Determination of adalimumab by HPLC with fluorescence detection using the König reaction.

Monoclonal antibody drugs (mAb) are widely used to treat various diseases. Keeping quality of mAbs is crucial to maximize efficacy and minimize adverse effects. To this end, mAb content in the drug product must be precisely quantified. As methods for the determination of mAbs, absorbance measurement at 280 nm, the ligand binding assay based on ELISA, or the LC-MS/MS method based on the surrogate peptide approach is usually used. However, these methods have drawbacks in terms of selectivity, reliability, and cost, respectively. The present method is based on the surrogate peptide approach where a peptide specific to the mAb is determined by a post-column derivatization LC system with fluorescence detection and the König reaction, which is usually used for the detection of cyanide and its derivatives. The detection mechanism was the production of cyanide from the surrogate peptide by chloramine T and the generated cyanide was detected by the König reaction. In this study, adalimumab was used as a model target protein. The calculated LOD and LOQ of the present method were 0.31 μg/mL and 0.94 μg/mL, respectively. The intra-day accuracies and precisions were 127.1 % and 2.94 % for 5 μg of adalimumab and 101.6 % and 10.2 % for 50 μg of adalimumab, respectively. The inter-day accuracies and precisions were 121.8 % and 5.71 % for 5 μg of adalimumab and 101.8 % and 6.98 % for 50 μg of adalimumab, respectively. Our quantitatively determined amount of adalimumab in Humira® was in good agreement with the specified value. This method only requires a conventional LC system, not an LC-MS/MS system. By extending the application of the König reaction, we open the door to a new surrogate peptide approach for the determination of proteins including monoclonal antibody drugs.