Suwannee River Natural Organic Matter: Isolation of the 2R101N Reference Sample by Reverse Osmosis

Suwannee River natural organic matter (SRNOM) is a well-known end member of NOM from an aquatic system, and is a reference material of the International Humic Substances Society (IHSS). In May 2012, an expedition to the Suwannee River to replenish this reference material yielded over 6 kg of freeze-dried NOM. The quantity of isolated NOM was unprecedented, easily exceeding the combined recoveries of the standard and reference samples that were collected by the IHSS from the Suwannee River in 1983, 1999, and 2003. The NOM was acquired from 36,890 L of filtered river water, which was concentrated 40-fold on-site using two portable reverse osmosis (RO) systems. After RO, the concentrated sample was desalted by cation exchange (CEX), freeze dried, and homogenized. Overall yield of dissolved organic carbon (DOC) was 84.2%, which is slightly lower than the yield of 88% in 1999 when RO and CEX were used to isolate the first sample of SRNOM, which is designated 1R101N. The final NOM sample supplied to the IHSS, which is designated 2R101N, contains only 3.89% inorganic ash, which reasonably allows most chemical analyses. Average river DOC concentration of 82.7 mg/L was higher than during prior sampling trips, which contributed to the historically high recovery of NOM. Increased DOC concentration may be related to the removal of water control structures from the river. This article describes the methods of isolation used in collecting the 2R101N reference sample as background for other articles in this special issue of Environmental Engineering Science and for future researchers who will use this IHSS sample.