The use of certified reference materials in the Romanian traceability scheme

 For ensuring the traceability and uniformity of measurement results, the main objectives of national metrology programmes in chemistry are to calibrate and verify measuring instruments, to evaluate the uncertainty of measurement results and to intercompare the analytical results, etc. The concept of traceability has developed recently in chemical measurements, thus, an attempt to implement the principles of metrological traceability especially by appropriateness calibration using composition certified reference materials (CRMs) is underlined. Interlaboratory comparisons are also a useful response to the need for comparable results. The paper presents some aspects and practices in the field of spectrometric measurement regarding the metrological quality of the traceability by calibrating the instruments using suitable and reliable CRMs. The uncertainty of results, as a measure of the reliability that can be placed on them, has been adequately described in different documents and, as a consequence, some examples of evaluating the measurement uncertainty are described. The relationship between uncertainty and traceability, as two fundamental concepts of metrology which are intimately linked, is underlined. Received: 12 November 1999 / Accepted: 10 December 1999     

The influence of collecting substrates on the single-particle characterization of real atmospheric aerosols

This work investigated the influence of three different collecting substrate materials, Ag and Al foils and grids for transmission electron microscopy (TEM grid), on the morphological and chemical compositional analysis of individual particles collected at an underground shopping area in Seoul, Korea. The feasibility of using each substrate in a quantitative single-particle analysis was evaluated by comparing particle morphologies, X-ray spectra, and elemental quantification results obtained for the three substrates. The morphologies and the quality of X-ray spectra for crystalline mineral particles were very similar among the three substrates. However, water-soluble, CNO-rich aerosols showed different morphologies among the three substrates, mainly due to the differences in the hygroscopic properties of the substrates. The quality of the X-ray spectra of the CNO-rich particles was optimal when collected on the TEM grid. To reliably assess the characteristic X-rays of the CNO-rich particles collected on the Ag and Al foils, appropriate data analysis had to be applied. Especially, the X-ray spectra of the CNO-rich particles collected on Al foil required a new background subtraction procedure. The overall relative abundances of the chemical species, obtained from the three collecting substrates, were in good agreement with each other and single-particle characterization of the real aerosol sample was feasible on the different substrates. However, the TEM grid substrate was the most appropriate for single-particle analysis of the water-soluble CNO-rich particles as: (i) it retains the original morphology and size of the particles, (ii) it allows high contrast in the backscattered electron image (BSEI) mode, and (iii) it provides a high peak-to-background ratio (P/B) with small and correctable interferences in the X-ray spectra.     

聚二甲基硅氧烷芯片自由酶反应器检测葡萄糖

应用电泳中介微分析(EMMA)技术,构建聚二甲基硅氧烷(PDMS)芯片自由酶反应器, 在线检测葡萄糖(Glu),在十字形的芯片通道上,采用自制的碳纤维微电极检测葡萄糖氧化酶(GOD)催化氧化Glu生成的H2O2,并对检测电位、GOD浓度、GOD进样时间、分离电压等参数进行了优化,测定了该自由酶反应器的线性范围和检出限,考察了其重现性及稳定性.结果表明,此自由酶反应器制作方便,操作简单,重现性好,Glu浓度在0.1～20 mmol/L之间有较好的线性关系(r=0.997),检出限为19.8 μmol/L(S/N=3).     

下地幔温压下(Mg,Fe)SiO3钙钛矿的相稳定性——对冲击回收样品的微观分析

 在60~110 GPa冲击压力（估算温度为2 300~4 800 K）范围内进行了5发原始样品为(Mg_0.92,Fe_0.08)SiO₃顽火辉石的冲击压缩回收实验，对回收样品进行的X射线衍射（XRD）和红外吸收光谱（IR）分析结果表明：（1）回收样品的主相均是单链状结构硅酸盐，而非钙钛矿结构；（2）回收样品中均未观察到氧化物SiO₂和(Mg_0.92,Fe_0.08)O的XRD 和IR特征谱线；（3）回收样品的XRD、IR特征谱线变得简略，并发现了与原始样品有某些不同的特征谱线，随冲击压力增加，这种变化趋于明显；（4） 通过对比冲击压力在85 GPa以下和97 GPa以上回收样品的XRD、IR特征谱线，没有观察到明显的新谱线特征出现。结合先前的冲击Hugoniot状态方程实验数据分析，可以认为：在冲击压缩过程中样品处于钙钛矿结构，在冲击卸载过程中样品发生了由钙钛矿结构向单链状结构的逆转相变；特别是，在实验的温度压力范围内，不可能发生由(Mg_0.92,Fe_0.08)SiO₃向SiO₂和(Mg_0.92,Fe_0.08)O的化学分解相变，顽火辉石的高压相——钙钛矿结构是稳定的。回收样品和原始样品的谱线差异可能对应于高压加载或卸载过程引起的某种晶格畸变，而高压加载导致钙钛矿型顽火辉石晶格畸变的可能性更大。这一结果将对下地幔矿物学模型的建立和下地幔地震波探测结果的解释提供基础物理依据。     

High-Spatial-Resolution Low-Energy Electron Beam X-Ray Microanalysis

 Performing X-ray microanalysis at beam energies lower than those conventionally used (< 10 keV) is known to significantly improve the spatial resolution for compositional analysis. However, the reduction in the beam energy which reduces the X-ray interaction diameter also introduces analytical difficulties and constraints which can diminish the overall analytical performance. This paper critically assesses the capabilities and limitations of performing low beam energy, high spatial resolution X-ray microanalysis. The actual improvement in the spatial resolution and the reduction in the X-ray yield are explored as the beam energy is reduced. The consequences for spectral interpretation, quantitative analysis and imaging due to the lower X-ray yield and the increased occurrence of X-ray line overlaps are discussed in the context of currently available instrumentation.     

Improved peak capacity for CE separations of enzyme inhibitors with activity‐based detection using magnetic bead microreactors

A technique for separating and detecting enzyme inhibitors was developed using CE with an enzyme microreactor. The on‐column enzyme microreactor was constructed using NdFeB magnet(s) to immobilize alkaline phosphatase‐coated superparamagnetic beads (2.8 μm diameter) inside a capillary before the detection window. Enzyme inhibition assays were performed by injecting a plug of inhibitor into a capillary filled with the substrate, AttoPhos. Product generated in the enzyme microreactor was detected by LIF. Inhibitor zones electrophoresed through the capillary, passed through the enzyme microreactor, and were observed as negative peaks due to decreased product formation. The goal of this study was to improve peak capacities for inhibitor separations relative to previous studies, which combined continuous engagement electrophoretically mediated microanalysis and transient engagement electrophoretically mediated microanalysis to study enzyme inhibition. The effects of electric field strength, bead injection time and inhibitor concentrations on peak capacity and peak width were investigated. Peak capacities were increased to ≥20 under optimal conditions of electric field strength and bead injection time for inhibition assays with arsenate and theophylline. Five reversible inhibitors of alkaline phosphatase (theophylline, vanadate, arsenate, L ‐tryptophan and tungstate) were separated and detected to demonstrate the ability of this technique to analyze complex inhibitor mixtures.     

Ratio-contrast imaging of dual-energy absorption for element mapping with a scanning transmission X-ray microscope

The detection of chemical mapping with a spatial resolution of 30 nm has been achieved with a scanning transmission X‐ray microscope at the Shanghai Synchrotron Radiation Facility. For each specimen, two absorption images were scanned separately with energies E₁ and E₂: E₁ was focused on the absorption edge of the chosen element and E₂ was focused below the edge. A K‐edge division method is proposed and applied to obtain the element mapping. Compared with the frequently used K‐edge subtraction method, this ratio‐contrast method is shown to be more accurate and sensitive in identifying the elements of interest, where the definition of the contrast threshold is simple and clear in physics. Several examples are presented to illustrate the effectiveness of the method.     

Spatial resolution limitation in Auger microanalysis of compounds

The width of the resolved gap between the features of Auger images was calculated by Rayleigh criterion. When the threshold contrast is provided, this width is almost independent of the examined specimen nature and is defined only by probing electron beam diameter. The relation between the irradiation dose, contrast and spatial resolution is deduced. The flexible dependence allowing to evaluate both the real and maximum attainable spatial resolution of Auger images is obtained.     

Monte Carlo correction programme for PC

A Monte Carlo correction program for quantitative microanalysis on PC computer is introduced in this paper. The elastic scattering is described by the screened Rutherford cross section. Instead of computing the energy loss according to the actual path between two scatterings we have defined the Bethe inelastic cross section determined by the Bethe-slowing-down approximation. It is assumed that it causes no angular departure of the scattered electron. In the second model we took into account the angular dependence of inelastic scattering assuming that the primary electron interacts with quasi-free atom electrons. On the basis of these two models analytical Monte Carlo programmes were developed and experimentally tested on some oxide glass. Our results are fully comparable to those obtained by ten world microprobe laboratories using classical ZAF correction or Bence-Albee methods. We have found that introducing angular part of the inelastic cross section analytical results did not significantly change. All of our results were carried out for bulk specimens but extending it to layers is under the development.