Multimatrix Variation Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry as a Tool for Determining the Bonding of Nitrogen Atoms in Alkaloids

Surface-Assisted Laser Desorption/Ionization Mass Spectrometry with a Two-Dimensional Au Nanoparticle Array for Soft Ionization

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a valuable technique for detecting small molecules in environmental and medicinal studies. We investigated dot-like and 2D-array gold nanoparticle-based SALDI-MS substrates that excite surface plasmons and enhance the desorption/ionization of sample molecules via charge transfer between the substrate and sample molecules. We aimed to optimize the nondissociative detection of sample molecules by efficiently transferring energy while suppressing excess internal energy. SALDI-MS measurements using crystal violet (CV) molecules revealed ion intensity and spectral pattern differences between the dot-like and 2D-array substrates. SALDI-MS measurements using dot-like substrates suggested two desorption/ionization processes: internal energy supply and charge transfer between the substrate and sample molecules. However, SALDI-MS measurements using 2D-array substrates suggested that the internal energy supply was suppressed. As a result, the dot-like substrate provided higher desorption/ionization efficiency but increased fragmentation, whereas the 2D-array substrate was suitable for highly sensitive and nondissociative SALDI-MS measurements. This study contributes to the optimization of SALDI-MS measurements and advances our understanding of energy transfer and sample molecule dissociation.

Diaminoanthraquinone Enhances Alkaloid Ionization in MALDI-MS

The alkaloids epinastine, 3-methylxanthine and camptothecin were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The ionization efficiencies of epinastine and 3-methylxanthine were improved upon the addition of 1,5-diaminoanthraquinone (DAAQ). DAAQ did not show ultraviolet absorbance peaks at wavelengths around 337 nm and 355 nm that are used in conventional MALDI-MS instruments. In addition, the DAAQ ion peak was very weak relative to those of the analytes due to the low absorbance efficiency. These properties of DAAQ are advantageous for the DAAQ-MALDI-MS analysis of alkaloids.