Marine dissolved organic carbon and nitrogen (DOC and DON) are major global carbon and nutrient reservoirs, and their characterization relies on extraction methods for preconcentration and salt removal. Existing methods optimize for capturing and describing DOC. Here, we report an optimized analytical strategy to recover marine DON for subsequent molecular characterization. Retention efficiencies between 5% and 95% are reported for seven solid phase extraction (SPE) sorbents, with PPL recovering 23% of marine DON compared to 95% recovered with C₁₈. Additional comparisons of the effect of varying sample volumes and elution speed, and the resulting molecular composition of DON extracts, were investigated using C₁₈ and PPL sorbents. Sample volumes > 200 mL decreased DON retention efficiency independent of SPE sorbent, and gravity elution recovered 1.7- to 4.2-fold more DON compared to vacuum elution. Characterization of extracted DON by negative-ion electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) highlights compositional differences between DON species recovered by each method. DON isolated with optimized methods includes low molecular weight (< 600 Da) peptide-like compounds with low O:C ratios (0.2 to 0.5) that are not detected by other SPE sorbents (e.g., PPL). The majority of additional DON isolated with this approach was undetectable by direct infusion negative mode FT-ICR MS analysis.

中文翻译：

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固相萃取回收海洋溶解有机氮的定量和定性比较

海洋溶解有机碳和氮（DOC 和 DON）是全球主要的碳和营养物库，其表征依赖于预浓缩和除盐的提取方法。现有方法针对捕获和描述 DOC 进行了优化。在这里，我们报告了一种优化的分析策略，用于回收海洋 DON 以进行后续分子表征。据报道，七种固相萃取 (SPE) 吸附剂的保留效率在 5% 至 95% 之间，PPL 回收了 23% 的海洋 DON，而 C 18 回收了 95 _%。_{使用 C 18}研究了不同样品体积和洗脱速度的影响以及 DON 提取物所得分子组成的额外比较和 PPL 吸附剂。样品体积 > 200 mL 会降低 DON 保留效率，与 SPE 吸附剂无关，并且与真空洗脱相比，重力洗脱回收的 DON 多 1.7 至 4.2 倍。通过负离子电喷雾电离傅里叶变换离子回旋共振质谱 (FT-ICR MS) 对提取的 DON 进行表征，突出了每种方法回收的 DON 种类之间的成分差异。采用优化方法分离的 DON 包括具有低 O:C 比（0.2 至 0.5）的低分子量 (< 600 Da) 肽类化合物，其他 SPE 吸附剂（例如 PPL）无法检测到这些化合物。通过直接输注阴性模式 FT-ICR MS 分析无法检测到通过这种方法分离出的大部分额外 DON。