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Abstract
This paper investigates the relationship between apparent size distribution and molecular complexity of dissolved organic matter from the natural environment. We used a high pressure size exclusion chromatography (HPSEC) method coupled to UV-Vis diode array detection (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) in order to compare the apparent size of natural organic matter, determined by HPSEC-UV and the molecular mass determined online by ESI-MS. We found that there was a clear discrepancy between the two methods, and found evidence for an important pool of organic matter that has a strong UV absorbance and no ESI-MS signal. Contrary to some previous research, we found no evidence that apparently high molecular weight organic matter is constituted by aggregates of low molecular weight (<1000 Da) material. Furthermore, our results suggest that the majority of apparent size variability within the ESI ionisable pool of organic matter is due to secondary interaction and exclusion effects on the HPSEC column, and not true differences in hydrodynamic size or intermolecular aggregation.
Highlights
Dissolved organic matter (DOM) in aquatic environments is by far the most abundant form of organic matter in natural waters
Coupling HR-electrospray ionisation mass spectrometry (ESI-MS) to High pressure size exclusion chromatography (HPSEC) imposes important restrictions on the mobile phase used in the chromatography, in that it has to be volatile and high ionic strength should be avoided
Poly(styrene sulfonate) standards (PSS) was used, as in most recent literature, as a charged polymer that is similar in hydrodynamic size to natural humic substances,[17,31,32,37] but the validity of PSS standards or any other model compound in representing the HPSEC retention of DOM must be questioned, as DOM is so chemically diverse.[17,31,32,37]
Summary
Dissolved organic matter (DOM) in aquatic environments is by far the most abundant form of organic matter in natural waters.
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