Low Mass Range Research Articles

Assessing the potential of sputtered gold nanolayers in mass spectrometry imaging for metabolomics applications.

Mass spectrometry imaging (MSI) is a molecular imaging technique that maps the distribution of molecules in biological tissues with high spatial resolution. The most widely used MSI modality is matrix-assisted laser desorption/ionization (MALDI), mainly due to the large variety of analyte classes amenable for MALDI analysis. However, the organic matrices used in classical MALDI may impact the quality of the molecular images due to limited lateral resolution and strong background noise in the low mass range, hindering its use in metabolomics. Here we present a matrix-free laser desorption/ionization (LDI) technique based on the deposition of gold nanolayers on tissue sections by means of sputter-coating. This gold coating method is quick, fully automated, reproducible, and allows growing highly controlled gold nanolayers, necessary for high quality and high resolution MS image acquisition. The performance of the developed method has been tested through the acquisition of MS images of brain tissues. The obtained spectra showed a high number of MS peaks in the low mass region (m/z below 1000 Da) with few background peaks, demonstrating the ability of the sputtered gold nanolayers of promoting the desorption/ionization of a wide range of metabolites. These results, together with the reliable MS spectrum calibration using gold peaks, make the developed method a valuable alternative for MSI applications.

Review—Laser Ablation Ionization Mass Spectrometry (LIMS) for Analysis of Electrodeposited Cu Interconnects

In this contribution highly sensitive and quantitative analytical methodologies based on femtosecond Laser Ablation Ionization Mass Spectrometry (fs-LIMS) for the analysis of model systems and state-of-the-art Cu interconnects are reviewed and discussed. The method development introduces in a first stage a 1D chemical depth profiling approach on electrodeposited Cu films containing periodically confined organic layers. Optimization of measurement conditions on these test platforms enabled depth profiling investigations with vertical resolution at the nm level. In a second stage, a matrix-free laser desorption methodology was developed that allowed for preliminary molecular identification of the embedded organic contaminants beyond elementary composition. These studies provided specific fragmentation markers in the lower mass range, which support a previously proposed reaction mechanism responsible for successful leveling employing a new class of plating additives for Damascene processes. Further combined LIMS and Scanning Auger Microscopy (SAM) studies on through-silicon-vias (TSV) interconnects confirmed the embedment upon plating of the organic additives at the upper side-walls of the TSV channel in the boundary between the Cu seed layer and the electrodeposited Cu.

Consolidating tender coconuts as a source of safe natural large volume parenteral fluid under regulatory oversight

Purpose: To investigate reported absence of hyperkalema episodes due to high [K+] and the absence of hypersensitivity reactions due to tracer proteins in tender coconut water following IV infusion. To establish tender coconuts as a prospective natural large volume parenteral ‘dosage unit’. Method: Fluid from nuts identified with ‘Rosette Alba’ sign to be of 5-6 months maturity were evaluated. Important tests performed were the shelf life, direct tapping of the fluid, hemolysis and the molecular mass studies of tracer proteins by SDS PAGE gel electrophoresis. Results: Calculations indicate that [K+] dropped by 1/6th -1/9th in blood following IV infusion of fluid. Proteins are in the low molecular mass range of 10,000 Da, hence below potent antigen range. Conclusion: Drastic dilution of [K+] and the presence of hyperkalemia antidotal ingredients in the fluid and the low molecular mass of the proteins found in low concentration of 0.2 % and IV administration bypassing immunogenic subcutaneous route could be the possible reasons for absence of hyperkalemia and hypersensitivity reactions. The study did not show any dosage parameter that adversely restrains IV infusion potential of tender coconut water.

A "Soft" and "Hard" Ionization Method for Comprehensive Studies of Molecules.

Ambient mass spectrometry can be rapidly and directly effective for molecular studies, while there still seems to be a gap between two major groups of electrospray ionization (ESI)- and atmospheric pressure chemical ionization (APCI)-related techniques, for detection of moderately polar to polar and low polar to nonpolar molecules in a relatively low mass range, respectively. Here, an extensively applicable "soft" and "hard" ionization method, spray-dependent plasma mass spectrometry (SDP MS), was established for detecting various molecules with diverse polarities or molecular weights. By SDP MS, both fragment ions and intact molecular ions can be obtained. Significantly, cluster ions of aggregates in high mass range formed by weak molecular interactions can also be well recorded, much softer than traditional ESI MS. By filling the gap between ESI-based and APCI-based ionization techniques, SDP MS would enhance MS performance for comprehensive molecular studies and be extensively applicable in fields of organic synthesis, biological chemistry, medical chemistry, and clinical diagnosis.

Optical Ring Cavity Search for Axion Dark Matter.

We propose a novel experiment to search for axion dark matter that differentiates the phase velocities of the left- and right-handed polarized photons. Our optical cavity measures the difference of the resonant frequencies between two circular polarizations of the laser beam. The design of our cavity adopts a double-pass configuration to realize a null experiment and give a high common mode rejection of environmental disturbances. We estimate the potential sensitivity to the axion-photon coupling constant g_{aγ} for the axion mass m≲10^{-10} eV. In a low mass range m≲10^{-15} eV, we can achieve g_{aγ}≲3×10^{-16} GeV^{-1}, which is beyond the current bound by several orders of magnitude.

Monolithic thin-layer chromatography plates with covalently bonded matrix for hyphenation with matrix-assisted laser desorption/ionization.

Monolithic layers prepared by the copolymerization of ethylene dimethacrylate and glycidyl methacrylate and deposited onto the surface of glass and silicon plates were investigated as thin-layer chromatography separation media in hyphenated thin-layer chromatography with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis. Varying composition of the polymerization mixture and polymerization conditions layers of different porosities and MALDI-MS compatibility were synthesized. Compatibility with MALDI-MS was tested using polyethylene glycol and it was demonstrated that layers prepared without glycidyl methacrylate are not compatible with MALDI-MS and do not allow obtaining any mass spectra. Best results were achieved with layers containing 19 to 29% glycidyl methacrylate. These layers allow the measurement of mass spectra without additional depositing matrix compounds supplying mass spectra almost "clean" in low molar mass range.

Glycosylamines-based reactive matrix designed for imaging acidity in Ponkan fruit using matrix assisted laser desorption/ionization mass spectrometry imaging

Current imaging techniques, such as position emission tomography, magnetic resonance imaging and optical imaging, have been developed and applied to imaging acidity in live tissues for years, but they still have some limitations. In the present study, a reliable and interference-free pH imaging method based on matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) was established for the first time. A novel reactive matrix, named glycosyl-3-aminoquinoline (Gly-3AQ), was designed and synthesized here not only to overcome the background interference in the low mass range of MALDI but also provide a new function of acid-responsiveness for the matrix. This matrix was responsive to pH change due to its acid-catalyzed hydrolysis and the hydrolysis product 3-aminoquinoline (3-AQ) has an increase of peak intensity with pH decrease. The Gly-3AQ-based MALDI pH detection method is demonstrated to have good acid-responsiveness in the range of pH 2.0–7.0, and when pH changes 0.5, relative abundance of 3-AQ changes about 1.5 folds. The method showed a very prominent advantage, that is, free-interference when analyzing real samples. Validation for the method revealed pH calibration curve had good linearity (R > 0.9953) with relative standard deviation less than 13.8%. This method was applied to analyze and visualize acidity variation of citrus during development and the changed acidity underwent relative quantitation and statistical analysis. The newly developed reactive matrix has potential application to in-situ MSI of acidity in the biomedical field.

Dark matter (DM) searches through studying DM-nucleon coupling strength

Dark matter (DM) interacts with ordinary matter through weakly coupling to nucleons. We analyze the coupling strength for DM-proton and DM-neutron respectively utilizing the available data from the most sensitive experiments, XENON1T and SuperCDMS, for a higher (>10 GeV/c2) and a lower mass (<10 GeV/c2) range of DM particles. Subsequently, we calculate the coupling strength constrained by the DAMA claim and a similar experiment (KIMS) using CsI. The results indicate that XENON1T and SuperCDMS are almost fully sensitive to the DM-nucleon coupling strength predicted by the Fermi weak interaction in the higher mass range. As a result, XENON1T is sensitive to the expected small energy associated with the DM-nucleon weak interaction and hence XENON1T provides a strong constrain on the effective mass of DM from ∼1 MeV/c2 to ∼100 MeV/c2, which excludes the mass range of DM between 10 GeV/c2 to 104 GeV/c2 from being detected. In the lower mass range, four experiments are all not sensitive to the DM-nucleon coupling strength expected from the Fermi weak interaction. The DM-nucleon coupling strength, (Zfp+Nfn)2, determined by the DAMA data can be fully ruled out by the most sensitive experiments. This work launches new direction for the current DM experiments to provide the constrains on DM-nucleon coupling strength, which sheds light on DM-nucleon coupling properties between impinging DM particles and target nucleons with null experimental results.

Comments on stellar evolution

Given the limited space in this contribution, it is not possible to go into the details of the exciting astrophysical topic of stellar evolution and nucleosynthesis. It is attempted to emphasize the basics of this basic concept of the hydrostatic evolution of stars as they are driven by the interplay between gravity and nuclear energy generation, which is expressed by the virial theorem. In the case of massive stars roughly above $ 8 {\rm M}_{\odot}$ , the breakdown of the hydrostatic evolution, due to the lack of nuclear energy generation, leads to gravitational collapse followed either by a successful supernova explosion, leaving a neutron star behind, or by a black hole, which is the ultimate end stage. The stars of masses in the lower mass range end their evolution as white dwarfs. The nucleosynthesis process in stars is a complex task. Most of the elements and their isotopes, especially the heavy elements, are produced in an explosive environment, or in the late stages of the asymptotic giant branch stars. The present paper will concentrate mainly on the evolutionary aspects, due to the to limited space given here.

Z-pole test of effective dark matter diboson interactions at the CEPC

We investigate the projected sensitivity to effective dark matter (DM)–diboson interaction during the high luminosity Z-pole and 240 GeV runs at the proposed Circular Electron Positron Collider (CEPC). The proposed runs at the 91.2 GeV e^+e^- center of mass energy offers an interesting opportunity to probe effective dark matter couplings to the Z boson, which can be less stringently tested in non-collider searches. We investigate the prospective sensitivity for dimension 6 and dimension 7 effective diboson operators to scalar and fermion dark matter. These diboson operators can generate semi-visible Z boson decay, and high missing transverse momentum mono-photon signals that can be test efficiently at the CEPC, with a small and controllable Standard Model gamma bar{nu }nu background. Projected sensitivities for the effective gamma Z coupling efficient kappa _{gamma Z}< (1030,hbox {GeV})^{-3}, (1970,hbox {GeV})^{-3} for scalar DM, kappa _{gamma Z}< (360,text {GeV})^{-3}, (540,text {GeV})^{-3} for fermion DM are obtain for 25 hbox {fb}^{-1} and 2.5hbox {ab}^{-1}Z-pole luminosities assuming the optimal low dark matter mass range. We also compare the CEPC sensitivities to current direct and indirect search limits on these effective DM-diboson operators.

Differentiation and Relative Quantitation of Disaccharide Isomers by MALDI-TOF/TOF Mass Spectrometry.

Saccharide isomer differentiation has been a challenge in glycomics, as the lack of technology to decipher fully the diverse structures of compositions, linkages, and anomeric configurations. Several mass spectrometry-based methods have been applied to the discrimination of disaccharide isomers, but limited quantitative analyses have been reported. In the present study, MALDI-LIFT-TOF/TOF has been investigated to differentiate and relatively quantify underivatized glucose-containing disaccharide isomers that differ in composition, connectivity or configuration. N-(1-naphthyl)ethylenediamine dihydrochloride (NEDC) was used as a highly sensitive matrix without matrix interferences in low mass range, thus yielding intense chloride-attached disaccharide ions [M + Cl]-, which could be fragmented to give diagnostic characteristic fragment patterns for distinguishing these isomers. Three different types of disaccharide isomers were successfully relatively quantified in a binary mixture using the specific product ion pairs. Finally, this method was utilized to identify and relatively quantify two disaccharide isomers in Medicago leaf (maltose and sucrose) without numerous preparation steps. In general, this method is a fast, effective, and robust method for rapid differentiation and quantitation of disaccharide isomers in complex medium.

DBDA as a Novel Matrix for the Analyses of Small Molecules and Quantification of Fatty Acids by Negative Ion MALDI-TOF MS.

Matrix interference ions in low mass range has always been a concern when using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to analyze small molecules (<500 Da). In this work, a novel matrix, N1,N4-dibenzylidenebenzene-1,4-diamine (DBDA) was synthesized for the analyses of small molecules by negative ion MALDI-TOF MS. Notably, only neat ions ([M-H]-) of fatty acids without matrix interference appeared in the mass spectra and the limit of detection (LOD) reached 0.3 fmol. DBDA also has great performance towards other small molecules such as amino acids, peptides, and nucleotide. Furthermore, with this novel matrix, the free fatty acids in serum were quantitatively analyzed based on the correlation curves with correlation coefficient of 0.99. In addition, UV-Vis experiments and molecular orbital calculations were performed to explore mechanism about DBDA used as matrix in the negative ion mode. The present work shows that the DBDA matrix is a highly sensitive matrix with few interference ions for analysis of small molecules. Meanwhile, DBDA is able to precisely quantify the fatty acids in real biological samples. Graphical Abstract ᅟ.

Magnetic fields of intermediate mass T Tauri stars

Aims. In this paper, we aim to measure the strength of the surface magnetic fields for a sample of five intermediate mass T Tauri stars and one low mass T Tauri star from late-F to mid-K spectral types. While magnetic fields of T Tauri stars at the low mass range have been extensively characterized, our work complements previous studies towards the intermediate mass range; this complementary study is key to evaluate how magnetic fields evolve during the transition from a convective to a radiative core.

The spatially resolved star formation history of CALIFA galaxies

This paper presents the mass assembly time scales of nearby galaxies observed by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record method of the stellar populations to the complete sample of the 3rd CALIFA data release, with a total of 661 galaxies, covering stellar masses from 10$^{8.4}$ to 10$^{12}$ M$_{\odot}$ and a wide range of Hubble types. We apply spectral synthesis techniques to the datacubes and process the results to produce the mass growth time scales and mass weighted ages, from which we obtain temporal and spatially resolved information in seven bins of galaxy morphology and six bins of stellar mass (M$_{\star}$) and stellar mass surface density ($\Sigma_{\star}$). We use three different tracers of the spatially resolved star formation history (mass assembly curves, ratio of half mass to half light radii, and mass-weighted age gradients) to test if galaxies grow inside-out, and its dependence with galaxy stellar mass, $\Sigma_{\star}$, and morphology. Our main results are as follows: (a) The innermost regions of galaxies assemble their mass at an earlier time than regions located in the outer parts; this happens at any given M$_{\star}$, $\Sigma_{\star}$, or Hubble type, including the lowest mass systems. (b) Galaxies present a significant diversity in their characteristic formation epochs for lower-mass systems. This diversity shows a strong dependence of the mass assembly time scales on $\Sigma_{\star}$ and Hubble type in the lower-mass range (10$^{8.4}$ to 10$^{10.4}$), but a very mild dependence in higher-mass bins. (c) All galaxies show negative $\langle$log age$\rangle_{M}$ gradients in the inner 1 HLR. The profile flattens with increasing values of $\Sigma_{\star}$. There is no significant dependence on M$_{\star}$ within a particular $\Sigma_{\star}$ bin, except for the lowest bin, where the gradients becomes steeper.

Sequencing Larger Intact Proteins (30-70 kDa) with Activated Ion Electron Transfer Dissociation.

The analysis of intact proteins via mass spectrometry can offer several benefits to proteome characterization, although the majority of top-down experiments focus on proteoforms in a relatively low mass range (<30 kDa). Recent studies have focused on improving the analysis of larger intact proteins (up to ~75 kDa), but they have also highlighted several challenges to be addressed. One major hurdle is the efficient dissociation of larger protein ions, which often to do not yield extensive fragmentation via conventional tandem MS methods. Here we describe the first application of activated ion electron transfer dissociation (AI-ETD) to proteins in the 30-70 kDa range. AI-ETD leverages infrared photo-activation concurrent to ETD reactions to improve sequence-informative product ion generation. This method generates more product ions and greater sequence coverage than conventional ETD, higher-energy collisional dissociation (HCD), and ETD combined with supplemental HCD activation (EThcD). Importantly, AI-ETD provides the most thorough protein characterization for every precursor ion charge state investigated in this study, making it suitable as a universal fragmentation method in top-down experiments. Additionally, we highlight several acquisition strategies that can benefit characterization of larger proteins with AI-ETD, including combination of spectra from multiple ETD reaction times for a given precursor ion, multiple spectral acquisitions of the same precursor ion, and combination of spectra from two different dissociation methods (e.g., AI-ETD and HCD). In all, AI-ETD shows great promise as a method for dissociating larger intact protein ions as top-down proteomics continues to advance into larger mass ranges. Graphical Abstract ᅟ.

Oxidative radical driven cleavage of peptide backbone caused by matrix-assisted laser desorption/ionization-in-source decay with low matrix-to-peptide molar ratios

The influence of matrix-to-analyte molar ratio (M/A) on the formation of in-source decay (ISD) fragment ions was examined by matrix-assisted laser desorption/ionization (MALDI) of peptides with the hydrogen-donating matrix 5-amino-1-naphthol (5,1-ANL). MALDI-ISD performed at a low M/A of 6.3:1 resulted in unexpected backbone cleavages that formed (a+16) and y-ions, while ISD spectra at M/A of 630:1 gave the usual fragments of c-, z’-, z-ANL and w-ions. Although the (a+16) and y-ions observed at lower M/A values could not be rationalized by conventional ISD reactions, they were in agreement with the radiolytic products caused by the oxidation of peptides with hydroxyl radical HO. MALDI mass spectra obtained at low M/A showed oxidized analyte ions [M+nO]+ (n=1–4). In addition, the spectra acquired in the low mass range showed peaks corresponding to H±, H3O±, H2O+ (or NH4+), HO−, O2− and HO2−. These results suggest that MALDI-ISD experiments performed at lower M/A values can generate active radical species such as HO, H and HO2, which leads to the oxidative radical driven cleavage of peptides.

14C mean residence time and its relationship with thermal stability and molecular composition of soil organic matter: A case study of deciduous and coniferous forest types

Soil organic matter (SOM) plays a critical role in the global terrestrial carbon cycle, and a better understanding of soil processes involved in SOM stability is essential to determine how projected climate-driven changes in soil processes will influence carbon dynamics. We used 14C signature, analytical thermal analysis, and ultrahigh resolution mass spectrometry to determine the influence of deciduous and coniferous forest vegetation type and soil depth on the stability of soil C. The 14C mean residence time (MRT) of the illuvial B horizon soils averaged 1350years for the deciduous soils and 795years for the coniferous soils. The difference of MRT between mineral soils by forest type may be due to the saturation of extractable Fe and Al minerals binding sites by SOM in the coniferous soils, allowing greater transport of modern SOM from the O horizon down the soil profile, as compared with the non-saturated minerals in the deciduous soil profile. The molecular mass distribution of the deciduous water-extractable aromatic SOM fraction was shifted to a lower mass range in the lower portion of B horizon soil compared with the upper portion, indicating preferential sorption of the higher mass aromatic fraction. The shift in the mass distribution of the aromatic fraction in the coniferous soil was much less than in the deciduous soil, which supports the view that the extractable metal minerals had reached saturation. We conclude that greater transport of modern O horizon SOM to the lower mineral B horizons in the coniferous soil profile resulted in its radiocarbon enrichment and shorter estimated MRT. Our findings highlight the importance of forest vegetation type, soil depth and transport mechanisms on SOM stability, and suggest important ecological implications for changes in forest composition on the terrestrial C cycle.

From the peat bog to the estuarine mixing zone: Common features and variances in riverine dissolved organic matter determined by non-targeted analysis

Abstract Land-derived dissolved organic matter (DOM) is able to transport iron and other trace metals from natural organic matter (NOM)-rich areas like peat bogs via rivers to the open ocean and therefore plays a pivotal role in the iron supply of coastal marine organisms. Iron is distributed over all DOM size-fractions and predominantly found in large clusters in river waters, but a shift towards lower molecular weight is observed on the way to the mixing zone. As the involved ligands are still largely unknown, a workflow was established targeting low molecular weight DOM constituents between 100 and 700 Da to provide an additional tool for DOM characterization employing the high performance of time-of-flight mass spectrometry (TOFMS) in the low mass range. An estuarine mixing zone sample from the Halladale River with high iron content, a natural organic matter-(NOM) rich creek water sample from Craggie Burn, which is a tributary of the Halladale River (Scotland, UK), and a NOM sample from the Suwannee River (Georgia, USA) were investigated by reversed phase and hydrophilic interaction liquid chromatography combined with electrospray-ionization time-of-flight mass spectrometry. Non-targeted evaluation of the accurate mass data employing state-of-the-art feature detection and alignment tools was performed. Several compounds could be identified utilizing authentic standards clearly demonstrating that the employed workflow is able to provide valid information about low molecular weight constituents of DOM. It was shown that the three investigated samples share a significant proportion of the annotated molecular formulas though they vary in seawater content and origin, especially in the protein type region of the van Krevelen plot. Those compounds seem to be resistant to salting out or further degradation. Moreover, the lignin and tannin type region is largely overlapping in the Craggie Burn and the Suwannee River samples, but almost completely absent in the Halladale River sample. Therefore, our findings support the view that land-derived lignin and tannin structures can transport iron to the estuary, where they are degraded and ligand exchange takes place.

Mayfly and fish species identification and sex determination in bleak (Alburnus alburnus) by MALDI-TOF mass spectrometry

Besides food quality control of fish or cephalopods, the novel mass spectrometry (MS) approaches could be effective and beneficial methods for the investigation of biodiversity in ecological research. Our aims were to verify the applicability of MALDI-TOF MS in the rapid identification of closely related species, and to further develop it for sex determination in phenotypically similar fish focusing on the low mass range. For MALDI-TOF MS spectra analysis, ClinProTools software was applied, but our observed classification was also confirmed by Self Organizing Map. For verifying the wide applicability of the method, brains from invertebrate and vertebrate species were used in order to detect the species related markers from two mayflies and eight fish as well as sex-related markers within bleak.Seven Ephemera larvae and sixty-one fish species related markers were observed and nineteen sex-related markers were identified in bleak. Similar patterns were observed between the individuals within one species. In contrast, there were markedly diverse patterns between the different species and sexes visualized by SOMs. Two different Ephemera species and male or female fish were identified with 100% accuracy. The various fish species were classified into 8 species with a high level of accuracy (96.2%). Based on MS data, dendrogram was generated from different fish species by using ClinProTools software. This MS-based dendrogram shows relatively high correspondence with the phylogenetic relationships of both the studied species and orders.In summary, MALDI-TOF MS provides a cheap, reliable, sensitive and fast identification tool for researchers in the case of closely related species using mass spectra acquired in a low mass range to define specific molecular profiles. Moreover, we presented evidence for the first time for determination of sex within one fish species by using this method. We conclude that it is a powerful tool that can revolutionize ecological and environmental research.

Using MALDI-TOF MS imaging and LC-HRMS for the investigation of the degradation of polycaprolactone diol exposed to different wastewater treatments

Polymers are used in high amounts in a wide range of applications from biomedicine to industry. Because of the growing awareness of the increasing amounts of plastic wastes in the aquatic environment during recent years, the evaluation of their biodegradability deserves special attention. In the past, most efforts were dedicated to studying the biodegradation of polyesters in soil and compost, while very little research has been conducted on their fate in wastewater. Here, we assessed the ability of bacterial communities residing in the aerobic and denitrification tank from a wastewater treatment plant (WWTP) to degrade the polymeric ester polycaprolactone diol (PCLD; average molecular weight of 1250 Da). Following the incubation of the solid polymer in WWTP tanks, matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) was used to provide evidence for hydrolytic reactions and to study differences in the spatial degradation on the PCLD surface. It was demonstrated that regardless of the wastewater type, the chemical structure on the PCLD surface underwent modifications after 7 days of exposure. Apart from the parent PCLD peak series in MALDI-MSI mass spectra, the presence of a second oligomer series with mass peaks spaced by m/z 114 (as in PCLD) was observed. It was proposed to correspond to polycaprolactone (PCL) originating from the hydrolytic cleavage of the diethylene glycol from PCLD. Their ion masses were detected at m/z 104 below the PCLD peaks and their structures were proposed as PCL cyclized oligomers. Differences in the spatial distribution of low MW ions (<800) between the aerobic and denitrifying exposed samples in MALDI MSI were also noticeable. While the ions at m/z 221.1, 247.1 and 449.2 predominated in the aerobic exposed sample, those at m/z 475.5 and 677.4 were characteristic of the denitrifying one. The MALDI-MSI measurements in the low mass range were complemented with LC-HRMS analysis to determine plausible structures of the major degradation products. Ten transformation products (TPs) were detected in the denitrifying wastewater experiment, five of them were the result of ester hydrolysis forming caprolactone oligomers (TPs 220, 334, 448, 562, and 676) while the other series corresponded to formation of PCL chain with a terminal diethylene glycol, likewise formed by ester hydrolysis (TPs 246, 360, 474, 588, and 702).Graphical abstractInvestigation of the polymer degradation in WWTPs by MALDI-MSI and LC-HRMS