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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #8-9)

All PT roads led to Rome: Proficiency Testing Workshop by Brian Brookman; Antonio Menditto; Marina Patriarca (pp. 409-410).

Performance of MM-estimators on multi-modal data shows potential for improvements in consensus value estimation by Stephen L. R. Ellison (pp. 411-419).

The performance of a number of robust estimators in the presence of distinct secondary subsets of data is assessed. Estimators examined include the kernel mode recommended by IUPAC, the MM-estimator described by Yohai and, for comparison, the mean, median, and Huber estimate. The performance of the estimators was compared by application to simulated data with one major and one minor mode, and with known minor mode location and proportion of data in the minor mode. The MM-estimator generally performed better than classical and Huber estimates and also provided better precision than the kernel mode at lower minor mode proportions (20% or less). At high minor mode proportion (30%), the kernel density mode provided smaller mean bias and better precision at modest minor mode offsets.

Keywords: Robust statistics; MM-estimate; Proficiency testing; Kernel density

PT/EQA standards and guidelines: some remarks on quality and reliability of test items by Maria Belli (pp. 421-426).

Current standards and international guides on PTs/EQAs consider the achievement of the quality and reliability of PT test items as important steps. Similarity to the materials routinely analysed and sufficient homogeneity and stability of the properties of interest are the main quality characteristics required. PT test items are carriers of the property values used as reference to evaluate laboratory performances. Requirements for PT test items are practically the same as those given for reference materials. ISO-REMCO defines reference material as “Material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be, fit for its intended use in a measurement processes”. In the case of PT test items, they should have a degree of homogeneity and stability to be fit for the purpose of identifying deviations among laboratories. This paper reports some remarks on the main characteristics of PT test items, using ISPRA experience as RM producer.

Keywords: Proficiency test items; PT; Reference materials; Quality

Criteria to define the standard deviation for proficiency assessment for the determination of essential trace elements in serum: comparison of Z-scores based on the Horwitz function or on biological variability by Josiane Arnaud; Robert L. Jones; Alain LeBlanc; Mi-Young Lee; Olav Mazarrasa; Patrick Parsons; Marina Patriarca; Andrew Taylor; Jean-Philippe Weber; Cas Weykamp (pp. 427-430).

A critical issue in the organisation of Proficiency Testing/External Quality Assessment Schemes is the definition of the criteria against which the performance of individual laboratories should be evaluated. Organisers of EQAS in Occupational and Environmental Laboratory Medicine ( http://www.occupational-environmental-laboratory.com ) collaborate to define common acceptable levels of performance. The aim of this study was to compare the Horwitz function to the Fraser’s approach. Sets of results obtained from the distribution of test materials in the Network schemes (for the measurands: copper, selenium or zinc in serum) were used to calculate Z-scores according to both approaches. Quality specifications derived from both approaches were also compared to the standard deviations obtained. Except for selenium, Horwitz criteria suggests a more stringent evaluation than Fraser criteria, the latter being very stringent as regard the participant analytical variability.

Keywords: Quality specifications; Trace elements; Human serum; Human plasma; Proficiency testing; Horwitz; Fraser

Official proficiency tests of the organisation for the prohibition of chemical weapons: current status and future directions by Vinita Dubey; Sanila Velikeloth; Maciej Sliwakowski; Gary Mallard (pp. 431-437).

The Organisation for the Prohibition of Chemical Weapons (OPCW) has been organising and conducting Official Proficiency Tests (PT) since 1996 in accordance with ILAC-G13 to certify laboratories for the analysis of authentic samples under the provision of Chemical Weapons Convention. The tests are part of a mechanism to ensure that there are laboratories that have proven competence in the analysis of chemicals related to the Convention. Laboratories that have successfully completed the tests are designated by the Director General of the OPCW for analysis of authentic samples. To maintain the Designated Laboratory status, a laboratory must take and pass at least one of the two proficiency tests offered per calendar year. Unlike many proficiency tests, the OPCW PT is qualitative, that is the laboratories must determine if any of a very large set (essentially infinite) of chemicals relevant to the Convention are present in the samples. The tests are organised with the assistance of two laboratories, one preparing the test samples, and the other evaluating the test results. The paper provides an overview of the current status of these PTs and outlines salient features regarding procedure and scope of tests, selection of assisting laboratories, scoring and performance rating of participating labs. The emerging issues are also briefly discussed.

Keywords: Proficiency tests; Designated laboratories; Chemical weapons; Organisation for the Prohibition of Chemical Weapons

External Quality Assessment in laboratory medicine: is there a rationale to determine frequency of surveys? by Annette Thomas (pp. 439-444).

Frequency of EQA surveys vary greatly between organisations, countries, discipline and analyte. They may be determined by: scientific opinion, clinical opinion; related to the prevalence of a disease; the relative frequency of laboratory analysis, a function of the analytical complexity of the investigation, a feature of the error rate of the investigation or simply based on availability or cost of the sample. Recently a survey was undertaken on EQA Schemes in Laboratory Medicine to determine the frequency of rounds per year and the number of samples distributed per round. The median for all disciplines was 4 rounds per year, with 28% of all Schemes having a frequency of 4 times per year. Similar results were observed for Haematology and Microbiology with a median of 3 rounds a year with 46% and 49%, respectively operating a frequency of one or two rounds per year. The median for Biochemistry was 6 rounds per year with 33% of Schemes having a monthly frequency. The number of samples per round varied from 1 (31%) to more than 20 (0.5%), with the majority of Schemes providing between 1 and 3 samples per round (83%).

Keywords: External quality assessment; Proficiency testing; Frequency; Laboratory medicine; Pathology

Analytical performance is improved by regular participation in proficiency testing: an analysis of data from the Aquacheck proficiency testing scheme by Matthew Whetton; Helen Finch (pp. 445-448).

Analysis of historical data from the Aquacheck proficiency testing scheme demonstrates improvement in the performance of participants correlated to the frequency of participation. Analysis of the spread of results returned by all participants, defined by the percentage relative standard deviation (RSD) and the performance (Z) scores awarded to the individual participants, indicates that the overall performance for the group of participants is consistent. However, when the frequency of participation is analysed, it can be clearly seen that those laboratories who participated in the majority of the distributions available reported 10–15% more acceptable (Z-scores between +2 and −2) results than those labs who took part with a greatly reduced frequency. When ‘more difficult’ analytes are considered, those laboratories who participated in greater than 75% of available rounds reported up to 30% more acceptable results than those laboratories who participated in 25% or fewer, of the available rounds.

Keywords: Performance improvement; Proficiency testing

Regular participation in proficiency testing provides long term improvements in laboratory performance: an assessment of data over time by Wayne Gaunt; Matthew Whetton (pp. 449-454).

Data from various proficiency testing schemes, operated by LGC Standards, was collated and reviewed to determine whether regular involvement within third party, proficiency testing, either over a prolonged period of time or via multiple participation, had improved the performance of those laboratories taking part. Three statistical evaluations were applied to historical PT results, a review of improvements over time, demonstrated by the evaluation of satisfactory performance scores achieved, a review of the relative robust standard deviations obtained from multiple methods and a focused review of one analyst participating in proficiency testing over a prolonged period of time. In each case the data indicated that long term participation and evaluation via proficiency testing had resulted in consistent and sustained improvements in laboratory performance.

Keywords: Proficiency testing; Statistics; Analyse trends

Proficiency testing of animal nutrition laboratories by Gilberto Batista de Souza; Ana Rita A. Nogueira; Vitor R. Del-Santo; Cristina Maria C. Picchi; Edílson S. Guimarães; Waldomiro Barioni Jr (pp. 455-460).

The Embrapa Cattle-Southeast research unit conducts a program to compare the results provided by laboratories that perform animal feed analyses. Fifty-two laboratories, representing all the Brazilian regions, have participated in the program. The assays included are those normally carried out by animal nutrition laboratories on animal feed and mineral supplements, a total of 22 different analyses. Four rounds of the program are performed annually. Each package provided to the laboratories for testing contains three kinds of animal feed (three each of forage and commercial feed), along with three mineral supplements. For the evaluation of assigned values and standard deviation, the median and robust standard deviation of the participants’ results are used. This paper reports the experience in coordinating the Brazilian interlaboratory comparison exercise.

Keywords: Animal nutrition; Proficiency testing; Inter-laboratory comparisons

Instability of mercury in specimens of human urine for external quality assessment by Andrew Taylor; Robert L. Jones; Alain Leblanc; Olav Mazarrasa; Mi-Young Lee; Patrick J. Parsons; Marina Patriarca; Jean-Philippe Weber; Cas Weykamp (pp. 461-466).

An under-recovery of inorganic mercury added to urine and a wide range of results is observed in quality assessment schemes (EQAS) for trace elements. Furthermore, the under-recoveries are inconsistent suggesting features associated with the urine matrix may make the mercury unavailable for measurement. To investigate the instability of mercury in urine the following experiments were set up: (1) a sample of Hg²⁺ in water with various ‘stabilizers’ added was sent to UK external quality assessment scheme participants. (2) Urine was collected from volunteers who also completed a 3-day food diary. Hg, Ca, Mg, Se, uric acid, phosphate, creatinine, reducing substances and protein were measured. Inorganic mercury was spiked into the urine, stabilizers were added and the mercury determined following storage. The results confirmed under-recovery of mercury in association with the urine matrix. Further investigations of how urinary components affect the measurement of mercury are necessary.

Keywords: Occupational and environmental laboratory medicine; External quality assessment; Mercury in urine

Comparison of different approaches to the statistical evaluation of proficiency tests by Jaroslava Srnková; Jiří Zbíral (pp. 467-471).

The objective of this study was to compare different z-score calculation for the results from proficiency testing programmes. The comparison was carried out on the data from proficiency tests for four different matrices and for all analytes included in the proficiency testing programmes organised by UKZUZ institute from the year 2005 to 2007. It represented 99 samples (three periods per year and eleven samples distributed in each period); the number of determined analytes was 108 in each period. The total number of investigated data sets was 953. Three different approaches to z-score calculation were compared. The results gave reasonably comparable evaluation in most cases but sometimes UKZUZ method proved to be rather strict. The procedure using the robust average and robust standard deviation calculated according to Algorithm A described in ISO 13528 was found to be the most suitable for matrices and level of measurands in UKZUZ proficiency tests.

Keywords: Proficiency tests; z-score calculation; Soils; Plants; Feedstuffs; Sludge; Sediments

Proficiency testing for measurement of radon (²²²Rn) in drinking water by Irma Mäkinen; Ulla-Maija Hanste (pp. 473-476).

The Finnish Environment Institute in collaboration with the Radiation and nuclear safety authority (STUK) carried out the proficiency test for measurement of radon (²²²Rn) in water. Samples were taken from two drilled wells in November 2007. STUK has supplied the regional laboratories with RADEK MKGB-01 equipment based on gamma spectrometry. Two samples for this PT were taken from two drilled wells. Ground water moves irregularly in the process and cracks of the bedrock which is why each participant received an individual sample. Each participant’s sample was measured also by STUK using liquid scintillation counter (LSC) as the reference method in this proficiency test. In estimating laboratory performance the results that deviated less than ±10% from the value measured by STUK using LSC were regarded satisfactory. In total, 73% of the results in the analysis of the sample R1 and 82% in the analysis of the sample R2 deviated less than 10% from the values measured by STUK. The results reported by the participants were generally smaller than the results measured by STUK. The deviation between each participant’s result and the result measured by STUK with the LSC was −7.4% (Sample R1) and −6.2% (Sample R2). Due to the lack of certified reference materials and a reliable proficiency testing data, it is impossible to check the traceability of radon measurements by using the reference method (LSC) at this moment.

Keywords: Proficiency testing; Radon; Drinking water

Proficiency test on incurred and spiked pesticide residues in cereals by Mette Erecius Poulsen; Hanne B. Christensen; Susan S. Herrmann (pp. 477-485).

A proficiency test on incurred and spiked pesticide residues in wheat was organised in 2008. The test material was grown in 2007 and treated in the field with 14 pesticides formulations containing the active substances, alpha-cypermethrin, bifentrin, carbendazim, chlormequat, chlorpyrifos-methyl, difenconazole, epoxiconazole, glyphosate, iprodione, malathion, pirimicarb, prochloraz, spiroxamin and trifloxystrobin. After harvest, the test material was additionally spiked in the laboratory with three pesticides, that where the residues were too low, and axozystrobin. In total, 72 laboratories submitted results and z-scores were calculated for all laboratories and pesticides, except for glyphosate where only five laboratories submitted results and summed weighted z-scores were calculated for the laboratories with a sufficient scope. For several pesticides, the submitted results were strongly depending on the extraction procedure and consequently the assigned values were calculated based on part of the results. Acceptable z-scores were obtained by 56–97% of the participants.

Keywords: Proficiency test; Cereals; Preparation of test material; Pesticide residues; Incurred pesticides

Measurement of PAHs in environmental matrices: results from an interlaboratory comparison on the different steps of the measurement procedure by Stefania Balzamo; Paolo de Zorzi; Sabrina Barbizzi; Elisa Calabretta; Monica Potalivo; Silvia Rosamilia (pp. 487-495).

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.

Keywords: PAHs; Reference material; Interlaboratory comparison (ILC)

Inter-laboratory comparison scheme for fuel sector, LABKAR in Turkey by Özlem Türker Bayrak; Ender Okandan; Hale Üçkardeş (pp. 497-502).

Fuel sector is one of the powerful sectors in Turkish industry. The implementation of a new law for regulating the fuel sector had enforced the quality control of fuels sold to public. This resulted in several accredited fuel-testing laboratories to emerge. Thus, a scheme to evaluate their proficiency in measurements became an important requirement. The inter-laboratory comparison scheme LABKAR for gasoline, diesel oil, LPG, lubricating oil and biodiesel samples have evolved to fulfill this need. In this paper, LABKAR is introduced; the results obtained from the program are analyzed and discussed. The kernel densities of the participants’ results show that the use of robust mean as a consensus value is appropriate for fuel samples. Although the number of rounds is not enough to derive strict conclusions, it is seen that the performance of the scheme based on the standard deviations and coefficient of variations is improving in each round. It has been observed that the number of laboratories receiving “action” or “warning” is decreasing, which indicates that they are benefiting from the scheme.

Keywords: Inter-laboratory Comparison; LABKAR; Fuel sector; Turkey

Proficiency testing in food microbiology “Aqua”: enumeration of Staphylococcus aureus by M. Grimaldi; M. Mancin; R. Trevisan; R. Mioni (pp. 503-505).

In 1999 the Food Microbiology laboratory of the Istituto Zooprofilattico Sperimentale delle Venezie (IZSVe) started an interlaboratory comparison program for food microbiological tests, known as “Aqua, interlaboratory comparisons for quality assurance”. Aqua produces the test samples, applies statistical methods to estimate homogeneity and stability, processes and evaluates the results. The proficiency testing results allow to evaluate the performance of the laboratories, to identify possible differences and non-conformity, to demonstrate the competence and the quality of results, in order to take suitable corrective and/or preventive action after the individuation of the causes. Moreover, elaborating the results of several proficiency testing by using the control chart method, it is possible to evaluate the trend of the laboratory and to verify that the results are in statistical quality control.

Keywords: Proficiency testing Aqua; Food microbiology; Statistical elaboration

Proficiency testing in analytical chemistry, microbiology and laboratory medicine: working discussions on current practice and future directions by Maria Belli; Brian Brookman; Beatriz de la Calle; Vivienne James; Michael Koch; Nineta Majcen; Antonio Menditto; Tracey Noblett; Roberto Perissi; Kees van Putten; Piotr Robouch; Tommy Šlapokas; Philip Taylor; Daniel Tholen; Annette Thomas; Barry Tylee (pp. 507-512).

A summary of the working group (WG) discussions on proficiency testing (PT) and external quality assessment (EQA) held at the Eurachem Workshop, Rome, 5–7 October 2008 is provided. The eight WG’s covered a range of issues concerned with current practice and future directions; how frequently should laboratories participate in PT/EQA? (WG1); developments in PT/EQA within the EU—what is required in future? (WG2); what issues do developing countries face with regards to PT/EQA? (WG3), what issues are specific to microbiology PT/EQA? (WG4); what new fields are emerging for PT/EQA? (WG5); what will be the impact of the new ISO/IEC 17043 standard? (WG6); do current PT/EQA schemes meet the needs of participants? (WG7); and what are the issues that affect the quality of proficiency test items? (WG8). Delegates with different backgrounds were on each WG in order to capture a range of views and experience from a number of different sectors. Working group representatives included PT/EQA providers, participants in PT/EQA schemes and end users of PT results such as accreditation bodies and regulatory authorities, from countries around the world.

Keywords: Proficiency testing; External quality assessment; Accreditation

Interlaboratory comparisons: towards global chemical safety (pp. 513-513).

Congress, conferences, workshops and courses (pp. 515-516).

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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #8-9)

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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #8-9)