Producing SI-traceable reference values for Cd, Cr and Pb amount contents in polyethylene samples from the Polymer Elemental Reference Material (PERM) project using isotope dilution mass spectrometry

 The present paper describes the certification of the amount content of Cd, Cr and Pb in two different polyethylene materials within the third phase of the Polyethylene Elemental Reference Material (PERM) project. The analytical procedure to establish the reference values for Cd, Cr and Pb amount contents in these materials is based on isotope dilution mass spectrometry used as a primary method of measurement. Cd and Pb were measured with inductively coupled plasma-mass spectrometry and Cr with positive thermal ionization-mass spectrometry. The decomposition of the polymer matrix was carried out using a high pressure asher. Reference values for amount content, traceable to the SI-system, have been obtained for these three elements in both of the polyethylene samples of PERM. For each of the certified amount content values an uncertainty budget was calculated using the method of propagation of uncertainties according to ISO and EURACHEM guidelines. The measurement procedures, as well as the uncertainty calculations, are described for all three elements. In order to keep the whole certification process as transparent as possible, the preparations of various reagents and materials as well as the sample treatment and blending are described in detail. The mass spectrometry measurements and the data treatment are also explained carefully. The various sources of uncertainty present in the procedure are displayed in the uncertainty budgets. The obtained combined uncertainties for the amount content values were less than 2% relative (k=1) for all investigated elements. The amount contents were in the μmol/kg range, corresponding to mg/kg levels. Received: 21 October 1999 / Accepted: 29 January 2000     

EAL interlaboratory comparison Wa1 – Testing of potable water

 The accreditation of laboratories has emphasized the use of interlaboratory comparisons as a tool to monitor the comparability and accuracy of results laboratories produce. An interlaboratory comparison for water laboratories was organized among European Cooperation for Accreditation (EA) member countries; 30 laboratories, 7 of which were not accredited, from 14 European countries participated in this intercomparison. All the laboratories were chosen by the appropriate national accreditation bodies, with the instruction to select as participants those laboratories which act as national reference laboratories in this field. About 90% of the data collected was considered satisfactory after statistical treatment. Non-accredited laboratories performed as well as accredited laboratories. The laboratories were asked to take corrective action and report the corrections to the accreditation bodies. A great variation in the reported uncertainties of the results was observed. There seems to be a need to organize EA interlaboratory comparisons for national reference laboratories analysing water. It is obvious that even reference laboratories need training in how to estimate the uncertainty of results. Received: 22 July 1998 · Accepted: 21 September 1998     

分光光度法测定室内空气中甲醛含量不确定度评定

对室内空气中甲醛含量分析测试过程的误差进行了辨别.在此基础上评定了分析结果的不确定度.不确定度主要来源于样品采集、样品处理、标准溶液、标准曲线制作以及其它仪器的使用.依据不确定度评定的步骤,分析和计算得到了各分量不确定度和合成不确定度.     

Role of measurement uncertainty in conformity assessment in legal metrology and trade

There is increasing interest in the role of measurement uncertainty in conformity assessment, particularly where measurements are in support of fair trade, health & safety and the environment. A lack of clarity, however, in treating measurement uncertainties and in setting specification limits for compliance may sometimes lead to drastic consequences. Examples concerning conformity assessment, particularly in the measurement of trace quantities (Cd in plastics and antibiotic trace residues in shrimps), are amongst cases identified in the ongoing EU project MetroTrade, which can be significant impediments to international trade. This paper considers the present status of the role of measurement uncertainty in conformity testing, covering both recent work in international standardisation and physical metrology (e.g. OIML recommendations on weighing). One conclusion is that, while much has been achieved, there still exists some work to be done in order to facilitate acceptance of conformity from both customer and supplier and avoid perceived barriers to trade and serious international trade disputes.Presented at the MetroTrade Workshop on Traceability and Measurement Uncertainty in Testing, 30–31 January 2003, Berlin, GermanyAn erratum to this article can be found at     

Quantification of uncertainties involved in the conformational study of polymers by light scattering

Gel permeation chromatography (GPC) combined with a multi-angle light scattering (MALS) is a very powerful characterization technique because it provides both absolute molecular weight (M_w) and the radius of gyration (R_g) throughout the separated slices obtained by GPC. This combination of M_w and R_g, can be used to obtain information about the conformation of polymer chains in solutions and the branching of molecules. Due to the interesting properties obtained for polymers, it is essential to quantify the effect of different error sources in light scattering measurements as well as in the data treatment that highly affect the accuracy of obtained molar mass and radius of gyration. Usually, the results obtained for M_w and R_g in this analysis are dispersed for determined ranges of retention time and to have both reliable R_g and M_w for calculation, only high confidence data points have to be chosen. This range is arbitrarily chosen by the user for the data observation.In this work a new method of calculation to obtain R_g and M_w by means of GPC–MALS technique has been developed. As a first point, a data analysis procedure was set in order to describe both R_g and M_w vs. retention time and to determine the range where experimental data are confident. Several aspects in the data analysis have been studied. The polynomial fit function, the influence of the concentration of the sample, the reproducibility of the experiments and the conformational scaling law have been investigated by statistic technique in order to quantify the uncertainties involved.     

分析测试实验室内部质量控制中移动极差合并统计监控技术下的不确定度动态测量评估

本文采用统计质量保证技术(SQA,statistical quality rassurance)对被测体系的精密度和偏离性能做过持续性的监控分析。SQA技术的采用可以连续地表现出分析测量体系的能力,该技术的应用能确保测试数据的有效性,有利于分析测量体系潜在问题的分析。在此基础上,本文进一步提出了平均移动极差(MR)合并统计动态监控技术一本研究认为,采用该技术来进行分析测量系统的动态不确定度评估,其贡献量可由质控样品(QC)和线性拟合两部分合成。这一结论的得出能最大限度合成各种变异因素的影响,避免相关性的复杂计算,有利于分析测试实验室内部质量控制过程中测量系统的不确定度评估。     

Comparison of different methods to estimate the uncertainty in composition measurement by chromatography

Natural gas is a mixture that contains hydrocarbons and other compounds, such as CO₂ and N₂. Natural gas composition is commonly measured by gas chromatography, and this measurement is important for the calculation of some thermodynamic properties that determine its commercial value. The estimation of uncertainty in chromatographic measurement is essential for an adequate presentation of the results and a necessary tool for supporting decision making. Various approaches have been proposed for the uncertainty estimation in chromatographic measurement. The present work is an evaluation of three approaches of uncertainty estimation, where two of them (guide to the expression of uncertainty in measurement method and prediction method) were compared with the Monte Carlo method, which has a wider scope of application. The aforementioned methods for uncertainty estimation were applied to gas chromatography assays of three different samples of natural gas. The results indicated that the prediction method and the guide to the expression of uncertainty in measurement method (in the simple version used) are not adequate to calculate the uncertainty in chromatography measurement, because uncertainty estimations obtained by those approaches are in general lower than those given by the Monte Carlo method.     

Effectively designed molecularly imprinted polymers for selective isolation of the antidiabetic drug metformin and its transformation product guanylurea from aqueous media

In the present study, two novel molecularly imprinted polymers (MIPs) with remarkable recognition properties for metformin and its transformation product, guanylurea, have been prepared for their selective, enrichment, isolation and removal from aqueous media. The prepared adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and swelling experiments. The performance of the prepared MIPs was evaluated by various parameters including the influence of pH, contact time, temperature and initial compound concentration. The effects on the adsorption behavior of the removal process parameters were studied and the equilibrium data were fitted by the Langmuir and Freundlich models. Due to the imprinting effect, adsorption performance of MIPs was always superior to its corresponding NIP (non-imprinted polymer), with maximum adsorption capacity ∼80 mg g⁻¹ for both MIPs. Stability and reusability of the MIPs up to the 5th cycle meant that they could be applied repeatedly without losing substantial removal ability. In the next step, the prepared MIP nanoparticles were evaluated as sorbents in a dispersive solid phase extraction (D-SPE) configuration for selective enrichment and determination of metformin and guanylurea in different aqueous matrices. Under the working extraction conditions, the D-SPE method showed good linearity in the range of 50–1000 ng L⁻¹, repeatability of the extractions (RSD 2.1–5.1%, n = 3), and low limits of detection (1.5–3.4 ng L⁻¹). The expanded uncertainty of the data obtained was estimated following a bottom-up approach. The proposed method combined the advantages of MIPs and D-SPE, and it could become an alternative tool for analyzing the residues of METF and its transformation product GUA in complex water matrices, such as wastewaters.     

ICP-AES法测定蔬菜、水果中锌含量的不确定度评定

不确定度[1-3]在我国各行业的应用发展不均衡,在蔬菜、水果检测方法的评定方面鲜有报道。ICP作为一种灵敏度高、快速、高效的检测手段在食品、环保及其它领域得到了广泛的应用,其检测结果不确定度的评定较为重要。本文以ICP法测定番茄中的锌为例,对ICP法测定蔬菜、水果中重金属     

Uncertainty of nitrogen determination by the Kjeldahl method

 The uncertainty of the Kjeldahl method for determination of nitrogen in insulin was evaluated according the procedure described in the Guide to the Expression of Uncertainty in Measurement. The relative standard uncertainty of the method was found to be 0.19%, compared to the relative intermediate precision experimentally found to be 0.085%. The uncertainty components were organized in Tables, which allowed an easy overview and evaluation. The largest contribution to the uncertainty came from volumetric equipment. Systematic uncertainty budgets such as the design presented here facilitate the uncertainty evaluation process and makes it easier to compare uncertainty evaluations performed by different analysts. Received: 5 April 1999 / Accepted: 31 August 1999