High-Resolution Ambient MS Imaging of Negative Ions in Positive Ion Mode: Using Dicationic Reagents with the Single-Probe

Abstract

We have used the Single-probe, a miniaturized sampling device utilizing in-situ surface microextraction for ambient mass spectrometry (MS) analysis, for the high resolution MS imaging (MSI) of negatively charged species in the positive ionization mode. Two dicationic compounds, 1,5-pentanediyl-bis(1-butylpyrrolidinium) difluoride [C5(bpyr)2F2] and 1,3-propanediyl-bis(tripropylphosphonium) difluoride [C3(triprp)2F2], were added into the sampling solvent to form 1+ charged adducts with the negatively charged species extracted from tissues. We were able to detect 526 and 322 negatively charged species this way using [C5(bpyr)2F2] and [C3(triprp)2F2], respectively, including oleic acid, arachidonic acid, and several species of phosphatidic acid, phosphoethanolamine, phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, and others. In conjunction with the identification of the non-adduct cations, we have tentatively identified a total number of 1200 and 828 metabolites from mouse brain sections using [C5(bpyr)2F2] and [C3(triprp)2F2], respectively, through high mass accuracy measurements (mass error <5 ppm); MS/MS analyses were also performed to verify the identity of selected species. In addition to the high mass accuracy measurement, we were able to generate high spatial resolution (~17 µm) MS images of mouse brain sections. Our study demonstrated that utilization of dicationic compounds in the surface microextraction with the Single-probe device can perform high mass and spatial resolution ambient MSI measurements of broader types of compounds in tissues. Other reagents can be potentially used with the Single-probe device for a variety of reactive MSI studies to enable the analysis of species that are previously intractable.

Using Dicationic Ion-Pairing Compounds To Enhance the Single Cell Mass Spectrometry Analysis Using the Single-Probe: A Microscale Sampling and Ionization Device

“…In our previous single-probe MS imaging studies using these two dicationic compounds, we have also found that the nonadduct ions have relatively lower intensities compared with those observed in experiments without using the dicationic compounds. 44 Similar ionization suppression effects are likely to be also present in the SCMS results. Further work is needed to prepare the optimal dicationic compound solutions to maximize the number of metabolite detections for both negatively and positively charged metabolites.…”

Metabolomic Fingerprints of Individual Algal Cells Using the Single-Probe Mass Spectrometry Technique

“…Despite these limitations, single-cell MS technique holds great promise for environmental research. The Single-probe MS technique has been successfully used to study live single cancer cells ( Pan et al, 2014 , 2016 ), to map biomolecules on animal tissues with high spatial resolutions ( Rao et al, 2015 , 2016a ,b), and to analyze the extracellular metabolites inside spheroids ( Sun et al, 2017 ). With respect to the ability to detect a large range of cellular metabolites from single cells (i.e., from only a few pico-litters of cytoplasm sampled from a cell with a diameter of approximately10 μm), the Single-probe MS setup provides excellent detection sensitivity.…”

Applications of the Single-probe: Mass Spectrometry Imaging and Single Cell Analysis under Ambient Conditions

“…For example, sampling solvents containing reagents ( e.g. , dicationic compounds) have been used to perform reactive MSI experiments, allowing for a significant increase in the number of metabolites identified per experiment 20 . The other advantage of the single-probe is the integrated design, which provides the ease of operation during the entire data acquisition process.…”