Conditions to obtain precise and true measurements of the intramolecular C distribution in organic molecules by isotopic C nuclear magnetic resonance spectrometry

Intramolecular ¹³C composition gives access to new information on the (bio) synthetic history of a given molecule. Isotopic ¹³C NMR spectrometry provides a general tool for measuring the position-specific ¹³C content. As an emerging technique, some aspects of its performance are not yet fully delineated. This paper reports on (i) the conditions required to obtain satisfactory trueness and precision for the determination of the internal ¹³C distribution, and (ii) an approach to determining the “absolute” position-specific ¹³C content. In relation to (i), a precision of <1% can be obtained whatever the molecule on any spectrometer, once quantitative conditions are met, in particular appropriate proton decoupling efficiency. This performance is a prerequisite to the measurement of isotope fractionation either on the transformed or residual compound when a chemical reaction or process is being studied. The study of the trueness has revealed that the response of the spectrometer depends on the ¹³C frequency range of the studied molecule, i.e. the chemical shift range. The “absolute value” and, therefore, the trueness of the ¹³C NMR measurements has been assessed on acetic acid and by comparison to the results obtained on the fragments from COOH and CH₃ by isotopic mass spectrometry coupled to a pyrolysis device (GC-Py–irm-MS), this technique being the reference method for acetic acid. Of the two NMR spectrometers used in this work, one gave values that corresponded to those obtained by GC-Py–irm-MS (thus, the “true” value) while the other showed a bias, which was dependent to the range covered by the resonance frequencies of the molecule. Therefore, the former can be used directly for studying isotope affiliations, while the latter can only be used directly for comparative data, for example in authenticity studies, but can also be used to obtain the true values by applying appropriate correction factors. The present study assesses several key protocol steps required to enable the determination of position-specific ¹³C content by isotopic ¹³C NMR, irrespective of the NMR spectrometer: parameters to be adjusted, performance test using [1,2-¹³C₂]acetic acid, generation of correction factors.     

三峡水利枢纽激光监测系统的有关问题

在已设计建成并已正常运转 10多年的真空中三点法激光测坝变形系统的基础上 ,本文对长距 离三峡水利枢纽相应系统的有关光学、激光问题进行了基本判断和必要建议 .     

A simplified compression test for the estimation of the Poisson's ratio of viscoelastic foams

This paper describes a simplified procedure for determining the Poisson's ratio of homogeneous and isotropic viscoelastic materials. A cylindrical shaped material is axially excited by an electromagnetic shaker and consequent displacement waves are investigated. Using a frequency sweep as an excitation signal, the frequency domain displacement response is measured upstream and sideways of the sample itself. A plane cross-section analytical model of the experimental setup is used to estimate Poisson's ratio through a minimisation-based procedure, applied to radial displacement once the complex modulus has been directly determined under the assumption of spring-like behaviour of the axial displacement. The results are presented and discussed for different materials and compared to well-established quasi-static and finite element simulations.     

Current interlaboratory precision of exchangeable soil fraction measurements

 In addition to conventional aqua regia and EDTA extracts for monitoring trace metals in soils, the technique of examining exchangeable soil fractions has been suggested to estimate soil contamination and trace metal availability to plants. In order to establish a useful method for soil monitoring, interlaboratory precision as a primary selection criterion has been investigated. In order to assess the quality of data provided by laboratories participating in the organization of the Austrian Governmental Agricultural Research Institutes (ALVA), three soil samples have been analysed in a common ring test, annually, for the last 20 years. In addition to the annual list of parameters used for soil monitoring, within ALVA two NH₄-acetate extracts were run in 1994, three NH₄-acetate and NH₄NO₃ extracts in 1995 and three LiCl extractions in 1998. The procedures were tested for analytical precision and environmental indications in up to 12 laboratories, with respect to Cd, Cr, Cu, Ni, Pb and Zn. Due to the low extraction efficiency, for determinations in the resultant solutions, graphite furnace AAS was preferably selected, except for Zn and Cu. Flame-AAS and ICP-OES were not sensitive enough for non-contaminated sites. Interlaboratory precision of the data was in the range 10–65% coeff.var., and thus within the range of data given in the appendix of DIN 19730 (NH₄NO₃), as well as in a previous BCR report. Indications from exchangeable fractions seemed to be good for Zn and Cu, whereas they were impossible for Cr. Received: 25 October 1998 / Accepted: 26 January 1999     

雨量预报方法的评价模型

建立了一个关于雨量预报方法的评估模型.首先,用软件分析与处理每天四个时段、每个时段等距离网格点上的雨量数据;其次,为了找到评价两种不同预测雨量方法的评价指数,对每个观察点上搜寻出与之距离最近的四个网格点,并用与之距离的倒数作为权重.每个点上评价指数定义为此最近四个点雨量加权和与预报值的比率.本文定义了两种雨量预报方法的综合评价指数.其一,定义精确性指数为预测雨量与真实雨量的偏差平方和的算术平方根;其一,将雨量数据转化为对应的等级,定义同级率指数为预测雨量与实际雨量占总点数的比例.对这两种评价指数的分析均说明预报方法一优于预报方法二.最后,对模型进行推广.     

Exhaust gas analysers and optimised sampling, uncertainties and costs

Decision-making in the conformity assessment of exhaust gas analysers with due account of measurement uncertainty and limited sampling is considered. Risks of incorrect decisions where test results lie in the vicinity of a specification limit are assessed in terms of percentage probability and the costs of measurement and environmental consequences, with examples based on the metrological requirements on these analysers stipulated in the new EU Measurement Instrument Directive. An optimised uncertainty methodology is proposed for the first time in legal metrology based on quantitative testing of new instruments for type approval and initial verification, and gives valuable insight into traditional rules limiting uncertainty in conformity assessment in general. Further, an analysis of subsequent verification of exhaust gas analysers in use in society, leads to a new optimised uncertainty methodology based on attribute sampling.

Synthesis monitoring of SBA-15 nanostructured materials

The SBA-15 materials were synthesized by the hydrothermal method using tetraethyl orthosilicate as silica source and P123 as template agent. The synthesis process was accomplished varying the time during the hydrothermal processing. For the synthesis monitoring, a small amount of sample was removed at different times, and analyzed by thermal analysis in order to determine the temperature ranges related to water desorption, template decomposition and silanol condensation for the SBA-15 nanostructured materials, as well as to estimate their quality. The samples were characterized by X-ray diffraction, infrared absorption spectroscopy, scanning electron microscopy, BET surface area and pore size distribution. The activation energy relative to decomposition of P123 template was determined from TG curves, using multiple heating rates and applying the model free kinetics. From the obtained data, it is possible to monitor the hydrothermal synthesis of SBA-15 in order to control the properties and conditions to prepare ordered materials.     

ISO 5725 and GUM: comparison and comments

We compare the approach to measure uncertainties proposed in ISO 5725 and GUM from a statistician point of view. In particular we give some warnings to the application of the expanded uncertainty introduced in GUM when the input variables are few and we report some considerations on the relevant role of the interactions among the input variables in the measurement equation as well as the role of statistical design of experiments to measure uncertainties.

Determination of spiramycin and neospiramycin antibiotic residues in raw milk using LC/ESI‐MS/MS and solid‐phase extraction

A simple confirmatory method for the determination of spiramycin and its metabolite neospiramycin in raw milk using LC ESI MS/MS is presented. Macrolide residues in raw milk were extracted by ACN, and sample extracts were further cleaned up and concentrated using SPE cartridges. Both spiramycin and neospiramycin were protonated in electrospray positive ion mode to form singly and/or doubly charged pseudomolecular ions. Data acquisition was achieved using multiple reaction monitoring, i.e., two transitions, for quantification and confirmation. Matrix‐matched standard calibration curves were utilized to achieve the best accuracy for the method. The method performance was evaluated according to both a conventional validation procedure and a designed experimental result. The measurement uncertainty arising from accuracy and precision was estimated. The method accuracy, expressed as a percentage of an overall recovery, was from 82.1 to 108.8%, and its intermediate precision was less than 20%. LC/ESI‐MS/MS method LODs (S/N ? 3:1) of spiramycin and neospiramycin were less than 1.0 μg/kg.     

大口径凸非球面反射镜的拼接检测算法研究

大口径凸非球面子孔径拼接干涉检测中的各子孔径之间为离轴形式,各子孔径之间除了平移和倾斜变换外,还含有旋转变换,测量结果中不可避免地会出现参考面未对准的情况,当进行数据拟合处理时,需要把由未对准造成的误差去除。本文在平面检测的最小二乘拟合基础上,对拟合算法进行了改进,从而实现了离轴子孔径的拼接检测拟合。为了验证算法的有效性,采用Matlab对口径为1m的大口径凸非球面的子孔径拼接检测的拟合过程进行了仿真实验,实验结果表明,离轴式大口径凸非球面干涉检测的子孔径拼接可采用改进后的最小二乘法拟合而成,且拟合精度可达到0.0048λ。