Direct measurement of sulphur isotope composition in lichens by continuous flow-isotope ratio mass spectrometry (CF-IRMS)
Bibliographic record
Abstract
An on-line analytical method has been developed for the routine measurement of S isotopic composition in lichens using continuous flow-isotope ratio mass spectrometry (CF-IRMS). 15 mg (equivalent to about 9 μg S) of chemically-untreated lichen powder (Alectoria sarmentosa) together with V2O5 was weighed into 40 mg Sn capsules and then combusted directly in an oxidation-reduction reactor (packed with WO3, pure Cu and quartz wool, heated to 1050°C) of an elemental analyzer, connected to the IRMS via an open-split interface. All combusted gases were carried in a stream of He gas (at 80 mL/min) through a trap (75% Mg(CIO4)2 + 25% quartz chips) to remove H2O(g). A 1.2 m Teflon column (Poropak™ QS, heated to 75 °C) was used to chromatographically separate SO2 from CO2 and N2. The separated gases were transferred into the IRMS through the interface where excess CO2 was diluted by the supply of He (set at 25 psi). Using these parameters over 150 samples can be analyzed successively, changing the H2O trap and cleaning residual ash from the combustion reactor after every 40 samples. -- Mean δ34SCDT values of +6.3 ± 0.4 0/00 (calibrated using sulphates) and +6.1 ± 0.3 0/00 (calibrated using sulphides) measured on a homogenized, composite lichen sample collected from the Botanical Garden of Memorial University of Newfoundland, show excellent agreement with those acquired by dual inlet (DI)-IRMS (+6.2 ± 0.2 0/00), and by on-line CF-IRMS in which samples are chemically pretreated to convert S to BaSO4 (+5.9 ± 0.3 0/00). Four different lichen samples with various S concentrations and δ34S values collected from various locations in Newfoundland also show excellent accuracy and precision compared to DI technique. Lichen samples containing as little as 5-6 μg S (equivalent to about 9 mg lichen powder) produce valid isotopic measurements without a loss of precision. No memory effects were observed over a δ34SCDT value range of +6 to +16 0/00. Compared to DI-IRMS and CF-mineral methods, analytical time and reasonable S amount required per CF-lichen analysis are reduced greatly to 15 mins and 9 μg S, respectively. -- The developed CF-lichen method was applied to young and old portions of single lichen strands (25-35 cm in length) collected from Come-By-Chance oil refinery area, eastern Newfoundland to investigate variations of S isotopic composition with time. There were systematic variations in S isotope signatures (δ34SCDT) between old (+6.2 to +10.9 0/00) and young (+5.1 to +8.2 0/00) portions, suggesting that the old portions may preserve the S isotopic signatures before the refinery operation while those of the young portions show the present S isotopic signatures. This study demonstrates that the micro analytical capability of the developed CF-lichen method can successfully be applied to other studies which require very small amount of organic material with low S concentrations. \n
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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) | 0.002 | 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 source (direct Gemma or distilled Codex), 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".