Post-column denaturation-assisted hydrophobic interaction chromatography-mass spectrometry for rapid and in-depth characterization of positional isomers in cysteine-based antibody-drug conjugates

Antibody-drug conjugates (ADCs) represent a significant advancement in targeted cancer therapy, offering the potential to selectively deliver cytotoxic drugs to tumor cells while minimizing systemic toxicity. However, the structural complexity of ADCs, particularly those conjugated through cysteine residues, poses significant analytical challenges. Due to the hydrophobicity of ADCs, Hydrophobic interaction chromatography (HIC) is often the method of choice to analyze the drug-to-antibody ratio (DAR). However, it requires high-concentration salts, which are often incompatible with mass spectrometry (MS) analysis. By employing ammonium acetate as an MS-compatible salt and integrating a 4-way liquid junction cross configuration for simultaneous introduction of the makeup flow and splitting the flow right before coupling to a mass spectrometer, we achieve high-quality separation and sensitive mass spectrometric analysis. This innovative setup allows for simultaneous DAR measurement and positional isomer characterization by switching the makeup flow solvent from water to a denaturation solution. Our method offers a streamlined and effective approach to ADC characterization, facilitating the identification of positional isomers without the need for fractionation or multiple chromatographic steps. The versatility and robustness of this HIC-MS method are demonstrated through the analysis of two ADCs, highlighting its potential for broad application in ADC development and quality control.