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

Abstract

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.

Survival yield comparison between ESI and SAII: Mechanistic implications

“…Recently, it has been shown that solid matrices produce almost identical charge state ions when introduced to the inlet of an atmospheric pressure ionization mass spectrometer [7,29]. Unlike ESI and SAII, 3-NBN acts as a matrix producing analyte ions near room temperature where it is a solid [30,31]. Assuming charged particles are intermediates in all processes that produce highly charged ions, it is not obvious how the charged solid particles can produce ions of similar charge state to liquid droplets.…”

Localization and imaging of gangliosides in mouse brain tissue sections by laserspray ionization inlet

“…I-B), which operates independent of a voltage or a laser ( 56 ). MAII and LSII depend on the appropriate matrix (57)(58)(59), similar to MALDI ( 60-63 ), but do not require absorption at the laser wavelength employed. In LSII, the laser ablation only acts as the method to transfer a matrix/analyte sample into the inlet of the mass spectrometer, permitting the use of highly focused lasers to improve spatial resolution.…”

“…Approximately 20 laser shots were summed for each spectrum. LSII-MS was performed on the SYNAPT G2 by converting the nano-ESI source to a LSII source according to published procedure (54)(55)(56)(57)(58)(59)68 ) using the 337 nm nitrogen laser employed for LSII-MS on the LTQ Velos.…”

“…The absence of fragmentation with 2,5-DHAP matrix may be the result of lower thermal requirements in LSII ( 53,72 ). We are currently investigating mechanistic arguments that may assist in providing an explanation for these observations ( 58,59 ). The mass spectrum of purchased GD1 using 2,5-DHAP as matrix is shown in Fig.…”

“…To demonstrate that the observed fragmentation was a consequence of MALDI and not simply caused by instrumentation differences relative to the LTQ Velos, supplementary Fig. VII-B shows an LSII acquisition of GD1 with 2,5-DHAP on the SYNAPT G2 using the nano-ESI source converted to a LSII source ( 54,55,(57)(58)(59)68 ). Abundant [M-2H] 2 Ϫ ions are observed without adduction or fragmentation.…”