Characterizing the properties of dissolved organic matter isolated by XAD and C-18 solid phase extraction and ultrafiltration

Abstract

The properties of aquatic dissolved organic matter (DOM) isolated by solid phase extraction (SPE) C-18 cartridges, ultrafiltration, and XAD chromatography are compared. Samples taken from the Suwannee River, Georgia, USA and McDonalds Branch in the Pine Barrens, New Jersey, USA were chosen to represent waters where DOM originates from predominantly terrestrially-derived (allochthonous) precursors. Pony Lake, Antarctica represented an exclusively algal/microbiallyderived (autochthonous) DOM. Fluorescence, UV absorption, 13 C NMR spectroscopy, and high-pressure size exclusion chromatography (HPSEC) were employed to discern differences and similarities between the DOM isolated by these three methods. Only subtle differences between isolation methods were observed for the terrestrially derived DOM samples when assayed by light and Aquat. Sci. 67 (2005) 61-71Aquatic Sciences fluorescence spectroscopy. Conversely, the Pony Lake DOM isolates exhibit greater variability when analyzed by these methods. 13 C-NMR analyses showed structural differences between the methods for all samples. HPSEC analysis also revealed differences with the C-18 isolates exhibiting the highest molecular weights. Thus, it appears that each method isolates sufficiently different fractions of DOM that can only be delineated when a consortium of analytical methods are used to assay the samples. Nonetheless real differences between autochthonous and allochthonous derived DOM were observed with the algal-derived samples exhibiting high fluorescence ratios and lower aromaticity relative to the terrestrially derived materials. These results demonstrate that caution must be exercised when interpreting DOM reactivity data that rely upon the use of specific fractions.

Evaluating the triplet state photoreactivity of dissolved organic matter isolated by chromatography and ultrafiltration using an alkylphenol probe molecule

“…Solid-phase extraction of our samples using C-18 resin was performed using the technique of Schwede- Thomas et al (2005). Our samples were acidified to a pH range of 2-3 and pumped through a cleaned and conditioned (10 L of Milli-Q water) C-18 column (Mega Bond Elute; Varian Corp.) followed by an elution step with neat methanol as the mobile phase.…”

“…The resin is made up of polystyrene beads that sorb protonated hydrophobic organic acids at low pH followed by elution at high pH (Thurman and Malcolm 1981;Aiken et al 1992). Solid-phase extraction uses a stationary phase comprising C 18 alkyl groups bonded to silica (SPE C-18), and it isolates both the hydrophobic acid and hydrophobic neutral fractions of dissolved organic matter (Louchouarn et al 2000;Kaiser et al 2003;Kim et al 2003Kim et al , 2006Schwede-Thomas et al 2005). The SPE C-18 method uses smaller volumes of water (liters to tens of liters) and uses either a filter disk (Kim et al 2003(Kim et al , 2006 or cartridges (Kaiser et al 2003;Schwede-Thomas et al 2005).…”

“…Solid-phase extraction uses a stationary phase comprising C 18 alkyl groups bonded to silica (SPE C-18), and it isolates both the hydrophobic acid and hydrophobic neutral fractions of dissolved organic matter (Louchouarn et al 2000;Kaiser et al 2003;Kim et al 2003Kim et al , 2006Schwede-Thomas et al 2005). The SPE C-18 method uses smaller volumes of water (liters to tens of liters) and uses either a filter disk (Kim et al 2003(Kim et al , 2006 or cartridges (Kaiser et al 2003;Schwede-Thomas et al 2005). Like the XAD-8 method, DOM isolated by SPE C-18 tends to be enriched in chromophoric moieties, but also contains an abundance of hydrophobic aliphatic components (Kaiser et al 2003;Schwede-Thomas et al 2005).…”

“…The SPE C-18 method uses smaller volumes of water (liters to tens of liters) and uses either a filter disk (Kim et al 2003(Kim et al , 2006 or cartridges (Kaiser et al 2003;Schwede-Thomas et al 2005). Like the XAD-8 method, DOM isolated by SPE C-18 tends to be enriched in chromophoric moieties, but also contains an abundance of hydrophobic aliphatic components (Kaiser et al 2003;Schwede-Thomas et al 2005).…”

“…Molecules smaller than the MWCO (1000 Daltons is the preferred choice) pass through the membrane, and the high molecular weight (HMW) fraction is captured in the retentate. TFUF isolation of DOM has been shown to be less selective than the two chromatographic methods and appears to capture more of the nonchromophoric carbohydrate fraction (Aluwihare et al 1997Everett et al 1999;Repeta et al 2002;Schwede-Thomas et al 2005;Quan and Repeta 2007).…”