Quantitative Recovery of Dissolved Organic Nitrogen? Exploring a New Method Integrating Ultrafiltration with C18 and PPL Solid-Phase Extraction Resins

Marine Dissolved organic nitrogen (DON) is central to the ocean’s nitrogen cycle. However, in particular the refractory lower molecular weight (LMW) DON pool, constituting the large majority of all DON, remains poorly understood, primarily due to isolation and characterization challenges.  Although early work targeting LMW DON composition used PPL solid-phase extraction (SPE), modest recoveries limit interpretation. Nevertheless, recent experiments suggest that new approaches may achieve vastly larger DON recoveries. NMR data indicating that heterocyclic nitrogen compounds quantitatively dominate LMW DON are consistent independent work indicating far higher potential DON recovery with non-polar SPE, exceeding 90% recovery in some small-scale isolations. If born out at larger scale, these observations suggest that coupling HMW DON filtrations together with multiple resin types targeting polar and non-polar LMW compounds might enable nearly quantitative DON recovery, while simultaneously separating more labile and refractory fractions.  Here we test this idea, reporting a new method coupling C18 and PPL resins with 1 kDa ultrafiltration (UF). We first report LMW DON recovery efficiencies by PPL vs. C-18, evaluating the composition and representativeness of each fraction with a combination of isotopic analysis (δ¹⁵N-DON), biomarkers (DL, δ¹⁵N, δ¹³C -amino acids), and ¹⁵N CP/MAS NMR. Finally, we evaluate a unified three part method coupling UF, PPL and C-18 for quantitative DON recovery relative composition at each stage.  

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Primary Presenter: Lingyu Ma, University of California, Santa Cruz (lma104@ucsc.edu)

Authors:

Lingyu Ma, University of California, Santa Cruz  (lma104@ucsc.edu)

Yuchen Sun, University of California, Santa Cruz  (ysun290@ucsc.edu)

Stephanie Christensen, University of California, Santa Cruz  (stchrist@ucsc.edu)

Matthew McCarthy, University of California, Santa Cruz  (mdmccar@ucsc.edu)