Strontium Isotope Ratio Analysis

Strontium (Sr) has four naturally occurring stable isotopes: 88Sr, 87Sr, 86Sr and 84Sr. The isotopic composition of 87Sr/86Sr varies geographically on both a local and global scale. Variations in the 87Sr/86Sr isotopic ratio arise from the natural b-decay of 87Rb to 87Sr. The relationship between Rb concentration and the age of the sample, allows the 87Sr/86Sr isotope abundance ratio to be a powerful tool for many disciplines such as geochronology, provenance studies, and archaeology.

Strontium isotopes have become a powerful tool for geochemists. The combination of the Rb/Sr elemental ratio and the 87Sr/86Sr isotopic ratio has been used to calculate metamorphic and metasomatic ages, as well as a range of kinetic and equilibrium processes. The 87Sr/86Sr isotopic ratio has been measured in rocks, sediments, and water samples and used as a geological tracer for fluid/rock interaction and mixing processes (1). Apart from its applications in geoscience, 87Sr/86Sr has been used for provenance studies to facilitate the identification and origin of samples such as wine and cheese (2). Strontium Isotopes have been used to study the migration patterns of animals such as fish (3). Food authentication is receiving increasing attention to protect consumers by ensuring that they are getting what they pay for and the producers by identifying fraudulent products. For the protection of consumers and producers’ analytical methods must be validated for the prevention of fraud and mislabeling and to guarantee the origin of the products. Strontium isotopic ratios measured in modern and archaeological materials are used to identify the geographic origin of humans, animals and materials (4). Archaeological studies to date artifacts and structures can use strontium isotopes through the correlation of seawater and carbonate sediments that precipitated at the time of creation (5).

To ensure the highest accuracy and precision of strontium isotopic ratio measurements it is necessary to separate the lead from the sample matrix and interferants. There are different methods and instruments for doing this, depending on the type and amount of sample, the accuracy and precision required. An ICP-QQQ-MS is used to verify that effective separation and concentration are obtained before analysis.

Stable metal isotope measurement can be achieved through thermal ionization mass spectrometry (TIMS), Inductively Coupled Plasma Mass Spectrometer equipped with a Dynamic Reaction Cell (DRC), or a Multi Collector ICP Mass Spectrometer (MC-ICP-MS). While a TIMS instrument can produce excellent precision as it is not reliant on an instable plasma source, the MC-ICP-MS instruments at Brooks Applied Labs offer the flexibility, speed, and precision necessary for commercial testing. Our results include all appropriate QA/QC which are not usually available from academic institutions. The Nu Plasma 1700 is a unique High Resolution Multi Collector ICP-MS from Nu Instruments providing the ultimate in high resolution isotope ratio measurements. The instrument has been designed with a high dispersion and large geometry to provide a no compromise high resolution capability whilst still maintaining flat top peaks for high precision measurements with minimal loss in sensitivity.

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1. 1.  Argentino, Claudio & Lugli, Federico & Cipriani, Anna & Panieri, Giuliana. (2021). Testing miniaturized extraction chromatography protocols for combined 87Sr/86Sr and δ88/86Sr analyses of pore water by MC‐ICP‐MS. Limnology and Oceanography: Methods. 19. 10.1002/lom3.10435.
   2.  Fortunato, Giuseppino et al. “Application of strontium isotope abundance ratios measured by MC-ICP-MS for food authentication.” Journal of Analytical Atomic Spectrometry 19 (2004): 227-234.
   3.  Irrgeher, Johanna & Prohaska, Thomas & Sturgeon, Ralph & Mester, Zoltán & Yang, Lu. (2013). Determination of Strontium Isotope Ratios in a Biological Tissue using MC-ICPMS. Analytical Methods. 5. 1687-1694. 10.1039/C3AY00028A.
   4.  Gerritzen, Carina & Goderis, Steven & James, Hannah & Snoeck, Christophe. (2024). Optimizing Zr-doped MC-ICP-MS sample-standard bracketing to simultaneously determine 87Sr/86Sr and δ88Sr for high sample-throughput. Spectrochimica Acta Part B: Atomic Spectroscopy. 217. 106955. 10.1016/j.sab.2024.106955.
   5.  Puente-Berdasco, B. & Rodríguez, J. & Ballesteros, Daniel & Painchault, A. & Nehme, Carole & Mouralis, Damase & Ibarguchi, José & Martín-Izard, A. & Garcia Alonso, Jose. (2022). Measurement of 87 Sr/ 86 Sr in limestones after acid leaching and direct injection in a liquid chromatograph coupled to a multicollector ICP-MS. Journal of Analytical Atomic Spectrometry. 37. 10.1039/D1JA00340B.