Liquid chromatography/mass spectrometry for targeted sphingolipid analysis. The method was slightly modified from [65] . Briefly, each sample was extracted according to published protocol then dried and reconstituted in 100 mL of methanol : water : formic acid (74:25:1) containing 5 mM ammonium formate. An Agilent 6400 QQQ (Agilent Technologies, Santa Clara, CA) was used for analysis coupled to an 1100 Series LC equipped with HPLC Chip interface (Agilent Technologies Santa Clara, CA). Solvent A consisted of methanol : water : formic acid [65] with the following source conditions: gas temperature 300uC, gas flow 4 L/minute, capillary voltage 1900 V. The fragmentor voltage was set to 180 V in all cases. Data were processed with Agilent Mass Hunter software version B03.01.