Investigation of Ionic Liquid Matrices in MALDI FTMS Analyses of Biological Compounds

by Wilkins, Charles L.; Jones, Jeffrey J.; Batoy, S. Mariccor A. B.; Liyanage, Rohanna; Lay, Jackson O., Jr.

Room temp. ionic liq. matrixes (ILMs) have recently been investigated for use in matrix-assisted laser desorption/ionization(MALDI) mass spectrometry (MS) and proven to be advantageous. Literature accounts of ILM performance for biol. samples document increased sensitivity and ionization efficiency. Most liq. matrixes are highly vicious at room temp. and retain low vapor pressures in low and ultra low vacuum conditions. This property allows for the analyte to become evenly distributed within the matrix, and thus improves spot-to-spot reproducibility of the anal. These claims were investigated here, and seem to be supported for MALDI TOF applications with proteins, oligonucleotides and phospholipids. However, proteins and oligonucleotides do not behave in the same way when ILMs are used for MALDI FTMS. In the present study, when a 3 T MALDI FTMS is used, proteins and oligonucleotides fragment under conditions that produce mainly parent ion spectra when a solid matrix is used. Thus, ILM matrix behavior is different than with MALDI time-of-flight mass spectrometry. Fragmentation is apparently slower than the time required to accelerate ions in a MALDI TOF mass spectrometer, but is readily obsd. by MALDI FTMS. Therefore, fragmentation of these mols. must occur on relatively slow time scale. As trapping time is extended, increased fragmentation of proteins and oligonucleotides is obsd. Furthermore, phospholipids do not fragment extensively when ILMs are used even though when solid matrixes are used, they are well documented to cause significant fragmentation for this category of compds.