能力验证计划中防止数据串通的措施

为保证能力验证结果评价有效、可信、公平,对能力验证计划防止数据串通的措施进行了探讨。从样品设计、样品量发放、检测周期3个方面介绍了防止数据串通的措施,以CNAS PT0017–T029"离子色谱法测定水中Cl~–,SO_4^(2–)及NO_3~–三种阴离子的含量"能力验证计划为例,讨论能力验证计划防止数据串通措施的具体实施方法。结果显示,设计分割水平样品、减少样品发放量、缩短能力验证结果上报周期等几种措施可以有效地防止能力验证数据的串通,为能力验证活动的健康发展提供了参考。     

Determination of PCBs in river sediment samples—proficiency test for selected Polish laboratories

Eighteen Polish laboratories participated in a proficiency test for the determination of PCBs in river sediment. The participants used their in-house method. The aim of the exercise was to obtain information about the state of the art of PCB analysis in environmental samples. Five PCBs (IUPAC nos. 52, 118, 138, 153 and 180) were selected for the test. The relative standard deviation of the analytical results submitted varied from 45 to 65%, with an outlier rate of 7%. The averages of the results for all analytes were in good agreement with reference values.     

Quality control in extended measurement campaigns: selection of contract laboratories by proficiency testing exemplified for the trace analysis of anilines in groundwater

An interlaboratory comparison for the determination of aniline, nine methylated anilines and chlorinated anilines in contaminated groundwater (each compound between 1 µg L^?1 and 750 µg L^?1) was conducted as proficiency test for the selection of contract laboratories for a groundwater monitoring campaign. For the 13 participants, two different test sample series were prepared from a stabilized real case groundwater. Series A was the groundwater as sampled in the field and series B was prepared from series A by spiking with selected anilines. Homogeneity and stability investigations revealed that contaminated groundwater provides a viable basis for the preparation of ring test samples for the determination of anilines. Analytical procedures were limited to the standardized liquid–liquid extraction or solid-phase extraction in combination with gas chromatography/mass spectrometry (DIN 38407-16:1999). The robust consensus values were evaluated according to the standardized protocol of DIN 38402-45:2013. Robust reproducibility standard deviations ranged largely between 20?% and 60?% depending on the analyte. The proficiency assessment of individual participants combined the qualitative aspect of correct peak identification with the quantitative determination of individual concentrations within set limits in a unified approach. It could be shown that the accreditation status of laboratory and the existence of a standardized analytical procedure do not substitute a problem-related proficiency assessment of potential contractors.     

Evaluation of the performance of 57 Japanese participating laboratories by two types of z-scores in proficiency test for the quantification of pesticide residues in brown rice

A proficiency test for the analysis of pesticide residues in brown rice was carried out to support upgrading in analytical skills of participant laboratories. Brown rice containing three target pesticides (etofenprox, fenitrothion, and isoprothiolane) was used as the test samples. The test samples were distributed to the 57 participants and analyzed by appropriate analytical methods chosen by each participant. It was shown that there was no significant difference among the reported values obtained by different types of analytical method. The analytical results obtained by National Metrology Institute of Japan (NMIJ) were 3 % to 10 % greater than those obtained by participants. The results reported by the participant were evaluated by using two types of z-scores, that is, one was the score based on the consensus values calculated from the analytical results of participants, and the other one was the score based on the reference values obtained by NMIJ with high reliability. Acceptable z-scores based on the consensus values and NMIJ reference values were achieved by 87 % to 89 % and 79 % to 94 % of the participants, respectively. Graphical Abstract

Distribution of z and z_NMIJ-scores for isoprothiolane     

Uncertainty in aflatoxin B<Subscript>1</Subscript> analysis using information from proficiency tests

We describe how to calculate uncertainty in the determination of aflatoxin B₁ in nuts and maize using an HPLC method with prederivatisation with trifluoroacetic acid and fluorescence detection. The uncertainty is easily calculated using the information obtained from the participation in several proficiency tests. All the sources of uncertainty are grouped in two terms: (1) matrix variability, intermediate precision and sample heterogeneity, and (2) method concordance. This methodology has the advantage that no extra work needs to be done because all the information to calculate uncertainty comes from proficiency tests. The uncertainty values were calculated using samples whose concentration ranged between 2 and 20 g L^–1. The relative standard uncertainty computed for aflatoxin B₁ was 16.3%.     

Proficiency testing for quality assurance of allergens methods

Proficiency testing is an external quality control check, whereby the quality of an analytical result is checked against criteria that are set independently of the laboratory carrying out the analysis. Participants in a proficiency test are encouraged to use the method of their choice to determine the analyte in question. The collated results submitted by the participants are used to derive the best estimate of the ‘true’ level, or assigned value, of the analyte, as a consensus value of the whole data set. Generally, the data submitted will be normally distributed and from a single population, but if a data set is found to be multimodal, then the selection of one of the modes as the assigned value is possible where there is supporting data, typically methodology information. Unless there are independent grounds for preferring one mode over another, it is not possible to set an assigned value or calculate z-scores. However, the analysis of allergens has presented proficiency testers with a new challenge, since it has become apparent that quantitative results may be dependent on the brand of enzyme-linked immunosorbent assay kit used, the specific analyte targeted (e.g. total content or allergen protein content) and the limit of detection achievable. FAPAS® has run more than 40 proficiency tests for allergen analysis over the past 7 years, during which time methods have been developed and improved and the requirements for determination of food ingredient allergens has increased. Two case studies are presented which highlight some of the issues around the use of allergen measurement methods.

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Figure A selection of food items which might cause allergenic or intolerance reactions

     

Harmonization and transferability of performance assessment: experience from four serum aluminum proficiency testing schemes

Proficiency testing schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. Where several schemes operate in the same analytical sector, there are risks that assessments of performance may be in conflict. Performance assessment for the determination of trace elements such as aluminum in serum is particularly important due to the high risk of contamination and therefore erroneous results. The objectives of this work were (1) to compare several mathematical models to establish a predefined standard deviation for proficiency assessment and (2) to evaluate the influence of instrumental methods and proficiency testing scheme on the assessment of performance for serum aluminum measurements. For this purpose, three samples were sent to the participants of four proficiency testing schemes. Assigned values were calculated according to algorithm A according to ISO 13528 and standard deviation for proficiency assessment according to three methods based on individual variability, state of the art or previous proficiency testing results. The method based on individual variability produced a more stringent standard deviation compared to analytical imprecision based on the state of the art. The instrumental methods gave similar results, whereas significant differences were observed between the four proficiency testing schemes indicating that harmonization of the standard deviation for proficiency assessment fails to allow transferability from one proficiency testing scheme to another and that additional factor(s) contribute to variability in performance assessment.     

in situ interlaboratory comparisons for dissolved oxygen concentration and pH

Organization, benefits, and possible drawbacks of in situ interlaboratory comparison are discussed using the example of dissolved oxygen concentration and pH measurements organized at the University of Tartu. In situ interlaboratory comparisons are intercomparison measurements, where all the participants (with their technical equipment and using their own competence) are measuring the same sample continuously at the same time, at the same site. In the field of proficiency testing–especially in chemical measurements–the in situ schemes are not yet widespread. Their main advantage emerges in the fields where, due to non-stability of samples, traditional comparison schemes can fail. Direct exchange of experience between the participants and presentations during measurements may add the value to in situ interlaboratory comparison. Dissolved oxygen concentration and pH measurements are among the most widespread chemical measurements. Both measurements are complex and less robust than often considered. In this paper, we describe in situ interlaboratory comparisons of dissolved oxygen concentration and pH organized at University of Tartu Testing Centre. Electronic Supplementary Material  Supplementary material is available for this article if you access the article at . The Final Report of the DO Concentration and pH Intercomparison is available in the electronic supplementary material.

Designs of experiment for proficiency testing with a limited number of participants

Metrological designs of experiment for proficiency testing (PT) with a limited number of participants are discussed. The designs are based on development of in-house reference materials (IHRMs) with traceable assigned values and fit-for-purpose uncertainties, used in a PT scheme as the measurement standards. When adequate certified reference materials (CRMs) are available, a comparative approach for IHRM development, using simultaneous analysis of IHRM and CRM test portions in pairs, is proposed for PT objectives. In the case where adequate CRMs are not available – for example, in the field of analysis of unstable aqueous systems – the function of the measurement standard for PT can be fulfilled by a synthetic IHRM prepared gravimetrically using non-adequate, non-aqueous CRMs or pure substances. The CRM or the pure substance is used as a spike for fortification of a natural water sample, while the natural water sample is used as a working IHRM for the spike determination. In this case the traceability chain is longer, since two IHRMs are added for one quantity determination, but it remains unbroken.Presented at the Second International Conference on Metrology –Trends and Applications in Calibration and Testing Laboratories, 4–6 November 2003, Eilat, Israel     

Rapid screening and determination of nerve agent metabolites in human urine by LC-MS/MS

Qualitative screening procedures have been developed for the rapid detection and identification of the metabolites of nerve agents in the urine samples and extracts using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The combination of negative electrospray ionization (ESI) using a C₁₈ column and water-methanol mobile phase modified with ammonium formate provides a rapid screening procedure for nerve agent degradation products with limit of detection of 1 ng/mL in the precursor-ion analysis. Also, determination of the alkyl methylphosphonic acids was carried out by the SRM scan mode with the limit of detection of 0.1 ng/mL. These procedures will be applicable to the trace analysis of metabolites of nerve agents in human urine matrices in the Organisation for the Prohibition of Chemical Weapons (OPCW) proficiency test.     

Bromine determination by neutron activation analysis and its distribution in the atmosphere

Bromine, one of the main participants in ozone layer destruction, is 10 to 100 times more effective than chlorine. There are two principal sources of methyl bromide emissions: the oceans and some pesticides that are used in farming. In this work, bromine was detected in premium and magna sin gasolines (2.86±0.96 and 1.54±0.38 ppm, respectively) as well as in condensed water found in exhaust pipes of vehicles. In addition, samples of rainwater were also analyzed to determine atmospheric bromine concentration. In water samples Br concentrations ranging from 2.09 to 0.06 ppm were found. The techniques utilised in our research were neutron activation analysis and high voltage electrophoresis, the latter to determine the chemical form of bromine in condensed water samples. Finally, suspended particles from rainwater were also analysed by scanning electron microscopy (SEM).     

Proficiency testing schemes: solutions for homogeneity control

The organisation of the homogeneity control of samples prepared for proficiency testing schemes (PTS) is a challenge for the PTS organisers and engenders logistical and financial problems. Samples used in PTS need to be homogeneous in order to be sure that if a laboratory has a result different from the other laboratories, its error can be attributed to its analysis method and not to its sample. The present paper describes the solutions found by the Bureau Interprofessionnel dEtudes Analytiques (Bipea) in order to answer the homogeneity control requirement. The methodologies of homogeneity control are adapted to specific characteristics of the products proposed in Bipeas PTS. The first methodology of control, the preparation approach, concerns specific PTS where the samples are formulated and where the assigned values are known and chosen. The second methodology, the target approach, concerns mainly the field of the environment and implies the choice of homogeneity targets. The third methodology, the global approach, concerns the agricultural and agro-food fields and involves comparison of near-IR spectra samples. Each methodology of control has its advantages and disadvantage and is suited to specific products prepared with specific preparation procedures. It has to be stressed that the solutions developed answer quality requirements but are not a substitute for the use of adapted and detailed preparation procedures with validated and regularly checked devices and for the a posteriori control of the results of the laboratories.     

Proficiency testing on the analytical control of precious metal production

Our experience of executing proficiency testing programs on the analysis of precious metals and precious metal bearing materials is summarized. Six proficiency testing programs of the ”distributed sample testing” type were carried out using samples essentially distinct from each other: (I) certified samples of fine gold and fine silver, and (II) recoverable raw (scrap and catalyst waste) containing precious metals of unknown contents. The test results were assessed using the London Bullion Market Association (LBMA) rules and by Z-criteria using the ISO/IEC Guide 43 scale. Satisfactory results were presented by all participants for the analysis of certified samples of fine gold and fine silver. The results of catalyst waste analysis agreed rather well, whereas the scrap analysis revealed an essential discrepancy in the data for some samples. The reasons for such discrepancies are discussed. Received: 9 June 2000 Accepted: 21 November 2000     

The variance of a consensus

In proficiency tests the consensus of the participants' results is often used as the assigned value to calculate z-scores. Where the consensus is quantified as the robust mean of n results, the standard error of the assigned value is often taken to be , where is the robust standard deviation estimated from the same data ¹ . As some of the results are downweighted in robust estimation, is too large a denominator, so that tends to have a somewhat low bias. This bias is shown to be inconsequential for proficiency testing purposes. However, an unbiased estimate can be obtained by using the bootstrap.

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Canadian interlaboratory survey of lead in lyophilized bovine whole blood

Summary A Canadian co-operative blood-Pb interlaboratory survey was conducted based on lyophilized bovine blood samples with different endogenous lead contents. The samples were prepared from whole blood of a non-exposed cow and another fed with a single dose of lead acetate trihydrate. The mean values computed for the three samples analyzed by 12 participants were 40, 229, and 91 g Pb/l, respectively. These results showed a negative bias of 20%, 0.4% and 14% with respect to the target values of 50, 230 and 106 g Pb/l, respectively.

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Kanadischer Labor-Ringversuch für Blei in lyophilisiertem Rindervollblut

Zusammenfassung Die Proben zu diesem Ringversuch wurden hergestellt aus dem Blut einer nicht-exponierten Kuh und einer weiteren, die eine einmalige Dosis von Bleiacetattrihydrat erhielt. Die errechneten Mittelwerte für drei Proben, die von 12 Teilnehmern analysiert wurden, betrugen 40, 229 und 91 g Pb/l. Die Ergebnisse zeigten eine negative Abweichung von 20%, 0,4% bzw. 14% in bezug auf die Sollwerte von 50, 230 bzw. 106 g Pb/l.

     

The determination of an accepted reference value from proficiency data with stated uncertainties

Proficiency data with stated uncertainties represent a unique opportunity for testing that the reported uncertainties are consistent with the Guide to the expression of uncertainty in measurement (GUM). In most proficiency tests, however, this opportunity is forfeited, because proficiency data are processed without regard to their uncertainties. In this paper we present alternative approaches for determining a reference value as the weighted mean of all mutually consistent results and their stated uncertainties. Using an accepted reference value each reported uncertainty estimate can be expressed as an E _n number, but a value of confirms its validity only if the uncertainty of the reference value is negligible in comparison.Reference values calculated for results from an International Measurement Evaluation Programme (IMEP-9) by “bottom up” as well as “top down” methods were practically identical, although the first strategy yielded the lowest uncertainty. A plot of individual coefficients of variation (CV) versus E _n numbers helps interpretation of the proficiency data, which could be used to validate relative uncertainties down to <1%.     

Validation of an environmental friendly segmented flow method for the determination of phenol index in waters as alternative to the conventional one

Phenolic compounds are a sort of common pollutants in water. Phenol index becomes an expedite indicator for the evaluation of the contamination level of water samples, in spite of the knowledge of the individual phenol and its derivatives are also important.In this work, an environmental friendly method for the determination of phenols, using a segmented flow system based on the conventional method's reactions without the liquid-liquid extraction step, was validated.Three linear dynamic ranges using C₆H₅OH: 1-10 μg l⁻¹, 10-200 μg l⁻¹ and 0.2-2.5 mg l⁻¹, with a coefficient of variation lower than 2%, were obtained. Several method's performance parameters were determined: limits of detection, limits of quantification, precision through duplicate analysis and trueness using the reference materials purchased from LGC Promochem, RTC no. QCI-043-2 Lot:P1. Measurement uncertainty was evaluated using an interlaboratory approach based on proficiency testing data. Relative combined uncertainty for phenols in water samples, , of 0.054 were obtained, in according to those imposed by the Portuguese Legislation: target for 1 μg l⁻¹ of phenol (surface waters) and target for 500 μg l⁻¹ of phenol (wastewaters).A high efficiency reduction and elimination of reagents and wastes, reduction of analysis time and exposition of the analyst were also obtained.     

Homogeneity determination of Cd in plastic CRMs using solid sampling atomic absorption spectrometry

Summary Four types of plastic with four different nominal Cd concentrations in the range of 40 to 400 mg/kg were sampled, homogenized and certified at CBNM on behalf of VDA (Verband der Automobilindustrie). The homogeneity control of these materials was performed using solid sampling graphite furnace Zeeman atomic absorption spectrometry. On each of the four materials 60 analyses were carried out on micro samples (60 to 250 g per analysis, depending on the Cd content) taken from 60 different wire cuts. Homogeneity assessments and determination of the minimum sample mass are made and discussed.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel. Belgium. Papers edited by R. F. M. Herber, Amsterdam.     

Proficiency testing as a tool to assess the performance of visual TLC quantitation estimates

The use of rapid and inexpensive nonlaboratory-based screening tests for drug quality assessments is recommended as a component of a drug quality assurance program in poor resource settings. We have established routine Minilab test procedures to screen product quality and a proficiency testing program to determine the competency of the inspectors and reliability of results. Samples for the proficiency testing were prepared by pulverizing a standard reference tablet of the appropriate drug and making serial dilutions with starch to obtain concentrations of 0, 40, and 100%. The samples, which were labeled only with the drug name and an identifying letter, were given to inspectors for quality screening using Minilab procedures. In round 1 of the proficiency test, only 3 of 28 substandard samples were correctly identified. Round 2 of the proficiency test, which was administered after a performance qualification test for the analytical method, showed much improvement: 19 of 27 substandard drugs were correctly identified, while 5 out of 9 inspectors made the correct inference on the quality of 45 samples. However, in both rounds, 2 inspectors failed to identify substandard samples, indicating that their technical competencies need to be improved for the reliability of the results. Although the thin-layer chromatography screening methods provide a rapid means for drug quality assessment, they need to be put in the hands of competent users. The inclusion of a proficiency test in the screening program provides a measure of determining competency of the personnel and reliability of the results.     

Matrix materials for proficiency testing: optimization of a procedure for spiking soil with gamma-emitting radionuclides

The IAEA Reference Materials Group of the Chemistry Unit, Agency’s Laboratories Seibersdorf, has developed and optimized a procedure for spiking some environmental matrices with gamma-emitting radionuclides. This paper describes the spiking procedure, homogeneity testing of the spiked material, and assignment of property values and their associated uncertainties for the radionuclides ⁵⁴Mn, ⁶⁵Zn, ⁶⁰Co, ¹⁰⁹Cd, ¹³⁴Cs, ¹³⁷Cs, ²¹⁰Pb, and ²⁴¹Am. This procedure has already been successfully used in an IAEA proficiency test on the determination of ¹³⁷Cs and ²¹⁰Pb in spiked soil and has been found to be appropriate for production of soil materials for proficiency testing and internal quality control samples. The main advantage of this procedure is a low uncertainty arising from heterogeneity, which was found to be less than 1.2% for all the analytes studied.