Fig. 1. Phosphoinositide regioisomer measurement by PRMC-MS.

a Schematic structures of the eight phosphoinositide classes. Note that phosphatidylinositol mono- and bisphosphate (PIP and PIP₂) classes each contain three regioisomers. b Scheme depicting the general workflow of PRMC-MS. SIS, surrogate internal standard lipids. c Mass spectra from PRMC-MS analyses of C37:4 (1-heptadecanoyl-2-eicosatetraenoyl) standard chemicals representing each of the eight phosphoinositide classes. Mixed, a mixture of PIP or PIP₂ regioisomers. d, e Linear regression analyses of peak area vs pmol (d) and fmol (e) concentrations of the indicated phosphoinositides. Amounts of standard phosphoinositides analyzed were 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 5, 10, 50 pmol in d and 2, 5, 10, 20, 50, 100 fmol in e (see also Supplementary Table 1). The C37:4 (1-heptadecanoyl-2-eicosatetraenoyl) molecular species of each phosphoinositide class was used. Data were the mean ± SD (n = 4 technical replicates). Source data are provided as a Source Data file.