Method development for poly(diallyldimethylammonium chloride) determination in proteinaceous samples and its role in downstream technology development of monoclonal antibody production

Poly(diallyldimethylammonium chloride) (pDADMAC) is a cationic polyelectrolyte bearing one positive charge per monomer unit. This structure enables its application as flocculating agent. It can be used in the downstream processing of biological drug production. Due to its potential toxicity, its concentration in the drug substance should be reduced to a sufficiently low level, which is realized by chromatographic steps of downstream processing. To prove proper clearance, appropriate analytical method should be developed, which should be able to measure low pDADMAC concentration in matrices with high protein content. It is a challenge due to the size and composition of pDADMAC. Its molar weight (∼300 kDa) is commensurable with that of mAbs (∼150 kDa) or rather their dimers. It hampers the applicability of size-exclusion chromatography. For reversed-phase HPLC the protein content of the samples should be removed, which is especially challenging due to electrostatic interaction between protein and the pDADMAC analyte. The development and qualification of an RP-HPLC method is presented in this study. The protein removal is realized by precipitation using ammonium sulfate, which is a quick and simple method. The method was found to be able to measure pDADMAC concentration accurately and precisely in samples with up to 85 g/L protein concentration.