The Institute of Earth Sciences, The Hebrew University, Jerusalem, 91904, Israel.
Rapid Commun Mass Spectrom. 2013 Dec 30;27(24):2789-96. doi: 10.1002/rcm.6751.
Dimethyl sulfide (DMS) is the major volatile sulfur species emitted to the atmosphere from the oceans. The sulfur isotope ratio ((34)S/(32)S) of DMS may offer a way to calculate the contribution of marine DMS to global sulfur cycling. The S-isotopic analysis of DMS is difficult due to its low concentrations in natural seawater and high chemical reactivity. Here we present a sensitive, precise and accurate method for determining the S-isotopic composition of natural DMS and its precursor, dimethylsulfoniopropionate (DMSP), in seawater.
The method was based on a purge of DMS from aqueous solutions or natural seawater to a cryogenic trap and subsequent separation of DMS by gas chromatography. The separated DMS was then transferred from the gas chromatograph to a multicollector inductively coupled plasma mass spectrometer (GC/MC-ICPMS system) for measurement of (34)S/(32)S ratios. Correction for mass bias was accomplished using standard-sample bracketing with peaks of SF6 as a reference gas.
Results obtained from synthetic DMS and DMSP dissolved in artificial seawater show >98% recovery of DMS and very good precision (0.1 to 0.3‰), accuracy and linearity (0.2‰) for the 26-179 picomoles (pmol) of DMS or DMSP injected. The system was tested with natural seawater from Eilat (Red Sea, Israel) and similar precision and accuracy for both DMS and DMSP were obtained. The δ(34)S values of DMS and DMSP from Eilat seawater were 19.2 ± 0.2‰ and 19.7 ± 0.2‰, respectively.
The coupling of a purge-and-trap system with a GC/MC-ICPMS system was shown to be a sensitive, accurate and robust approach for the S-isotope analysis of nanomolar (nM) concentrations of DMS and DMSP from aqueous solutions and natural seawater.
二甲基硫（DMS）是海洋向大气排放的主要挥发性硫物种。DMS 的硫同位素比值（(34)S/(32)S）可能提供一种计算海洋 DMS 对全球硫循环贡献的方法。由于天然海水中 DMS 浓度低且化学反应性高，因此 DMS 的 S-同位素分析具有一定难度。本研究提出了一种灵敏、精确和准确的方法，用于测定天然 DMS 及其前体二甲基巯基丙酸酯（DMSP）在海水中的 S-同位素组成。
该方法基于从水溶液或天然海水中吹扫 DMS 到低温阱，然后通过气相色谱分离 DMS。分离出的 DMS 随后从气相色谱仪转移到多接收电感耦合等离子体质谱仪（GC/MC-ICPMS 系统），用于测量 (34)S/(32)S 比值。通过使用六氟化硫（SF6）作为参比气体的标准-样品内标法进行质量偏差校正。
从人工海水中溶解的合成 DMS 和 DMSP 获得的结果表明，DMS 的回收率超过 98%，DMS 或 DMSP 注入量为 26-179 皮摩尔（pmol）时，具有非常好的精密度（0.1 至 0.3‰）、准确性和线性（0.2‰）。该系统用来自以色列埃拉特（红海）的天然海水进行了测试，DMS 和 DMSP 的精密度和准确性相似。埃拉特海水的 DMS 和 DMSP 的 δ(34)S 值分别为 19.2 ± 0.2‰和 19.7 ± 0.2‰。
将吹扫-捕集系统与 GC/MC-ICPMS 系统相结合，是一种灵敏、准确和强大的方法，可用于从水溶液和天然海水中分析纳摩尔（nM）浓度的 DMS 和 DMSP 的 S-同位素。
