Extension of metal oxide laser ionization mass spectrometry to analytes with varied chemical functionalities

Applications of metal oxide laser ionization mass spectrometry (MOLI MS) have been limited to compounds that provide protons for ionization upon adsorption to a metal oxide surface. The addition of a small molecule, which can act as a proton source and extend MOLI MS applications to a wider variety of analytes, was investigated.

Mass spectrometric measurements were made with a PerSeptive Biosystems Voyager DE-STR MALDI mass spectrometer, using NiO-based MOLI to generate ions. NiO was pretreated in this study with a number of small molecules to act as proton sources during ionization. Peptides, monosaccharides, and a crude oil sample were analyzed with pretreated and untreated NiO.

Candidate small molecule proton donors were evaluated based on their effect on signal-to-noise ratio and peak intensity for tristearin. The best performing proton source was used for subsequent analyses. The analysis of monosaccharides, peptides and compounds in heavy crude oil was enhanced by the use of proton source treated NiO for MOLI MS. Proton/cation exchange following ionization was observed.

Addition of a proton source to NiO enhanced the MOLI MS response for peptides, carbohydrates, and compounds in a crude oil sample. Efficient ionization of these samples effectively extended applications of MOLI MS beyond lipid analytes containing esters.