PEth concentration (µmol/L) Relative response (analyte/IS) Supplemental Data Figure 1. LC-ESI-MS calibration curves prepared with two PEth species Calibration curves for the LC-ESI-MS method were prepared by spiking PEth-negative whole blood with PEth-16:0/18:1 or PEth-18:1/18:1 reference material in the concentration range 0.2–7.0 µmol/L. Both r2 values were >0.999. Inset: Calibration curve prepared with PEth-16:0/18:1 in the concentration range 0.2–20.0 µmol/L (equation: y = 1.0000x + 0.2155; r2 = 0.998). 1 2 3 4 5 6 7 8 PEth concentration (µmol/L) Relative response (analyte/IS) PEth-16:0/18:1 PEth-18:1/18:1 10 15 20