Structural investigation of mM Ni(II) complex isomers using transmission XAFS: the significance of model development

High‐accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N‐n‐propyl‐salicylaldiminato) nickel(II) (n‐pr Ni) and bis(N‐i‐propyl‐salicylaldiminato) nickel(II) (i‐pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple‐scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT‐like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i‐pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χ_r² = 2.94. The structure of (n‐pr Ni) is best modelled with a distorted square planar geometry, χ_r² = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k‐range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.     

High‐accuracy X‐ray absorption spectra from mM solutions of nickel (II) complexes with multiple solutions using transmission XAS

A new approach is introduced for determining X‐ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X‐ray absorption fine structure (XAFS) along the lines of the high‐accuracy X‐ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N‐n‐propyl‐salicylaldiminato) nickel(II) and bis(N‐i‐propyl‐salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mM and 1.5 mM dilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X‐ray absorption near‐edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordination geometries. For the first time, (transmission) XAS of the isomers have been determined from low‐concentration solutions on an absolute scale with a 1–5% accuracy, and with relative precision of 0.1% to 0.2% in the active XANES and XAFS regions after inclusion of systematic corrections.     

顶空气相色谱法测定医用透明质酸钠凝胶中乙醇残留量的不确定度

按YY 0308-2004要求,采用顶空气相色谱法测定了医用透明质酸钠凝胶中的乙醇残留量,依据JJF l059-1999,CNAS-GL 06,对测量结果的不确定度来源进行了系统分析,并对各不确定度分量进行了评定和量化,计算了合成标准不确定度和扩展不确定度,测定结果为(344.10±37.51)μg/g,k=2。结果表明,影响测量结果的主要因素为标准曲线拟合引入的不确定度。     

X射线荧光光谱法测定铝合金中铜元素的测量不确定度评定

利用X射线荧光光谱法(XRF)对硬铝合金中铜元素进行测定,分析了测量不确定度来源,并对不确定度分量进行评定,经计算得出合成标准不确定度和扩展不确定度。当硬铝合金中铜的质量分数为4.33%时,扩展不确定度为0.17%(k=2)。     

柚皮素标准物质的研制及不确定度评定

建立了柚皮素标准物质的研制和定值方法。通过红外光谱和核磁共振氢谱对样品进行定性分析,经过柱层析纯化、干燥、混匀后,分装得到120瓶样品。采用质量平衡法和差示扫描量热法进行定值分析(质量平衡法包括液相色谱面积归一化法、水分、无机杂质和残留溶剂的测定)。运用液相色谱法考察了样品的均匀性和稳定性,并对定值结果进行了不确定度评定。结果显示,研制的柚皮素标准物质具有良好的均匀性和稳定性,定值结果为99.2%,扩展不确定度为0.2%,有效期6个月。     

电感耦合等离子体质谱法测定岩石中47种元素的不确定度评定

采用封闭酸溶电感耦合等离子体质谱(ICP-MS)法测定岩石样品,分别对47种元素的测量结果不确定度进行评定。通过分析测试方法和测量条件,得到测量结果的不确定度主要由样品称量、样品溶液定容和样品溶液中元素浓度测量引入。在实验室质控条件下,对各不确定度分量进行评定和计算,其中随机因素导致的不确定度采用期间精密度试验综合评价,即采用A类方法评定。共完成了16个岩石国家标准物质(GBW 07103~GBW 07123)47种元素测量结果的不确定度合成,并参照GB/T 6379.2-2004,建立了含量w与扩展不确定度U之间的关系模型,运用这一关系模型可得到测量结果的不确定度估计值,只要测量过程本身或所使用的设备未变化,就不需要再重复进行不确定度评估。     

如何给工科学生讲波函数(3)

本文介绍作者在华中理工大学给二年级工科学生讲波函数的思路与方法 .     

An alternative to the effective number of degrees of freedom

 In order to calculate the expanded uncertainty when one or more of the components of the standard uncertainty is based on a small number of degrees of freedom, the ISO Guide recommends utilising the 'effective number of degrees of freedom'. Calculating and utilising the 'effective number of degrees of freedom' to obtain a confidence interval both depend upon approximations, which, however, are adequate for determining an expanded uncertainty. This paper puts forward an alternative and simpler approximation which is also adequate but which is much easier to apply than the multi-step process given in the ISO Guide. Received: 2 July 1998 · Accepted: 12 August 1998     

Assessment of compliance of analytical results with regulatory or specification limits

 In some cases the compliance of a measurement result with a limit value will be unclear and a 'judgment' is required based on agreed criteria. Recent developments in the estimation of measurement uncertainty have opened up the possibility of a more rational approach to such problems. This paper briefly reviews some of the issues and current practices and suggests a pragmatic way forward. Received: 26 August 1998 · Accepted: 31 August 1998