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<p>Chlorophyll-<i>a</i> is the most abundant chlorophyll pigment produced by marine phytoplankton, and it bears the isotope signature of the nitrate source assimilated in the N-atoms that are embedded in its porphyrin ring. The chloropigment and its degradation product, <i>i.e.</i>, pheophytin-<i>a</i>, could be well preserved in marine sediment, usually at nanomolar level. A sensitive and accurate measurement of the δ<sup>15</sup>N of chloropigment is capable of providing rich information to greatly enhance our understanding of past nitrogen cycling, which therefore is urgently needed. Hereby, we present a successful method based on two-step HPLC separation followed by ‘denitrifier method’. The N-content in acetone and potassium persulfate (K<sub>2</sub>S<sub>2</sub>O<sub>8</sub>) are very critical to the precision and accuracy of the measurements, because they constitute the majority of the N contamination to the Chl-<i>a</i> samples. In this method, the recrystallized K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> that is used as oxidization reagent was discovered to have a δ<sup>15</sup>N background of −15‰, consolidated by repeated examinations over a period of two months. This <sup>15</sup>N background of K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> would cause −1‰–−2‰ deviation on the δ<sup>15</sup>N of sample that contains nanomolar level N, and highlight the need to examine the δ<sup>15</sup>N of recrystallized K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> when it is used to oxidize samples of organic nitrogen. The overall measurement of δ<sup>15</sup>N pigment is reliable and has an average analytical precision better than ±0.5‰ (1σ). This study establish a sensitive method for accurate measurement of the δ<sup>15</sup>N of nano-molar level chlorophyll pigment, and with no doubts will advance its wide application in marine nitrogen cycling studying.</p>

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A Sensitive Method for the δ15N Measurement of Nanomolar Chl-a in Marine Environment

  • 期刊论文

  • 发表日期：

    2026年1月23日

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  • Yu Xin,
  • Maojun Yan,
  • Zhenwei Yan,
  • Jiping Wang

摘要

Chlorophyll-a is the most abundant chlorophyll pigment produced by marine phytoplankton, and it bears the isotope signature of the nitrate source assimilated in the N-atoms that are embedded in its porphyrin ring. The chloropigment and its degradation product, i.e., pheophytin-a, could be well preserved in marine sediment, usually at nanomolar level. A sensitive and accurate measurement of the δ15N of chloropigment is capable of providing rich information to greatly enhance our understanding of past nitrogen cycling, which therefore is urgently needed. Hereby, we present a successful method based on two-step HPLC separation followed by ‘denitrifier method’. The N-content in acetone and potassium persulfate (K2S2O8) are very critical to the precision and accuracy of the measurements, because they constitute the majority of the N contamination to the Chl-a samples. In this method, the recrystallized K2S2O8 that is used as oxidization reagent was discovered to have a δ15N background of −15‰, consolidated by repeated examinations over a period of two months. This 15N background of K2S2O8 would cause −1‰–−2‰ deviation on the δ15N of sample that contains nanomolar level N, and highlight the need to examine the δ15N of recrystallized K2S2O8 when it is used to oxidize samples of organic nitrogen. The overall measurement of δ15N pigment is reliable and has an average analytical precision better than ±0.5‰ (1σ). This study establish a sensitive method for accurate measurement of the δ15N of nano-molar level chlorophyll pigment, and with no doubts will advance its wide application in marine nitrogen cycling studying.