Liquid chromatography/MS (LC/MS). Normal-phase LC-electrospray ionization (ESI)/MS of lipids was performed using an Agilent 1200 Quaternary LC system, coupled to a QSTAR XL quadrupole timeof-flight tandem mass spectrometer (Applied Biosystems). LC was performed on an Ascentis Si HPLC column (5 mm, 25 cm62.1 mm). The elution program has been described previously (Guan et al., 2011).