Limits for the detection of (poly-)phosphoinositides by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS)

Matrix-assisted laser desorption and ionization time-of-flight mass spectro metry (MALDI-TOF MS) has been recently established as a powerful tool for t he analysis of biomoLecules. Here, MALDI-TOF MS was used for the detection of (poly-)phosphoinositides (PPI). PPI possess higher molecular weights tha n other phospholipids and a high phosphorylation-dependent negative charge. Both features affect the MALDI detection limits expressed as the minimum o f analyte on the sample plate resulting in a signal-to-noise-ratio of S/N = 5. Using 2,5-dihydroxybenzoic acid (DHB) as matrix the detection limit for phosphatidylinositol (PI) is seven times higher than for phosphatidylcholi ne (PC) and further increases with increasing phosphorylation or in mixture s with other well-detectable pho spholipids. For phosphatidylinositol-tris- phosphate (PIP3) in a mixture with PC, the limit is about 20 times higher t han for PI. The consequences for the experimental conditions are discussed. It is advisable to pre-separate PPI from biological lipid mixtures prior t o the application of MALDI-TOF MS. (C) 2001 Elsevier Science Ireland Ltd. A ll rights reserved.