Direct Temperature-resolved Mass Spectrometry Research Articles

Secco painting technique revealed in non-restored Pompeian murals by analytical and imaging techniques

The fresco technique appears to have been widely used on Roman mural paintings. The close observation of many of such murals suggests, however, the application of a secco technique over the fresco background. In this work, for the first time, fragments from Pompeian mural paintings that had never been restored have been investigated by optical microscopy, reflectance transformation imaging, micro-Energy-Dispersive X-Ray Fluorescence, micro-Fourier Transform Infrared Spectroscopy, and Direct Temperature-resolved Mass Spectrometry. A small number of fragments from restored paintings from the same Archaeological Park was also analyzed by the same techniques for the sake of comparison. The results of this multi-analytical approach that involves - for the first time on this type of samples - scientific photographic investigation, point out to the use of a protein-based medium, most probably egg, to execute the secco layers. On the other hand, wax was ubiquitous in samples taken from restored mural paintings. This last evidence further highlights the importance of selecting appropriate candidates for the study of original organic binders.

Identification of Synthetic Organic Pigments (SOPs) Used in Modern Artist's Paints with Secondary Ion Mass Spectrometry with MeV Ions.

This work reports on the first systematic study using secondary ion mass spectrometry with MeV ions (MeV-SIMS) for analysis of synthetic organic pigments (SOPs) that can be usually found in modern and contemporary art paints. In order to prove the applicability of the method to different chemical classes of SOPs, 17 pigments were selected for the analyses. The focus was on blue and green phthalocyanines, yellow and red (naphthol AS) azo pigments, red quinacridone, anthraquinone, and diketopyrrolo-pyrrole pigments. Since there are no reference spectra available for this technique, pure pigment powders were measured first to create a database. Simple two-component paint systems were also prepared for testing purposes by mixing synthetic organic pigments with alkyd and acrylic binders. Commercial paints that contain the SOPs with identical C.I. numbers as in the prepared two-component samples were analyzed. All pigments were successfully identified in commercial products in the MeV-SIMS mass spectra through molecular and larger specific fragment ion peaks in the positive-ion mode. The main advantages of MeV-SIMS over other techniques used in SOPs identification, like pyrolysis gas chromatography mass spectrometry (Py-GC/MS), direct-temperature resolved mass spectrometry (DTMS), and laser desorption ionization mass spectrometry (LDIMS), can be summarized as follows: (i) pigments and binders can be detected simultaneously in the same mass spectrum acquired over a short measurement time (up to 500 s), (ii) only small sample flakes are required for the measurements, which are analyzed without any chemical treatment prior to the analyses, (iii) samples are not consumed during the analyses and can be reused for other measurements, e.g., multielemental analysis by other ion beam analysis (IBA) techniques, such as particle-induced X-ray emission (PIXE). Compared to, e.g., Raman spectroscopy, the significant benefit of MeV-SIMS is the exact identification of the SOPs in the paints even if pigments of similar structures are measured.

Revealing the composition of organic materials in polychrome works of art: the role of mass spectrometry-based techniques.

The most recent advances in the identification and determination of organic constituents in paintings and other polychrome objects using mass spectrometry (MS)-based techniques are reviewed. The latest achievements in gas chromatography (GC)-MS and pyrolysis (Py-) GC-MS are mainly related to sample pretreatment protocols and to the employment of double-shot or laser desorption pyrolysis, respectively. MS techniques based on soft ionization methods such as matrix assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) are discussed. So far, MALDI and ESI MS have been mainly used in the characterization of proteinaceous materials, but further applications are definitely emerging, e.g., in the fields of lipids, resins, and organic colorants analysis. Chemical imaging by time-of-flight secondary ion mass spectrometry (TOF SIMS), formerly applied to the detection and localization of lipid binders and inorganic materials, has been recently extended to proteins. Finally, the potential of niche techniques such as direct temperature resolved mass spectrometry (DTMS) and direct analysis in real time (DART) MS are outlined.

Analysis of old master paintings by direct temperature-resolved time-of-flight mass spectrometry: Some recent developments

Direct temperature-resolved mass spectrometry (DTMS) is an analytical technique in which small (μg) amounts of sample are applied to a filament and introduced into the ion source of a mass spectrometer. It is a fast fingerprinting method particularly suitable for the characterization of oils, resins, waxes, and other compound classes in tiny complex samples from paintings. DTMS results reported thus far have been obtained using instruments with nominal mass resolution. Higher mass resolutions can be achieved by magnetic sector mass spectrometers only at the expense of a severe loss of sensitivity. Modern time-of-flight mass spectrometers, however, do provide both high resolution and high sensitivity simultaneously. The availability of accurate mass information adds another dimension to DTMS. The difference between the nominal and accurate mass, the mass defect, may be graphically presented in so-called ‘Kendrick plots’. These can be used as fingerprints, enabling a quick overview of the main features in high-resolution mass spectra of complex mixtures. This paper combines DTMS with Kendrick mass defect analysis applied to a series of reference compounds commonly found in paintings. Finally, we also present the results of analysis of samples taken from the 17th-century painting of Saul and David by Rembrandt van Rijn (Mauritshuis, The Hague) that has been recently subjected to extensive conservation treatment.

Microscopic, mass spectrometric and spectroscopic characterisation of the mordants used for gilding on wall paintings from three post-Byzantine monasteries in Thessalia, Greece

The main churches of three monasteries in Thessalia, Central Greece are decorated with wall paintings from the post-Byzantine period. The main goal of the present study is to offer insights into the decorative technique of mordant gilding, especially the chemical composition of the mordants and the effects on them of ageing. Light microscopic (LM) examination was carried out on samples taken from the gilded areas of the paintings to view their layer build-up. Direct temperature resolved mass spectrometry (DTMS) under electron ionisation (EI) and chemical ionisation (CI) conditions led to the identification mainly of the organic, as well as some inorganic compounds. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) gave an account of the elemental composition on selected cases. The results from samples taken from different wall paintings were compared with each other to observe their differences and similarities. Furthermore, the three churches in question are believed to have been painted by the same painter, who has only been identified in one of them. Hence, the comparison of the wall paintings as far as the mordant gilding technique is concerned provided additional evidence on the identity of the painter in the other two churches.

Characterisation of the transparent surface coatings on post-Byzantine icons using microscopic, mass spectrometric and spectroscopic techniques

Icons are frequently covered with superimposed transparent layers of varnish and glaze that often obscure their image and disrupt their study and conservation treatment. Using a combination of microscopic, mass spectrometric and spectroscopic techniques, a micro-analytical methodology was developed for the characterisation of these surface coatings. More specifically, light microscopy (LM), electron ionisation direct temperature resolved mass spectrometry (EI-DTMS), pyrolysis gas chromatography mass spectrometry (Py-GC/MS), imaging Fourier transform infrared spectroscopy (imaging-FTIR) and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX) were used to investigate the coatings present on the surface of five Greek post-Byzantine icons. The results showed that the aged layers of varnish and glaze contain various mixtures of materials, including diterpenoid (DTP) and triterpenoid (TTP) resins, linseed oil, lead-containing dryers, egg, and beeswax. This study also elucidated issues regarding the initial application and the later interventions on those coatings, their interaction with each other, as well as some effects observed on the underlying paint layers.

The use of direct temperature-resolved mass spectrometry (DTMS) in the detection of organic pigments found in acrylic paints used by Sam Francis

When analyzed in the dry, powdered form, most of the hundreds of modern synthetic organic pigments that have been introduced throughout the 20th century can be effectively characterized by direct temperature-resolved mass spectrometry (DTMS) [S.Q. Lomax, M. Schilling, T. Learner, in: T. Learner, P. Smithen, J.W. Krueger, M. Schilling (Eds.), Modern Paints Uncovered, Getty Conservation Institute, Tate Modern, London, 2007, p. 105]. However, their detection in paint formulations is often far more difficult, as these pigments are usually present in only very low concentrations, due to their relatively high tinting strengths. The situation is also more complex when one attempts to identify these pigments from microscopic samples of paint taken from actual works of art, due to the frequent manipulation, mixing, or adulteration of paints by artists during their application. A project aiming to characterize the wide range of pigments found in the paints of Sam Francis (American, 1923–1994) prompted work to investigate more fully the sensitivity of a DTMS system by comparing various ionization conditions, including electron impact (EI) at 70 and 16 eV, and chemical ionization (CI) with iso-butane in both positive- and negative-ion modes. Overall, it was found that negative-ion CI conditions showed the best results for detecting the majority of synthetic organic pigments tested: the very limited fragmentation it produced in most of the pigments resulted in a much stronger and more readily detectable molecular ion that could be more easily distinguished from the lower m/ z-value ions typically coming from other components in the paints.

A direct temperature-resolved tandem mass spectrometry study of cholesterol oxidation products in light-aged egg tempera paints with examples from works of art

Cholesterol ( 1) constitutes approximately 5% of the lipid fraction of eggs. The compound is therefore abundant in fresh egg tempera paints. The fate of cholesterol upon light ageing of egg tempera paint binding medium was investigated by direct temperature resolved mass spectrometry (DTMS) and tandem mass spectrometry (DTMSMS). Cholesterol oxidation products (COPs) such as 5,6-epoxycholestan-3-ol ( 2) and 3-hydroxycholest-5-en-7-one ( 3) were positively identified in light-aged egg binding medium. Given the fast rate of oxidation of cholesterol, the corresponding oxidation products are better markers for egg tempera than the cholesterol molecule itself. Cholesterol and COPs were discovered in paints on German baroque altar pieces from the 16th and 18th C and in a 20th C glaze on a Mark Rothko Seagram Mural painting at Tate by DTMS fingerprinting analysis of paint microsamples.

Direct temperature mass spectrometric study on the depth-dependent compositional gradients of aged triterpenoid varnishes

The depth profiles of aged dammar and mastic films, which were uncovered by optimized KrF excimer laser ablation (248 nm, 25 ns), were examined by direct temperature-resolved mass spectrometry (DTMS). The results establish the generation of depth-dependent compositional gradients in triterpenoid resins as a consequence of aging, for the first time on the molecular level. Electron ionization DTMS total ion currents show that the required temperature to volatilize the polar compounds and the relative amount of pyrolysis products of the high molecular weight condensed fraction is reduced when the upper layer of varying thickness of the films had been removed by the laser. The relative abundance of characteristic ion fragments of known oxidized triterpenoid compounds gradually decreased with depth. In contrast, the ion fragments of original resin molecules became more abundant with depth. The mass spectra of the bulk of the films resembled that of the control samples, which were not subjected to aging. Multivariant factor discriminant analysis quantified the oxidative gradients and showed that a depth of 15 μm from the surface of the aged films is the threshold between highly and much less deteriorated material.

Evaluation of the “added value” of SIMS: A mass spectrometric and spectroscopic study of an unusual Naples yellow oil paint reconstruction

Naples yellow-containing oil paints aged under natural and artificial conditions were investigated as model systems to evaluate the potential of secondary ion mass spectrometry (SIMS) when used in combination with other mass spectrometric and spectroscopic analytical methods. Although the advantage of SIMS is the simultaneous detection of organic and inorganic components and their spatial distribution, the methodology has limitations in compound sensitivity and shows bias towards certain constituents. Gas chromatography–mass spectrometry (GC/MS) shows dicarboxylic fatty acids to be main components in the paint, but SIMS detects these compounds poorly. Electrospray ionisation mass spectrometry (ESI-MS) shows a broad range of glyceryl derivatives of mono- and dicarboxylic fatty acids (mono-, di- and triglyceride derivatives), while SIMS only detects the mono- and diglycerides of the monocarboxylic acids. Compared to SIMS, direct temperature-resolved mass spectrometry (DTMS) offers greater insight into how the various constituents are incorporated into the paint film, but SIMS data supports the information provided by Fourier transform infrared (FTIR) on metal soap formation. The surface sensitivity of SIMS is an advantage for probing paint constituent distributions and was exploited to examine variations in the composition of the top and bottom of a paint film, and the spatial correlation between metal and fatty acid composition in metal soap aggregates. Disadvantages of SIMS are the low yields and matrix dependency of the organic species in the paint matrix. Application of an ultra-thin gold coating overcomes this, and enhances the organic secondary ion yields leading to more accurate spatial distribution.

Photodegradation of estuarine dissolved organic matter: a multi-method assessment of DOM transformation

A multi-method approach was applied to study changes in dissolved organic matter (DOM) at three estuarine sites with varying salinity, as well as changes resulting from experimental photodegradation. Following measurement of ultraviolet and visible absorption spectra of bulk samples, DOM was isolated using C18 solid phase extraction. The extract was characterized using high performance size exclusion chromatography (HP-SEC) and molecular level characterization was conducted via direct temperature-resolved mass spectrometry (DT-MS) and electrospray ionization mass spectrometry (ESI-MS). The molecular weight distribution of DOM as determined from HP-SEC and ESI-MS varied between techniques, but generally decreased down estuary and with photodegradation for both approaches. Relative differences in molecular weight were significantly correlated with the ratio of absorption coefficients at 254/365nm. Additionally, photobleaching was significantly correlated with mass spectral characteristics from both DT-MS and ESI-MS. Principal component analysis of DT-MS spectra showed that photoexposure removed different mass spectral characteristics depending on sampling site; however, upon photodegradation, the mass spectral characteristics of both marine DOM and terrestrially dominated DOM approached a common spectrum. We interpret this spectrum, characterized by fragments from aromatic and carbohydrate-like precursors, as photochemically refractory DOM. Our results show that multiple approaches that characterize different aspects of DOM can provide complementary information about its sources and transformation. More specifically, photobleaching results in decreased light absorbance, decreased molecular weight and shifts in the relative abundance of classes of compounds (and broad shifts in m/z values); moreover, these transformations result in photodegraded samples from a low-salinity site which are compositionally similar to samples collected from a mid-salinity site further downstream.

Dissolved organic matter characteristics within the Lake Superior watershed

Within the aquatic carbon cycle, dissolved organic carbon (DOC) plays key roles: as a link between terrestrial and aquatic systems, a major food source for biota, a player in photochemical reactions and a sunscreen/competitor for light for aquatic organisms. The molecular-level composition of the dissolved organic matter (DOM) is believed to determine the efficacy of DOM in these roles. While much detailed compositional information is available on selected DOM isolates from both freshwater and marine systems, relatively few studies have presented molecular information for multiple sites within the same system and few of these have focused upon large lakes. Therefore, we present an initial study of surface water DOM characteristics in a temperate large lake (Lake Superior, USA) and selected tributaries. UV–visible spectroscopy, electrospray mass spectrometry and Fourier transform infrared spectroscopy (FTIR) analyses of bulk DOM, along with FTIR and direct temperature-resolved mass spectrometry analyses of C 18 extracts, illustrate a shift from higher molecular weight organic matter enriched in protein and lignin at the tributary sites toward compositionally different material in the open lake. Differences in optical characteristics and DOC concentration between tributary and open lake sites are consistent with possible photodegradation of tributary DOM. Comparison of our FTIR data with those from a previous Chesapeake Bay study indicates that DOM in both the freshwater tributaries and the open lake contain a wider range of aromatic and carbohydrate components than that in the saltwater tributary and bay. This highlights the need for further cross system comparisons of natural organic matter composition.

Evaluating the photoalteration of estuarine dissolved organic matter using direct temperature-resolved mass spectrometry and UV-visible spectroscopy

Direct temperature-resolved mass spectrometry (DT-MS) was used to evaluate the molecular-level photodegradation of dissolved organic matter (DOM) isolated from three sites in a Chesapeake Bay subestuary (swamp- and marsh-influenced up-river, midestuarine, and bay mouth). From each site, filtered (<0.1 or <0.2 μm) water samples were irradiated in solarsimulated ultraviolet light followed by isolation of the DOM using C18-solid-phase extraction and subsequent DT-MS analysis. To provide background DOM photoreactivity data for the water samples, we also determined dissolved inorganic carbon (DIC) photoproduction and chromophoric dissolved organic matter (CDOM) photobleaching. DIC photoproduction was correlated with initial DOM light absorbance, initial dissolved organic carbon (DOC) concentration, and photobleaching. Changes in DT-MS characteristics within the extracts (in particular, the loss of an “aromatic” signal believed to be from reworked terrestrial material) were found to correlate linearly with the absorbance of the corresponding water samples. A relationship between photobleaching and DT-MS characteristics was also observed, with the upstream samples asymptotically approaching a constant “molecular-level” value as photobleaching increased. Both relationships appeared to be independent of absorbance wavelength in the ultraviolet. Following irradiation, the swamp/marsh-dominated upstream samples resembled the down-stream samples in terms of absorption spectra and MS-determined molecular-level characteristics. These shifts indicate that terrestrially-derived DOM may be more difficult to differentiate from marine DOM upon photodegradation, which has implications regarding evaluating the terrestrial impact within the marine DOM pool.

A laboratory simulation of the carbonization of sunflower achenes and seeds

The current project describes physical and chemical alterations that result from the thermal exposure of sunflower achenes and seeds. Specifically, achenes and seeds were heated at temperatures ranging from 130 to 600 °C under anoxic conditions for 60 min. Changes were measured in mass, relative percentages of C and N, internal and external morphology, molecular composition by direct temperature-resolved mass spectrometry (DTMS) under EI conditions, and the reflectance on polished specimens. The main constituents of sunflower seeds are lipids and protein, while the pericarps or hulls enclosing the seeds have a ligno-cellulosic structure. The morphology of achenes and seeds remains intact following exposure which makes the identification of the residues possible. The results of the sunflower experiments were compared to previous experiments conducted with peas and wheat grains. Up to approximately 340 °C, the molecular conversion of polysaccharide and protein rich peas and wheat grains follow similar pathways, while the lignin present in sunflower achenes follows its own unique pathway, resulting in a different molecular composition. At higher temperatures the molecular composition of the three propagules becomes identical. In addition the reflectance of the three propagules is identical confirming the similarity in molecular composition. Lipids show a different behaviour compared to the other three biopolymers; from 370 °C no oils are observed in the heated specimens and the DTMS-EI measurements show no lipid markers. Apart from evaporation of the triacylglycerides it is suggested that steroids have a high resistance against thermal degradation and are converted into aromatic moieties.

Identifying biomolecular origins of solid organic residues preserved in Iron Age Pottery using DTMS and MVA

The chemical characterisation of solid organic residues found in ceramic vessels, can provide archaeologists with valuable information about ancient diets. Although several selective analytical techniques have been applied to the analysis of specific classes of compounds, such as extractable lipids, waxes, terpenoids and protein fragments, a non-selective analytical technique is required to characterise and categorise complete solid organic residues. In this study, Direct Temperature-resolved Mass Spectrometry (DTMS) is used for the characterisation of 34 solid residues situated on vessels recovered from an indigenous settlement from the Roman period at Uitgeest – Groot Dorregeest (The Netherlands). Sample preparation is limited to grinding very small samples (5–10 μg) and suspending them in water. DTMS analysis of aliquots (1–2 μL) of this suspension gave information about a broad range of organic compounds, such as lipids, polynuclear aromatic hydrocarbons, markers for residual proteins and polysaccharides, and for newly formed complex condensed polymers. Multivariate analysis of the DTMS spectra identified five different chemotypes: groups of residues with comparable chemical characteristics. The biomolecular origin of each of these chemotypes is identified by comparison with experimentally charred reference materials. The chemotypes A 1 and A 2 consist of charred residues identified as starch-rich foods (mixed with animal or plant products), chemotype C consists of protein-rich charred animal products without starch, chemotype B contains smoke condensates from wood fires, and chemotype D consists of special protein-rich and lipid-free foods or non-food products.

Between Myth and Reality: Mummy Pigment from the Hafkenscheid Collection

A nineteenth-century mummy pigment (Hafkenscheid paint material collection) was analysed by direct temperature-resolved mass spectrometry (DTMS) and gas chromatography/mass spectrometry (GC/MS, Py-GC/MS, Py-TMAH-GC/MS). Megilp and asphalt (Hafkenscheid collection) reference samples were analysed under similar conditions. The mummy pigment investigated is complex. Py-GC/MS data indicated a pre-treated asphalt, i.e. only (di)benzothiophene- and traces of hopane-asphalt markers were left in the sample. DTMS, GC/MS and Py-TMAH-GC/MS results for the pigment pointed to the presence of slightly aged mastic resin and conifer resin and a complex lipid fraction. A poorly oxidized linseed oil and additions of beeswax, seen as long chain normal fatty acids, and another fat of a bacterial, fungal or human origin showing myristic acid, C6:1-C16:1 and C18:1 mono-unsaturated fatty acids, iso and anteiso fatty acids were found. The main components, mastic resin and linseed oil, suggest a megilp combined with a black mummy-like pigment. In spite of the degraded asphalt, the unusual fat and the beeswax found, a connection between Egyptian mummies and the Hafkenscheid mummy pigment cannot be proven.

Isolation and characterization of estuarine dissolved organic matter: Comparison of ultrafiltration and C 18 solid-phase extraction techniques

Characterization of dissolved organic matter (DOM) from aquatic environments has always been constrained by the ability to obtain a representative fraction of the DOM pool for analysis. Ultrafiltration or extraction, commonly using XAD or C 18 sorbents, is therefore generally used to concentrate and desalt DOM samples for further analyses. In this study, we compared ultrafiltration and C 18 solid-phase extraction disks (SPE) as DOM isolation methods for estuarine samples. We also evaluated the use of the C 18 SPE disks to isolate low-molecular-weight DOM (LMW-DOM) in the filtrate from ultrafiltration. The isolates from both methods and the LMW-DOM C 18-extracts were characterized using Fourier transform infrared spectroscopy (FTIR) and direct temperature-resolved mass spectrometry (DT-MS). Based on mass balance and blank measurements, we found that the C 18 SPE disks can be used to isolate bulk DOM and LMW-DOM from estuarine samples. FTIR and DT-MS analysis show that C 18-extracted DOM and ultrafiltered high-molecular-weight DOM (HMW-DOM) differ markedly in chemical composition. The HMW-DOM is enriched in (degraded) polysaccharides along with aminosugars when compared with the C 18-extracted DOM. The C 18-extracted DOM appears enriched in aromatic compounds, probably from lignin and/or aromatic amino acids in proteins. C 18 SPE of LMW-DOM samples from ultrafiltration increases the recovery of DOM from the total sample up to about 70%, compared to around 50% using ultrafiltration alone. Thus, a majority of the DOM can be isolated from estuarine samples by a combination of these techniques.

Changes in dissolved organic matter characteristics in Chincoteague Bay during a bloom of the pelagophyteAureococcus anophagefferens

Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, occurs in coastal bays along the northeast coast of the United States. This species was identified in Chincoteague Bay, Maryland, in 1997 and has bloomed there since at least 1998. Time series of dissolved organic matter (DOM) concentrations and characteristics are presented for two sites in Chincoteague Bay: one that experienced a brown tide bloom in 2002 and one that did not. Characteristics of the bulk DOM pool were obtained using dissolved organic carbon (DOC) and ultraviolet-visible (UV-Vis) measurements (spectral slope and specific UV absorbance). High molecular weight DOM (HMW-DOM) was characterized in terms of DOC concentration, carbon: nitrogen (C:N) ratio, isotopic signature, and molecular-level characteristics as determined by direct temperature resolved mass spectrometry (DT-MS). Compositional changes in the DOM pool are associated with brown tide blooms, although a direct relationship between DOM characteristics and bloom development could not be confirmed. DOC measurements suggest that during the brown tide bloom, HMW-DOM was released into the surface water. UV-Vis analysis on the bulk DOM and molecular-level characterization of the HMW-DOM using DT-MS show that this material was optically active and more aromatic in nature. Based upon C:N ratio and HMW-DOC measurements, it appears that this HMW-DOM was more nitrogen enriched. Whether this material was released as exudates or was due to lysis ofA. anophagefferens could not be determined.

“Cellular” vs. “detrital” POM: a preliminary study using fluorescent stains, flow cytometry, and mass spectrometry

The mass of nonliving particulate organic matter (POM) in marine waters can be significantly greater than that in living cells, yet very little is known about the composition and ultimate fate of this “detrital” POM. In recent marine chemistry studies, flow cytometry has been used to provide further insights into the composition, source, and fate of chlorophyll-fluorescing POM (which includes living algal cells) vs. detrital POM within natural waters. In this study, we extend such morphological characterization of POM beyond the use of chlorophyll autofluorescence and particle size or light scatter. Instead, nucleic acid staining with SYTO-13 and flow cytometry sorting were used to identify and isolate “cellular” and “detrital” subclasses of POM from samples collected in the Lafayette River and the Elizabeth River (subestuaries in the lower Chesapeake Bay). The resulting subclasses, as well as aliquots of unsorted POM sample, were then analyzed by direct temperature-resolved mass spectrometry. We show that “cellular” and “detrital” subclasses differ significantly from each other, and that detrital POM appears chemically distinct from the bulk POM. We then suggest further applications for flow cytometry approaches in aquatic organic biogeochemistry.

Laboratory simulations of the transformation of peas as a result of heating: the change of the molecular composition by DTMS

Peas ( Pisum sativum L.) consist mainly of cotyledons and their bulk material is starch and proteins. Their structure is rather confined. Peas were heated at temperatures ranging from 130 to 700 °C under anoxic conditions for maximum 2 h. For each temperature a separate experiment was carried out in a pre-heated oven. Direct temperature-resolved mass spectrometry (DTMS) under electron impact (EI) and chemical ionization (CI, NH 3) conditions measured the molecular composition of each solid residue. Fourier-transform infrared (FTIR) spectroscopy was carried out on residues heated at higher temperatures. The resulting solid products of the heating process still show the original markers for polysaccharides and proteins up to 270 °C. Concurrently three phases can be considered, each characterized by its own products. The first phase, from 270 up to 310 °C, shows monosaccharides, protein fragments and aromatic compounds. The second phase, from 310 °C up to a transitional stage from 400 to 440 °C, releases various aromatic and heterocyclic compounds. The third phase at higher temperatures shows a highly C-enriched product that releases CO, CO 2, HCN, SO and SO 2. The EI and CI experiments fail to discriminate between the pyrolysis products of polysaccharides and proteins between 250 and 400 °C. FTIR shows in this temperature range the development of an aromatic network. An earlier classification based on the changes of the physical and bulk chemical properties as a function of the temperature corresponds well with the classification based on the molecular changes. Residues of heated peas, usually called carbonized peas, are found in the archaeological record. Our study suggests that peas should have been heated up to least 310 °C before their residues survive natural degradation processes.