Interlaboratory Study to Improve the Quality Control of Methylmercury Determination in Sediment

The results are presented of an interlaboratory study on methylmercury (MeHg) in sediment carried out by a group of European laboratories within the framework of a project managed by the EC Standards, Measurements and Testing Programme (formerly BCR). The aim of this exercise was to evaluate the performance of current methods used for MeHg determination in sediment in order to improve the state-of-the-art prior to the certification of a candidate reference material. The paper describes the organization of the interlaboratory study, the preparation of the sediment material used, the techniques evaluated and the results obtained by the participating laboratories. The outcome of the collaborative project showed that certification could be contemplated, providing that certain analytical techniques were optimized, especially with regard to extraction methods.     

用经验模型评估环境样品测量不确定度

利用水样、土壤和沉积物标准样品定值数据,建立了评估环境样品测量结果不确定度的经验模型。讨论了判断模型质量的指标。用建立的经验模型估算了实际标样和能力验证数据不确定度,并与实测结果进行了比较。探讨了利用本模型计算的相对标准偏差允许限用于实验室内部质量管理与控制的可行性。经验模型能帮助客户判断送检样品检测结果在临界值时能否满足相关要求。     

Interlaboratory programme for the quality control of trimethyllead determination in the environment

Determinations of the trimethyllead moiety in environmental samples are carried out by a number of laboratories in Europe. To verify the quality of such determinations, the Measurements and Testing Programme (formerly BCR) of the European Commission organised an interlaboratory exercise which allowed discussion and comparison of the different techniques used so far in lead speciation analyses. In addition, this first step enabled a study of the feasibility of the preparation of candidate reference materials (CRMs) for the determination of the trimethyllead moiety in simulated rainwater to be carried out. The solutions used in this study were carefully prepared and their homogeneity and stability verified. This paper describes the organisation and the results of the intercomparison and discusses the further development of the project.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part II

This is the part II of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS–MS) detection in LC (as opposed to the “conventional” detectors). The Part II starts with briefly introducing the main quantitation methods and then addresses the performance related to quantification: linearity of signal, sensitivity, precision, trueness, accuracy, stability and measurement uncertainty. The last section is devoted to practical considerations in validation. With every performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to handle it, specifically in the case of LC–MS methods.     

An interlaboratory capillary zone electrophoresis-UV study of various monoclonal antibodies,instruments, and ε-aminocaproic acid lots

Capillary zone electrophoresis ultraviolet (CZE-UV) has become increasingly popular for the charge heterogeneity determination of mAbs and vaccines. The ε-aminocaproic acid (eACA) CZE-UV method has been used as a rapid platform method. However, in the last years, several issues have been observed, for example, loss in electrophoretic resolution or baseline drifts. Evaluating the role of eACA on the reported issues, various laboratories were requested to provide their routinely used eACA CZE-UV methods, and background electrolyte compositions. Although every laboratory claimed to use the He et al. eACA CZE-UV method, most methods actually deviate from He's. Subsequently, a detailed interlaboratory study was designed wherein two commercially available mAbs (Waters’ Mass Check Standard mAb [pI 7] and NISTmAb [pI 9]) were provided to each laboratory, along with two detailed eACA CZE-UV protocols for a short-end, high-speed, and a long-end, high-resolution method. Ten laboratories participated each using their own instruments, and commodities, showing excellence method performance (relative standard deviations [RSDs] of percent time-corrected main peak areas from 0.2% to 1.9%, and RSDs of migration times from 0.7% to 1.8% [n = 50 per laboratory], analysis times in some cases as short as 2.5 min). This study clarified that eACA is not the main reason for the abovementioned variations.     

Assessing bias in total mercury results after removing a subsample from the bottle

U.S. EPA Method 1631 for total mercury (THg) analysis in water recommends that bromine monochloride (BrCl) be added to the original bottle in which the sample was collected, to draw into solution any Hg that may have adsorbed to the bottle walls. The method also allows for the removal of a subsample of water from the sample bottle for methylmercury (MeHg) analysis prior to adding BrCl. We have demonstrated that the removal of a subsample from the sample bottle prior to THg analysis can result in a positive concentration bias. The proposed mechanism for the bias is that ‘excess’ inorganic Hg, derived from the subsample that was removed from the bottle, adsorbs to the bottle walls and is then drawn into solution when BrCl is added. To test for this bias, we conducted an interlaboratory comparison study in which nine laboratories analysed water samples in fluorinated polyethylene (FLPE) bottles for THg after removing a subsample from the sample bottle, and analysed a replicate sample bottle from which no subsample was removed. We received seven complete data sets, or 63 unique sample pairs. The positive concentration bias between the bottles was significant when comparing all samples in aggregate (1.76 ± 0.53 ng/L after subsample removal, 1.57 ± 0.58 ng/L with no subsample removal, P < 0.05), however when comparing each of the three samples individually, the only significant bias was in the saline sample (Site UJ; 1.51 ± 0.31 ng/L after subsample removal, 1.32 ± 0.47 ng/L with no subsample removal, P < 0.05). Based on the findings presented here, we conclude that water chemistry, volume of water poured off, and the sample storage temperature explain some but not all of the observed bias, and we recommend collecting THg and MeHg samples in separate bottles whenever possible.     

French round-robin test of X-ray stress determination on a shot-peened steel

A round-robin test of X-ray residual stress determination was performed by the Groupement Français d'Analyse des Contraintes and involved 16 laboratories. The standard deviation of the measurements was about 36 MPa, but a posttreatment of the raw data with the same soft-ware reduced the dispersion to 19 MPa. Analysis of the uncertainty sources (goniometer alignment, operator, counting statistics, nonlinearity of the material, etc.) revealed that the main sources come from the data treatment and the operator.     

Interlaboratory GC/MS response factor precision

A quality control procedure for Fused Silica Capillary Column Gas Chromatography/Mass Spectroscopy (FSCC GC/MS) was tested and shown to produce similar response factors at five Spectroscopy (FSCC GC/MS) was tested and shown to produce similar response factors at five laboratories. The average relative standard deviation (RSD) of interlaboratory response factors for fifty three compounds of environmental interest determined at each laboratory at nominal injected weights of 20, 100, and 200 ng was found to be 18.9% for four of the five laboratories which participated in this work. These data demonstrate that similar response factors can be attained in routine GC/MS measurements when adequate quality control is maintained.     

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.

Interlaboratory study to improve the quality of trace element determinations in rainwater

This is the first publication which describes the development of a reference material (RM) for the determination of 11 trace elements (Cu, Pb, Mn, Ni, Zn, Fe, Cd, Co, V, As and Al) in rainwater at microgram per liter concentrations. An interlaboratory comparison study for the determination of trace elements in rainwater was carried out for material performance studies to establish analyte concentrations with a stated uncertainty. Fifteen reputed laboratories from Asia, Europe and North America participated in the study. These laboratories used their regular in-house methods to analyze the rainwater samples. The aim of this study is to establish concentration levels of trace elements in rainwater based on interlaboratory study results. Details of the production, homogeneity and stability of the reference sample are given in this article. The organization of the study and the quality assurance measures undertaken at the organizer's laboratory are described. The analytical results obtained from individual laboratories and the analytical methods used for the determination of trace elements in rainwater are discussed. Based on the results obtained from the intercomparison study, certified values as well as informative values are assigned to the 11 trace elements in rainwater.