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  • 1
    Language: English
    In: Analytical chemistry, 06 October 2015, Vol.87(19), pp.9563-6
    Description: The analysis of dissolved organic matter (DOM) using high-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) poses challenges in molecular formula assignment. The consideration of (13)C isotopes provides new insights into the consistent elemental formula solutions. Modern software helps to overcome misinterpretation, but false assignments of molecular classes to mass peaks have rarely been elucidated until now. It will be demonstrated that this can be important with formula assignments comprising exactly five nitrogen and two sulfur atoms in DOM data sets: the molecular class CHON5S2. The existence of such components in DOM under tripeptide Met-His-Cys formed with the formula C14H23O4N5S2 cannot be excluded; however, components containing 5 N and 2 S should be suspected to not be highly abundant. The true elemental compositions of such unusual "N5S2 moieties" were calculated using Suwannee River fulvic acid (SRFA) data from the literature and one data set from acidic pit lake pore water. The replacement of a H3N5S2 moiety with a (13)C1(12)C5O4 moiety explained more than 95% of the questionable "N5S2 moieties". This finding was proved by calculation of δ(13)C‰ values from relative peak intensities.
    Keywords: Software ; Computer Programs ; Lakes ; Fourier Transforms ; Data Sets ; Dissolved Organic Matter ; Porosity ; Mathematical Analysis ; Analysis (MD) ; Chemical Analysis (Ep) ; Chemical Analysis (Ed) ; Chemical Analysis (EC);
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    In: Limnology and Oceanography, March 2016, Vol.61(2), pp.445-459
    Description: The trend of increasing dissolved organic carbon (DOC) in surface waters motivated us to gain a mechanistic understanding of DOC exchange at the sediment water interface in lakes. We quantified seasonal DOC and solute fluxes under different redox conditions, in a small drinking water reservoir using sediment core incubations. Processes governing benthic DOC exchange were microbial production of DOC and interaction with mineral surfaces. Mobilization of DOC in anoxic sediments seemed to be closely linked to reductive dissolution of ferric minerals as shown by the strong positive correlation ( = 0.99) between DOC and Fe fluxes. Oxidized surface sediments were an efficient DOC trap where DOC was bound to ferric minerals. Redox conditions appeared to be the primary regulator of the DOC exchange, resulting in sedimentary uptake of DOC (−1.8 mmol m d) only under oxic conditions. DOC production was regulated by temperature, leading to higher DOC fluxes (up to 2.4 mmol m d) in summer. The sediment was a net sink of DOC (−0.2 tonnes yr) but this was small compared with the annual DOC load (15 tonnes yr) of the reservoir. However, the benthic DOC flux was about 10–20% of the dissolved carbon flux at the sediment–water interface, making it a significant process in the lake internal carbon cycle. Climate change is supposed to promote reducing conditions at the bottom of lakes, which might increase benthic DOC production in the future.
    ISSN: 0024-3590
    E-ISSN: 1939-5590
    Source: John Wiley & Sons, Inc.
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  • 3
    Language: English
    In: Limnology and Oceanography, 03/2016, Vol.61(2), pp.445-459
    Description: The trend of increasing dissolved organic carbon (DOC) in surface waters motivated us to gain a mechanistic understanding of DOC exchange at the sediment water interface in lakes. We quantified seasonal DOC and solute fluxes under different redox conditions, in a small drinking water reservoir using sediment core incubations. Processes governing benthic DOC exchange were microbial production of DOC and interaction with mineral surfaces. Mobilization of DOC in anoxic sediments seemed to be closely linked to reductive dissolution of ferric minerals as shown by the strong positive correlation ([r.sup.2] = 0.99) between DOC and Fe fluxes. Oxidized surface sediments were an efficient DOC trap where DOC was bound to ferric minerals. Redox conditions appeared to be the primary regulator of the DOC exchange, resulting in sedimentary uptake of DOC (-1.8 mmol [m.sup.-2] [d.sup.-1]) only under oxic conditions. DOC production was regulated by temperature, leading to higher DOC fluxes (up to 2.4 mmol [m.sup.-2] [d.sup.-1]) in summer. The sediment was a net sink of DOC (-0.2 tonnes [yr.sup.-1]) but this was small compared with the annual DOC load (15 tonnes [yr.sup.-1]) of the reservoir. However, the benthic DOC flux was about 10-20% of the dissolved carbon flux at the sediment-water interface, making it a significant process in the lake internal carbon cycle. Climate change is supposed to promote reducing conditions at the bottom of lakes, which might increase benthic DOC production in the future. doi: 10.1002/lno.10224
    Keywords: Carbon – Environmental Aspects ; Drinking Water – Environmental Aspects ; Reservoirs (Water) – Environmental Aspects;
    ISSN: Limnology and Oceanography
    E-ISSN: 00243590
    E-ISSN: 19395590
    Source: Wiley (via CrossRef)
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  • 4
    In: PLoS ONE, 2015, Vol.10(11)
    Description: An increasing number of studies constrain the importance of iron for the long-term retention of phosphorus (P) under anoxic conditions, i.e. the formation of reduced iron phosphate minerals such as vivianite (Fe 3 (PO 4 ) 2 ⋅8H 2 O). Much remains unknown about vivianite formation, the factors controlling its occurrence, and its relevance for P burial during early sediment diagenesis. To study the occurrence of vivianite and to assess its relevance for P binding, surface sediments of two hydrologically contrasting waters were analysed by heavy-liquid separation and subsequent powder X-ray diffraction. In Lake Arendsee, vivianite was present in deeper sediment horizons and not in the uppermost layers with a sharp transition between vivianite and non-vivianite bearing layers. In contrast, in lowland river Lower Havel vivianite was present in the upper sediment layers and not in deeper horizons with a gradual transition between non-vivianite and vivianite bearing layers. In both waters, vivianite occurrence was accompanied by the presence of pyrite (FeS 2 ). Vivianite formation was favoured by an elevated iron availability through a lower degree of sulphidisation and was present at a molar ratio of total sulphur to reactive iron smaller than 1.1, only. A longer lasting burden of sediments by organic matter, i.e. due to eutrophication, favours the release of sulphides, and the formation of insoluble iron sulphides leading to a lack of available iron and to less or no vivianite formation. This weakening in sedimentary P retention, representing a negative feedback mechanism (P release) in terms of water quality, could be partly compensated by harmless Fe amendments.
    Keywords: Research Article
    E-ISSN: 1932-6203
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  • 5
    Language: English
    In: Analytical Chemistry, Oct 6, 2015, Vol.87(19), p.9563(4)
    Description: The article describes the molecular formula assignments comprising exactly five nitrogen and two sulfur atoms in dissolved organic matter (DOM) data sets: the molecular class CHO[N.sub.5][S.sub.2] using using high-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). It is found that the presence of such components in DOM under tripeptide Met-His-Cys formed with the formula [C.sub.14][H.sub.23][O.sub.4][N.sub.5][S.sub.2] cannot be excluded, however, components containing 5 N and 2 S should not be assumed to be highly abundant.
    Keywords: Fourier Transforms – Usage ; Mass Spectrometry – Analysis ; Peptides – Chemical Properties
    ISSN: 0003-2700
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Analytical and Bioanalytical Chemistry, 2014, Vol.406(30), pp.7977-7987
    Description: Formula assignment is one of the key challenges in evaluation of dissolved organic matter analyses using ultrahigh resolution mass spectrometry (FTICR MS). The number of possible solutions for elemental formulas grows exponentially with increasing nominal mass, especially when non-oxygen heteroatoms like N, S or P are considered. Until now, no definitive solution for finding the correct elemental formula has been given. For that reason an approach from the viewpoint of chemical feasibility was elucidated. To illustrate the new chemical formula assignment principle, a literature data set was used and evaluated by simplified chemical constraints. Only formulas containing a maximum of one sulphur and five nitrogen atoms were selected for further data processing. The resulting data table was then divided into mass peaks with unique component solutions (singlets, representing unequivocal formula assignments) and those with two or more solutions (multiple formula assignments, representing equivocal formula assignments). Based on a [double bond equivalent (DBE) versus the number of oxygen atoms ( o )] frequency contour plot and a frequency versus [DBE minus o ] diagram, a new assessment and decision strategy was developed to differentiate multiple formula assignments into chemically reliable and less reliable molecular formulas. Using this approach a considerable number of reliable components were identified within the equivocal part of the data set. As a control, a considerable proportion of the assigned formulas deemed to be reliable correspond to those which would have been obtained by CH 2 -based Kendrick mass defect analysis. We conclude that formula assignment in complex mixtures can be improved by group-wise decisions based on the frequency and the [DBE minus o ] values of multiple formula assignments. Graphical Abstract A typical frequency versus [DBE − o] diagram and assessment of molecular classes for their reliability
    Keywords: FTICR MS ; DOM ; Formula assignment ; DBE minus ; Δ
    ISSN: 1618-2642
    E-ISSN: 1618-2650
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  • 7
    Language: English
    In: Analytical and Bioanalytical Chemistry, 2016, Vol.408(10), pp.2461-2469
    Description: Molecular formula assignment is one of the key challenges in processing high-field Fourier transform ion cyclotron resonance mass spectrometric (FT-ICR-MS) datasets. The number of potential solutions for an elemental formula increases exponentially with increasing molecular mass, especially when non-oxygen heteroatoms like N, S or P are included. A method was developed from the chemical perspective and validated using a Suwannee River Fulvic Acid (SRFA) dataset which is dominated by components consisting exclusively of C, H and O (78 % CHO). In order to get information on the application range and robustness of this method, we investigated a FT-ICR-MS dataset which was merged from 18 mine pit lake pore waters and 3 river floodplain soil waters. This dataset contained 50 % CHO and 18 % CHOS on average, whereas the former SRFA dataset contained only 1.5 % CHOS. The mass calculator was configured to allow up to five nitrogen atoms and up to one sulphur atom in assigning formulas to mass peaks. More than 50 % multiple-formula assignments were found for peaks with masses 〉 650 Da. Based on DBE −  O frequency diagrams, many CHO, CHOS 1 , CHON 1 and CHON 1 S 1 molecular series were ultimately assigned to many m / z and considered to be reliable solutions. The unequivocal data pool could thus be enlarged by 523 (6.8 %) CHOS 1 components. In contrast to the method validation with CHO-rich SRFA, validation with sulphur-rich pit lake samples showed that formulas with a higher number of non-oxygen heteroatoms can be more reliable assignments in many cases. As an example: CHOS molecular series were reliable and the CHO classes were unreliable amongst other molecular classes in many multiple-formula assignments from the sulphur-rich pit lake samples. Graphical abstract An exemplary frequency versus DBE −  O diagram. CHOS components but not CHO (and not CHON 2 or CHON 2 S) components were considered here reliable
    Keywords: DOM ; FT-ICR-MS ; Formula assignment ; CHOS/CHON molecular series ; Validation
    ISSN: 1618-2642
    E-ISSN: 1618-2650
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  • 8
    Language: English
    In: Chemosphere, December 2017, Vol.188, pp.208-217
    Description: Humic substances (HS) are ubiquitous organic compounds able to affect mobility and availability of arsenic (As) in aquatic systems. Although it is known that associations between HS and As occur mainly via iron (Fe)-cationic bridges, the behaviour and distribution of this metalloid in HS- and Fe-rich environments is still not fully understood. In this paper, the quality of HS from different rivers in Brazil and Germany and its influence on the behaviour of As(V) under different Fe(III) concentrations were investigated. HS were extracted from four different rivers (Cascatinha, Holtemme, Selke and Warme Bode), characterised and fractionated into different molecular weight sizes (10, 5 and 1 kDa). Complexation tests were performed using an ultrafiltration system and 1 kDa membranes. All data was analysed using the Kohonen neural network (SOM – Self organising maps). All samples, except Selke, exhibited similar results of free As (〈1 kDa). The results suggested that associations between HS, Fe and As were dependent on nitrogen (N)–aromatic carbon (C), amount of sulphur (S) and the molecular size of the HS. Although all HS appeared to be similar after looking at most variables analysed, the SOM could discriminate them into three different groups. Characterisation of the HS indicated that they had terrestrial material (from C plants) as precursor material. Most of the As and Fe was distributed in the fractions of higher (〉10 kDa) and lower (〈1 kDa) size. HS quality is an important factor to take into account when studying the behaviour of As in HS-rich environments.
    Keywords: Ternary Complex ; Dissolved Organic Matter ; Arsenic Distribution ; Ultrafiltration ; Self-Organising Maps (Som) ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 9
    Language: English
    In: Chemosphere, December 2016, Vol.164, pp.290-298
    Description: The distribution of metals and metalloids among particulate, dissolved, colloidal, free, and labile forms in natural waters is of great environmental concern since it determines their transportation behaviour and bioavailability. Organic matter can have an important role for this distribution process, since it is an important complexing agent and ubiquitous in the aquatic environment. We studied the distribution, mobility and bioavailability of Al, As and Fe in natural waters of a mining area (Quadrilátero Ferrífero, Brazil) and the influence of organic matter in these processes. Water samples were taken from 12 points during the dry and rainy seasons, filtrated at 0.45 μm and ultrafiltrated (〈1 kDa) to separate the particulate, colloidal and free fractions. Diffusive gradients in thin films (DGT) were deployed at 5 sampling points to study the labile part of the elements. Total and dissolved organic carbon and the physicochemical parameters were measured along with the sampling. The results of ultrafiltration (UF) and DGT were compared. The relationship among the variables was studied through multivariate analysis (Kohonen neural network), which showed that the seasonality did not impact most of the samples. Fe and Al occurred mainly in the particulate fraction whereas As appeared more in the free fraction. Most of the dissolved Fe and Al were inert (colloidal form) while As was more labile and bioavailable. The results showed that sampling points with a higher quantity of complexed Fe (colloidal fraction) showed less labile As, which may indicate formation of ternary complexes among organic matter, As and Fe.
    Keywords: Dissolved Organic Matter ; Metal Speciation ; Humic Substances ; Multivariate Analysis ; Kohonen Neural Network ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 10
    Language: English
    In: Science of the Total Environment, 15 May 2017, Vol.586, pp.770-781
    Description: Peatlands can be a potential source of dissolved organic matter (DOM) in fresh water catchment areas. The quantity and quality of DOM can differ between pristine, degraded and rewetted peatlands. Due to the large scale and continuing losses of peatlands, their conservation and restoration has been increasingly emphasized. Mostly rewetting measures are required to improve the hydrology of damaged peatlands, which is a precondition for the resettlement of peat-forming plant species. Thus, in term of DOM, there is a special need to understand how rewetting measures affect DOM characteristics and concentrations. To estimate the potential leaching of humic substances from rewetted areas two natural sites were compared with four artificially rewetted sites in a peatland area of the Harz Mountains National Park, Germany. This was done with regards to DOM quality by combining the results from Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS, measured at one time in Spring) and excitation-emission-matrix fluorescence spectroscopy (EEMF, measured monthly for the period of one year). The DOM quality was significantly less variable in the pristine peatland soil water compared to the rewetted peatland soil waters, from both a spatial and a seasonal perspective. The soil water from the rewetted peatland sites showed a higher degree of humification compared to pristine peatland. DOC concentration was mostly consistent in the pristine peatland over the year. The rewetted peatlands showed higher DOC levels in Summer months and lower DOC in Winter months compared to the pristine peatland. It can be concluded that the rewetting of peatlands is coupled with high concentrations of DOC in soil water and its quality is highly aromatic (as reflected by the observed values from the humification index) during times with elevated temperature. The results may have a significant input for dynamic catchment area studies with regards to rewetting peatland sites.
    Keywords: Doc ; Fluorescence Indices ; Van Krevelen Diagrams ; Spatial Resolution ; Seasonality ; Harz Mountains ; Germany ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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