Accurate Sr isotope determination of human bone and tooth samples by LA‐MC‐ICP‐MS: A comment on “Meijer et al., (2019)”

Abstract

The in‐situ Sr isotope determination of low‐Sr bioapatites is challenging and requires monitoring several interferences, among others, Ar‐CaPO. In particular, the analysis of human bones and teeth has revealed several pitfalls, which affect the ability to obtain accurate results. In this commentary, I review the data from the paper of Meijer et al. (2019), trying to address some accuracy issues arising, in my opinion, from polyatomic interferences. After a tentative calibration of their data, using the 1/88Sr signal (V−1) as a proxy of the Sr content, the enamel specimens (enamel Ar‐CaPO corrected 87Sr/86Sr ratio = 0.7078 ± 0.0032; mean ± 2σ) are closer to the likely local bioavailable Sr (bone Ar‐CaPO corrected 87Sr/86Sr ratio = 0.7071 ± 0.0011; mean ± 2σ).

From the Piedmont to the Coast: LA‐ICP‐MS 87Sr/86Sr evidence for short‐term, long‐distance mobility in the American Southeast

“…Rare earth element concentrations are low, indicative of minimal diagenetic alteration of enamel from the burial environment (Balter et al, 2012). Moreover, Sr concentrations are sufficiently high to minimize interfering isotopes during LA-ICP-MS (Balter et al 2008;Horstwood et al 2008;Lugli 2019). Single bulk enamel 87 For all Harris Creek individuals, isotopic equifinality does not appear to be a factor in geographical identification errors.…”

Strontium isotope evidence for Neanderthal and modern human mobility at the upper and middle palaeolithic site of Fumane Cave (Italy)

“…Therefore, as we had relatively low strontium concentrations for the Neanderthals in our study, we chose to apply a correction to account for potential interference from the ablation processes. We used the method outlined in Horstwood et al [ 47 ] and more recently applied by Lugli [ 54 ] and Lugli et al [ 48 ]. We produced a calibration using the slope of the regression line of the standards calculated from plotting the relative difference between the solution and laser ablation 86Sr/87Sr values against measured 1/88Sr (as a measure of strontium concentration).…”

On the road again—a review of pretreatment methods for the decontamination of skeletal materials for strontium isotopic and concentration analysis

“…The amount of strontium measured in archeological materials is measured in different ways, for instance, strontium concentration (published as ppm or parts per mil), or 1/ 88 Sr (V −1 ) (produced with various mass spectrometers as a proxy for strontium concentration) (Copeland et al 2008;Knudson et al 2010;Lugli 2019;Montgomery 2010. When plotted against strontium isotopic values, they have been used to indicate dietary variation within a population (e.g., marine vs. terrestrial), and differentiate individuals living in coastal or more inland societies, since Sr concentrations are higher in marine environments (Graustein 1988(Graustein , 1989Lewis et al 2017;Perry et al 2017;Price et al 1985;Sealy et al 1991;Reynard and Balter 2014).…”

“…Measuring concentration data or its proxies can demonstrate the systematic differences in absolute isotopic values produced in solution vs. laser ablation (LA) modes of analysis (Lewis et al 2017;Lugli 2019Simonetti et al 2008). According to Simonetti et al (2008), 87 Sr/ 86 Sr values produced via the LA mode were more radiogenic than the solution values from the enamel of the same individual.…”

“…Therefore, the isotopic data would benefit from being analyzed in conjunction with trace elements, if not to determine the dietary variation within a population but to offset any analytical artifacts left by machinery (Nowell and Horstwood 2009;Simonetti et al 2008). These are due to isobaric interferences from other elements that share isotopes with an identical mass number, such as 87 Rb and 87 Sr (Lugli 2019;Nowell and Horstwood 2009;Simmonetti et al 2008). Ultimately, analyzing both concentration and isotopic data ensures that the data is accurate and reliable, especially with rare and important samples where it might not be possible to reanalyze at a future date.…”