Development of an immunoassay for a quaternary ammonium compound, benzyldimethyldodecylammonium chloride

A competitive enzyme-linked immunosorbent assay (CELISA), based on polyclonal antibodies, was developed to measure benzyldimethyldodecylammonium chloride (BDD12AC), a component of benzalkonium chloride (BAK). The polyclonal antibodies recognized free benzyldimethyldodecylammonium bromide (BDD12AB) in an indirect competitive ELISA with a 50% inhibition (IC50) of 0.66±0.20 μg/ml and a detection limit of 0.043±0.033 μg/ml. The two other components of BAK, benzyldimethyltetradecylammonium chloride (BDT14AC) and benzyldimethylhexadecylammonium chloride (BDH16AC), were recognized to varying degrees by the antibodies. The antibodies did not cross-react with other compounds such as fatty acids and alcohols, amino acids, amines, and short-chain quaternary ammonium compounds. Cross-reactivity was observed with other alkyldimethylbenzylammonium compounds (ADBACs). The CELISA and HPLC were used to measure the amount of pure BDD12AB spikes in milk and BDD12AC in five commercial products. HPLC analysis correlated well with CELISA analysis for spiked samples.