pH计检定仪期间核查方法

介绍pH计检定仪的4种期间核查方法:传递比较法、多台对比法、留样测量法、实验室间比对法。传递比较法能直接反应pH计检定仪的变化,适用于已建立pH计检定仪检定装置的单位;多台对比法与留样测量法方便、快捷,可操作性强,适合大多数单位进行pH计检定仪的期间核查;实验室间比对法对设备要求较低,但需要协调的单位较多,周期较长,费用较高,实用性差。     

气相色谱仪灵敏度及检测限的测量不确定度评定

按JJF1059-1999《测量不确定度评定与表示》和JJG700-1999《气相色谱仪检定规程》评定了气相色谱仪检测器灵敏度或检测限测量的不确定度。给出了评定灵敏度及检测限的测量不确定度数学模型,并对各不确定度分量进行了评定。浓度型检测器灵敏度或检测限的相对扩展不确定度均为4.4%(k=2),质量型检测器检测限的相对扩展不确定度为3.8%(k=2)。依据JJF1033-2008《计量标准考核规范》采用比对法验证了灵敏度和检测限测量不确定度的合理性。     

电导率仪检定/校准结果质量控制

为确保电导率仪检定/校准结果的有效性,采取使用标准物质、人员比对、留存样品的重复检测、设备比对、使用可溯源结果的仪器、盲样测试等内部质量控制方式以及实验室间比对等质量控制方式。内部质量控制方式具有方便、快捷等优点,但不能发现实验室日常检验工作的漏洞与不足,不能识别与同行机构之间的差异;实验室间比对克服了实验室内比对的缺点,但具有样品传递周期长,前期准备时间长,费用高等缺点。比较上述各种质量控制方法的优缺点,为其它设备检定/校准结果质量控制提供参考。     

气相色谱仪FID检出限的测量不确定度

通过分析测量气相色谱仪FID检出限过程中各分量引入的测量不确定度,对FID栓出限的测量不确定度进行了评定。FID栓出限的相对不确定度为1.7％,扩展不确定度为3.4％（k=2）,采用比对法验证了评定结果的合理性。     

天然气气相色谱仪检定装置的建立

为了保证天然气工业用气相色谱仪分析结果准确可靠和量值溯源有效,依据JJG 1055—2009《在线气相色谱仪》、JJF1033—2016《计量标准考核规范》等规程规范要求,配置建标所需计量标准器,研究开展了重复性试验、不确定度评定、检定结果的验证等工作,建立了天然气气相色谱仪检定装置,通过了国家市场监督管理总局的现场考...     

电化学氧测定仪计量比对结果与分析

为做好电化学氧测定仪专项核查工作,加强对检定机构的监督管理,2021年青岛市计量技术研究院作为主导实验室,组织山东省11家已经建立电化学氧测定仪标准装置或氧气分析仪和氧气检测报警器标准装置的计量检定机构进行电化学氧测定仪计量比对。通过比对方案的有效实施和比对数据的统计计算,研究计量比对结果及各参比实验室存在的问题。根据11家参比实验室提交的数据,计算得出所有参比实验室的E_n值的绝对值均不大于1,比对结果均为满意;根据各参比实验室提交的文件材料,发现相关参比实验室在实验操作、数据记录、不确定度评定方面存在问题,提出应加强检定记录和检定证书的审核、人员培训、基础知识的学习的针对性意见。     

日本检定协会与宁波检验检疫局进行技术交流

不久前，日本检定协会（SK）中山一常务理事一行3人再次到宁波检验检疫局进行食品检测实验现场考核和交流。根据SK要求，宁波检验检疫局技术人员严格按照实验室SOP规定，对蜂蜜中的喹诺酮类药物检测进行了现场操作演示，SK技术专家认真查看了每一操作步骤，并仔细询问实验室质量管理体系的相关事宜。     

置信椭圆在能力验证中的应用

能力验证是判断和监控检测/校准实验室能力的有效手段,同时也是评价实验室技术能力的重要依据之一。为更好地考核实验室技术能力,能力验证样品通常设计成分割水平样品,即组织者为每个参加能力验证的实验室提供两份目标值水平略有差     

总悬浮颗粒物测试仪检定结果的不确定度评定

对总悬浮颗粒物测试仪检定结果的不确定度进行了评定,分析了检定过程中不确定度的主要来源,如计量标准、测量重复性、检定装置示值误差等.对各不确定度分量进行了量化,求得检定结果的相对扩展不确定度为1.8%(k=2).对检定结果不确定度评定的合理性进行了验证.     

控制图在直读光谱仪期间核查中的应用

期间核查是指在两次校准(或检定)的间隔期内进行的核查,核查对象有仪器设备、标准物质、计量基准、传递标准或工作标准,以判断所使用的设备、标准物质等是否保持检定时的置信度,满足检验工作的需要。此外,ISO/IEC 17025:2005《检测和校准实验室能力的通用要求》中第5.5设备和第5.6测量溯源性两个要素中都提到期间核查[1];CNAS-CL01:2010《检测和校准实验室能力认可     

Measurement of PAHs in environmental matrices: results from an interlaboratory comparison on the different steps of the measurement procedure

Proficiency testing (PT) is becoming a feature of laboratory accreditation and the PT results are used to assess the technical competence of the participating laboratories. ISPRA (former APAT) plays an important role in supporting the Italian laboratories belonging to the network of the Regional Environmental Agencies to improve the quality of their analytical measurements. As a consequence, ISPRA organized an interlaboratory comparison to assess the performance of the laboratories on PAH measurement procedure. The interlaboratory comparison was drawn separating the different steps of the measurement (from the extraction to the instrumental measurement). Two matrix reference materials: (1) a polluted soil and (2) an extract reference material of the same polluted soil and a “blind” PAH mixture standard stock solution were distributed to 59 Italian laboratories. The results of interlaboratory comparison showed a significant dispersion of the PAH measurements that masks the effects of the different extraction and cleanup procedures used, but it is consistent with the results of other European interlaboratory comparisons.     

The BIOREMA project—Part 2: International interlaboratory comparison for biodiesel test methods

The results of an interlaboratory comparison, using various measurement methods to carry out biodiesel testing, are presented and the findings are discussed. The interlaboratory comparison was organised within the framework of an EU-funded project called BIOREMA. A general overview of the project and results of an interlaboratory comparison on bioethanol are published as Part 1 and 2 of this series of papers. In the study presented here, reference values, provided by national metrology institutes and expert laboratories, were used for evaluating the results. Consensus values, derived from the results of all participants, were used to assess any bias between the results from the national metrology institutes and testing laboratories. The emphasis in this interlaboratory comparison was not the performance rating of the individual laboratories, but recognising and interpreting differences caused by the measurement methods applied. For most biodiesel parameters, a good agreement of measurement results was found among different methods, and between the consensus and reference values. The study material was a rapeseed oil fatty acid methyl ester, for which it was demonstrated that it is feasible to prepare and characterise reference materials for biodiesel with well-established reference values for many parameters.     

Ion chromatographic precision measurement procedure for electrolytes in human serum: validation with the aid of primary measurement procedures

In order to make analytical measurement results traceable to the SI units in the field of clinical chemistry, an ion chromatographic (IC) measurement procedure has been developed which allows the amount of substance of the four so-called electrolytes Na, K, Mg and Ca as well as that of Li to be determined efficiently in human serum and with high accuracy. The IC measurement procedure was validated using primary measurement procedures confirmed by international comparison measurements and is proposed for use as a transfer standard when comparing measurements with clinical reference laboratories. The solutions used for calibration were gravimetrically prepared from pure substances (salts). Their chemical compositions had been iteratively fitted to those of the samples. The serum samples were mineralized by microwave-assisted digestion. The following relative expanded uncertainties for the average elemental contents were obtained: Li 0.4%, Na 0.14%, K 0.6%, Mg 0.8% and Ca 0.4%.     

Ion chromatographic precision measurement procedure for electrolytes in human serum: validation with the aid of primary measurement procedures

In order to make analytical measurement results traceable to the SI units in the field of clinical chemistry, an ion chromatographic (IC) measurement procedure has been developed which allows the amount of substance of the four so-called electrolytes Na, K, Mg and Ca as well as that of Li to be determined efficiently in human serum and with high accuracy. The IC measurement procedure was validated using primary measurement procedures confirmed by international comparison measurements and is proposed for use as a transfer standard when comparing measurements with clinical reference laboratories. The solutions used for calibration were gravimetrically prepared from pure substances (salts). Their chemical compositions had been iteratively fitted to those of the samples. The serum samples were mineralized by microwave-assisted digestion. The following relative expanded uncertainties for the average elemental contents were obtained: Li 0.4%, Na 0.14%, K 0.6%, Mg 0.8% and Ca 0.4%.

     

Metrological compatibility—a key issue in future accreditation

Global acceptance of measurement results from accredited laboratories is linked to their metrological compatibility, defined in VIM 3 as a comparison between all measurement results in a set. It is therefore most unfortunate that a recent IUPAC/CITAC Guide applies the same term to a comparison between a certified value and the measured quantity values in a set.     

Evaluation of a Brazilian ion chromatography interlaboratory study

This paper describes a Brazilian interlaboratory program study on anion measurement in synthetic water. The program described is promoted regularly since 2007 and recommended the use of ion chromatography as analytical technique for all participant laboratories. Two samples (X and Y) with different anion (fluoride, chloride, nitrite-N, nitrate-N, sulfate and phosphate-P) concentration levels were twice distributed in 2011. Each sample on each round had the homogeneity, and the stability tested for a period of 15 days. Upon ensuring the homogeneity and stability, the samples were distributed to 39 laboratories located around the country. The aim of this study was to verify the laboratories’ precision and to establish the measurement comparability among Brazilian laboratories that routinely use ion chromatography for water sample analysis. It was also possible to identify the most frequent sources of systematic and random errors for each measured anion, related to the ion chromatography technique. Some specific metrological issues related to the geographical region are discussed.     

Method validation and verification in liquid scintillation counting using the long-term uncertainty method (LTUM) on two decades of proficiency test data

Results from proficiency tests gathered over the past two decades by the laboratory for low level radioactivity measurements for liquid scintillation counting of ³H (184 results) and ¹⁴C (74 results) are used to verify the validated measurement methods used by the laboratory, in particular the estimated uncertainty budget of the method and its reproducibility and stability. A linear regression approach is used for the analysis of the results, described in the literature as the long term uncertainty in measurement method. The present study clearly indicates the advantages of using proficiency test results in identifying possible constant or proportional bias effects as well as the possibility to compare the laboratory performance with the performance of peer laboratories.

     

Purity verification and measurement uncertainty

In chemical analysis, laboratories are required to verify the purity of reference material being used. Also, the contributions from the verification procedure, where significant, have to be included in the estimation of the total measurement uncertainties of the test results. One common verification procedure is to use another source of the same material if an appropriate certified reference material were not available. This involves a comparison test where the purity value of the reference standard is determined using a second source reference standard as the “calibrant”. In normal practice, the standard uncertainty of the purity value of a reference standard is estimated according to the probability distribution function (PDF) of the possible purity values of the reference standard concerned. With the use of Monte Carlo simulation technique, this paper attempted to study the effect of verification process on that PDF and thus the associated standard uncertainty as well. Also, the effects of parameters like the purity of the second source reference standard, the method precision and the acceptable range set for the comparison test on the verification outcome were discussed.     

Interlaboratory comparison for the determination of five residual organochlorine pesticides in ginseng root samples by gas chromatography

An interlaboratory comparison study for the determination of 5 residual organochlorine pesticides (hexachlorobenzene and 4 hexachlorocyclohexane isomers) in ginseng root was performed. This program [Asia Pacific Laboratory Accreditation Cooperation (APLAC) T049] was the first of its kind for an herbal matrix and involved the participation of 70 laboratories from 26 countries worldwide. Consensus mean values were computed statistically from the reported results, which were eventually used to assess the performance of individual laboratories in terms of the z-scores. The distribution of analytical data was found to be widespread, with standard deviation ranging from 43.9 to 55.9%, and the result patterns obtained were similar to those residue pesticide programs using other matrixes. Although the estimation of measurement uncertainty is a crucial requirement for all quantitative tests for laboratories that meet the requirements of International Organization for Standardization/International Electrotechnical Commisssion (ISO/IEC) 17025, some laboratories in this program had difficulties and showed unfamiliarity with respect to that quality criterion. It was recommended that laboratories review and rectify the situation promptly so that they would have a better understanding of measurement uncertainty or the test service provided.     

Comprehensive method comparisons: getting more from the data

It is an established procedure in laboratories to verify measurement methods by comparison of results from patient samples (split sample). The information retrieved and evaluated from a comparison is often limited to a scatter plot, a regression analysis and a differential plot. However, many more features and performance criteria are available from the same data. Access to a comprehensive set of information can also be used to harmonize results by recalibration and estimate any risk in applying alternate methods or surrogates to reference methods. Common principles for comparison of results are explained. Well known and new relations between commonly used methods and their limitations are discussed. A new application of the empirical folded density functions is introduced, and the use of a simplified error grid in the evaluation of a comparison is explored. Parametric and nonparametric pairwise significance tests and a convenient option of partitioning and limiting the dataset, ordinary linear and Deming regression functions, including uncertainties of the constants are provided in an Excel spreadsheet that is submitted as a downloadable supplemental file. The information harboured in a split sample comparison of methods is explored in detail. Procedures cover the main content of CLSI recommendations EP9, EP21 and EP27. Several additional practical procedures are described in a submitted single spreadsheet program.