Murphy David Thomas, Allen Charlotte M, Ghidan Osama, Dickson Andrew, Hu Wan-Ping, Briggs Ethan, Holder Peter W, Armstrong Karen F
School of Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Queensland, Australia.
Institute for Future Environments, Queensland University of Technology, Brisbane, Queensland, Australia.
Rapid Commun Mass Spectrom. 2020 Mar 15;34(5):e8604. doi: 10.1002/rcm.8604.
Strontium isotopes are valuable markers of provenance in a range of disciplines. Limited amounts of Sr in low-mass samples such as insects mean that conventional Sr isotope analysis precludes their use for geographic origins in many ecological studies or in applications such as biosecurity. Here we test the viability of using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) with N O as a reaction gas for accurately determining Sr isotopes in insects with Sr < 100 ng.
Strontium isotopes were determined in solution mode using ICP-MS/MS with 0.14 L/min N O as a reaction gas to convert Sr into SrO for in-line separation of Sr from Rb. The Sr isotope reference standards NIST SRM 987, NIST SRM 1570a and NIST SRM 1547 were used to assess accuracy and reproducibility. Ten insect species collected from the wild as a proof-of-principle application were analysed for Sr concentration and Sr isotopes.
Using ICP-MS/MS we show for the first time that internal mass bias correction of Sr O/ Sr O based on Sr O/ Sr O works to give for NIST SRM 987 a Sr/ Sr ratio of 0.7101 ± 0.012 (RSD = 0.17%) and for NIST SRM 1570a a Sr/ Sr ratio of 0.7100 ± 0.009 (RSD = 0.12%), which are within error of the accepted values. The first Sr/ Sr ratio of NIST SRM 1547 is 0.7596 ± 0.0014. Strontium analyses were run on 0.8 mL of 0.25-0.5 ppb Sr, which equates to 2-4 ng of Sr. Strontium isotope analysis with a precision of >99.8% can be achieved with in-line separation of Sr from Rb at least up to solutions with 25 ppb Rb.
A minimum of 5 mg of insect tissue is required for Sr isotope analysis. This new ICP-MS/MS method enables Sr isotope analysis in single insects, allowing population-scale studies to be feasible and making possible applications with time-critical uses such as biosecurity.
锶同位素是一系列学科中用于溯源的重要标记物。在昆虫等低质量样本中，锶的含量有限，这意味着传统的锶同位素分析排除了它们在许多生态研究或生物安全等应用中用于确定地理来源的可能性。在此，我们测试了使用电感耦合等离子体串联质谱法（ICP-MS/MS）并以一氧化二氮（N₂O）作为反应气来准确测定锶含量小于100纳克（ng）的昆虫中锶同位素的可行性。
采用ICP-MS/MS以0.14升/分钟的一氧化二氮作为反应气，在溶液模式下测定锶同位素，将锶转化为氧化锶（SrO）以便在线分离锶（⁸⁷Sr）和铷（⁸⁷Rb）。使用美国国家标准与技术研究院（NIST）的锶同位素参考标准物质NIST SRM 987、NIST SRM 1570a和NIST SRM 1547来评估准确性和重现性。作为原理验证应用，对从野外采集的10种昆虫进行了锶浓度和锶同位素分析。
使用ICP-MS/MS，我们首次表明基于⁸⁶SrO/⁸⁸SrO对⁸⁷SrO/⁸⁶SrO进行内部质量偏差校正后，对于NIST SRM 987，⁸⁷Sr/⁸⁶Sr比值为0.7101±0.012（相对标准偏差RSD = 0.17%）；对于NIST SRM 1570a，⁸⁷Sr/⁸⁶Sr比值为0.7100±0.009（RSD = 0.12%），均在公认值的误差范围内。NIST SRM 1547的首个⁸⁷Sr/⁸⁶Sr比值为0.7596±0.0014。在0.8毫升浓度为0.25 - 0.5皮克/毫升（ppb）的锶溶液上进行锶分析，这相当于2 - 4纳克的锶。通过在线分离锶和铷，至少在铷含量高达25 ppb的溶液中，可实现精度大于99.8%的锶同位素分析。
进行锶同位素分析至少需要5毫克昆虫组织。这种新的ICP-MS/MS方法能够对单个昆虫进行锶同位素分析，使种群规模的研究变得可行，并使生物安全等对时间要求严格的应用成为可能。
