Determination of Sr isotopes in calcium phosphates using laser ablation inductively coupled plasma mass spectrometry and their application to archaeological tooth enamel |
| |
Authors: | M.S.A. Horstwood J.A. Evans |
| |
Affiliation: | a NERC Isotope Geosciences Laboratory, British Geological Survey, Nicker Hill, Keyworth, Nottingham NG12 5GG, UK b Division of Archaeological, Geographical and Environmental Sciences, School of Life Sciences, University of Bradford, UK |
| |
Abstract: | The determination of accurate Sr isotope ratios in calcium phosphate matrices by laser ablation multi-collector ICP-MS is demonstrated as possible even with low Sr concentration archaeological material. Multiple on-line interference correction routines for doubly-charged REE, Ca dimers and Rb with additional calibration against TIMS-characterised materials are required to achieve this. The calibration strategy proposed uses both inorganic and biogenic apatite matrices to monitor and correct for a 40Ca-31P-16O polyatomic present at levels of 0.3-1% of the non-oxide peak, which interferes on 87Sr causing inaccuracies of 0.03-0.4% in the 87Sr/86Sr isotope ratio. The possibility also exists for synthetic materials to be used in this calibration. After correction for interferences total combined uncertainties of 0.04-0.15% (2SD) are achieved for analyses of 13-24 μg of archaeological tooth enamel with Sr concentrations of ca. 100-500 ppm using MC-ICP-MS. In particular, for samples containing >300 ppm Sr, total uncertainties of ∼0.05% are possible utilising 7-12 ng Sr. Data quality is monitored by determination of 84Sr/86Sr ratios.When applied to an archaeological cattle tooth this approach shows Sr-isotope variations along the length of the tooth in agreement with independent TIMS data. The 40Ca-31P-16O polyatomic interference is the root cause of the bias at mass 87 during laser ablation ICP-MS analysis of inorganic and biogenic calcium phosphate (apatite) matrices. This results in inaccurate 87Sr/86Sr ratios even after correction of Ca dimers and doubly charged rare earth elements. This interference is essentially constant at specific ablation conditions and therefore the effect on 87Sr/86Sr data varies in proportion to changes in the Sr concentration of the ablated material. Complete elimination of this interference is unlikely through normal analytical mechanisms and therefore represents a limitation on the achievable accuracy of LA-(MC-)ICP-MS 87Sr/86Sr data without rigorous calibration to known reference materials. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|