Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography

Duarte, Regina M.B.O.; Barros, Ana Margarida; Duarte, Armando C.

doi:10.1016/j.chroma.2012.06.022

Cited by 23 publications

(18 citation statements)

References 46 publications

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“…Over the last decade, however, the combination of information-rich/selective detectors, improved column technology, and NOM-specific method development, has led to robust fractionation of NOM into physiochemically distinct components, revealing previously unobtainable compositional detail. [15][16][17][18][19][20][21][22] Differences between humic substances from distinct origins and stages of transformation can readily be determined. [18][19][20][21][22][23][24] These experiments have shown that fractionation increases the number of detectible constituents.…”

Section: Introductionmentioning

confidence: 99%

Benefits of multidimensional fractionation for the study and characterization of natural organic matter

Brown

Jackson

Bythell

et al. 2016

Journal of Chromatography A

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The belief that chromatographic separation of complex environmental mixtures or natural organic matter (NOM) produces featureless humps from which little, if anything, can be learned is still pervasive. Meanwhile improvements in chromatography and the use of information-rich detection methods have led to meaningful fractionation and revealed consistent data. Here, we build on this work and developed a robust, facile two-dimensional separation with high orthogonality between dimensions. We illustrate that re-injections of fractions (both in the first and in the second dimension) leads to individual peaks at the expected retention times and use information-rich detection to investigate the basis on which NOM is fractionated. We demonstrate unprecedentedly feature-rich chromatograms are observed even with standard UV detection for polar NOM fractions. The second stage of fractionation is demonstrated to separate isomers, providing a direct look at isomeric complexity in NOM as well as a tool to reduce it. Consistent with expectation, but confirmed for the first time through mass spectral data, radicals were detected for NOM components that were generally nonpolar and grouped in the condensed aromatic structure - like region of van Krevelen plots. High-resolution tandem mass spectral data, furthermore, suggests that many higher-MW components of fulvic acids (especially the highly oxidized ones) have formulas that do not match any known compounds in the literature, supporting the hypothesis that fulvic acids are a unique compound-class. Combined, the data illustrate that meaningful reduction in complexity reveals new compositional and structural detail and avails new avenues of investigation.

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Section: Introductionmentioning

confidence: 99%

Benefits of multidimensional fractionation for the study and characterization of natural organic matter

Brown

Jackson

Bythell

et al. 2016

Journal of Chromatography A

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“…The schematics of the instrumentation setup and the complete description of the LC£LC system used in this experimental procedure can be found in Duarte et al (2012) The first dimension, using an Acclaim Mixed-Mode HILIC-1 column (Dionex; diameter: 4.6 mm; length: 150 mm; comprised 5-mm high-purity, porous, spherical silica particles with 120 A diameter pores bonded with alkyldiol functional groups) was operated in isocratic mode, under PALC conditions, using a mobile phase composition comprising 20 mM of ammonium acetate (pH adjusted to 6.0 with 1.1 mM of acetic acid) and 10% (v/v) of acetonitrile. The flow rate in the first dimension was 0.020 mL min ¡1 and the temperature of the analytical column was maintained at 30 C. The second dimension using a PSS Suprema 30 A analytical column (Polymer Standards Service GmbH; diameter 8 mm; length 150 mm; particle size 10 mm; separation range 100-30,000 Da; stationary phase polyhydroxymethacrylate copolymer) was also operated in isocratic mode with a mobile phase composition comprising 20 mM of ammonium hydrogen carbonate (pH 8.0) and 11% (v/v) of acetonitrile.…”

Section: Instrumentation and Chromatographic Conditionsmentioning

confidence: 99%

“…The development of chromatographic conditions applied in this study followed the method suggested by Duarte et al (2012) for PALC£SEC analysis of Fulvic acids as reference materials. The authors used PSS standards to calibrate an SEC column identical to the one applied in the present study.…”

Section: Assessing the Separation Mechanisms In Both Dimensionsmentioning

confidence: 99%

Profiling Water-Soluble Organic Matter from Urban Aerosols Using Comprehensive Two-Dimensional Liquid Chromatography

Matos

Freire

Duarte

et al. 2015

Aerosol Science and Technology

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Comprehensive two-dimensional liquid chromatography (LC£LC) coupled with a diode array detector (DAD) has been used for the first time to investigate chemical heterogeneity and map the hydrophobicity versus molecular weight distribution of the most hydrophobic acid fractions in water-soluble organic matter (WSOM) from fine atmospheric aerosols collected over different seasons at a urban location. The use of LC£LC-DAD, combining the use of two independent separation mechanisms (per aqueous liquid chromatography [PALC] versus sizeexclusion chromatography [SEC]), has shown a great potential for unraveling and resolving the heterogeneity of WSOM, further providing a deeper insight into how size-distinguished aerosol WSOM fractions differ in hydrophobicity during different seasonal events. The combination of PALC£SEC-DAD data with an already proposed data treatment procedure revealed that the WSOM samples collected during warm seasons are enriched in aliphatic structures, while those collected during colder seasons exhibit a higher degree of structures with conjugation of p-bonds (e.g., aromatics) alongside aliphatic structures.

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“…Nevertheless, pure water was investigated here as a spray solvent because NOM does ionize quite effectively from it, and it is reasonable to hypothesize that analyzing NOM from its natural solvent without any additives might produce the most representative results. Furthermore, a significant fraction of NOM generally elutes under highly aqueous mobile phase compositions in chromatographic separations . Thus, the effect of high water concentrations on representativeness is also relevant for online liquid chromatography (LC) MS experiments.…”

Section: Resultsmentioning

confidence: 99%

Fact or artifact: the representativeness of ESI-MS for complex natural organic mixtures

2014

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Because mass spectrometers provide their own dispersion and resolution of analytes, electrospray ionization mass spectrometry (ESI-MS) has become a workhorse for the characterization of complex mixtures from aerosols to crude oil. Unfortunately, ESI mass spectra commonly contain multimers, adducts and fragments. For the characterization of complex mixtures of unknown initial composition, this presents a significant concern. Mixed-multimer formation could potentially lead to results that bare no resemblance to the original mixture. Conversely, ESI-MS has continually reflected subtle differences between natural organic matter mixtures that are in agreement with prediction or theory. Knowing the real limitations of the technique is therefore critical to avoiding both over-interpretation and unwarranted skepticism. Here, data were collected on four mass spectrometers under a battery of conditions. Results indicate that formation of unrepresentative ions cannot entirely be ruled out, but non-covalent multimers do not appear to make a major contribution to typical natural organic matter spectra based on collision-induced dissociation results. Multimers also appear notably reduced when a cooling gas is present in the accumulation region of the mass spectrometer. For less complex mixtures, the choice of spray solvent can make a difference, but generally spectrum cleanliness (i.e. representativeness) comes at the price of increased selectivity.

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Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography

Cited by 23 publications

References 46 publications

Benefits of multidimensional fractionation for the study and characterization of natural organic matter

Benefits of multidimensional fractionation for the study and characterization of natural organic matter

Profiling Water-Soluble Organic Matter from Urban Aerosols Using Comprehensive Two-Dimensional Liquid Chromatography

Fact or artifact: the representativeness of ESI-MS for complex natural organic mixtures

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