| 1. |
- Hanson, Blair, et al.
(author)
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DOM Molecular Weight Fractionation and Fluorescence Quantum Yield Assessment Using a Coupled In-Line SEC Optical Property System
- 2022
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In: ACS ES and T Water. - : American Chemical Society (ACS). - 2690-0637. ; 2:12, s. 2491-2501
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Journal article (peer-reviewed)abstract
- Size exclusion chromatography (SEC) in combination with optical measurements has become a popular form of analysis to characterize dissolved organic matter (DOM) as a function of molecular size. Here, SEC coupled with in-line absorbance scans and fluorescence emission scans was utilized to derive apparent fluorescence quantum yield (φf) as a function of molecular weight (MW) for DOM. Individual instrument-specific SEC-fluorescence detector correction factors were developed by comparison of an SEC-based excitation emission matrix (EEM) to an EEM generated by a calibrated benchtop fluorometer. The method was then applied to several sample sets to demonstrate how to measure the φf of unknown DOM samples and to observe changes to φf following a processing mechanism (ozonation). The φf of riverine water samples and DOM fulvic acid isolates from Suwannee River and Pony Lake increased from < 0.5% to a maximum of 2.5-3% across the medium- to low-MW range. Following ozonation of PLFA, φf increased most notably in the large-MW fractions (elution volumes < 40 mL). Overall, this method provides a means by which highly fluorescent size fractions of DOM can be identified for more detailed analyses of chemical composition and its changes through different processing mechanisms.
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| 2. |
- Hawkes, Jeffrey A., et al.
(author)
-
An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry : Are we getting the same answer?
- 2020
-
In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 18:6, s. 235-258
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Journal article (peer-reviewed)abstract
- High-resolution mass spectrometry (HRMS) has become a vital tool for dissolved organic matter (DOM) characterization. The upward trend in HRMS analysis of DOM presents challenges in data comparison and interpretation among laboratories operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with reference samples so that data can be robustly compared among research groups. To this end, four identically prepared DOM samples were each measured by 16 laboratories, using 17 commercially purchased instruments, using positive-ion and negative-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified similar to 1000 common ions in both negative- and positive-ion modes over a wide range of m/z values and chemical space, as determined by van Krevelen diagrams. Calculated metrics of abundance-weighted average indices (H/C, O/C, aromaticity and m/z) of the commonly detected ions showed that hydrogen saturation and aromaticity were consistent for each reference sample across the instruments, while average mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments.
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