Complementary ESI and APPI high resolution mass spectrometry unravel the molecular complexity of a soil humeome.

High resolution mass spectrometry (HRMS) can resolve thousands of compounds in complex mixtures such as natural organic matter. However, HRMS is seldom sufficient to fully resolve the molecular heterogeneity of Humus in the soil matrix, especially if no preliminary simplification of Humus complexity is applied and if a single ionization technique is used. Here we show that HRMS, when applied with both photoionization (APPI) and electrospray ionization (ESI) and combined with the extensive molecular simplification provided by a humeomic fractionation, significantly increases identification of the molecular composition of soil Humus. Different sequential extractions separate the soil Humeome in three organosoluble fractions (ORG1-3) and two hydrosoluble fractions (AQU2 and RESOM), which showed distinct molecular characteristics. The ORG fractions were particularly homogeneous and rich in alkyl compounds including unsaturated hydrocarbons and lipid compounds found mainly in ORG 1 and ORG 3, but also aromatic compounds comprising lignin-like molecules and condensed structures mainly detected in ORG2. The AQU2 fractions revealed greater complexity and heterogeneity due to the simultaneous detection of sugars, amino sugars, tannins and N-containing compounds not detectable in appreciable concentrations in other fractions. The most recalcitrant RESOM fraction contained highly reduced molecules and condensed structures. The combined use of APPI and ESI showed a marked selectivity in the detection of chemically different molecules separated in each fraction, thereby enhancing their molecular characterization. Specifically, APPI tended to ionize less oxidized and N-containing molecules, and compounds with high concentrations of unsaturation or aromatics, while ESI was more prone to detect highly oxidized compounds consisting of large O/C ratios. Our findings indicate that the combination of a soil Humeome fractionation with a detailed high resolution characterization of differently ionized molecules in the separated fractions enables a far deeper understanding of the molecular composition of soil Humus and the comprehension of its environmental reactivity.

Molecular properties of the Humeome of two calcareous grassland soils as revealed by GC/qTOF-MS and NMR spectroscopy.

A Humeomic fractionation revealed the humus molecular composition of two uncropped calcareous soils of Northern France and differentiated the soils Humeome by extracting humic components first unbound to the organo-mineral matrix and then liberated from their progressively stronger intermolecular and intramolecular ester and ether linkages. We separated organo- (ORG1-3) and water-soluble (AQU2 and AQU4) fractions, a final extractable fraction (RESOM) and soil residues. Organo-soluble fractions were studied by GC coupled with high-resolution mass spectrometry (GC/qTOF-MS), all fractions underwent mono- and two-dimensional liquid-state NMR (except for the iron-rich AQU4 fraction), while solid-state 13C-CPMAS-NMR spectroscopy analyzed soil residues. The Calcaric Leptosol (A) showed a larger mass extraction than the Calcaric Cambisol (B), and a greater cumulative C and N content in its Humeome. Both soils showed the greatest weight yield for AQU4 fraction, followed by ORG2, RESOM, ORG1, AQU2, and ORG3. ORG2 was the most differentiating fraction between the two soils for both compound concentration and diversity, showing a larger C content for soil A than for soil B and a different distribution in aromatic compounds, fatty acids, and dicarboxylic acids. No significant differences between soils were found for ORG 3, suggesting similar processes of OM stabilization for its recalcitrant components, mostly hydrophobic esters of alkanoic, hydroxy, and aromatic acids with linear alkanols. We confirmed that Humeomic fractionation coupled to advanced analytical instrumentations enabled a detailed molecular characterization of the soil Humeome and differentiated between the two calcareous grassland soils and the other soils previously subjected to Humeomics.

Comparison of preconcentration methods of the colloidal phase of a uranium-containing soil suspension.

Three methods of membrane separation by dead-end, tangential, and centrifugal ultrafiltration (UF) were considered in order to understand the physicochemical phenomena occurring during the preconcentration of the colloidal phase of soil water. The analytical approach used involved dynamic light scattering (DLS), transmission electron microscopy (TEM), determination of total organic carbon (TOC-metry) and mass spectrometry (ICP-MS). The mass amounts of the major components of the colloidal phase, i.e. Al, Fe and total organic carbon (TOC), as well as the mass amount of uranium considered as a trace element of environmental interest, were determined, both in soil water, and in the concentrates (i.e. retentates) and filtrates of this water obtained by the 3 methods tested. Dead-end ultrafiltration led to an enlargement of the size distribution towards larger sizes because of agglomeration/aggregation phenomena. This method also generated enrichment of concentrates, in particular in organic matter. The consequence was that large structures were observed coating or embedding the particles initially present individually dispersed in the test sample. The mass amounts of elements and TOC increased more importantly than expected, which confirmed the enrichment of the concentrates from the dissolved phase probably by sorption on colloidal objects. To a lesser extent similar effects were observed after tangential ultrafiltration. Such phenomena were not observed after centrifugal ultrafiltration. From a practical point of view, both tangential and centrifugal ultrafiltration proved to be both the most practical and the best suited for the preconcentration of soil water sample. Finally, centrifugal ultrafiltration has proved to be the best compromise given the preservation of colloidal particles and method practicality.

Publisher Correction: Effect of endogenous microbiota on the molecular composition of cloud water: a study by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS).

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Identification of Postblast Residues by DART-High Resolution Mass Spectrometry Combined with Multivariate Statistical Analysis of the Kendrick Mass Defect.

The coupling of an atmospheric pressure ionization source (Direct Analysis in Real Time, DART) and a high-resolution mass spectrometer (Orbitrap) has enabled the rapid and efficient analysis of a variety of energetic formulations. This approach was used to generate mass spectra for 83 plastic explosives and polymer samples in less than 2 min per sample. To manually interpret and identify all of the constituent polymers and other interesting features in the acquired mass spectra is a tedious and time-consuming challenge. Instead, a methodology based on the systematic calculation of Kendrick mass defects (KMDs) was developed and implemented. Its application allowed the identification of the polymeric support present in each energetic formulation. The presence of polyisobutylene in PG2 has been confirmed thanks to this approach, and a mixture of polyisobutylene, polybutadiene, and polystyrene has been confirmed in the Semtex 10 formulation. The developed methodology has also permitted the observation of changes that occur to the polymeric composition of these formulations after a blast. It appears that the most adequate way to describe post blast polymer samples is that they are less oxygenated and, above all, more unsaturated than the original starting material. These conclusions were deduced with the aid of principal component analysis, which served to establish the main factors that differentiate the samples.

Molecular characterization of organic matter in two calcareous soils: the effects of an acid decarbonation treatment.

The molecular composition of soil organic matter (SOM) of two calcareous soils highly rich in carbonates was assessed before and after decarbonation by acid washing with HCl through 13C-CPMAS-NMR spectroscopy and off-line thermochemolysis coupled with gas chromatography and mass spectrometry (THM-GC-MS). The acidic treatment promoted a considerable concentration of organic matter in both soils, thus improving the identification of molecules otherwise not easily detectable. Decarbonation induced only a slight loss of soil organic carbon (SOC), corresponding to 1.4 and 2.7% for A and B soils respectively. The acidic treatment also led to an increase in the organic carbon/total nitrogen (OC/N) ratio in soil A, while an opposite variation was found for the second soil. Moreover, variations in the concentration and molecular distribution of specific compound classes present in SOM were caused by the acid washing of soils. As confirmed by both 13C-CPMAS-NMR and thermochemolysis results, the molecules most susceptible to the acid treatment were the carbohydrates, lignin monomers (G14 and G15), fatty acids (C18 saturated and unsaturated), fatty acids of microbial origin (C15, C17, and C19), hydroxy acids (C16, C18), and dioic acids (C18) which represent the components weakly bound to the organic matrix. Our findings not only showed the efficacy of the decarbonation treatment of calcareous soils with 3 N HCl, but also indicated how the acidic washing can improve the differentiation of soils on the basis of SOM molecular characteristics. Graphical abstract.

Effect of endogenous microbiota on the molecular composition of cloud water: a study by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS).

A cloud water sample collected at the puy de Dôme observatory (PUY) has been incubated under dark conditions, with its endogenous microbiota at two different temperatures (5 and 15 °C), and the change in the molecular organic composition of this sample was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Microorganisms were metabolically active and strongly modified the dissolved organic matter since they were able to form and consume many compounds. Using Venn diagrams, four fractions of compounds were identified: (1) compounds consumed by microbial activity; (2) compounds not transformed during incubation; (3) compounds resulting from dark chemistry (i.e., hydrolysis and Fenton reactions) and, finally, (4) compounds resulting from microbial metabolic activity. At 15 °C, microorganisms were able to consume 58% of the compounds initially present and produce 266 new compounds. For this cloud sample, the impact of dark chemistry was negligible. Decreasing the temperature to 5 °C led to the more efficient degradation of organic compounds (1716 compounds vs. 1094 at 15 °C) but with the less important production of new ones (173). These transformations were analyzed using a division into classes based on the O/C and H/C ratios: lipid-like compounds, aliphatic/peptide-like compounds, carboxylic-rich alicyclic molecule (CRAM)-like structures, carbohydrate-like compounds, unsaturated hydrocarbons, aromatic structures and highly oxygenated compounds (HOCs). Lipid-like, aliphatic/peptide-like and CRAMs-like compounds were the most impacted since they were consumed to maintain the microbial metabolism. On the contrary, the relative percentages of CRAMs and carbohydrates increased after incubation.

New application of direct analysis in real time high-resolution mass spectrometry for the untargeted analysis of fresh and aged secondary organic aerosols generated from monoterpenes.

RATIONALE: Secondary organic aerosols (SOAs) represent a significant portion of total atmospheric aerosols. They are generated by the oxidation of volatile organic compounds (VOCs), and particularly biogenic VOCs (BVOCs). The analysis of such samples is usually performed by targeted methods that often require time-consuming preparation steps that can induce loss of compounds and/or sample contaminations. METHODS: Recently, untargeted methods using high-resolution mass spectrometry (HRMS) have been successfully employed for a broad characterization of chemicals in SOAs. Herein we propose a new application of the direct analysis in real time (DART) ionization method combined with HRMS to quickly detect several hundred chemicals in SOAs collected on a quartz filter without sample preparation or separation techniques. RESULTS: The reproducibility of measurements was good, with several hundred elemental compositions common to three different replicates. The relative standard deviations of the intensities of the chemical families ranged from 6% to 35%, with sufficient sensitivity to allow the unambiguous detection of 4 ng/mm2 of pinic acid. The presence of oligomers and specific tracers was highlighted by MSn (n ≤ 4) experiments, an achievement that is difficult to attain with other ultrahigh-resolution mass spectrometers. Contributions of this untargeted DART-HRMS method were illustrated by the analysis of fresh and aged SOAs from different gaseous precursors such as limonene, a ß-pinene/limonene mixture or scots pines emissions. CONCLUSIONS: The results show that it is possible to use DART-HRMS for the identification of tracers of specific aging reactions, or for the identification of aerosols from specific biogenic precursors.

Molecular Characterization of Cloud Water Samples Collected at the Puy de Dôme (France) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Cloud droplets contain dynamic and complex pools of highly heterogeneous organic matter, resulting from the dissolution of both water-soluble organic carbon in atmospheric aerosol particles and gas-phase soluble species, and are constantly impacted by chemical, photochemical, and biological transformations. Cloud samples from two summer events, characterized by different air masses and physicochemical properties, were collected at the Puy de Dôme station in France, concentrated on a strata-X solid-phase extraction cartridge and directly infused using electrospray ionization in the negative mode coupled with ultrahigh-resolution mass spectrometry. A significantly higher number (n = 5258) of monoisotopic molecular formulas, assigned to CHO, CHNO, CHSO, and CHNSO, were identified in the cloud sample whose air mass had passed over the highly urbanized Paris region (J1) compared to the cloud sample whose air mass had passed over remote areas (n = 2896; J2). Van Krevelen diagrams revealed that lignins/CRAM-like, aliphatics/proteins-like, and lipids-like compounds were the most abundant classes in both samples. Comparison of our results with previously published data sets on atmospheric aqueous media indicated that the average O/C ratios reported in this work (0.37) are similar to those reported for fog water and for biogenic aerosols but are lower than the values measured for aerosols sampled in the atmosphere and for aerosols produced artificially in environmental chambers.

Characterization of Fluorinated Polymers by Atmospheric-Solid-Analysis-Probe High-Resolution Mass Spectrometry (ASAP/HRMS) Combined with Kendrick-Mass-Defect Analysis.

Fluorinated polymers are a diverse and important class of polymers with unique applications. However, characterization of fluorinated polymers by conventional mass spectrometric methods is challenging because (i) their high fluorine contents make them insoluble or only sparingly soluble in most common solvents and (ii) commonly used matrices employed for MALDI do not desorb or ionize them efficiently. In this work, atmospheric-solid-analysis-probe (ASAP) high-resolution orbitrap mass spectrometry (HRMS) was used as a new tool for the molecular characterization of various fluorinated polymers, including polyvinylidene fluoride (PVDF) and fluorinated copolymers containing PVDF and chlorotrifluoroethylene (KEL-F 800) or PVDF and hexafluoropropylene (Viton A and Tecnoflon). The major peaks of the observed distributions were assigned compositions, but the high number of species required the use of an alternative method to treat such complex data. Kendrick-mass defects (KMD) were calculated on the basis of the "common-to-all" vinylidene difluoride repeating unit. By plotting the KMD as a function of the nominal Kendrick masses (NKM), specific patterns based on homologous series emerged. Kendrick maps were therefore drawn to simplify the mass spectra and provide confident peak assignments through homologous-series recognition. A specific fingerprint for each polymer has been identified, and the ability to discern the four species present in a blend through KMD analysis was demonstrated.

A systematic tandem mass spectrometric study of anion attachment for improved detection and acidity evaluation of nitrogen-rich energetic compounds.

The development of rapid, efficient, and reliable detection methods for the characterization of energetic compounds is of high importance to security forces concerned with terrorist threats. With a mass spectrometric approach, characteristic ions can be produced by attaching anions to analyte molecules in the negative ion mode of electrospray ionization mass spectrometry (ESI-MS). Under optimized conditions, formed anionic adducts can be detected with higher sensitivities as compared with the deprotonated molecules. Fundamental aspects pertaining to the formation of anionic adducts of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), 1,3,5-trinitro-1,3,5-triazinane (RDX), pentaerythritol tetranitrate (PETN), nitroglycerin (NG), and 1,3,5-trinitroso-1,3,5-triazinane energetic (R-salt) compounds using various anions have been systematically studied by ESI-MS and ESI tandem mass spectrometry (collision-induced dissociation) experiments. Bracketing method results show that the gas-phase acidities of PETN, RDX, and HMX fall between those of HF and acetic acid. Moreover, PETN and RDX are each less acidic than HMX in the gas phase. Nitroglycerin was found to be the most acidic among the nitrogen-rich explosives studied. The ensemble of bracketing results allows the construction of the following ranking of gas-phase acidities: PETN (1530-1458 kJ/mol) > RDX (approximately 1458 kJ/mol) > HMX (approximately 1433 kJ/mol) > nitroglycerin (1427-1327.8 kJ/mol).

LC-PDA/APCIitMS identification of algal carotenoid and oxysterol precursors to fatty acid esters in hydrolyzed extracts of the freshwater mussel Dreissena bugensis.

Carotenyl fatty acid esters (carotenyl-FAEs) were extracted in acetone from freeze-dried Dreissena bugensis (Lakes Erie and Ontario) and hydrolyzed to identify the carotenoid precursors. Analysis by liquid chromatography (LC) with photodiode array (PDA) and atmospheric pressure chemical ionization-ion trap mass spectrometry (APCIitMS) revealed the major hydrolysis products: fucoxanthinol (FOH) from fucoxanthin (FX, diatoms); mactraxanthin (MX) from violaxanthin (VX, chlorophytes); 4-fold higher levels of an unknown, tentatively identified as an adduct of two closely eluting C27H46O3 and C27H48O3 steryl triols. Enzymatic hydrolysis (Candida rugosa) of dreissenid extracts yielded FOH and MX, but residual carotenyl-FAEs remained. Alkaline hydrolysis yielded isoFOH, MX, and steryl triols, without residual carotenyl-FAEs: isoFOH decreased, but two FOH hemiketal by-products increased, when the dose of potassium hydroxide in methanol was too high. The PDA detector profiled carotenyl-FAEs and products of enzymatic and alkaline hydrolysis, without interference. The APCIitMS detector revealed carotenoid and oxysterol products of alkaline hydrolysis but was adversely affected by background from bile salts used for enzymatic hydrolysis. LC retention times and elution order were correlated to solubility parameters, calculated from the analyte structure, to cross-check MS interpretations. A multiple linear regression of LC retention times on solubility parameters for 12 carotenoid standards included FOH, isoFOH, and MX (r 2 0.97). The model revealed the close similarity of polar carotenoid metabolites to C27-steryl triols tentatively identified by APCIitMS, suggesting that further LC-MS analyses would be beneficial, to explicitly link oxysterols and the polar carotenoids, as metabolites of algal precursors in the dreissenid diet. Graphical abstract Methods of analysis and major neutral products of hydrolysis from fatty acid esters in D. bugensis.

Separation and identification of fatty acid esters of algal carotenoid metabolites in the freshwater mussel Dreissena bugensis, by liquid chromatography with ultraviolet/visible wavelength and mass spectrometric detectors in series.

LC with photodiode array and APCI-ion trap mass spectrometry has made it possible to tentatively identify 76 carotenyl fatty acid esters (cFAEs) in solvent extracts from Dreissena bugensis, collected from Lake Erie: 16 mono- and 33 diFAEs of fucoxanthinol (FOH), and 27 diFAEs of mactraxanthin (MX). FOH and MX, previously identified in cFAE hydrolysates, were confirmed as parent carotenoids of the cFAEs, and as primary metabolites of fucoxanthin and violaxanthin, respectively, derived from diatoms and chlorophytes in the dreissenids' diet. The most abundant fatty acid substituents of cFAEs were 16:0 and 16:1; abundant fatty acid biomarkers were 16:1 and 20:5, from diatoms, and 17:0, from bacteria. Cleanup of solvent extracts by solid phase extraction (Florisil) was necessary to reduce neutral background lipids, which interfered with detection of MX-diFAEs by APCI(+), and detection of FOH-diFAEs by APCI(+/-). The FOH-monoFAEs, MX-diFAEs and FOH-diFAEs were found to elute in a well-defined chromatographic order, by two regression models for retention times increasing as a function of: i) increasing number of carbons but decreasing number of double bonds in the fatty acid and decreasing number of non-esterified OH-groups on the parent carotenoids; ii) increasing dispersive but decreasing polar and hydrogen-bonding interactions, described by solubility parameters calculated for each cFAE. The best separations of the dreissenid cFAEs, with free OH-groups decreasing from four to one, were achieved between 20 and 68min, using a C18-column and moderately polar mobile phase (acetone, water), to obtain a reverse-phase gradient with a 56% decrease in hydrogen-bonding interactions.

Combined use of direct analysis in real-time/Orbitrap mass spectrometry and micro-Raman spectroscopy for the comprehensive characterization of real explosive samples.

Direct Analysis in Real Time (DART™) high-resolution Orbitrap™ mass spectrometry (HRMS) in combination with Raman microscopy was used for the detailed molecular level characterization of explosives including not only the charge but also the complex matrix of binders, plasticizers, polymers, and other possible organic additives. A total of 15 defused military weapons including grenades, mines, rockets, submunitions, and mortars were examined. Swabs and wipes were used to collect trace (residual) amounts of explosives and their organic constituents from the defused military weapons and micrometer-size explosive particles were transferred using a vacuum suction-impact collection device (vacuum impactor) from wipe and swap samples to an impaction plate made of carbon. The particles deposited on the carbon plate were then characterized using micro-Raman spectroscopy followed by DART-HRMS providing fingerprint signatures of orthogonal nature. The optical microscope of the micro-Raman spectrometer was first used to localize and characterize the explosive charge on the impaction plate which was then targeted for identification by DART-HRMS analysis in both the negative and positive modes. Raman spectra of the explosives TNT, RDX and PETN were acquired from micrometer size particles and characterized by the presence of their characteristic Raman bands obtained directly at the surface of the impaction plate nondestructively without further sample preparation. Negative mode DART-HRMS confirmed the types of charges contained in the weapons (mainly TNT, RDX, HMX, and PETN; either as individual components or as mixtures). These energetic compounds were mainly detected as deprotonated species [M-H](-), or as adduct [M + (35)Cl](-), [M + (37)Cl](-), or [M + NO3](-) anions. Chloride adducts were promoted in the heated DART reagent gas by adding chloroform vapors to the helium stream using an "in-house" delivery method. When the polarity was switched to positive mode, DART-HRMS revealed a very complex distribution of polymeric binders (mainly polyethylene glycols and polypropylene glycols), plasticizers (e.g., dioctyl sebacate, tributyl phosphate), as well as wax-like compounds whose structural features could not be precisely assigned. In positive mode, compounds were identified either as protonated molecules or ammonium adduct species. These results clearly demonstrate the complementarity of micro-Raman microscopy combined with DART-MS. The former technique provides structural information on the type of explosives present at the surface of the sample, whereas the latter provides not only a confirmation of the nature of the explosive charge but also useful additional information regarding the nature of the complex organic matrix of binders, plasticizers, polymers, oils, and potentially other organic additives and contaminants present in the sample. Combining these two techniques provides a powerful tool for the screening, comprehensive characterization, and differentiation of particulate explosive samples for forensic sciences and homeland security applications. Graphical Abstract Comprehensive characterization of explosive particles collected from swipe samples by micro-Raman and DART™-HRMS.

Use of experimental design in the investigation of stir bar sorptive extraction followed by ultra-high-performance liquid chromatography-tandem mass spectrometry for the analysis of explosives in water samples.

A method for the sensitive quantification of trace amounts of organic explosives in water samples was developed by using stir bar sorptive extraction (SBSE) followed by liquid desorption and ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The proposed method was developed and optimized using a statistical design of experiment approach. Use of experimental designs allowed a complete study of 10 factors and 8 analytes including nitro-aromatics, amino-nitro-aromatics and nitric esters. The liquid desorption study was performed using a full factorial experimental design followed by a kinetic study. Four different variables were tested here: the liquid desorption mode (stirring or sonication), the chemical nature of the stir bar (PDMS or PDMS-PEG), the composition of the liquid desorption phase and finally, the volume of solvent used for the liquid desorption. On the other hand, the SBSE extraction study was performed using a Doehlert design. SBSE extraction conditions such as extraction time profiles, sample volume, modifier addition, and acetic acid addition were examined. After optimization of the experimental parameters, sensitivity was improved by a factor 5-30, depending on the compound studied, due to the enrichment factors reached using the SBSE method. Limits of detection were in the ng/L level for all analytes studied. Reproducibility of the extraction with different stir bars was close to the reproducibility of the analytical method (RSD between 4 and 16%). Extractions in various water sample matrices (spring, mineral and underground water) have shown similar enrichment compared to ultrapure water, revealing very low matrix effects.

Development and validation of an isotope dilution ultra-high performance liquid chromatography tandem mass spectrometry method for the reliable quantification of 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) and 14 other explosives and their degradation products in environmental water samples.

A comprehensive method for the determination and characterization of 15 common explosive compounds in water samples by ultra-high pressure liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (APCI-MS/MS) is presented. The method allows the determination of 10 nitroaromatics, two nitroamines and three nitrate ester compounds. Among these, 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) was quantified and detected for the first time in our knowledge at trace levels (0.2 µg/L). Furthermore, the collision induced dissociation (CID) mass spectrum of TATB is discussed and a fragmentation mechanism is proposed. The signal for each explosive was normalized by isotopically-enriched congeners used as internal standards. The limits of detection (LOD) reached 20 ng/L, depending on the type of energetic molecule, which are adequate for water samples and the linearity was verified from 1.4 to 2 orders of magnitude. The sensitivity of the UHPLC-APCI-MS/MS approach allows direct injection of aqueous samples without preceding extraction for concentration. Besides, the method displays a good reliability with low signal suppression in various matrices such as spring water, mineral water, acidified water or ground water. The effectiveness of the method is demonstrated by the analysis of underground water samples containing traces of explosives from test fields in France.

Quantitative analysis of phosphoric acid esters in aqueous samples by isotope dilution stir-bar sorptive extraction combined with direct analysis in real time (DART)-Orbitrap mass spectrometry.

A novel hyphenated technique, namely the combination of stir bar sorptive extraction (SBSE) with isotope dilution direct analysis in real time (DART) Orbitrap™ mass spectrometry (OT-MS) is presented for the extraction of phosphoric acid alkyl esters (tri- (TnBP), di- (HDBP), and mono-butyl phosphate (H2MBP)) from aqueous samples. First, SBSE of phosphate esters was performed using a Twister™ coated with 24 µL of polydimethylsiloxane (PDMS) as the extracting phase. SBSE was optimized for extraction pH, phase ratio (PDMS volume/aqueous phase volume), stirring speed, extraction time and temperature. Then, coupling of SBSE to DART/Orbitrap-MS was achieved by placing the Twister™ in the middle of an open-ended glass tube between the DART and the Orbitrap™. The DART mass spectrometric response of phosphate esters was probed using commercially available and synthesized alkyl phosphate ester standards. The positive ion full scan spectra of alkyl phosphate triesters (TnBP) was characterized by the product of self-protonation [M+H](+) and, during collision-induced dissociation (CID), the major fragmentation ions corresponded to consecutive loss of alkyl chains. Negative ionization gave abundant [M-H](-) ions for both HDnBP and H2MnBP. Twisters™ coated with PDMS successfully extracted phosphate acid esters (tri-, di- and mono-esters) granted that the analytes are present in the aqueous solution in the neutral form. SBSE/DART/Orbitrap-MS results show a good linearity between the concentrations and relative peak areas for the analytes in the concentration range studied (0.1-750 ng mL(-1)). Reproducibility of this SBSE/DART/Orbitrap-MS method was evaluated in terms of %RSD by extracting a sample of water fortified with the analytes. The %RSDs for TnBP, HDnBP and H2MnBP were 4, 3 and 3% (n=5) using the respective perdeuterated internal standards. Matrix effects were investigated by matrix matched calibration standards using underground water samples (UWS) and river water samples (RWS). Matrix effects were effectively compensated by the addition of the perdeuterated internal standards. The application of this new SBSE/DART/Orbitrap-MS method should be very valuable for on-site sampling/monitoring, limiting the transport of large volumes of water samples from the sampling site to the laboratory.

Capabilities and limitations of direct analysis in real time orbitrap mass spectrometry and tandem mass spectrometry for the analysis of synthetic and natural polymers.

RATIONALE: Despite the widespread use of direct analysis in real time mass spectrometry (DART-MS), its capabilities in terms of accessible mass range and the types of polymers that can be analysed are not well known. The goal of this work was to evaluate the capabilities and limitations of this ionization technique combined with orbitrap mass spectrometry and tandem mass spectrometry, for the characterization (structural and polydispersity metrics) of various synthetic and natural polymers. METHODS: The capabilities and limitations of DART-MS (and -MS(2)), using an orbitrap mass spectrometer, for polymer analysis were evaluated using various industrial synthetic polymers and biopolymers. Stainless steel mesh screens secured on a movable rail were used as the sampling surface, onto which 5 µL of various polymers dissolved in tetrahydrofuran were added. Assignment of spectral features and calculation of molecular weight and polydispersity metrics were performed using Polymerix™ software and the results were compared with those obtained by gel-permeation chromatography (GPC). RESULTS: Protonated oligomers and ammonium adducts were instantaneously detected as the major ionisation products in positive ion mode. Only perfluoropolyethers (PFPEs) were ionised in negative mode and detected as [M](-·) ions. Only singly charged molecular species were observed for all oligomers under study, allowing for a rapid determination of the molecular weight and polydispersity metrics of polymers. At elevated DART gas temperatures (400-500°C) the molecular weight and polydispersity metrics compared fairly well with those obtained by GPC, with polymers whose masses ranged from 200 g x mol(-1) to 4000 g x mol(-1). CONCLUSIONS: DART-MS allowed the direct and rapid analysis (mass spectra and tandem mass spectra of all the polymers were acquired in seconds) based on the exact masses of their [M+H](+) and [M+NH4](+) ions (in the positive mode) or [M](-·) ions (for polymers having a high sensitivity toward electron-capture ionisation such as PFPEs), as well as the exact masses of their product ions, for both synthetic and natural polymers under ambient conditions without any sample pre-treatment.

A new liquid chromatography/electrospray ionization mass spectrometry method for the analysis of underivatized aliphatic long-chain polyamines: application to diatom-rich sediments.

Natural polyamines are found in all three domains of life and long-chain polyamines (LCPAs) play a special role in silicifying organisms such as diatoms and sponges where they are actively involved in the complex formation and nanopatterning of siliceous structures. With chain lengths extending up to 20 N-methylated propylamine repeat units, diatom LCPAs constitute the longest natural polyamines. Mixtures of natural LCPAs are typically purified in bulk using ion-exchange, size-exclusion and dialysis and then analyzed either by direct infusion mass spectrometry or by MALDI-TOF. Here, we describe a novel ion-pairing liquid chromatographic method that allows baseline separation, detection and structural elucidation of underivatized aliphatic methylated and non-methylated LCPAs with a wide range of chain lengths. Complete separation of synthetic mixtures of LCPA species differing by either a propylamine or an N-methylpropylamine unit is achievable using this method and chromatographic separation of natural, diatom frustule bound LCPAs extracted from sediment core samples is greatly improved. Using electrospray ionization mass spectrometry (ESI-MS), we detected singly [M+H](+) and multiply [M+nH](n+) charged protonated ions. The abundance of multiply charged LCPA species increased linearly as a function of LCPA chain length (N) and multiprotonated ions [M+nH](n+) were more abundant for longer chain polyamines. The abundance of multiply charged LCPAs along with the concomitant disappearance of the singly charged protonated molecular ion significantly increases the complexity of the MS spectra, justifying the need for good chromatographic separation of complex LCPA mixtures. This analytical procedure will likely constitute a powerful tool for the characterization, quantification, as well as the purification of individual LCPAs in natural and synthetic samples for studies of silica precipitation as well as nitrogen and carbon isotopic analysis used in paleoceanographic studies.