Compound‐specific isotopic analysis of amino acids (CSIA‐AA) is increasingly used in ecological and biogeochemical studies tracking the origin and fate of nitrogen (N). Its advantages include the potential for resolving finer‐scale trophic dynamics than possible with standard bulk SIA and for reconstructing historical changes in the food webs of consumers from analyses of specimens in preserved sample archives. For the latter, assessing the effects of chemical preservatives on δ¹⁵N_AA has been inconclusive because the conventional CSIA approach for derivatized AAs by gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS) has analytical errors (0.4–1.0‰) in the range expected from chemical preservation. Here, we show improved analytical precision (0.15 ± 0.08‰) for 11 underivatized AA standards analyzed by high‐pressure liquid chromatography followed by offline elemental analysis‐IRMS (HPLC/EA‐IRMS). Using this method, we report the first high‐precision tests of preservation effects on δ¹⁵N_AA in Northern Anchovy (Engraulis mordax ) kept 1.5‐yr in ethanol and up to 27‐yr in formaldehyde. We found minimal methodological induced fractionation for eight AAs, and preservation effects on δ¹⁵N were similar regardless of duration and preservative used. Although some of the AAs differed significantly from frozen control samples (AA average +1.0 ± 0.8‰), changes in δ¹⁵N in the source AA phenylalanine and trophic position estimates were statistically insignificant. Our results are encouraging for resolving fine‐scale natural variability using HPLC/EA‐IRMS on chemically preserved specimens and for ultimately reconstructing biogeochemical records and trophic dynamics over long time scales.

中文翻译：

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高压液相色谱法纯化的鱼类样品中氨基酸的化合物特异性δ15N分析相关的误差

氨基酸的化合物特异性同位素分析（CSIA‐AA）越来越多地用于生态和生物地球化学研究中，以追踪氮（N）的来源和命运。它的优势包括解决比标准散装SIA更精细的营养动力学的潜力，以及从保存的样本档案中的样本分析中重建消费者食物网中历史变化的潜力。对于后者，评估对δ化学防腐剂的效果¹⁵ Ñ _AA之所以没有定论，是因为采用气相色谱-燃烧-同位素比质谱（GC-C-IRMS）进行衍生化AA的常规CSIA方法在化学保存预期的范围内具有分析误差（0.4-1.0‰）。在这里，我们展示了11种未衍生的AA标准品的改进分析精度（0.15±0.08‰），这些标准品通过高压液相色谱法进行分析，然后进行离线元素分析-IRMS（HPLC / EA-IRMS）使用这种方法，我们报告的保存效果的第一高精度测试上δ ¹⁵ Ñ _AA北鳀鱼（鳀mordax）保持1.5-YR在乙醇中，最高达27年中的甲醛。我们发现最小的方法诱导分馏八节AA电池，保鲜效果上δ ¹⁵无论使用何种持续时间和防腐剂，N均相似。虽然一些的AA的从冷冻对照样品（AA平均1.0±0.8‰）显著不同，改变δ ¹⁵ N的源AA苯丙氨酸和营养位置估计在统计学上不显着。我们的结果令人鼓舞，对于使用HPLC / EA-IRMS解决化学保存标本上的细微自然变化，以及最终重建长期的生物地球化学记录和营养动力学，我们的结果令人鼓舞。