"On-off" elution mechanism facilitates the rapid LC/MS/MS-based analysis of peptide antibiotics in human plasma.

Individualized medication with peptide antibiotics, guided by therapeutic drug monitoring, is essential to treat infections caused by multidrug-resistant bacteria. Peptide antibiotics exhibit an "on-off" elution mechanism on a C18 column, leading to adsorption at the column inlet in all-aqueous conditions. Unlike small molecules, column length minimally influences their retention, with longer columns simply broadening peptide antibiotic peaks due to unnecessary post-column volume. Our theory suggests short columns can achieve comparable separation quality and enable faster analysis. Consequently, we developed a rapid LC-MS/MS method using an ultra-short (4 × 2.0 mm) column to quantify five peptide antibiotics in human plasma simultaneously. Calibration curves demonstrated strong linear regression (R2 > 0.996). The inter- and intra-accuracy at the three QC levels ranged from 86.7 % to 109.1 %, and at the LLOQ, it was between 87.6 % and 116.0 %. The precision for QCs and LLOQ was consistently below 11.7 % and 18.5 %, respectively. This method, characterized by simplicity and universality, was undoubtedly useful in clinically tailoring peptide antibiotic medication for individual patients.