Methods for the Determination of Stable Isotope Ratios of Multiple Nitrogen Species in Rainwater Using Distillation and Evaporation
Bibliographic record
Abstract
Nitrogen (N) isotope ratios (δ 15 N) of multiple N species including ammonium (NH 4 + ), nitrate (NO 3 − ), dissolved organic N (DON), and total dissolved N (TDN) can serve as indicators of the sources of wet N deposition. However, methods for sequential analysis of these multiple N species are not well developed. In this study, methods for the determination of δ 15 N of these multiple N species were proposed through a traditional distillation method for NH 4 + and NO 3 − , direct evaporation for TDN, and an isotope mass balance equation for δ 15 N-DON. A series of experiments were conducted 1) to find evaporation conditions including pH (<3.5 vs. 5.4) and evaporation methods (oven drying at 60 and 100°C, infra-red chamber, and freeze-drying), 2) to investigate precision and accuracy of distillation for δ 15 N of NH 4 + and NO 3 − , and 3) to determine δ 15 N-TDN by direct evaporation and δ 15 N-DON with mass balance equation. (NH 4 ) 2 SO 4 (‒4.0 ± 0.03‰), KNO 3 (‒4.2 ± 0.03‰), and CO(NH 2 ) 2 (‒5.4 ± 0.04‰) were used as reference materials for NH 4 + , NO 3 − , and DON, respectively. In this study, for the analysis of δ 15 N of NH 4 + and NO 3 − , the conventional distillation method was tested in an effort to save cost for laboratories equipped with the distillation system. Evaporation using oven at 60°C (but not 100°C), infra-red chamber, or freeze-drier after acidification to < pH 3.5 prevented 14 NH 3 loss. Analysis of the δ 15 N-NO 3 − (‒4.4 ± 0.1‰ to ‒3.9 ± 0.5‰) was reliable for a wide range of N content (0.1–0.5 mg), but analytical errors for δ 15 N-NH 4 + were as high as 2.1‰ when N content was small (e.g., 0.1–0.3 mg N) due to background contamination and potential interference by co-existing DON. Direct evaporation of solution containing NH 4 + , NO 3 − , and DON to dryness produced reliable δ 15 N-TDN with accuracy <0.15‰ and precision <0.21‰. However, the analytical errors of δ 15 N-DON were highly dependent on the content of co-existing NH 4 + as well as DON content. Therefore, the proposed protocol can be applied for rainwater containing a high NH 4 + concentration (>2.0 mg N L −1 assuming that 200 ml of sample is used for distillation).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".