Developing new matrices for laser-assisted mass spectrometry

As we concentrated on imaging of small metabolites, we were forced to develop new matrices for the MALDI measurements as the available ones did not show satisfactory selectivity or sensitivity in negative ion mode. The first matrix (9-aminoacridine, 9AA) was shown to be very useful for analysis of small acids (Shroff et al. 2007 Rapid Commun. Mass Spectrom.) or if used altogether with halide anions for analysis of neutral oligosaccharides (Becher et al. 2008 Rapid Commun. Mass Spectrom.).

However, the 9AA still shows matrix related peaks in MALDI spectra obscuring signals for some metabolites. Major advances in matrix selection and design have been made using the Brønsted-Lowry acid-base theory and DFT calculations. From the results we were able to perform a rational design of “ionless” MALDI matrices (named Matrix Assisted Ionization and Laser Desorption, MAILD (Shroff, Svatos 2009 Rapid Commun. Mass Spectrom. 23, 2380-2382; Shroff, Svatos 2009 Anal. Chem., Shroff et al. 2009 PNAS). A patent application (PCT ) has been filled. Based on the better understanding of parameters related to matrix performance, we are currently designing and synthesizing a large series of 2nd generation MAILD matrices. A further direction in removing background ions from the MALDI spectra is to use nanostructured MALDI targets (Muck et al. 2010 Lab on a Chip). In this study we have developed silicon nanowires structured targets doped with lithium for the analysis of lipids in a campus cooperation with the Institute of Photonic Technology (IPHT).