The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield

Robinson, Kenneth N.; Steven, Rory T.; Race, Alan; Bunch, Josephine

doi:10.1007/s13361-019-02193-8

Cited by 15 publications

(13 citation statements)

References 64 publications

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“…It is estimated that for numerous analyte classes less than one in a million of the ejected molecules are concomitantly ionized. [8] In addition, molecules with high ion affinities can cause ion suppression effects by abstracting charges from other compounds during the MALDI process. Common examples for ion suppression are phosphatidylcholines (PC), which in the positive ion mode notoriously hamper the detection of the many other lipid classes present in complex tissues.…”

Section: Introductionmentioning

confidence: 99%

Single‐Photon‐Induced Post‐Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging**

et al. 2022

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Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a rapidly growing method in many elds of the life sciences. For many analyte classes, however, its sensitivity is limited due to poor ionization e ciencies. To mitigate this problem, we here introduce a novel and cost-effective postionization scheme at high repetition rates based on the interplay of single-photon photoionization and subsequent charge transfer reactions. Importantly, the ne vacuum conditions of a dual ion-funnel ion source effectively thermalize the evolving MALDI plume and enable ample gas-phase reactions as well as the addition of chemical dopants that crucially support chemical ionization. Supported by acetone dopant, [M + H] + /[M-H] − signals of numerous glycerophospho-, sphingo-, and further lipids, registered from mammal brain and kidney sections, were boosted by up to three orders of magnitude, similar to results obtained with laser-based postionization (MALDI-2). Experiments utilizing deuterated matrix and dopant, however, indicate complex ionization pathways different from MALDI2.

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Section: Introductionmentioning

confidence: 99%

Single‐Photon‐Induced Post‐Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging**

et al. 2022

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“…Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is increasingly used to visualize the distribution of biomolecules such as peptides, lipids, glycans, and metabolites in thin tissue sections. − However, a notable limitation of the method is given by low ion yields for many analyte classes. Many experimental and theoretical studies indicate that less than 1 out of a million molecules that are transferred from the solid to the gaseous phase are also ionized. − Notorious ion suppression effects, which are, for instance, caused by the presence of ubiquitous quaternary ammonium group-carrying phosphatidylcholines (PC) can furthermore reduce the sensitivity for less well ionizing analytes in MALDI-MSI imaging experiments. , …”

Section: Introductionmentioning

confidence: 99%

Detailed Characterization of the Postionization Efficiencies in MALDI-2 as a Function of Relevant Input Parameters

Potthoff

Dreisewerd

Soltwisch

2020

J. Am. Soc. Mass Spectrom.

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A recently introduced technique based on MALDI with laser-induced postionization (PI), also named MALDI-2, increases the ion yields for numerous classes of lipids, metabolites, and carbohydrates in MALDI-MS imaging experiments under certain experimental conditions. Here, we used a semiautomatic LabVIEW-based protocol to investigate and optimize the efficiency of the PI process dependent on four relevant input parameters and a dense parameter grid: pulse energies of the two lasers, delay between the laser pulses, and buffer gas pressure in the ion source. All experiments were conducted with a modified MALDI-2 Synapt G2-S mass spectrometer (Waters) and use of a focal spot size on the sample of 15–17 μm. A wavelength-tunable optical parametric oscillator (OPO) laser served for PI at 260 or 280 nm. The investigated MALDI matrices were: 2,5-dihydroxybenzoic acid (positive ion mode, +), 2,5-dihydroxyacetophenone (+), α-cyano-4-hydroxycinnamic acid (+), norharmane (negative-ion mode, −), and 1,5-diaminonapthalene (−). A porcine brain extract served as lipid standard. In the positive-ion mode, a maximum boost for the generated [M + H]+ species was found with a N2 buffer gas pressure of ∼2 mbar and a delay between the laser emissions of ∼10 μs. Higher optimal delay settings of several 10 μs were registered for the two studied matrices in negative-ion mode. With regard to the laser fluences, best PI efficiencies were reached using maximum available ablation and PI laser pulse energies of up to 25 and 160 μJ, respectively. For analytes not profiting from MALDI-2, best ion signal yields were recorded for ablation laser pulse energies of around 7 μJ, depending on the MALDI matrix. At higher laser pulse energies, sizable fragmentation is observed for these ions. The PI laser pulse energy did not have any influence on the ion signals of these species. For optimal ion yield of all analyte species, best results were obtained with an ablation laser pulse energy of ∼7 μJ and a PI laser pulse energy of ∼160 μJ. Our comprehensive data set provides valuable insight into the mechanisms underlying the MALDI-2 processes and could help to further optimize this emerging technique.

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“…Ionization efficiencies are molecule-and source-dependent and have been reported to be in the range of 10 -3 -10 -9 . 25 Further limits to sensitivity include ion suppression effects whereby certain lipid species, such as PC in positive-ion mode analysis, can lower the ionization efficiencies of other lipid classes. 26 These phenomena limit both the achievable sensitivity and breadth of lipid coverage obtained for MALDI-MSI experiments.…”

Section: Introductionmentioning

confidence: 99%

Mass Spectrometry Imaging of Lipids using MALDI Coupled with Plasma-Based Post-Ionisation on a Trapped Ion Mobility Mass Spectrometer

Michael

Mutuku

Ucur

et al. 2022

Preprint

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Here we report the development and optimization of a mass spectrometry imaging (MSI) platform that combines atmospheric-pressure matrix-assisted laser desorption/ionization platform with plasma post-ionization (AP-MALDI-PPI) and trapped ion mobility spectrometry (TIMS). We discuss optimal parameters for operating the source, characterize the behaviour of a variety of lipid classes in positive- and negative-ion modes and explore the capabilities for lipid imaging using murine brain tissue. The instrument generates high signal-to-noise for numerous lipid species, with mass spectra sharing many similarities to those obtained using laser post-ionization (MALDI-2). The system is especially well suited for detecting lipids such as phosphatidylethanolamine (PE) as well as numerous sphingolipid classes and glycerolipids. For the first time, the coupling of plasma-based post-ionization with ion mobility is presented and we show the value of ion mobility for the resolution and and identification of species within rich spectra that contain numerous isobaric/isomeric signals that are not resolved in the m/z dimension alone, including isomeric PE and demethylated phosphatidylcholine lipids produced by in-source fragmentation. The reported instrument provides a powerful and user-friendly approach for MSI of lipids.

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The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield

Cited by 15 publications

References 64 publications

Single‐Photon‐Induced Post‐Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging**

Single‐Photon‐Induced Post‐Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging**

Detailed Characterization of the Postionization Efficiencies in MALDI-2 as a Function of Relevant Input Parameters

Mass Spectrometry Imaging of Lipids using MALDI Coupled with Plasma-Based Post-Ionisation on a Trapped Ion Mobility Mass Spectrometer

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