Matrix Assisted Ionization: New Aromatic and Nonaromatic Matrix Compounds Producing Multiply Charged Lipid, Peptide, and Protein Ions in the Positive and Negative Mode Observed Directly from Surfaces

• Published in: Journal of the American Society for Mass Spectrometry Vol. 23; no. 10; pp. 1625 - 1643
• Main Authors: Li, Jing, Inutan, Ellen D., Wang, Beixi, Lietz, Christopher B., Green, Daniel R., Manly, Cory D., Richards, Alicia L., Marshall, Darrell D., Lingenfelter, Steven, Ren, Yue, Trimpin, Sarah
• Format: Journal Article
• Language: English
• Published: New York Springer-Verlag 01.10.2012; Elsevier; Springer Nature B.V
• Subjects: Analytical Chemistry; Animals; Anthracene; Aromatic compounds; Aromaticity; Bioinformatics; Biotechnology; Cattle; Chemistry; Chemistry and Materials Science; Conjugation; Exact sciences and technology; Functional groups; Humans; Hydrogen-Ion Concentration; Ionization; Ions; Ions - chemistry; Laboratory Chemicals - chemistry; Lipids - chemistry; Mass spectra; Mass spectrometry; Models, Molecular; Organic Chemicals - chemistry; Organic Chemistry; Peptides - chemistry; Physical properties; Proteins - chemistry; Proteomics; Research Article; Spectrometric and optical methods; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - instrumentation; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Temperature; Multiply charged ions; Dissolved MAII; Laserspray ionization inlet LSII; Matrix assisted inlet ionization (MAII); Solvent assisted inlet ionization (SAII); Electron transfer dissociation (ETD); Laserspray ionization vacuum (LSIV); Linear and nonaromatic matrices; Solvent-free; Tandem mass spectrometry; Multicharged ion; Peptides; Electron transfer dissociation; Matrix assisted inlet ionization; Lipids; Matrix effect; Protein; Sample preparation; Photoionization; Laser beam; Ionization; Solvent free
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1007/s13361-012-0413-z

Matrix assisted inlet ionization (MAII) is a method in which a matrix:analyte mixture produces mass spectra nearly identical to electrospray ionization without the application of a voltage or the use of a laser as is required in laserspray ionization (LSI), a subset of MAII. In MAII, the sample is introduced by, for example, tapping particles of dried matrix:analyte into the inlet of the mass spectrometer and, therefore, permits the study of conditions pertinent to the formation of multiply charged ions without the need of absorption at a laser wavelength. Crucial for the production of highly charged ions are desolvation conditions to remove matrix molecules from charged matrix:analyte clusters. Important factors affecting desolvation include heat, vacuum, collisions with gases and surfaces, and even radio frequency fields. Other parameters affecting multiply charged ion production is sample preparation, including pH and solvent composition. Here, findings from over 100 compounds found to produce multiply charged analyte ions using MAII with the inlet tube set at 450 °C are presented. Of the compounds tested, many have –OH or –NH 2 functionality, but several have neither (e.g., anthracene), nor aromaticity or conjugation. Binary matrices are shown to be applicable for LSI and solvent-free sample preparation can be applied to solubility restricted compounds, and matrix compounds too volatile to allow drying from common solvents. Our findings suggest that the physical properties of the matrix such as its morphology after evaporation of the solvent, its propensity to evaporate/sublime, and its acidity are more important than its structure and functional groups.