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See detailPolymer topology revealed by ion mobility coupled with mass spectrometry
Morsa, Denis ULg; Defize, Thomas ULg; Dehareng, Dominique ULg et al

in Analytical Chemistry (in press)

Hyperbranched and star shaped polymers have raised tremendous interests because of their unusual structural and photochemical properties which provide them potent applications in various domains, namely ... [more ▼]

Hyperbranched and star shaped polymers have raised tremendous interests because of their unusual structural and photochemical properties which provide them potent applications in various domains, namely in the biomedical field. In this context, the development of adequate tools aiming to probe particular three-dimensional features of such polymers is of crucial importance. In this present work, ion mobility coupled with mass spectrometry was used to experimentally derive structural information related to cationized linear and star-shaped poly-ε-caprolactones as a function of their charge state and chain length. Two major conformations were observed and identified using theoretical modeling: (1) near spherical conformations whose size is invariant with the polymer topology for long and lightly charged chains and (2) elongated conformations whose size varies with the polymer topology for short and highly charged chains. These conformations were further confirmed by collisional activation experiments based on the ejection thresholds of the coordinated cations that vary according to the elongation amplitude of the polymer chains. Finally, a comparison between solution and gas-phase conformations highlights a compaction of the structure with a loss of specific chain arrangements during the ionization and desolvation steps of the electrospray process, fueling the long-time debated question related to the preservation of the analyte structure during the transfer into the mass spectrometer. [less ▲]

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See detailThe use of Ion Mobility Mass Spectrometry for isomer composition determination extracted from Se-rich yeast
Far, Johann ULg; Delvaux, Cédric ULg; Kune, Christopher ULg et al

in Analytical Chemistry (2014), just accepted

The isomer ratio determination of a selenium-containing metabolite produced by Se-rich yeast was performed. Electrospray Ionization and Ion Mobility Mass Spectrometry (IM-MS) were unsuccessfully used in ... [more ▼]

The isomer ratio determination of a selenium-containing metabolite produced by Se-rich yeast was performed. Electrospray Ionization and Ion Mobility Mass Spectrometry (IM-MS) were unsuccessfully used in order to resolve the isomers according to their Collisional Cross Section (CCS) difference. The isomer ratio determination of 2,3-dihydroxypropionylselenocystathionine was performed after multidimensional liquid chromatography preconcentration from a water extract of Se-rich yeast using preparative size exclusion, anion exchange and capillary reverse phase columns coupled to IM-MS. 4’-nitrobenzo-15-crown-5 ether, a Selective Shift Reagent (SSR), was added after the last chromatographic dimension in order to specifically increase the CCS of one of the isomers by the formation of a stable host-guest system with the crown-ether . Both isomers were consequently fully resolved by IM-MS and the relative ratio of the isomers was determined: 11-13% and 87-89%. The present data compared favorably with literature to support the analytical strategy despite the lack of authentic standard for method validation. In addition, computational chemistry methods were successfully applied to design the SSR and to support the experimental data. [less ▲]

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See detailSpatiotemporal monitoring of the antibiome secreted by Bacillus biofilms on plant roots using MALDI mass spectrometry imaging
Debois, Delphine ULg; Jourdan, Emmanuel; Smargiasso, Nicolas ULg et al

in Analytical Chemistry (2014), 86(9), 4431-4438

Some soil Bacilli living in association with plant roots can protect their host from infection by pathogenic microbes and are therefore being developed as biological agents to control plant diseases. The ... [more ▼]

Some soil Bacilli living in association with plant roots can protect their host from infection by pathogenic microbes and are therefore being developed as biological agents to control plant diseases. The plant protective activity of these bacteria has been correlated with the potential to secrete a wide array of antibiotic compounds upon growth as planktonic cells in isolated cultures under laboratory conditions. However, in situ expression of these antibiotics in the rhizosphere where bacterial cells naturally colonize root tissues is still poorly understood. In this work, we used Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI MSI) to examine spatio-temporal changes in the secreted antibiome of B. amyloliquefaciens developing as biofilms on roots. Non-ribosomal lipopeptides such as the plant immunity elicitor surfactin or the highly fungitoxic iturins and fengycins were readily produced albeit in different time-frames and quantities in the surrounding medium. Interestingly, MS/MS experiments performed directly from the gelified culture medium, also allowed to identify a new variant of surfactins released at later time points. However, no other bioactive compounds such as polyketides were detected at any time, strongly suggesting that the antibiome expressed in planta by B. amyloliquefaciens does not reflect the vast genetic arsenal devoted to the formation of such compounds. This first dynamic study reveals the power of MALDI MSI as tool to identify and map antibiotics synthesized by root-associated bacteria and more generally, to investigate plant-microbe interactions at the molecular level. [less ▲]

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See detailDetermination of the Al2O3 content in NaF-AlF 3-CaF2-Al2O3 melts at 950 °c by raman spectroscopy
Malherbe, Cédric ULg; Eppe, Gauthier ULg; Gilbert, Bernard ULg

in Analytical Chemistry (2014)

Thein situ control of the chemical composition of industrial aluminum smelter is a challenge mainly for physicochemical reasons: high temperature, high surrounding electromagnetic field, and the highly ... [more ▼]

Thein situ control of the chemical composition of industrial aluminum smelter is a challenge mainly for physicochemical reasons: high temperature, high surrounding electromagnetic field, and the highly corrosive molten salt electrolyte to deal with. In previous works, we proposed that Raman spectroscopy is a method of choice that could be adapted to real smelters. The laboratory study presented here relies on reproducible Raman spectra recorded on molten mixtures whose compositions are identical to those used during the production of aluminum. A normalization procedure for the Raman spectra is proposed based on the equilibria taking place in the bath. In addition, we discuss two quantitative models to determine the alumina content from the Raman spectra of the molten NaF−AlF3−CaF2−Al2O3 electrolytes. Univariate and multivariate approaches are applied to determine both theCOx (alumina content) and the CR (NaF/AlF3 molar ratio) by Raman spectroscopy without referring to an additional internal reference of intensity. The procedure was successfully tested and validated on industrial samples. [less ▲]

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See detailDevelopment of a Standard Reference Material for Metabolomics Research
Phinney, K; Ballihaut, G; Bedner, M et al

in Analytical Chemistry (2013), 85(24), 11732-11738

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health (NIH), has developed a Standard Reference Material (SRM) to support technology ... [more ▼]

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health (NIH), has developed a Standard Reference Material (SRM) to support technology development in metabolomics research. SRM 1950 Metabolites in Human Plasma is intended to have metabolite concentrations that are representative of those found in adult human plasma. The plasma used in the preparation of SRM 1950 was collected from both male and female donors, and donor ethnicity targets were selected based upon the ethnic makeup of the U.S. population. Metabolomics research is diverse in terms of both instrumentation and scientific goals. This SRM was designed to apply broadly to the field, not towards specific applications. Therefore, concentrations of approximately 100 analytes, including amino acids, fatty acids, trace elements, vitamins, hormones, selenoproteins, clinical markers, and perfluorinated compounds (PFCs), were determined. Value assignment measurements were performed by NIST and the Centers for Disease Control and Prevention (CDC). SRM 1950 is the first reference material developed specifically for metabolomics research. [less ▲]

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See detailIn-Source Decay during Matrix-Assisted Laser Desorption/Ionization Combined with the Collisional Process in an FTICR Mass Spectrometer
Asakawa, Daiki; Calligaris, David; Zimmerman, Tyler et al

in Analytical Chemistry (2013), 85

The type of ions detected after in-source decay (ISD) in a MALDI source differs according to the ion source pressure and on the mass analyzer used. We present the mechanism leading to the final ISD ions ... [more ▼]

The type of ions detected after in-source decay (ISD) in a MALDI source differs according to the ion source pressure and on the mass analyzer used. We present the mechanism leading to the final ISD ions for a Fourier transform-ion cyclotron resonance mass spectrometer (FTICR MS). The MALDI ion source was operated at intermediate pressure to cool the resulting ions and increase their lifetime during the long residence times in the FTICR ion optics. This condition produces not only c′, z′, and w fragments, but also a, y′, and d fragments. In particular, d ions help to identify isobaric amino acid residues present near the Nterminal amino acid. Desorbed ions collide with background gas during desorption, leading to proton mobilization from Arg residues to a less favored protonation site. As a result, in the case of ISD with MALDI FTICR, the influence of the Arg residue in ISD fragmentation is less straightforward than for TOF MS and the sequence coverage is thus improved. MALDI-ISD combined with FTICR MS appears to be a useful method for sequencing of peptides and proteins including discrimination of isobaric amino acid residues and site determination of phosphorylation. Additionally we also used new software for in silico elimination of MALDI matrix peaks from MALDI-ISD FTICR mass spectra. The combination of high resolving power of an FTICR analyzer and matrix subtraction software helps to interpret the low m/z region of MALDI-ISD spectra. Finally, several of these developed methods are applied in unison toward a MALDI ISD FTICR imaging experiment on mouse brain to achieve better results. [less ▲]

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See detailSelected Protein Monitoring in Histological Sections by Targeted MALDI-FTICR in-source decay Imaging.
Calligaris, David ULg; Longuespée, Rémi ULg; Debois, Delphine ULg et al

in Analytical Chemistry (2013), 85(4), 2117-26

MALDI mass spectrometry imaging (MALDI MSI) is a rapidly growing method in biomedical research allowing molecular mapping of proteins on histological sections. The images can be analyzed in terms of ... [more ▼]

MALDI mass spectrometry imaging (MALDI MSI) is a rapidly growing method in biomedical research allowing molecular mapping of proteins on histological sections. The images can be analyzed in terms of spectral pattern to define regions of interest. However, the identification and the differential quantitative analysis of proteins require off line or in situ proteomic methods using enzymatic digestion. The rapid identification of biomarkers holds great promise for diagnostic research but the major obstacle is the absence of rapid and direct method to detect and identify with a sufficient dynamic range a set of specific biomarkers. In the current work, we present a proof of concept for a method allowing identifying simultaneously a set of selected biomarkers on histological slices with minimal sample treatment using in-source decay (ISD) MSI and MALDI-Fourier transform ion cyclotron resonance (FTICR). In the proposed method, known biomarkers are spotted next to the tissue of interest, the whole MALDI plate being coated with 1,5-DAN matrix. The latter enhances MALDI radical-induced ISD, providing large tags of the amino acid sequences. Comparative analysis of ISD fragments between the reference spots and the specimen in imaging mode allows for unambiguous identification of the selected biomarker while preserving full spatial resolution. Moreover, the high resolution/high mass accuracy provided by FTICR mass spectrometry allows the identification of proteins. Well-resolved peaks and precise measurements of masses and mass differences allow the construction of reliable sequence tags for proteins identification. The method will allow the use MALDI-FTICR MSI as method for rapid targeted biomarker detection in complement to classical histology. [less ▲]

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See detailCharacterization of Volatile Organic Compounds from Human Analogue Decomposition Using Thermal Desorption Coupled to Comprehensive Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry
Stefanuto, Pierre-Hugues ULg; Stadler, Sonja; Brokl, Michal et al

in Analytical Chemistry (2013), 85(2), 998-1005

Complex processes of decomposition produce a variety of chemicals as soft tissues, and their component parts are broken down. Among others, these decomposition byproducts include volatile organic ... [more ▼]

Complex processes of decomposition produce a variety of chemicals as soft tissues, and their component parts are broken down. Among others, these decomposition byproducts include volatile organic compounds (VOCs) responsible for the odor of decomposition. Human remains detection (HRD) canines utilize this odor signature to locate human remains during police investigations and recovery missions in the event of a mass disaster. Currently, it is unknown what compounds or combinations of compounds are recognized by the HRD canines. Furthermore, a comprehensive decomposition VOC profile remains elusive. This is likely due to difficulties associated with the nontarget analysis of complex samples. In this study, cadaveric VOCs were collected from the decomposition headspace of pig carcasses and were further analyzed using thermal desorption coupled to comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (TD-GC × GC−TOFMS). Along with an advanced data handling methodology, this approach allowed for enhanced characterization of these complex samples. The additional peak capacity of GC × GC, the spectral deconvolution algorithms applied to unskewed mass spectral data, and the use of a robust data mining strategy generated a characteristic profile of decomposition VOCs across the various stages of soft-tissue decomposition. The profile was comprised of numerous chemical families, particularly alcohols, carboxylic acids, aromatics, and sulfides. Characteristic compounds identified in this study, e.g., 1-butanol, 1-octen-3-ol, 2-and 3-methyl butanoic acid, hexanoic acid, octanal, indole, phenol, benzaldehyde, dimethyl disulfide, and trisulfide, are potential target compounds of decomposition odor. This approach will facilitate the comparison of complex odor profiles and produce a comprehensive VOC profile for decomposition. [less ▲]

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See detailIon-Mobility mass spectrometry as a potential tool to assign disulfide bonds arrangements in peptides with multiple disulfide bridges.
Echterbille, Julien ULg; Quinton, Loïc ULg; Gilles, Nicolas et al

in Analytical Chemistry (2013)

Disulfide bridges play a major role in defining the structural properties of peptides and proteins. However, the determination of the cysteine pairing is still challenging. Peptide sequences are usually ... [more ▼]

Disulfide bridges play a major role in defining the structural properties of peptides and proteins. However, the determination of the cysteine pairing is still challenging. Peptide sequences are usually achieved using MS/MS spectra of the totally reduced unfolded species but the cysteine pairing information is lost. On the other hand, MS/MS experiments performed on native folded species show complex spectra composed of non-classical ions. MS/MS alone does not allow the cysteine pairing nor the full sequence of an unknown peptide to be determined. The major goal of this work is to set up a strategy for the full structural characterization of peptides including disulfide bridges annotation in the sequence. This strategy was developed by combining Ion Mobility Spectrometry (IMS)and Collision Induced Dissociation(CID). It is assumed that the opening of one S-S bridges in a peptide leads to a structural evolution which results in a modification of IMS drift time. In the presence of multiple S-S bridges, the shift in arrival time will depend on which disulfide(s) has (have) been reduced and on the shape adopted by the generated species. Due to specific fragmentations observed for each species, CID experiments performed after the mobility separation could provide not only information on peptide sequence, but also on the localization of the disulfide bridges. To achieve this goal, synthetic peptides containing two disulfides were studied. The openings of the bridges were carried out following different experimental conditions such as reduction, reduction/alkylation or oxidation. Due to disulfide scrambling highlighted with the reduction approaches, oxidation of S-S bonds into cysteic acids appeared to be the best strategy. Cysteines connectivity was then unambiguously determined for the two peptides, without any disulfide scrambling interference. [less ▲]

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See detailUsefulness of Information Criteria for the Selection of Calibration Curves
Rozet, Eric ULg; Ziemons, Eric ULg; Marini Djang'Eing'A, Roland ULg et al

in Analytical Chemistry (2013), 85

The reliability of analytical results obtained with quantitative analytical methods is highly dependant upon the selection of the adequate model used as calibration curve. To select the adequate response ... [more ▼]

The reliability of analytical results obtained with quantitative analytical methods is highly dependant upon the selection of the adequate model used as calibration curve. To select the adequate response function or model the most used and known parameter is the determination coefficient R². However it is well known that it suffers many inconvenient, such as leading to overfitting the data. A solution proposed is to use the adjusted determination coefficient R²adj that aims at reducing this problem. However there is another family of criteria that exists to allow the selection of an adequate model: the information criteria AIC, AICc and BIC. These criteria have rarely been used in analytical chemistry to select the adequate calibration curve. This works aims at assessing the performance of the statistical information criteria as well as R² and R²adj for the selection of an adequate calibration curve. They are applied to several analytical methods covering liquid chromatographic methods as well as electrophoretic ones involved in the analysis of active substances in biological fluids or aimed at quantifying impurities in drug substances. In addition, Monte-Carlo simulations are performed to assess the efficacy of these statistical criteria to select the adequate calibration curve. [less ▲]

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See detailDirect determination of the NaF/AlF3 molar ratio by raman spectroscopy in NaF-AlF3-CaF2 melts at 1000° C
Malherbe, Cédric ULg; Gilbert, Bernard ULg

in Analytical Chemistry (2013)

For the last 40 years, Raman spectroscopy has been very useful in investigating the structure of corrosive molten salts, such as the cryolite-based melts widely used as electrolyte in the Hall-Heroult ... [more ▼]

For the last 40 years, Raman spectroscopy has been very useful in investigating the structure of corrosive molten salts, such as the cryolite-based melts widely used as electrolyte in the Hall-Heroult process. Even if this process remains the most economically efficient for metallic aluminum electro-production, it suffers from a high energy loss, which is dependent on the melt composition. Therefore, controlling the chemical composition of the electrolyte is essential. The present paper proposes to apply Raman spectroscopy for the direct determination of the NaF-AlF3 molar ratio in NaF-AlF3-CaF2-based melts. Despite the experimental difficulties, a calibration curve based on equilibria taking place in the melt has been developed and the procedure has been successfully compared to industrial samples of known compositions. The possible exportation of the laboratory scale procedure to an industrial environment application for the control of the Hall-Heroult process is finally discussed. [less ▲]

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See detailIdentification and Relative-quantification of Glycans by Matrix-assisted Laser Desorption/Ionization In-Source Decay with Hydrogen Abstraction
Akasawa, Daiki; Smargiasso, Nicolas ULg; De Pauw, Edwin ULg

in Analytical Chemistry (2012)

The use of specific matrices allows enhancing the scope of in-source decay (ISD) applications in matrix-assisted laser desorption ionization (MALDI) thanks to the specificity of analyte-matrix chemistry ... [more ▼]

The use of specific matrices allows enhancing the scope of in-source decay (ISD) applications in matrix-assisted laser desorption ionization (MALDI) thanks to the specificity of analyte-matrix chemistry. The use of an oxidizing matrix, 5-nitrosalicylic acid (5-NSA) for MALDI-ISD of glycans is shown to promote fragmentation pathways involving radical precursors. Both glycosidic and cross-ring cleavages are promoted by hydrogen abstraction from hydroxyl group of glycans by 5-NSA molecules. Cross-ring cleavage ions are potentially useful in linkage analysis, one of the most critical steps of glycan characterization. Moreover, we show here that isobaric glycans could be distinguished by structure specific ISD ions, and that the molar ratio of glycan isomers in the mixture can be estimated from their fragment ions abundance. The use of 5-NSA also opens the possibility to perform pseudo-MS3 analysis of glycans. Therefore, MALDI-ISD with 5-NSA is a useful method for identification of glycans and semi-quantitative analysis of mixture of glycan isomers. [less ▲]

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See detailSelection and characterization of PCB-binding DNA aptamers.
Mehta, Jaytry; Rouah-Martin, Elsa; Van Dorst, Bieke et al

in Analytical Chemistry (2012), 84(3), 1669-76

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that resist natural degradation and bioaccumulate in nature. Combined with their toxicity, this leads them to cause cancer and ... [more ▼]

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that resist natural degradation and bioaccumulate in nature. Combined with their toxicity, this leads them to cause cancer and other health hazards. Thus, there is a vital need for rapid and sensitive methods to detect PCB residues in food and in the environment. In this study, PCB-binding DNA aptamers were developed using PCB72 and PCB106 as targets for aptamer selection. Aptamers are synthetic DNA recognition elements which form unique conformations that enable them to bind specifically to their targets. Using in vitro selection techniques and fluorometry, an aptamer that binds with nanomolar affinity to both the PCBs has been developed. It displayed high selectivity to the original target congeners and limited affinity toward other PCB congeners (105, 118, 153, and 169), suggesting general specificity for the basic PCB skeleton with varying affinities for different congeners. This aptamer provides a basis for constructing an affordable, sensitive, and high-throughput assay for the detection of PCBs in food and environmental samples and offers a promising alternative to existing methods of PCB quantitation. This study therefore advances aptamer technology by targeting one of the highly sought-after POPs, for the first time ever recorded. [less ▲]

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See detailQuality by design compliant analytical method validation
Rozet, Eric ULg; Ziemons, Eric ULg; Marini Djang'Eing'A, Roland ULg et al

in Analytical Chemistry (2012), 84

The concept of quality by design (QbD) has recently been adopted for the development of pharmaceutical processes to ensure a predefined product quality. Focus on applying the QbD concept to analytical ... [more ▼]

The concept of quality by design (QbD) has recently been adopted for the development of pharmaceutical processes to ensure a predefined product quality. Focus on applying the QbD concept to analytical methods has increased as it is fully integrated within pharmaceutical processes and especially in the process control strategy. In addition, there is the need to switch from the traditional checklist implementation of method validation requirements to a method validation approach that should provide a high level of assurance of method reliability in order to adequately measure the Critical Quality Attributes (CQAs) of the drug product. The intended purpose of analytical methods is directly related to the final decision that will be made with the results generated by these methods under study. The final aim for quantitative impurity assays is to correctly declare a substance or a product as compliant with respect to the corresponding product specifications. For content assays, the aim is similar: making the correct decision about product compliance with respect to their specification limits. It is for these reasons that the fitness of these methods should be defined, as they are key elements of the Analytical Target Profile (ATP). Therefore, validation criteria, corresponding acceptance limits and method validation decision approaches should be settled in accordance with the final use of these analytical procedures. This work proposes a general methodology to achieve this in order to align method validation within the QbD framework and philosophy. β-expectation tolerance intervals are implemented to decide about the validity of analytical methods. The proposed methodology is also applied to the validation of analytical procedures dedicated to the quantification of impurities or active product ingredients (API) in drug substances or drug products and its applicability is illustrated with two case studies. [less ▲]

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See detailAn analytical pipeline for MALDI in-source decay mass spectrometry imaging
Zimmerman, Tyler ULg; Debois, Delphine ULg; Mazzucchelli, Gabriel ULg et al

in Analytical Chemistry (2011), 83(15), 6090-6097

In-source decay (ISD) fragmentation as combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry allows protein sequencing directly from mass spectra. Acquisition of MALDI-ISD ... [more ▼]

In-source decay (ISD) fragmentation as combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry allows protein sequencing directly from mass spectra. Acquisition of MALDI-ISD mass spectra from tissue samples is achieved using an appropriate MALDI matrix, such as 1,5-diaminonaphthalene (DAN). Recent efforts have focused on combining MALDI-ISD with mass spectrometry imaging (MSI) to provide simultaneous sequencing and localization of proteins over a thin tissue surface. Successfully coupling these approaches requires the development of new data analysis tools, but first, investigating the properties of MALDI-ISD as applied to mixtures of protein standards reveals a high sensitivity to the relative protein ionization efficiency. This finding translates to the protein mixtures found in tissues and is used to inform the development of an analytical pipeline for data analysis in MALDI-ISD MS imaging, including software to identify the most pertinent spectra, to sequence protein mixtures, and to generate ion images for comparison with tissue morphology. The ability to simultaneously identify and localize proteins is demonstrated by using the analytical pipeline on three tissue sections from porcine eye lens, resulting in localizations for crystallins and cytochrome c. The variety of protein identifications provided by MALDI-ISD-MSI between tissue sections creates a discovery tool, and the analytical pipeline makes this process more efficient. [less ▲]

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See detailEffective temperature of ions in traveling wave ion mobility spectrometry
Morsa, Denis ULg; Gabelica, Valérie ULg; De Pauw, Edwin ULg

in Analytical Chemistry (2011), 83(14), 5775-5782

Traveling wave ion mobility spectrometers (TW IMS) operate at significantly higher fields than drift tube ion mobility spectrometers. Here we measured the fragmentation of the fragile p ... [more ▼]

Traveling wave ion mobility spectrometers (TW IMS) operate at significantly higher fields than drift tube ion mobility spectrometers. Here we measured the fragmentation of the fragile p-methoxybenzylpyridinium ion inside the TW ion mobility cell of the first-generation SYNAPT HDMS spectrometer. The ion’s vibrational internal energy was quantified by a vibrational effective temperature Teff,vib, which is the mean temperature of the ions inside the cell that would result in the same fragmentation yield as observed experimentally. Significant fragmentation of the probe ion inside the TW IMS cell was detected, indicating that field heating of the ions takes place in TW IMS. For typical small molecule IMS conditions, Teff,vib = 555 ± 2 K. The variations of the effective temperature were studied as a function of the IMS parameters, and we found that Teff,vib decreases when the wave height decreases, when the pressure increases, or when the wave speed increases. The energy transfer efficiency of argon is higher than for He, N2 or CO2. Teff,vib being directly related to the ion speed inside the TW IMS, our results also provide new insight on the ion movement in TW IMS. We also discuss the influence of field heating of ions for calibration and structural studies in TW IMS. [less ▲]

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See detailMALDI in-source decay of high mass protein isoforms: application to alpha- and beta-tubulin variants.
Calligaris, David ULg; Villard, Claude; Terras, Lionel et al

in Analytical Chemistry (2010), 82(14), 6176-6184

Tubulin is one of the major targets in cancer chemotherapy and the target of more than twenty percent of the cancer chemotherapic agents. The modulation of isoform content has been hypothesized as being a ... [more ▼]

Tubulin is one of the major targets in cancer chemotherapy and the target of more than twenty percent of the cancer chemotherapic agents. The modulation of isoform content has been hypothesized as being a cause of resistance to treatment. Isoform differences lie mostly in the C-terminus part of the protein. Extensive characterization of this polypeptide region is therefore of critical importance. MALDI-TOF fragmentation of tubulin C-terminal domains was tested using synthetic peptides. Then, isotypes from HeLa cells were successfully characterized for the first time by in-source decay (ISD) fragmentation of their C-terminus coupled to a pseudo MS3 technique named T3-sequencing. The fragmentation occurred in-source, preferentially generating yn-series ions. This approach required guanidination for the characterization of the βIII-tubulin C-terminus peptide. This study is, to our knowledge, the first example of reflectron in-source decay (reISD) of the C-terminus of a 50 kDa protein. This potentially occurs via a CID-like mechanism occurring in the MALDI plume. There are now new avenues for top-down characterization of important clinical biomarkers such as βIII-tubulin isotypes, a potential marker of drug resistance and tumor progression. This paper raises the challenge of protein isotypes characterization for early cancer detection and treatment monitoring. [less ▲]

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See detailMALDI-In Source Decay Applied to Mass Spectrometry Imaging: A New Tool for Protein Identification.
Debois, Delphine ULg; Bertrand, Virginie ULg; Quinton, Loïc ULg et al

in Analytical Chemistry (2010), 82(10), 3969-4304

Matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) imaging is a powerful technique giving access to the distribution of a large range of biomolecules directly from a tissue section ... [more ▼]

Matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) imaging is a powerful technique giving access to the distribution of a large range of biomolecules directly from a tissue section, allowing, for example, the discovery of new pathological biomarkers. Nevertheless, one main difficulty lies in the identification of the detected species, especially proteins. MALDI-in source decay (ISD) is used to fragment ions directly in the mass spectrometer ion source. This technique does not require any special sample treatment but only the use of a specific MALDI matrix such as 2,5-dihydroxybenzoic acid or 1,5-diaminonaphthalene. MALDI-ISD is generally employed on classical, purified samples, but here we demonstrate that ISD can also be performed directly on mixtures and on a tissue slice leading to fragment ions, allowing the identification of major proteins without any further treatment. On a porcine eye lens slice, de novo sequencing was even performed. Crystallins not yet referenced in databases were identified by sequence homology with other mammalian species. On a mouse brain slice, we demonstrate that results obtained with ISD are comparable and even better than those obtained with a classical in situ digestion. [less ▲]

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See detailOptimization of Matrix Conditions for the Control of MALDI In-Source Decay of Permethylated Glycans.
Smargiasso, Nicolas ULg; De Pauw, Edwin ULg

in Analytical Chemistry (2010), sous presee

Due to its fastness and its easiness to use, MALDI-MS is currently an analytical tool widely used in glycomic applications. However, the MALDI ionization process could result in the so-called "in-source ... [more ▼]

Due to its fastness and its easiness to use, MALDI-MS is currently an analytical tool widely used in glycomic applications. However, the MALDI ionization process could result in the so-called "in-source decay", or ISD, of analytes, leading to complex spectra. On the other hand, ISD opens the possibility to perform pseudo-MS(3) experiments. This phenomenon must therefore be controlled in order to be used on demand as a supplementary tool for the analysis of permethylated glycans by MALDI mass spectrometry. For this purpose, several matrices were tested and MALDI imaging was used to determine optimal conditions promoting or, inversely, avoiding ISD of permethylated glycans. 2,5-DHB was shown to be a versatile matrix allowing one to induce or prevent ISD according to the location of laser shots. Inversely, it was shown that 9-aminoacridine forms homogeneous spots and avoids completely ISD. This matrix would therefore be suitable for automatic analysis. [less ▲]

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See detailIn Situ Lipidomic Analysis of Nonalcoholic Fatty Liver by Cluster TOF-SIMS Imaging
Debois, Delphine ULg; Bralet, Marie-Pierre; Le Naour, François et al

in Analytical Chemistry (2009), 81(8), 2823-2831

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