Quantifying Signature Peptides of Transporters

The Agilent 1290 series UPLC system and Agilent 6460 series MS/MS system (Agilent Technologies, Santa Clara, CA, United States) were hereby combined to quantify the signature peptides in the ESI-positive ionization mode. The conditions of mass spectrometry were as follows: a capillary voltage of 2,000 V; a gas flow of 8 L/min; a nebulizer of 30 psi; a gas temperature at 300°C; and a Delta EMV(+) of 400 V. Five milliliters of the sample was injected into the column (Agilent SB-C₁₈ column, 2.1 mm × 50 mm, 1.8 µm particles) and eluted at 0.4 mL/min with a gradient elution of water (with 0.05% v/v formic acid) (A) and acetonitrile (B) (0–1 min, 5–5% B; 1–4 min, 5–60% B; 4–5 min, 60–5% B; and re-equilibration for 3 min). According to previous experiments by the research group of Yi et al. (2018) (link), the sequences of characteristic peptides corresponding to UGT1A1 and the nine other transporters are listed in Table 1.