Negative ion mass spectra of brain lipid extract. ( A) Detection of all [M-H] - ions of glycerophospholipids by precursor ion scan of m/z 153. ( B) Detection of PI molecular species by precursor ion scanning of m/z 241. ( C) Detection of PS molecular species by neutrol loss of 87 D. ( D) Detection of PE molecular species by precursor ion scanning of m/z 196. GPL, glycerophospholipids; IS, internal standard; PI, phosphatidylinositol; PS, phosphatidylserine; PE, phosphatidylethanolamine.