Direct measurement of sulphur isotope composition in lichens by continuous flow-isotope ratio mass spectrometry (CF-IRMS)

Yun, Misuk (2000) Direct measurement of sulphur isotope composition in lichens by continuous flow-isotope ratio mass spectrometry (CF-IRMS). Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (17MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

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.

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