湖泊沉积物XRF元素连续扫描与常规ICP-OES分析结果的对比及校正——以兹格塘错为例

摘要

岩芯X荧光光谱扫描仪(XRF)可以无需破坏样品,直接通过对剖开岩芯表面扫描获知沉积物的元素化学组成,但目前少有关于XRF连续扫描方法测试结果精度和准确性的研究.本文以高原封闭咸水湖泊兹格塘错湖相沉积岩芯为研究对象,利用XRF方法进行了高分辨率连续扫描,同时在岩芯不同层位选取了60个样品利用ICP-OES方法进行元素测定,通过对比及相关性分析,探讨了岩芯XRF元素连续扫描结果相对于ICP-OES分析结果的可对比性及其影响因素.结果显示:XRF方法与ICP-OES方法所测K、Ca、Ti、Cr、Mn、Fe和Sr等元素结果的相关系数较高,XRF扫描强度的变化可以反映样品元素含量的变化;两种方法测得元素S的结果相关系数较低,即XRF方法得到的元素S扫描结果不能真实反映沉积物中元素S含量的变化,进一步证实了XRF方法对非金属变价元素测试的局限性;受含水量影响,XRF元素的扫描强度随含水量增加而降低,尤其是K、Ca和Fe等元素的扫描强度相对于其含量在岩芯剖面上呈现由岩芯底部到顶部逐渐降低的趋势,利用元素Cl的扫描强度作为沉积物含水量的代用指标,对K、Ca、Ti和Fe元素扫描结果进行校正.校正后XRF扫描强度与元素含量的相关系数得到明显提高,基于此对兹格塘错沉积物XRF元素扫描结果进行定鼍转换,转换结果与ICP-OES所测非常一致.这为XRF元素分析方法在湖泊沉积物元素分析上的应用提供有力的支持和依据.%Using an X-ray Fluorescen (XRF) core scanner, chemistry features of bulk sediment can be measured directly which does not destruct sediment surface nor split sediment cores. This method has been potentially and widely applied to core sediment analysis, but little is known about the effects of sediment physical properties on XRF core scanner measurements. Comparison of intensities obtained by XRF and the chemical concentration measured by Inductively Coupled Plasma-Optical Emission Spectroscopy ( ICPOES), indicates effects of physical properties varied from different elements on elemental intensities in the lacustrine sediments of a core from Zigetang Co in the central Tibetan Plateau. Correlation among elements K, Ca, Ti, Cr, Mn, Fe and Sr between the two measurement methods of the XRF and the ICP-OES is high, but the correlation is low for element stlfur. This indicates that XRF measurements for non-metal elements such as sulfur, which has a multi-chemical valence, could be strongly affected by sediment properties. Comparing the ratios between element intensities and concentration, we found that the lower XRF element intensities were related to the amount of water. Using the intensity of Cl as an indicator of water content, the element intensities of K, Ca, Ti and Fe in the core samples were corrected. The correlation coefficients of each pairs of the two datasets among K, Ca, Ti and Fe were significantly raised. These data sets with highly correlations were used to produce a transfer function to relate XRF element intensity with element concentration. Calculated element concentrations from the intensities show only minor differences from concentrations obtained by ICP-OES, indicating XRF core scanners are a very useful tool for measuring element concentration in lacustrine sediments.