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首页> 外文期刊>Journal of mass spectrometry: JMS >Oxygen isotope analysis of phosphate: improved precision using TC/EA CF-IRMS
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Oxygen isotope analysis of phosphate: improved precision using TC/EA CF-IRMS

机译：磷酸盐的氧同位素分析：使用TC / EA CF-IRMS改进了精度

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摘要

Oxygen isotope values of biogenic apatite have long demonstrated considerable promise for paleothermometry potential because of the abundance of material in the fossil record and greater resistance of apatite to diagenesis compared to carbonate. Unfortunately, this promise has not been fully realized because of relatively poor precision of isotopic measurements, and exceedingly small size of some substrates for analysis. Building on previous work, we demonstrate that it is possible to improve precision Of delta O-18(PO4) measurements using a 'reverse-plumbed' thermal conversion elemental analyzer (TC/EA) coupled to a continuous flow isotope ratio mass spectrometer (CF-IRMS) via a helium stream [Correction made here after initial online publication]. This modification to the flow of helium through the TC/EA, and careful location of the packing of glassy carbon fragments relative to the hot spot in the reactor, leads to narrower, more symmetrically distributed CO elution peaks with diminished tailing. In addition, we describe our apatite purification chemistry that uses nitric acid and cation exchange resin. Purification chemistry is optimized for processing small samples, minimizing isotopic fractionation of PO4-3 and permitting Ca, Sr and Nd to be eluted and purified further for the measurement of delta Ca-44 and Sr-87/Sr-86 in modern biogenic apatite and Nd-143/Nd-144 in fossil apatite. Our methodology yields an external precision of +/- 0.15 parts per thousand (1 sigma) for delta O-18(PO4). The uncertainty is related to the preparation of the Ag3PO4 salt, conversion to CO gas in a reversed-plumbed TC/EA, analysis of oxygen isotopes using a CF-IRMS, and uncertainty in constructing calibration lines that convert raw delta O-18 data to the VSMOW scale. Matrix matching of samples and standards for the purpose of calibration to the VSMOW scale was determined to be unnecessary. Our method requires only slightly modified equipment that is widely available. This fact, and the demonstrated improvement in precision, should help to make apatite paleothermometry far more accessible to paleoclimate researchers.
机译：长期以来，生物磷灰石的氧同位素值已被证明具有潜在的古热计量潜力，因为与碳酸盐相比，化石记录中的物质丰富且磷灰石对成岩作用的抵抗力更大。不幸的是，由于同位素测量的相对较差的精度以及某些用于分析的底物的尺寸过小，因此尚未完全实现这一承诺。在之前的工作基础上，我们证明，使用“逆铅锤式”热转换元素分析仪（TC / EA）与连续流同位素比质谱仪（CF）结合，可以提高delta O-18（PO4）测量的精度-IRMS）通过氦流[在线首次发布后，在此处进行了纠正]。对通过TC / EA的氦气流量的这种修改，以及相对于反应器中热点相对玻璃碳碎片堆积的仔细定位，会导致更窄，更对称分布的CO洗脱峰，并且拖尾减少。此外，我们描述了使用硝酸和阳离子交换树脂的磷灰石纯化化学方法。对纯化化学进行了优化，以处理小样品，最大程度地减少了PO4-3的同位素分馏，并允许洗脱Ca，Sr和Nd并进一步纯化以用于测量现代生物成因磷灰石中的δ-Ca-44和Sr-87 / Sr-86。化石磷灰石中的Nd-143 / Nd-144。对于δO-18（PO4），我们的方法得出的外部精度为千分之+/- 0.15（千分之一）。不确定性与制备Ag3PO4盐，在反向管道TC / EA中转化为CO气体，使用CF-IRMS分析氧同位素以及构建将原始O-18数据转换为标定线的校准线有关VSMOW规模。确定不需要将样品和标准品进行矩阵匹配以校准至VSMOW规模。我们的方法只需要稍作改动的设备即可广泛使用。这个事实以及精确度的提高，应该有助于使古气候研究人员更容易获得磷灰石古温度计。

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