Chorionic placental arteries homogenates from normotensive and preeclamptic donors were used for quantification of sphingolipids by LC - MS / MS . The levels of ceramide ( Cer ) species , sphingosine ( Sph ) , and S1P were analyzed by the Lipidomics Analytical Core at the Medical University of South Carolina , as previously described [ 67 ] . Lipid extraction was performed according to Bligh and Dyer [ 68 ] . For quantitative analysis of sphingolipid , eight - point calibration curves were generated for each target analyte . Synthetic as well as internal standards were spiked into an artificial matrix , and then subjected to an identical extraction procedure as the biological samples . These extracted standards were subsequently analyzed by the LC - MS / MS system operating in positive multiple reaction - monitoring ( MRM ) mode employing a gradient elution . Results were then calculated by plotting the sample area ratios against their corresponding standard . The MS analysis represents the mass level of particular sphingolipid ( in pmols ) per total sample used for lipid extract preparation . For the final data presentation , MS results were normalized to total protein ( mg ) .