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Three different LC–MS/MS methods using QqQ, Q-TOF and Q-Orbitrap were developed and compared for quantitation of a model mAb in biological fluids.The capabilities of HRMS combined with a simple sample treatment for fast and sensitive quantification of mAbs in complex matrices were revealed.The pharmacokinetic properties of Rendomab-B1 in mice over 15 days after administration were determined.Determination of the pharmacokinetic (PK) properties of therapeutic monoclonal antibodies (mAbs) is essential for their successful development as drugs. For this purpose, besides the traditional ligand binding assay (LBA), LC–MS/MS method using low resolution mass spectrometers (e.g. triple quadrupole (QqQ)) has become routinely used, however, complicated and lengthy sample pre-treatment (employing immuno-affinity) is often necessary for obtaining sufficient sensitivity and selectivity. In this study, we investigate the capabilities of high-resolution MS instruments for circumventing the complex sample preparation currently needed for sensitive LC–MS/MS-based quantification of mAbs. Employing a simple one-step sample pre-treatment workflow, we compare the ability of three different LC–MS platforms for absolute quantification of a representative monoclonal antibody Rendomab-B1 in serum and plasma. The samples are subjected to protein precipitation with methanol, followed by pellet digestion with trypsin prior to LC–MS analysis. AQUA peptides based on two surrogate mAb peptides selected from an extensive in-silico and experimental screening are used as internal standards. MS/MS acquisitions are developed and systematically examined for 1) a low-resolution QqQ operated in selected reaction monitoring (SRM) acquisition mode, 2) a high-resolution hybrid Quadrupole-Orbitrap (Q-Orbitrap) operated in parallel reaction monitoring (PRM) acquisition mode and 3) a high-resolution hybrid Quadrupole-Time-of-flight (Q-TOF) operated in SRM acquisition mode with enhanced duty cycle (EDC) function. The sensitivity of the high-resolution Q-Orbitrap and Q-TOF methods was significantly higher (LOD of 80 ng/mL) in serum/plasma samples than the low-resolution QqQ method. Finally, the real-world utility of the developed high-resolution MS method with minimized sample handling was demonstrated and validated by determining the PK profile of Rendomab-B1 in mice by a 10-point in vivo study over 15 days.