Quantitative imaging mass spectrometry of renal sulfatides: validation by classical mass spectrometric methods

摘要

In recent years, MALDI imaging MS (IMS) has become a common method in lipid analytics. It enables visualization of the differential distribution of lipids varying only in their acyl chain with good spatial resolution (>=7 |xm/pixel), as well as with high mass accuracy (<3 ppm rms) and high mass resolution (R = 100.000 at m/z 200) (1). Although much work has been put into increasing the sensitivity of this method by the use of different matrix substances (2-7) or improved sample preparation (8-14) that achieves more homogeneous cocrystallization (15), reliability of the semi-quantitative read out remains a matter of debate: Differences in the tissue structure (16) as well as specific matrix analyte interaction (17) are suspected to cause ion suppression followed by unreliable signal response (18). Ionization behaviors of specific molecules are hard to predict because they are influenced by a number of parameters (16, 19). Initially, Burnum et al. (2) picked up this issue in their work on spatial and temporal alterations of phospholipids during mouse embryo implantation. They compared the MALDI IMS data with LC-ESI-MS data obtained in positive or negative mode after laser microdissection (2).