Results Of Interlaboratory Comparison Research Articles

Response to Letter to the Editor regarding the “European Analytical Column No. 41”

Dear Sir, It is possible that the philosophy of consensus science may question, to some extent, the basis for both analytical chemistry and metrology [1]. Change of practices and procedures may be needed; genuine scientific results may be lost and theories that rely on data out of statistical control may incorrectly be proven true. There is an obligation of science to make fundamental changes, and consensus science may be a useful example of scientific methodology. There is no evidence in modern analytical chemistry for the idea that experts are able to distinguish between reliable and unreliable analytical results. The experts have no access to raw data of inter-laboratory comparisons (ILCs) and they have no access to raw data of scientific publications. Therefore, they are left with comparing highly processed data, which is unfortunate for comparisons in analytical sciences. Scientists are subjective when they propose a model and should remain objective when they compare theory to experiments. To the best of my knowledge, the staff never imposes contributions to the uncertainty. Laboratory staff prepare everything carefully and correctly in the laboratory, and even in cases where errors are committed, these errors are small and insignificant in the general picture of uncertainty. The main contribution to uncertainty is the apparatus long-time precision, which has been overlooked in uncertainty budgets [2]. If this contribution were included, would it increase the likelihood of correspondence between results in ILCs? Presumably, a university or a company would never employ incompetent staff to operate advanced apparatus. Accordingly, it is reasonable to assume that all results of ILCs belong to the same distribution. The analytical capability of laboratories cannot be checked unless the universal level of uncertainty of the involved method is known. It may safely be assumed that everyone who has invested in advanced scientific apparatus also has the competence to perform measurements. I agree that a two-step procedure for selection of qualified laboratories in advance of an ILC is not an option because that would be in conflict with consensus science. The idea of all laboratories showing equal degrees of competence is unattainable. Staff need acceptable working conditions and the results should be provided with a reasonable consumption of resources, labor, time etc. Nature does not care about ILCs and legislation. It cannot be decided by politics or debate whose fundamental constants in metrology or whose analytical results are right or wrong. We can only approach the true mechanisms of nature by performing measurements that possess a certain level of uncertainty. Hence, the method of consensus should be prevalent in science. Nothing can be decided by a single expert; results of many independent experts are required in order to maintain independence and credibility. It was interesting to me that the author of the ‘Letter to the Editor’ stated that outliers had been removed from the data set that constitutes the basis for certified reference materials (CRMs). Novel types of outliers, identified as ‘analytical outliers’, were invented for the occasion that supposedly should be distinguished from ‘statistical outliers’. It was not possible to find the technical reasons, as otherwise claimed possible. Hendrik Emons militates against better judgment: outliers were, in fact, rejected in BCR CRMs on the basis of statistical reasons and not due to technical reasons. Just a few examples: “The set of Lab 14 was rejected because its standard error exceeded s” [Bureau communautaire de reference, BCR Wholemeal flour CRM no. 189/Brown bread CRM no. 191] or “Laboratory 5 (TXRF) had an outlying variance for total Cr (Annex 1, Table 3a) and did not satisfy the criterion for This article is a response to the ‘Letter to the Editor’ to be found at DOI 10.1007/s00216‐013‐7141-5.

In-house quality control material of nicarbazin and narasin in eggs: preparation and inter-laboratory evaluation

Coccidiostats are a group of pharmacologically active substances widely used in veterinary practice. Their residues are detected relatively often in poultry tissues and egg samples analyzed as part of official residue control programs in the European Union. Therefore, accuracy of quantitative results needs to be monitored through internal and external quality control studies. In addition, the use of materials containing incurred residues would be welcome to for ongoing monitoring of the method accuracy. Unfortunately, in the field of veterinary drug residues, certified reference materials are often unavailable. Therefore, in-house quality control material of incurred lyophilized eggs containing narasin and nicarbazin has been produced and characterized. The eggs originated from hens receiving feed with coccidiostat premix Maxiban were mixed to obtain presumed concentrations of residues and freeze-dried. Homogeneity of the material was verified by the duplicate analysis of ten random samples, and the results proved that the between samples variation was negligible in comparison with the method repeatability. No measurable loss of analytes was observed within 1 year; the slope of the regression line of the results of stability measurements was not significantly different from zero. The assigned values were expressed as medians of the results of inter-laboratory comparison performed in four different European laboratories; the uncertainty of the material was estimated, taken into consideration all above tests, resulting in (14.4 ± 2.53) µg/kg for nicarbazin and (7.91 ± 1.52) µg/kg for narasin.

New Chinese National Reference Materials for Hydrogen and Oxygen Isotopes in Water

The Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences recently prepared four certified reference materials for hydrogen and oxygen stable isotopes in water, which are called ‘China Standard Water' (CSW)‐HO1–HO4 (hereafter referred to as HO1–HO4). These reference materials are intended for calibration purposes and provide reference values of their relative difference in 2H/1H and 18O/16O isotope‐amount ratios expressed in delta notation, normalised to the VSMOW–SLAP scale. The certified values of the reference materials were determined by an interlaboratory comparison of results from eleven participating laboratories. This paper describes in detail the production and certification procedure of the four reference materials. The first analytical data for the reference materials are also provided using a variety of analytical techniques, namely CO2–H2O equilibration and laser spectroscopy for δ18O and Cr reduction, as well as H2–H2O equilibration, laser spectroscopy, and high‐temperature conversion for δ2H. The reference values for materials HO1–HO4 and their associated uncertainties are assigned.

ОпрацюваннЯ результатіВ вимірюванЬ прИ проведеннІ міжлабораторниХ звіренЬ зА умоВ наявностІ систематичноЇ похИбкИ вимірюваннЯ

The methods of processing the results of interlaboratory comparisons are described in the paper. The supplementary comparisons for national standards are carried out with the purpose of confirming measurement and calibration capabilities of the corresponding national metrology institutes. The Guideline on COOMET supplementary comparison evaluation does not take into account the presence of systematic error in the results of comparisons. The Guidelines on Comparisons of groups of instruments for calibration of the same accuracy level (MI 1832-88) take into account a systematic component of the measurement error, but the results of comparisons are not verified for consistency, which is an objective confirmation of stated uncertainties. Thus, we propose to combine these two methods for objective demonstration of measuring data reliability. To confirm the method selected for processing the comparisons results, an experiment was conducted, comparisons of voltmeters of one accuracy class with higher accuracy class were made. The results of comparisons and their processing by the proposed combined method are given in the paper. Thus, the proposed method allows evaluating the systematic component of uncertainty and its correction, hence, the laboratory comparisons data are recognized as such that confirm given uncertainties.

Accuracy Investigation of Phthalate Metabolite Standards

Phthalates are ubiquitous compounds whose metabolites are usually determined in urine for biomonitoring studies. Following suspect and unexplained results from our laboratory in an external quality-assessment scheme, we investigated the accuracy of all phthalate metabolite standards in our possession by comparing them with those of several suppliers. Our findings suggest that commercial phthalate metabolite certified solutions are not always accurate and that lot-to-lot discrepancies significantly affect the accuracy of the results obtained with several of these standards. These observations indicate that the reliability of the results obtained from different lots of standards is not equal, which reduces the possibility of intra-laboratory and inter-laboratory comparisons of results. However, agreements of accuracy have been observed for a majority of neat standards obtained from different suppliers, which indicates that a solution to this issue is available. Data accuracy of phthalate metabolites should be of concern for laboratories performing phthalate metabolite analysis because of the standards used. The results of our investigation are presented from the perspective that laboratories performing phthalate metabolite analysis can obtain accurate and comparable results in the future. Our findings will contribute to improving the quality of future phthalate metabolite analyses and will affect the interpretation of past results.

Comparison of two analytical methods for the chemical characterization of flint from Lithuania and Belarus

In this paper, authors present the results of interlaboratory comparison of two different methods of determining the chemical composition of Lithuanian and Belarusian flint: direct current arc emission spectrophotometry (DCAES) and energy dispersive X-ray fluorescence (EDXRF). For this interlaboratory comparison, geological specimens from three Lithuanian and Belarusian flint sources, previously analysed by Baltrūnas et al.(2006a), were sent to the first author for a non-destructive EDXRF analysis. All three sources were important for prehistoric tool manufacturing during Lithuanian prehistory. Non-destructive EDXRF analyses of flint may be preferred in situations where it is important to conserve archaeological artifacts, whereas DCAES is capable of analyzing more elements with precision which may be needed to identify flint with overlapping Ca / Fe compositions that cannot be separated by non-destructive EDXRF. The interlaboratory comparison results we present here illustrate the importance of international cooperation among geoscientists and archaeologists interested in applying chemical and geological methods and data to study the economic, social and cultural processes operating during different times in the prehistoric past. Key words: flint, geochemistry, energy dispersive X-ray fluorescence (EDXRF) analysis, Lithuania, Belarus

Die Zukunft der Biomarker in der Demenzdiagnostik

Neurochemical dementia diagnostics (NDD) is a routine laboratory tool in the diagnostic process of patients with neurodegenerative disorders, such as Alzheimer's disease (AD). Currently, two groups of biomarkers analyzed in the cerebrospinal fluid (CSF) are being considered, namely amyloid β (Aβ) peptides and tau proteins, along with the hyperphosphorylated forms of the latter (p-tau). Current directions in the development of NDD include the following: 1. search for novel biomarkers with improved analytical or diagnostic performance; 2. search for biomarkers in the blood; 3. applications of novel technologies enabling better management of patient samples; 4. optimization of the analysis of the biomarkers already available (for example, by improved quality control and inter-laboratory comparison of results). This review presents the state of the art in the field of CSF-based NDD and also summarizes some of the hypotheses of how the future development of NDD tools might look.

Neurochemical dementia diagnostics in Alzheimer’s disease: where are we now and where are we going?

Neurochemical dementia diagnostics (NDD) is a routine laboratory tool used in the diagnostic process for patients with neurodegenerative disorders, such as Alzheimer’s disease. Currently, two groups of biomarkers analyzed in the cerebrospinal fluid are considered – namely amyloid-β peptides and Tau proteins – along with the hyperphosphorylated forms of the latter (pTau). Current directions in the development of NDD include the following: search for novel biomarkers with improved analytical or diagnostic performance; optimization of the analysis of the biomarkers already available (e.g., by improved quality control and interlaboratory comparison of results); applications of novel technologies enabling better management of patient samples; and search for biomarkers in the blood. This article presents the state-of-the-art in the field of cerebrospinal fluid-based NDD, and also summarizes some of the hypotheses of how the future development of NDD tools might look.

Nanoparticles in ambient air. measurement methods

Methods for the measurement of the parameters of aerosol particles with the use of an analyzer based on the differential mobility of nanoparticles and with a diffusion aerosol spectrometer are described and tested. A comparison of the results of measurements of the diameters of nanoparticles by the two methods is performed. Results of inter-laboratory comparisons of the analyzers based on the differential mobility of nanoparticles and studies of the electric motors of household appliances which are generators of the aerosols of nanoparticles with dimensions in the range 6–50 nm are presented.

Vandens skaitiklių patikros įrenginiai ir jų kalibravimo rezultatai

Lietuvoje yra daugiau kaip 1,5 mln. įvairaus pralaidumo vandens skaitiklių, kurių patikrai įsteigta daugiau kaip dešimt laboratorijų, naudojančių 32 vandens skaitiklių kalibravimo įrenginius. Darbe pateiktos pagrindinės patikros įrenginių schemos ir nurodyti metrologiniai reikalavimai, keliami šiems įrenginiams. Parodyta, kad reikiamų parametrų vandens srautą galima pasiekti dviem būdais – naudojant pastovaus lygio baką arba tiekiant vandenį siurbliais, kai vandens talpykla būna pakankamo dydžio. Pateikti laboratorijų lyginimo rezultatai, gauti kalibruojant daugiasrautį šalto vandens skaitiklį, rodo, kad rezultatų patikimumą lemia ne tik įrangos kokybė, bet ne mažiau svarbi yra ir laboratorijos personalo profesinė kompetencija.

Linking the Results of CIPM and RMO Key Comparisons With Linear Trends.

A statistical approach to link the results of interlaboratory comparisons with linear trends is proposed. This approach can be applied to the case that the comparison artifacts have the same nominal values or the measured quantities have the same magnitudes. The degrees of equivalence between the pairs of National Metrology Institutes that have not participated in the same comparisons, and their corresponding uncertainties are established. The approach is applied to link the CCEM-K2 and SIM.EM-K2 comparisons for resistance at 1 G Ω level.

Results of a low cycle fatigue inter-laboratory comparison on 1CrMoNiV rotor steel at elevated temperature

Following an initial intercomparison investigation carried out under a VAMAS programme, a similar venture has been carried out on a single source of 1Cr rotor steel at 525°C at a single total strain range of 0.5% and reversed strain rate of 6%/min (103/s). A key difference was that, for each specimen prior to testing at high temperature, bending measurements were performed at room temperature as a check on unixial alignment since this parameter had previously been suggested as a source of scatter in endurance. Fifteen laboratories participated in the comparison and 67 test results have been subjected to statistical analysis. There appeared to be no consistent effect of the magnitude of bending strain but it is concluded that a minimum of five repeat tests are required from each establishment for meaningful analyses to be made.

Development of Coal Ash Certified Reference Materials JSAC 0521 and 0522 for Determination of Inorganic Constituents

The Japan Society for Analytical Chemistry has developed coal ash certified reference materials (CRMs), JSAC 0521 and 0522, whose concentrations of principal constituents (Si, Al, Ca, Mg, Fe, K, Na, P, Sr, Ti, C and S), trace constituents (As, B, Be, Cd, Co, Cr, Cu, F, Hg, Mn, Ni, Pb, Se, V and Zn) and ignition loss were certified. JSAC 0521 and JSAC 0522 were prepared from Japanese coal ash and foreign coal ash, respectively. CRMs were checked according to the method of JSAC CRM QM002, and the homogeneities were shown to be excellent. Certified values were obtained from statistical analyses of the results of interlaboratory comparisons for coal ashes. Twenty one laboratories participated in this study, but the results for Cd and F were obtained from 11 and 6 laboratories, respectively. Precise results for Cd (11 laboratories) were obtained only by inductively coupled plasma-mass spectrometry (ICP-MS), atomic absorption spectrophotometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES) at a wavelength of 228.798 nm, because the line is not interfered in the presence of Fe and/or Pt. The results for F proved that, statistically, there is a difference in their extraction efficiency between distillation and pyrohydrolysis. Higher results were obtained by pyrohydrolysis than those by distillation ; a recovery of F was incomplete by one-time distillation. Only the results by pyrohydrolysis (6 laboratories) were employed in this study.

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.

Interlaboratory comparisons in EMF survey measurements

This article presents methods and results of interlaboratory comparison in the electromagnetic field (EMF) survey measurements performed by Electromagnetic Environment Protection Laboratory. Based on the results, the author analyzed factors affecting the precision of EMF measurements, in particular—difficult to estimate—the “human factor”. In practice, the human factor has never been taken into account in the EMF measurements accuracy estimations budget, and the author estimate the importance of this factor that may include even up to half of the total uncertainty of measurements. Taking into account all factors depredating the accuracy of measurements, the uncertainty of the survey EMF measurements was estimated at the level of 2–4 dB.

Results of interlaboratory comparisons of column percolation tests

Laboratory leaching tests may be used for source term determination as a basis for risk assessment for soil–groundwater pathway (leachate forecast) on contaminated sites in Germany. Interlaboratory comparisons on the evaluation of the reproducibility of column percolation tests were conducted within the framework of an integrated R + D program using three waste reference materials. The interlaboratory comparisons of column percolation tests showed good reproducibility of the results for inorganic and organic parameters as well as for the accompanying parameters. This is due to the stipulations concerning the time of contact between leachant and sample material as well as the sample placement in the columns. Different column dimensions used by the participants of the interlaboratory comparisons did not have any substantial influence on the column test results.

Must participation in an interlaboratory comparison be (very) frequent?

The usual statement about participation in an interlaboratory comparison (ILC), seems to be that it only yields a ‘snapshot’ of the performance of a measurement laboratory at a given point in time. It is also said that it is a ‘one shot best performance’, produced by using some excellent measuring system operated by an excellent analyst for the very purpose of showing an optimum performance on that occasion. Let us discuss the case were a result is submitted which is truly representative for the daily operations of each of two participants in an ILC involving many participants. Indeed, practical comparisons of measurement results usually occur between two parties in a context buyer-seller, inspectorinspected, regulator-regulated, accreditor-accredited, etc, almost never involving more than two laboratories. If one or both of the two participants’ results are ‘outlying’ in a comparative graph of all participants, the traditional way of looking at it, is that one measurement result ‘up there’ could be ‘down here’ next time, or inversely. Not a sensible observation, of course. The positions in the graph just are proof that the measurement uncertainty for one or for both of them, as defined in the ISO Guide for the Expresssion of Uncertainty in Measurement (GUM), were too optimistic i.e. incomplete. If it had been realistic i.e. reasonably complete, the measurement uncertainty of the one measurement result would have overlapped the second measurement result (maybe even completely overlapping its measurement uncertainty) and there would not have been a significant discrepancy between the two results. There is no need for frequent participation in an ILC to establish that. It just requires drafting a full (i.e. GUM) measurement uncertainty budget based on expert’s knowledge of the measurement procedures used, then participating once in an ILC and have this ‘confirmed’ by the independent check an ILC provides. Thus, it is somewhat expensive not to know the weaknesses in the type of measurement concerned: good knowledge would have avoided a wrong measurement result (i.e. a result which was too optimistic and displayed in the comparative graph with too small a ‘measurement uncertainty’). No frequent participation in ILCs is needed to arrive at that conclusion, just a well running internal precision control programme to ascertain that repeatability of the measurement capability shown in an ILC comparative graph is maintained. Conclusion from a one time participation only and ‘failing’: a too optimistic measurement uncertainty generates the incorrect conclusion that there are discrepancies between the two laboratories’ measurement results. How then can measurement results of ILCs be interpreted and how should the ILC be exploited? ILCs should offer a reliable i.e. traceable reference quantity value, instead of using the participants’ data to calculate a so-called ‘best’ consensus value, derived from participants’ performance. A reference value in an ILC should be traceable to a metrological reference, or be produced from a reference measurement procedure, agreed upon by the participants before the ILC. Both are external to the participants’ performance rather than derived from it. We can then observe on either of the two participants’ results that

Performance validation of a third-generation allergen-specific IgE assay in the clinical laboratory: Interlaboratory and intermethod comparison

Background Allergen-specific IgE (sIgE) measurements are used to help identify causative allergenic agents and to determine the degree of sensitization to facilitate treatment decisions. We examined the performance of a new third-generation chemiluminescent enzyme immunoassay for allergen-specific IgE (sIgE) on the continuous random access Immulite® 2000 system. Methods Detection limit and dilutional linearity were determined. Within-run and total precision were assessed according to the NCCLS EP5 guideline. Interlaboratory comparison of the new Immulite 2000 third-generation allergen-specific IgE assay was performed, as well as intermethod comparison against the Pharmacia FEIA, a second-generation assay. Results The detection limit was < 0.1 kU/l. Dilutional linearity held from 100 down to 0.2 kU/l. Regression analysis of the interlaboratory comparison results yielded: Immulite 2000(Laboratory 1) = 1.07 Immulite 2000(Laboratory 2) + 0.18 kU/l; r = 0.98, n = 3588 results. Intermethod comparison showed the following: Immulite 2000 = 0.83 (Pharmacia FEIA) + 0.42 kU/l; r = 0.79, n = 512 results. Bland–Altman analysis of the interlaboratory and intermethod comparisons indicated no systematic bias. Conclusions We confirmed the reported performance characteristics of the third-generation sIgE assay and found reasonably good interlaboratory and intermethod agreement. The extended range capability of the third-generation assay provides a new tool for investigating cutoffs and trends in childhood allergy disease progression at concentrations < 0.35 kU/l.

Reflections regarding uncertainty of measurement, on the results of a Nordic fatigue test interlaboratory comparison

This paper presents the experiences of calculation and reporting uncertainty of measurement in fatigue testing. Six Nordic laboratories performed fatigue tests on steel specimens. The laboratories also reported their results concerning uncertainty of measurement and how they calculated it. The results show large differences in the way the uncertainties of measurement were calculated and reported. No laboratory included the most significant uncertainty source, bending stress (due to misalignment of the testing machine, “incorrect” specimens and/or incorrectly mounted specimens), when calculating the uncertainty of measurement. Several laboratories did not calculate the uncertainty of measurement in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) [1].

Levels of 7-oxocholesterol in cerebrospinal fluid are more than one thousand times lower than reported in multiple sclerosis

In a recent publication [Diestel, A., O. Aktas, D. Hackel, I. Hake, S. Meier, C. S. Raine, R. Nitsch, F. Zipp, and O. Ullrich. 2003. Activation of microglial poly (ADP-ribose)-polymerase-1 by cholesterol breakdown products during neuroinflammation: a link between demyelination and neuronal damage. J. Exp. Med. 198: 1729-1740], extremely high levels of 7-oxocholesterol were reported in cerebrospinal fluid (CSF) of 11 patients with multiple sclerosis (MS) [7.4 +/- 0.3 mg/l (mean +/- SEM)]. The corresponding level of 12 subjects with other kinds of neurological diseases was reported to be 0.5 +/- 0.1 mg/l. Such high levels of 7-oxocholesterol were found to cause neuronal damage of living brain tissues. Using a highly accurate method for an assay of 7-oxocholesterol based on isotope dilution-mass spectrometry and anaerobic conditions during workup, we found that the level of 7-oxocholesterol in CSF from 29 Swedish patients with MS was only 1.2 microg/l (median, ranging from 0.4 to 4.6 microg/l), less than 1/1,000 th of the previously reported level. The level of 7-oxocholesterol in CSF from 24 Swedish control patients was 0.9 microg/l (0.3-2.3 microg/l), slightly but significantly lower than the CSF level in MS patients (P=0.002). In vitro-induced lipid peroxidation of the endogenous cholesterol in CSF increased the level of 7-oxygenated cholesterol metabolites, particularly 7-oxocholesterol, up to approximately 0.3 mg/l. These results are discussed in relation to the fact that 7-oxygenated steroids are easily artificially formed by autoxidation of cholesterol during workup procedures and analysis of sterols and oxysterols from biological samples.