Straight William H, Karr Jonathan D, Cox Julia E, Barrick Reese E
Duke Environmental Stable Isotope Laboratory (DEVIL), Duke University, Department of Biology & Nicholas School of the Environment and Earth Sciences, National Phytotron, Durham, NC 27708-0340, USA.
Rapid Commun Mass Spectrom. 2004;18(23):2897-903. doi: 10.1002/rcm.1706.
Although previous work has demonstrated that biological phosphates ('biophosphates') record significant changes in delta18O associated with variations in local climate and seasonality, the repeatability of these analyses between laboratories has not previously been tested. We serially sampled enamel on four Cretaceous dinosaur teeth for phosphate delta18O analysis at up to three different facilities. With the exception of one set of unprocessed enamel samples, the material supplied to each laboratory was chemically processed to silver phosphate. Each laboratory analyzed sample sets by pyrolysis (thermochemical decomposition) in a ThermoFinnigan TC/EA attached to a ThermoFinnigan Delta Plus mass spectrometer. Significant interference between phosphate samples and the NIST reference material 8557 barium sulfate (NBS 127) distorts some of the results. Samples analyzed immediately following NBS 127 may be depleted by 6 per thousand isotopically and in instrument peak amplitude response by 80%. Substantial interference can persist over the subsequent 20 silver phosphate samples, and can influence the instrument peak amplitude response from some organic standards. Experiments using reagent-grade silver phosphate link these effects to divalent cations, particularly Ca2+ and Ba2+, which linger in the reactor and scavenge oxygen evolved from pyrolysis of subsequent samples. Unprocessed enamel includes 40 wt% calcium and self-scavenges oxygen, disrupting the isotopic measurements for the first half of a set and depleting subsequent organic standards by up to 9 per thousand. In sets without NBS 127 or calcium, such interference did not occur and an interlaboratory comparison of results from enamel shows reproducible, significantly correlated peaked delta18O patterns with a 2-3 per thousand dynamic range, consistent with previous results from contemporaneous teeth. Whereas both unprocessed enamel and the NBS 127 barium sulfate should be applied to biological phosphate ('biophosphate') stable isotope research with caution, seasonal variations in enamel phosphate delta18O are a paleoecologically valuable, reproducible phenomenon in theropod dinosaur teeth.
尽管先前的研究表明，生物磷酸盐（“生物磷”）记录了与当地气候和季节性变化相关的δ18O显著变化，但此前尚未对不同实验室之间这些分析的可重复性进行测试。我们对四颗白垩纪恐龙牙齿的牙釉质进行了连续采样，以便在多达三个不同的实验室进行磷酸盐δ18O分析。除了一组未处理的牙釉质样本外，提供给每个实验室的材料都经过化学处理制成磷酸银。每个实验室通过连接到ThermoFinnigan Delta Plus质谱仪的ThermoFinnigan TC/EA进行热解（热化学分解）分析样本集。磷酸盐样本与NIST参考物质8557硫酸钡（NBS 127）之间的显著干扰会使一些结果失真。在NBS 127之后立即分析的样本，其同位素可能会减少6‰，仪器峰值幅度响应会减少80%。在随后的20个磷酸银样本中，大量干扰可能会持续存在，并会影响一些有机标准品的仪器峰值幅度响应。使用试剂级磷酸银的实验将这些影响与二价阳离子联系起来，特别是Ca2+和Ba2+，它们残留在反应器中，并清除后续样本热解产生的氧气。未处理的牙釉质含有40 wt%的钙，并能自我清除氧气，这会干扰一组样本前半部分的同位素测量，并使后续有机标准品的同位素减少多达9‰。在没有NBS 127或钙的样本组中，不会出现这种干扰，对牙釉质结果的实验室间比较显示，δ18O峰值模式具有可重复性、显著相关性，动态范围为2 - 3‰，与同期牙齿的先前结果一致。虽然未处理的牙釉质和NBS 127硫酸钡都应谨慎应用于生物磷酸盐（“生物磷”）稳定同位素研究，但牙釉质磷酸盐δ18O的季节性变化是兽脚亚目恐龙牙齿中一种具有古生态价值且可重复的现象。
