Quantification of P-G6 in plasma. (A-C) LC-MS/MS was used to generate a standard curve of P-G6 concentration in blood plasma. (A) LC-MS/MS parameters for in-source fragmentation and rigor of the calibration curve. (B) Generation of the quantifying peptide. (C) A stepped higher-energy collisional dissociation approach effectively fragmented P-G6 in a single MS/MS spectrum. Fragment ions: blue, b-ions; red, y-ions; green, glycan loss. Modified amino acid are in bold type. (D) Plasma concentration of P-G6 over time after IV administration of a single weight-based (8 µmol/kg) dose.