The correlation of laboratory performance in proficiency testing with other QA characteristics

Although it seems self-evident that proficiency testing (PT) and accreditation can be expected to improve quality, their relative benefits remain uncertain as does their efficacy. The study reported here examines the following issues: (a) Why do laboratories take part in PT schemes? (b) How does participation in PT fit in with a laboratory's overall quality assurance (QA) system? (c) Is there a link between a laboratory's performance in specific PT and it's QA system? (d) How does PT performance change with time and how do laboratories respond to poor performance? The overall conclusion is that there is no evidence from the present study that laboratories with third-party assessment (accreditation and certification) perform any better in PT than laboratories without. The validity of this conclusion and its significance for the future design and operation of such schemes requires further investigation. In particular, study is required of the degree to which good performance in open PT correlates with blind PT performance, where laboratories are not aware that the samples being analysed are part of a quality assessment exercise.     

Experiences from the assessment of proficiency testing providers

Following a pilot project in 2001–2002, UKAS accredited nine PT providers. During the course of the pilot and at subsequent surveillance visits, UKAS has gained experience in assessing organisations against the criteria detailed within ISO/IEC Guide 43-1:1997 and ILAC G13:2000. This article explores some of the key aspects that arose during the pilot and how UKAS has accommodated the addition of the accreditation of PT providers in to its range of services.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Practical uses of proficiency testing as valuable tools for validation and performance assessment in environmental analysis

Besides their role as an external quality control tool, PT results or samples could be used as an alternative to fulfil some of the quality assurance requirements such as analytical precision, uncertainty assessment, and internal quality control. This additional use of proficiency testing could help laboratories to reduce the financial impact of their quality assurance process. The purpose of this paper is to highlight some practical uses of PT results or samples in the environmental analytical field, which have been implemented at ISSeP (Institut Scientifique de Service Public), either for method validation or for internal quality control.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Proficiency testing as a tool for implementing internal quality control: the case of ochratoxin A in cocoa powder

This paper describes the interlaboratory study aimed at assessing the performance of 18 laboratories (14 national and 4 European) for Ochratoxin A (OTA) determination in cocoa powder samples. The study was tested at three levels of OTA covering the range in which presumably European regulatory limits could fall in the near future. For the extraction step, almost all laboratories used an aqueous solution of sodium hydrogen carbonate with the exception of one laboratory using dichloromethane consistently with the ELISA procedure adopted in the study. The clean-up step was performed by utilizing the immunoaffinity columns by the two main manufacturers (R-Biopharm Rhone and VICAM) and for the quantitative analysis, HPLC was used by all the participants except one using ELISA. From the output of the study, it can be concluded that at low level (0.19 μg/kg) 10 out of 18 (56%), at medium level (0.45 μg/kg) 11 out of 18 (61%), and at high level (1.45 μg/kg) 12 out of 18 (67%) results fell within the satisfactory ranges. This interlaboratory study provides an estimate of the performance of national and European laboratories involved in OTA determination in cocoa powder samples, which sounds extremely valuable in view of potential future legislation by the European Commission.     

Challenges in preparing water-matrix reference materials for PAHs and pesticides: examples from SWIFT-WFD proficiency-testing schemes

In accordance with Article 8 of the European Union (EU) Water Framework Directive (WFD), EU Member States are required to establish monitoring programs for the quality of the surface water and the groundwater within each river-basin district. As such data are the basis for regulatory decisions and measures required to achieve WFD environmental objectives, appropriate analytical quality-assurance and quality-control tools have to be implemented by the monitoring laboratories. In this respect, reference materials (RMs) play a key role. Within the framework of the SWIFT-WFD project (Screening methods for Water data InFormation in support of the WFD), several approaches to the preparation of matrix RMs for the analysis of polycyclic aromatic hydrocarbons and pesticides in water have been used in wide-scale proficiency-testing (PT) schemes. We present the different strategies employed in preparing water-matrix RMs for organic analytes. By reviewing the results from the SWIFT-WFD PT schemes, we reflect on the applicability and the suitability of the different approaches.     

Development and validation of an HPLC method for the determination of process-related impurities in pridinol mesylate, employing experimental designs

A simple high performance liquid chromatographic method for the determination of process-related impurities in bulk drug of the central anticholinergic compound pridinol mesylate, has been developed and validated. Spectroscopically characterized synthetic impurities were used as standards. The chromatographic separation was optimized employing an experimental design strategy, and was achieved on a C₁₈ column with a mobile phase containing 50 mM potassium phosphate buffer (pH 6.4), MeOH and 2-propanol (20:69:11, v/v/v), delivered at a flow rate of 1.0 mL min⁻¹. UV detection was performed at 245 nm. The optimized method was thoroughly validated, demonstrating to be selective, when the chromatogram was recorded with a diode-array detector and peak purities were evaluated (>0.9995). The method is robust and linear (r² > 0.99) over the range 0.05-2.5% (5-250% with regards to the 1% specification limit for both process-related impurities); it is also precise, regarding repeatability (RSD ≤ 1.5% for all of the analytes) and intermediate precision aspects and LOQ values for the impurities are below 0.01%. Method accuracy, evidenced by low bias of the results and analyte recoveries in the range of 99.1-102.7%, was assessed at five analyte concentration levels. The usefulness of the determination was also demonstrated through the analysis of different lots of pridinol mesylate bulk substance. The results indicate that the method is suitable for the quality control of the bulk manufacturing of pridinol mesylate drug substance.     

Certified reference material for quantification of polycyclic aromatic hydrocarbons in sediment from the National Metrology Institute of Japan

The National Metrology Institute of Japan has issued a certified reference material (CRM) of freshwater lake sediment for polycyclic aromatic hydrocarbon (PAHs) analyses. The certification used three extraction techniques: pressurized liquid extraction (PLE) with toluene, PLE with dichloromethane/ethyl acetate (1:1 by volume), and alkaline extraction (1 M KOH in methanol) in combination with microwave-assisted extraction. Both gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/dopant-assisted atmospheric pressure photoionization/MS (LC/DA-APPI/MS) analyses were used. Certified values are provided for 18 PAHs at 1–25 μg kg⁻¹ except for perylene (2.08 × 10³ μg kg⁻¹), and information values are provided for two. Since the values of PAHs in the CRM are much lower than those in other CRMs and are comparable to those found at sites with little human influence, the CRM is suitable for PAH monitoring in sediment and soil samples.     

基于均匀和正交试验设计的胶束电动毛细管色谱法同时测定消毒剂和抗抑菌产品中3种核苷类抗病毒药物

为防止消毒剂与抗抑菌产品中违规添加核苷类抗病毒药物,建立了胶束电动毛细管色谱（MEKC）同时分离测定消毒剂与抗抑菌产品中3种核苷类抗病毒药物（更昔洛韦、阿昔洛韦和喷昔洛韦）的新方法。通过3因素7水平均匀试验设计和4因素4水平的正交试验设计优化了十二烷基硫酸钠（SDS）、磷酸二氢钠（NaH₂PO₄）及硼砂（Na₂B₄O₇）在分离缓冲液中的浓度,最大限度地实现了3种核苷类抗病毒药物在短时间内的有效分离。以30.2 cm×50 μ m（有效长度为20 cm）未涂层熔融石英毛细管为分离柱,以25 mmol/L NaH₂PO₄+10 mmol/L Na₂B₄O₇（pH 7.41）+140 mmol/L（SDS）为分离缓冲溶液,分离电压为10 kV;进样压力为0.003 Pa,进样时间为4 s;检测波长为250 nm。3种抗病毒药物在一定的浓度范围内线性关系良好,相关系数r均不小于0.9995。3种抗病毒药物的检出限均为2.0 mg/kg,定量限均为7.0 mg/kg。低、中、高浓度加标回收率为85.4%~104.1%,相对标准偏差（RSD）均小于8.0%。该方法简便,快速,适于检测消毒剂与抗抑菌产品中更昔洛韦、阿昔洛韦和喷昔洛韦。     

Comparison of “bottom-up” and “top-down” strategies for the estimation of the uncertainty in organic elemental analysis

The estimation of uncertainty in organic elemental analysis for C, H, N and S is reported. Both “bottom up” and “top down” strategies are used for uncertainty calculations. The bottom up approach used the results of C, H, N, and S obtained from the homogeneity study of two pure chemicals (toluene-4-sulfonamide and 4(6)-methyl-2-thiouracil). Two calibration systems, K factor and calibration curve, were applied in this study and no significant differences were obtained. For the “top down” approach, we used the data obtained from a proficiency test on both pure chemicals from among 45 Spanish laboratories. Both approaches are compared and discussed below.     

In- and off-laboratory sources of uncertainty in the use of a serum standard reference material as a means of accuracy control in cholesterol determination

 Repeated subsampling or a hierarchical design of experiments combined with an analysis of variance (ANOVA) is demonstrated to be a useful tool in the determination of uncertainty components in amount-of-substance measurements. With the reference material of human serum as investigated here for total cholesterol, besides several in-laboratory sources of uncertainty, a vial-to-vial effect which can be regarded as an off-laboratory source was found to be significant. This knowledge might be essential when the material is used for calibration and for the self-assessment of a laboratory. Received: 29 October 1997 · Accepted: 26 November 1997