IsoForensics Inc, 421 Wakara Way, Suite 100, Salt Lake City, UT 84108, USA; University of Utah, Department of Biology, 257 South 1400 East, Salt Lake City, UT 84112, USA.
Anal Chim Acta. 2013 Oct 10;798:64-73. doi: 10.1016/j.aca.2013.08.054. Epub 2013 Sep 7.
The elements of human hair record specific information about an individual's health, diet, and surrounding environment. Strontium isotope ratios of human hair have attracted interest as they potentially record an individual's environment. Yet, separating the external environmental signals from the internal dietary indicators has remained a challenge. Here, we examined the effects of five different hair-cleaning methodologies to determine the extent that internal and external strontium signals can be isolated from human hair. In the first study of its kind, we employed an in-line strontium purification methodology and a multi-collector inductively coupled plasma mass spectrometer to obtain high-precision strontium isotope ratio of human hair and of leachates of the different washing treatments. We found that the different applications of an individual treatment removed a consistent amount of strontium from hair and that replicate analyses showed each treatment altered the strontium isotope ratios of hair consistently. A mass-balance approach was applied to demonstrate that strontium was quantitatively removed and was accounted for in either the treated hair or the leachate. We observed that strontium isotope ratio varied as a function of treatment aggressiveness so as to suggest that there was a fine-scale structuring of strontium within hair (transverse cross-sectional variations); these variations existed as differences in strontium concentrations and isotope ratios. As a result, the Sr isotope ratio of hair and hair leachates treated with the most aggressive cleaning methods reflected the isotope ratios of the interior and total exterior strontium signatures, respectively. The results of this study indicate that external environmental strontium signals can be distinguished from the internal signals and therefore permit the application of strontium isotope ratios of modern human hair for geospatial applications.
头发中的元素记录了个体健康、饮食和周围环境的特定信息。人类头发中的锶同位素比值引起了人们的兴趣，因为它们可能记录了个体的环境。然而，将外部环境信号与内部饮食指标区分开来一直是一个挑战。在这里，我们研究了五种不同的头发清洁方法，以确定从人类头发中分离内部和外部锶信号的程度。这是此类研究中的首次研究，我们采用了在线锶纯化方法和多接收电感耦合等离子体质谱仪，以获得高精度的人类头发和不同洗涤处理的浸出物的锶同位素比值。我们发现，不同的个体处理应用会从头发中去除一致量的锶，并且重复分析表明，每种处理都会一致地改变头发的锶同位素比值。我们应用质量平衡方法来证明锶被定量去除，并在处理过的头发或浸出物中得到了说明。我们观察到，锶同位素比值随处理的剧烈程度而变化，这表明头发内部存在锶的精细结构（横向横截面变化）；这些变化存在于锶浓度和同位素比值的差异中。因此，用最具侵略性的清洁方法处理过的头发和头发浸出物的 Sr 同位素比值分别反映了内部和总外部锶特征的同位素比值。这项研究的结果表明，可以将外部环境中的锶信号与内部信号区分开来，因此可以应用现代人类头发的锶同位素比值进行地理空间应用。
