report a selective ion chromatography method with electrochemical detection using IonPac AS7 column for estimation of residual cyanide in meningococcal serogroups A, C, W, Y and X bulk conjugates in presence of other interfering ions. Gold electrode and Ag/AgCl reference electrode ensures sensitivity and reproducibility of cyanide quantitation. The calibration curve of the method is linear having r² ≥0.990 over the concentration range 1.45 ng/mL to 93.10 ng/mL. The recovery of cyanide in bulk conjugates ranged between 96.0% and 108.9%. The limits of detection and quantitation were 0.50 ng/mL and 1.45 ng/mL which corresponds to 0.31 ng/μg and 0.91 ng/μg of polysaccharide respectively. The method validation and feasibility study were performed using Men W and Men X bulk conjugates respectively with in house residual cyanide specification due to unavailability of pharmacopeia guidelines. The method is reproducible and can accurately quantify residual cyanide in purified meningococcal bulk conjugates.