Determination of stable carbon isotope ratios for molecules in natural organic matter using ESI FT-ICR MS

RationaleDetermining the chemical constituents of natural organic matter (NOM) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICRMS) remains the ultimate measure for probing its source material, evolution, and transport; however, lability and the fate of organic matter (OM) in the environment remain controversial. FTICRMS-derived elemental compositions are presented in this study to validate a new interpretative method to determine the extent of NOM lability from various environments.MethodsFTICRMS data collected over the last decade from the same 9.4 tesla instrument using negative electrospray ionization at the National High Magnetic Field Laboratory in Tallahassee, Florida, was used to validate the application of a NOM lability index. Solid-phase extraction cartridges were used to isolate the NOM prior to FTICRMS; mass spectral peaks were calibrated internally by commonly identified NOM homologous series, and molecular formulae were determined for NOM composition and lability analysis.ResultsA molecular lability boundary (MLB) was developed from the FTICRMS molecular data, visualized from van Krevelen diagrams, dividing the data into more and less labile constituents. NOM constituents above the MLB at H/C ≥1.5 correspond to more labile material, whereas NOM constituents below the MLB, H/C <1.5, exhibit less labile, more recalcitrant character. Of all marine, freshwater, and glacial environments considered for this study, glacial ecosystems were calculated to contain the most labile OM.ConclusionsThe MLB extends our interpretation of FTICRMS NOM molecular data to include a metric of lability, and generally ranked the OM environments from most to least labile as glacial > marine > freshwater. Applying the MLB is useful not only for individual NOM FTICRMS studies, but also provides a lability threshold to compare and contrast molecular data with other FTICRMS instruments that survey NOM from around the world. Copyright © 2015 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.

There is growing evidence that changes in the molecular composition of natural organic matter (NOM) in water drives changes in the effectiveness of water treatment processes. Hence, there is a growing interest in obtaining more detailed characterisation of natural organic matter, than traditional methods can provide. High resolution mass spectrometry is one such technique that is increasingly being used for NOM analysis. Predominately, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), has been used but Orbitrap MS is emerging as a more available, smaller, and cheaper alternative. &amp;#160;Due to the high sensitivity of high-resolution mass spectrometry instrumental performance variation from day to day is a recognised problem. This means that samples measured on different days may not be directly comparable, likely due to slight variations in equipment operating conditions, laboratory ambient conditions and minor contamination left from other analysis. The aim of this study was to investigate the impact of this instrumental variation using a NOM standard mixture and ways to overcome it.To understand the Orbitrap MS instrumental variation from day to day, a freshly prepared NOM standard mixture was analysed on several days. The data files were compiled and analysed using Compound Discoverer software. The molecular weights observed were assigned to molecular formula using the software. As part of the data processing various strategies were explored to deal with batch effects, including data-driven normalisation, removal of data with lower relative abundance and Systematic Error Removal Using Random Forest (SERRF).For the NOM standard mixture, there were differences in the assigned molecular formulas as well as the relevant abundances. A total of 940 molecular formula were found for all the NOM mixture standard runs, with 357 found in more than one sample run. However, the compounds that were present in only one or two sample runs tended to have lower relative abundance, and hence removing compounds with lower relative abundance may reduce the influence of instrumental variation. In general, the greatest commonality across the sample runs was seen in the region where the H/C ratio was between 0.5-1.5 and the O/C ratio was

Natural organic matter (NOM) can affect the performance of water treatment processes, and serves as a main precursor for the formation of disinfection byproduct (DBPs) during chlorination. To minimize such undesirable effects, a better understanding of its structural information and reactivity toward chlorine is necessary. In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was used to study the molecular composition of NOM in source water. More than four thousand NOM components were resolved in the sample. NOM molecules with a low degree of oxidation (low O/C ratio) were found to be more reactive toward chlorine than those with high O/C ratio. Totally, 659 one-chlorine containing products and 348 two-chlorine containing products were detected in the chlorinated sample at a high confidence level. The chlorinated products can be arranged into series, which indicate they were originated from precursor compounds in series related by the replacement of CH(4) against oxygen. Of the 1007 chlorine-containing products observed in this study, only 7 molecular formulas can be found in previous studies, showing the distinct difference from previous studies. This study explored the reactivity of NOM toward chlorine on a molecular level, which was previously explained on the level of whole mixtures or fractions of NOM, and the identified chlorinated products may contribute to our knowledge of the unknown total organic halide (TOX).

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is the gold standard in MS petroleomics due to its ultrahigh resolution and mass accuracy. But its high acquisition and maintenance costs limit accessibility. High-field Orbitrap (HFO) mass spectrometry is emerging as a promising alternative, but further evaluation is needed to determine its effectiveness in key analytical challenges of petroleomics, such as the molecular characterization of crude oils from different geological origins. Ten crude oil samples from the Brazilian pre-salt region (five each of marine and lacustrine origin from two distinct sedimentary basins) were analyzed using ESI(-) FT-ICR MS and ESI(-) HFO MS (resolution: 840 000 at m/z 400). Molecular formula assignments were classified into heteroatom groups (NSO), and the data were interpreted using box plots, DBE vs. carbon number diagrams, and principal component analysis. HFO assigned ca. 2500 molecular formulae, compared to ca. 4500 assigned by FT-ICR. Despite this 45% lower performance, HFO preserved the overall profile of the major heteroatom classes. Notably, S1O4-containing compounds, which are critical markers, were identified at higher abundances with HFO, whereas marine and lacustrine oils were successfully discriminated based on NSO profiles, DBE, and carbon number. Marine oils exhibited higher oxygen content, DBE, and carbon number, whereas lacustrine oils showed relatively higher nitrogen content. Despite reduced performance in formula assignments as compared to FT-ICR, HFO successfully distinguished crude oils of different geochemical origins. The present results indicate therefore that HFO, although displaying inferior performance than FT-ICR, particularly above m/z 400, still displays good enough mass resolution and accuracy sufficient to provide high quality petroleomic data normally required in most, if not all, common MS petroleomic investigations.

Application of Fourier transform ion cyclotron resonance mass spectrometry to characterize natural organic matter

Fourier transform ion cyclotron resonance mass spectrometry equipped with electrospray ionization (ESI FT ICR MS) was successfully applied to determine molecular formulas of components in Arabian mix vacuum residue (AM-VR) by measurement of highly accurate m/z values of molecular ions and analysis of spectral pattern without any pre-separation procedures.

In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with quadrupolar detection (QPD), was applied for online liquid chromatography (LC) MS analysis of natural organic matter (NOM). Although FT-ICR MS has emerged as an important analytical technique to study NOM, there are few previous reports on online LC FT-ICR MS analysis of NOM due to the long acquisition time (2-8 s) required to obtain high-resolution mass spectra. The QPD technique provides a critical advantage over the conventional dipolar detection (DPD) technique for LC-MS analysis because a spectrum with the same resolving power can be obtained in approximately half the acquisition time. QPD FT-ICR MS provides resolving powers ( ) of ∼300000 and 170000 at m/ z 400 with acquisition times per scan of 1.2 and 0.8 s, respectively. The reduced acquisition time per scan allows increased number of acquisitions in a given LC analysis time, resulting in improved signal to noise ( S/ N) ratio and dynamic range in comparison to conventional methods. For example, 40% and 100% increases in the number of detected peaks were obtained with LC QPD FT-ICR MS, in comparison to conventional LC DPD FT-ICR MS and direct-injection FT-ICR MS. It is also possible to perform more quantitative comparison and molecular level investigation of NOMs with 2 μg of a NOM sample. The data presented herein demonstrate a proof of principle that QPD combined with LC FT-ICR MS is a sensitive analytical technique that can provide comprehensive information about NOM.

Determination of molecular formulas of natural organic matter molecules by (ultra-) high-resolution mass spectrometry: Status and needs

Monitoring the degradation and the corrosion of naphthenic acids by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and atomic force microscopy

Six coker gas oils (CGOs) and three basic fractions extracted from one of the CGOs by 0.1, 0.4, and 1 M HCl hydrochloric acid were characterized by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and compared to those analyzed by gas chromatography mass spectrometry (GC-MS). The ultra high mass resolving power and high mass accuracy of FT-ICR MS allow the assignment of a unique elemental composition to each peak in the mass spectrum. Basic nitrogen species were characterized by class, type, and carbon number. The mass spectra of the CGOs at the 200−500 Da mass range were similar, but the distribution of double bond equivalence (DBE) versus carbon number were different. Among the N, N2, NO, and NS that were identified in CGOs, the N class nitrogen species were dominant. The results showed that hydrotreating reduced the relative abundance of all class species, except for the N class species. This suggests that some N class species are refractory to hydrotreating. The molecular weight of nitrogen species in the acid-extracted basic nitrogen fraction of CGO was lower than that of its parent CGO. The N3, NO2, and N2O class species were clearly identified and concentrated in the basic nitrogen fraction, but were not detected in their parent CGO. The N class species with ring plus DBE value of 4−16 in the basic nitrogen fraction were also identified by GC-MS analysis.

Methanolysis of an extraction residue (ER) from Xianfeng lignite was carried out to obtain extracts 1–4 (E1–E4). The molecular compositions (MCs) of oxygen-containing species (OCSs) in E1–E4 were characterized using negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In addition, solid-state 13C nuclear magnetic resonance and X-ray photoelectron spectrometry were used to analyze the carbon types and oxygen functional groups (OFGs) in the ER. The results show that the carbon skeleton structures in the ER are dominated by aliphatic (50.2%) and aromatic (44.9%) carbons. Methylene and methoxy carbons are the most abundant among the aliphatic carbons. Each aromatic cluster contains three rings on average with two substituent groups on each ring. The OFGs in the ER include hydroxy, ether, carbonyl, and carboxyl groups, among which the hydroxy group is the most abundant. The ESI FT-ICR MS analysis shows that the molecular mass distributions of E1–E4 range from 150 to 500 u. The On (n = 1–6) class species are the predominant OCSs in E1–E4, with 0–14 double bond equivalent (DBE) values and 9–34 carbon numbers (CNs). The most abundant On class species in E1–E4 are O2, O2, O2–O3, and O3, respectively. The OCSs in E4 contain low abundances of O1 and O2 class species but relatively high abundances of O4–O6 class species. In addition, the On class species in E4 have narrower ranges of DBE values and CNs than those in E1–E3. A series of acidic species with different DBE values and CNs are assigned to alkanoic acids, alkanedioic acids, alkanetricarboxylic acids, alkylarenols, alkylarenediols, alkylarenetriols, and alkylarenoic acids. With high resolving power and mass accuracy, ESI FT-ICR MS is an effective technique for characterizing MC of the soluble portion from lignites, which will facilitate producing important chemicals from lignites.

The structural characteristics of the components of several vacuum residues from different geological sources (Taching, Sumatra light, Iranian heavy, Arabian mix, and Murban vacuum residues) were investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) without chromatographic pre-separation. The present approach can detect basic nitrogen compounds in vacuum residues with high selectivity. The mass spectra showed differences in both average and range of molecular weights depending on the origin. Accurate masses were used to estimate molecular formulas. All observed peaks were assigned to mononitrogen-containing compounds (major components) or both mononitrogen- and monosulfur- containing compounds (minor components). Homologue analysis for all estimated molecular formulas showed the analogies and peculiarities in components of the five vacuum residues. Every observed compound was sorted by hydrogen deficiency index (Z-value: [CnH2n + ZNmSs+H]+) and carbon number. The distribution center of the Z-values depended on the vacuum residue origin and the maximum value decreased as follows: Taching (−17) > Sumatra light (−19) > Iranian heavy (−21) ≥ Arabian mix (−21) > Murban (−25). Taching vacuum residue contained low absolute Z-values compared to the other vacuum residues from the Middle East. The results obtained by ESI FT-ICR MS were in good accordance with reported findings of highly condensed aromatic compounds in Middle East vacuum residues contains compared to Chinese vacuum residues.

Natural organic matter (NOM) occurs as an extremely complex mixture of large, charged molecules that are formed by secondary synthesis reactions. Due to their nature, their full characterization is an important challenge to scientists specializing in NOM as well as analytical chemistry. Ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis enables the identification of thousands of masses in a single measurement. A major challenge in the data analysis process of NOM using the FT-ICR MS technique is the need to sort the entire data set and to present it in an accessible mode. Here we present a simple targeted algorithm called the David Mass Sort (DMS) algorithm which facilitates the detection and counting of consecutive series of masses correlated to any selected mass spacing. This program searches for specific mass differences among all of the masses in a single spectrum against all of the masses in the same spectrum. As a representative case, the current study focuses on the analysis of the well-characterized Suwannee River humic and fulvic acid (SRHA and SRFA, respectively). By applying this algorithm, we were able to find and assess the amount of singly and doubly charged molecules. In addition we present the capabilities of the program to detect any series of consecutive masses correlated to specific mass spacing, e.g. COO, H(2), OCH(2) and O(2). Under several limitations, these mass spacings may be correlated to both chemical and biochemical changes which occur simultaneously during the formation and/or degradation of large mixtures of compounds.

Probing nitro(so) and chloro byproducts and their precursors in natural organic matter during UV/NH2Cl treatment by FT-ICR MS with machine learning insights

Ultrahigh resolution mass spectrometry, such as Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), can resolve thousands of molecular ions in complex organic matrices. A Compound Identification Algorithm (CIA) was previously developed for automated elemental formula assignment for natural organic matter (NOM). In this work, we describe software Formularity with a user-friendly interface for CIA function and newly developed search function Isotopic Pattern Algorithm (IPA). While CIA assigns elemental formulas for compounds containing C, H, O, N, S, and P, IPA is capable of assigning formulas for compounds containing other elements. We used halogenated organic compounds (HOC), a chemical class that is ubiquitous in nature as well as anthropogenic systems, as an example to demonstrate the capability of Formularity with IPA. A HOC standard mix was used to evaluate the identification confidence of IPA. Tap water and HOC spike in Suwannee River NOM were used to assess HOC identification in complex environmental samples. Strategies for reconciliation of CIA and IPA assignments were discussed. Software and sample databases with documentation are freely available.