Influence of Ion Source Geometry on the Repeatability of Topographically Guided LAESI-MSI

Abstract

Spatially resolving the relative distribution of analyte molecules in biological matter holds great promise in the life sciences. Mass spectrometry imaging (MSI) is a technique that can provide such spatial resolution but remains underused in fields such as chemical ecology, as traditional MSI sample preparation is often chemically or morphologically invasive. Laser ablation electrospray ionization (LAESI)-MSI is a variation of MSI particularly well-suited for situations where chemical sample preparation is too invasive but provides new challenges related to the repeatability of measurement outcomes. We assess the repeatability of LAESI-MSI by sampling a droplet of [ring- 13 C 6 ] l -phenylalanine with known concentration and expressing the resulting variability as a coefficient of variation, c v . In doing so, we entirely eliminate variability caused by surface morphology or underlying true sample gradients. We determine the limit of detection (LOD) for 13 C 6 -Phe by sampling from droplets with successively decreasing but known concentration. We assess the influence of source geometry on the LOD and repeatability by performing these experiments using four distinct variations of sources: one commercial and three custom-built ones. Finally, we extend our study to leaf and stem samples Arabidopsis thaliana and Gossypium hirsutum . We overcome the challenges of LAESI associated with three-dimensional surface morphology by relying on work previously published. Our measurements on both controlled standard and realistic samples give strong evidence that LAESI-MSI’s repeatability in current implementations is insufficient for MSI in chemical ecology.

Applications of ambient ionization mass spectrometry in 2022: An annual review

“…developed an ultrahigh‐throughput liquid atmospheric pressure MALDI approach for the analysis of peptides and enzymatic assays, achieving the impressive analysis of up to 60 samples per second under some conditions 27 . Other studies aiming to improve existing techniques have introduced a plasma treatment step to the DESI pipeline to increase ion signal, 186 studied the effects of ion source geometry on the reproducibility of LAESI imaging, 187 incorporated the use of helium as a nebulizing gas into DESI and ESI, 188 and developed a post‐acquisition mass recalibration method to reduce mass drift in DESI analysis 189 . Others have built custom REIMS devices using a soldering iron to improve analysis of poorly conductive samples, 190 incorporated an online derivatization step into multiphase flow EESI for the analysis of reactive sulfur species, 191 and modified the DART source to reduce undesirable oxidation when using nitrogen gas in place of helium 192 .…”

Mass spectrometry imaging technology in metabolomics: A systematic review

“…By contrast, DESI has become the most popular environmental MSI technology due to its simple, LAESI is a potential alternative to MALDI. Although LAESI has been applied successfully to various samples over the past decade, its use in MSI continues to be infrequent (Bartels & Svatos, 2022). The biggest limitation of LAESI-MSI is that its signal strength is related to water content, which makes it more difficult to compare different sample types.…”