International Interlaboratory Comparison Research Articles

Quantification of SARS-CoV-2 monoclonal IgG mass fraction by isotope dilution mass spectrometry.

The availability of serology assays to measure antibodies against the SARS coronavirus 2 (SARS-CoV-2) expanded rapidly during the Covid-19 pandemic. The interchangeable use of such assays to monitor disease progression and immune protection requires their standardization, for which suitably characterized monoclonal antibody materials can be useful. The methods, based on isotope dilution mass spectrometry, to value assign the mass fraction of such a material in solution within the context of an international interlaboratory comparison study (CCQM-P216) are described. The mass fraction in solution of a humanized IgG monoclonal antibody (mAb) against the SARS-CoV-2 Spike glycoprotein in the study sample has been value assigned through a combination of liquid chromatography, isotope dilution mass spectrometry (LC-ID-MS) methods and size exclusion chromatography with UV detection (SEC-UV). The former were developed for the quantification of amino acids and proteotypic peptides as surrogate analytes of the mAb while the latter was applied for the determination of the relative monomeric mass fraction. High-resolution mass spectrometry (hrMS) allowed the molecular weight evaluation and ruled out the presence of significant impurities. Method trueness was assessed using a subclass homologous IgG1 material value assigned by amino acid analysis. The assigned mass fraction of monomeric SARS-CoV-2 IgG in solution was 390 ± 16mg/g. The associated expanded uncertainty originated mainly from acid hydrolysis variability and Trypsin/Lys-C digestion variability and efficiency.

Interlaboratory comparison as a source of information about the problem

Methods of evaluation of interlaboratory comparison results are prescribed by ISO standards. Ruler is probably one of the most widely used length measuring instrument in the world. For laboratories that plan to be accredited for the calibration of Ruler, the acquisition of a specialized Measuring bench is not economically feasible. Confidence in the measured result depends on the measurement uncertainty, and where deficiencies are observed, the values that contribute to the measurement uncertainty should be investigated. This paper describes an interlaboratory comparison for a small number of laboratories on the example of a Measuring bench for calibrating Ruler and indicates the procedure for problem identification; diagnosis of causes; consideration of solutions; initiation of action for improvement and monitoring of the results of applied solutions. The authors documented the problem and listed the elements that contributed to "Unsatisfactory" result in interlaboratory comparisons. They described the actions they took to overcome the "Unsatisfactory" result, analyzed whether the proposed solutions led to "Satisfactory" result and took actions accordingly. The paper presents the results of the international interlaboratory comparison, which are a confirmation of the competence of the personnel, measuring calibration equipment and calibration method.

Production and certification of BOTS-1: bovine muscle-certified reference material for incurred veterinary drug residues.

A freeze-dried bovine muscle-certified reference material (CRM), known as BOTS-1 (DOI: https://doi.org/10.4224/crm.2018.bots-1 ), containing incurred residues of commonly used veterinary drugs was produced and certified for the mass fraction of eight veterinary drug residues. Value assignment was carried out using liquid chromatography tandem mass spectrometry (LC-MS/MS) methods in conjunction with isotope dilution and standard addition approaches involving stable isotope internal standards. Data from the National Research Council of Canada (NRC), Canadian Food Inspection Agency (CFIA), United States Department of Agriculture (USDA), and the Federal Office of Consumer Protection and Food Safety in Germany (BVL) were used for value assignment. Results for two drug residues were also obtained through an international inter-laboratory comparison CCQM-K141/P178 organized under the auspices of the International Bureau of Weights and Measures (BIPM). Quantitative NMR (1H-qNMR) was used to characterize primary standards of all veterinary drugs certified. The certified mass fractions of the veterinary drug residues were 490 ± 100µg/kg for chlorpromazine, 44 ± 4.4µg/kg for ciprofloxacin, 3.3 ± 1.4µg/kg for clenbuterol, 9.5 ± 0.8µg/kg for dexamethasone, 57 ± 4.8µg/kg for enrofloxacin, 3.0 ± 0.4µg/kg for meloxicam, 12.4 ± 1.2µg/kg for ractopamine, and 2290 ± 120µg/kg for sulfadiazine with expanded uncertainties quoted (95% confidence) which include the effects due to between-bottle inhomogeneity, instability during long-term storage and transportation, and characterization.

Thickness measurements of graphene oxide flakes using atomic force microscopy: results of an international interlaboratory comparison

Flake thickness is one of the defining properties of graphene-related 2D materials (GR2Ms), and therefore requires reliable, accurate, and reproducible measurements with well-understood uncertainties. This is needed regardless of the production method or manufacturer because it is important for all GR2M products to be globally comparable. An international interlaboratory comparison on thickness measurements of graphene oxide flakes using atomic force microscopy has been completed in technical working area 41 of versailles project on advanced materials and standards. Twelve laboratories participated in the comparison project, led by NIM, China, to improve the equivalence of thickness measurement for two-dimensional flakes. The measurement methods, uncertainty evaluation and a comparison of the results and analysis are reported in this manuscript. The data and results of this project will be directly used to support the development of an ISO standard.

International Interlaboratory Comparison of Thermogravimetric Analysis of Graphene-Related Two-Dimensional Materials

Research on graphene-related two-dimensional (2D) materials (GR2Ms) in recent years is strongly moving from academia to industrial sectors with many new developed products and devices on the market. Characterization and quality control of the GR2Ms and their properties are critical for growing industrial translation, which requires the development of appropriate and reliable analytical methods. These challenges are recognized by International Organization for Standardization (ISO 229) and International Electrotechnical Commission (IEC 113) committees to facilitate the development of these methods and standards which are currently in progress. Toward these efforts, the aim of this study was to perform an international interlaboratory comparison (ILC), conducted under Versailles Project on Advanced Materials and Standards (VAMAS) Technical Working Area (TWA) 41 "Graphene and Related 2D Materials" to evaluate the performance (reproducibility and confidence) of the thermogravimetric analysis (TGA) method as a potential new method for chemical characterization of GR2Ms. Three different types of representative and industrially manufactured GR2Ms samples, namely, pristine few-layer graphene (FLG), graphene oxide (GO), and reduced graphene oxide (rGO), were used and supplied to ILC participants to complete the study. The TGA method performance was evaluated by a series of measurements of selected parameters of the chemical and physical properties of these GR2Ms including the number of mass loss steps, thermal stability, temperature of maximum mass change rate (Tp) for each decomposition step, and the mass contents (%) of moisture, oxygen groups, carbon, and impurities (organic and non-combustible residue). TGA measurements determining these parameters were performed using the provided optimized TGA protocol on the same GR2Ms by 12 participants across academia, industry stakeholders, and national metrology institutes. This paper presents these results with corresponding statistical analysis showing low standard deviation and statistical conformity across all participants that confirm that the TGA method can be satisfactorily used for characterization of these parameters and the chemical characterization and quality control of GR2Ms. The common measurement uncertainty for each parameter, key contribution factors were identified with explanations and recommendations for their elimination and improvements toward their implementation for the development of the ISO/IEC standard for chemical characterization of GR2Ms.

International interlaboratory comparison of Raman spectroscopic analysis of CVD-grown graphene

There is a pressing need for reliable, reproducible and accurate measurements of graphene’s properties, through international standards, to facilitate industrial growth. However, trustworthy and verified standards require rigorous metrological studies, determining, quantifying and reducing the sources of measurement uncertainty. Towards this effort, we report the procedure and the results of an international interlaboratory comparison (ILC) study, conducted under Versailles Project on Advanced Materials and Standards. This ILC focusses on the comparability of Raman spectroscopy measurements of chemical vapour deposition (CVD) grown graphene using the same measurement protocol across different institutes and laboratories. With data gathered from 17 participants across academia, industry (including instrument manufacturers) and national metrology institutes, this study investigates the measurement uncertainty contributions from both Raman spectroscopy measurements and data analysis procedures, as well as provides solutions for improved accuracy and precision. While many of the reported Raman metrics were relatively consistent, significant and meaningful outliers occurred due to differences in the instruments and data analysis. These variations resulted in inconsistent reports of peak intensity ratios, peak widths and the coverage of graphene. Due to a lack of relative intensity calibration, the relative difference reported in the 2D- and G peak intensity ratios () was up to 200%. It was also shown that the standard deviation for values reported by different software packages, was 15× larger for Lorentzian fit functions than for pseudo-Voigt functions. This study has shown that by adopting a relative intensity calibration and consistent peak fitting and data analysis methodologies, these large, and previously unquantified, variations can be significantly reduced, allowing more reproducible and comparable measurements for the graphene community, supporting fundamental research through to the growing graphene industry worldwide. This project and its findings directly underpin the development of the ISO/IEC standard ‘DTS 21356-2—Nanotechnologies—Structural Characterisation of CVD-grown Graphene’.

Results from an international interlaboratory study on light‐ and elevated temperature‐induced degradation in solar modules

AbstractThis paper reports the results of an international interlaboratory comparison study on light‐ and elevated temperature‐induced degradation (LETID) on crystalline silicon photovoltaic (PV) modules. A large global network of PV module manufacturers and PV testing laboratories collaborated to design a protocol for LETID detection and screen a large and diverse set of prototype modules for LETID. Results across labs indicate the reproducibility of LETID testing is likely within ±1% of maximum power (PMP). In intentionally engineered LETID‐sensitive modules, mean degradation after the prescribed detection stress is roughly 6% PMP. In other module types the LETID sensitivity is smaller, and in some we observe essentially negligible degradation attributable to LETID. In LETID‐sensitive modules, both open‐circuit voltage (VOC) and short‐circuit current (ISC) degrade by a roughly similar magnitude. We observe, as do previous studies, that LETID affects each cell in a module differently. An investigation of the potential mismatch losses caused by nonuniform LETID degradation found that mismatch loss is insignificant compared to the estimated loss of cell ISC, which drives loss of module ISC. Overall, this work has helped inform the creation of a forthcoming standard technical specification for LETID testing of PV modules, IEC TS 63342 ED1, and should aid in the interpretation of results from that and other LETID tests.

The reproducibility of corrosion testing in supercritical water—Results of a second international interlaboratory comparison exercise

Supercritical water-cooled reactor candidate materials are typically corrosion-resistant alloys whose mass changes in supercritical water fluctuate around zero. A previous interlaboratory corrosion experiment exercise revealed large scatter in mass change results between laboratories. Here, we reduced systemic differences between laboratories by unilateral preparation of coupons and unilateral chemical cleaning. Type 310S stainless steel and Alloy 800HT test coupons were exposed for 1000 h to 550 °C, 25 MPa, deaerated water. Average mass loss for 310S and 800HT was 38 ± 26 and 51 ± 31 mg/dm2, respectively. Differences in mass transfer, galvanic and local corrosion, and average coupon temperature may explain the poor reproducibility.

Determination of trace elements in urine by inductively coupled plasma-tandem mass spectrometry – Biomonitoring of adults in the German capital region

A method was developed and validated for multi-element analyses of human urine samples using inductively coupled plasma-tandem mass spectrometry. The combination of a simple sample preparation and the state-of-the-art technique allows high-throughput and lowest limits of quantification up to 1 ng/L. Thereby coefficients of variation ranges from 0.4% (V) to 3.7% (Be), and 0.9% (Cd) to 4.8% (Ni) for intraday and interday precision, respectively. The method's performance is demonstrated by successful participation in international interlaboratory comparison programs as external quality assurance.Moreover, the method was applied for the analysis of first-morning void urine samples of adults (N = 77) living in the German capital region. 15 metals and metalloids (Astotal, Be, Bi, Cd, Co, Cr, In, Mn, Mo, Ni, Pb, Sn, Tl, V, and Zn) were determined. With exception of indium, all elements were found in urine samples above the limit of quantification, demonstrating the suitability to measure the general population's exposure to these metals and metalloids. The method presented here shall be used for analysis of urine samples collected in the upcoming German Environmental Survey, GerES VI, a cross-sectional, population-representative study.

Top-down and bottom-up approaches for the estimation of measurement uncertainty in coagulation assays

The assessment of measurement uncertainty (MU) in clinical laboratories is essential to the reliable interpretation of results in clinical laboratories. However, despite the introduction of various methods for the expression of uncertainty in measurement, the MUs of coagulation tests have not been extensively studied. The aim of this study was to quantify the MU of various coagulation assays according to international guidelines and to report an expected confidence in the quality of coagulation assays. We selected activated partial thromboplastin time, international normalized ratio (INR), protein C/S, antithrombin, fibrinogen, and Factor V/VIII/X to quantify the MUs of two coagulation testing systems: ACL TOP 750 CTS (Instrumentation Laboratory, Bedford, MA, USA) and STA Compact (Diagnostica Stago, Asnières-sur-Seine, France). We used international standards and interlaboratory comparison results in accordance with international guidelines in a top-down approach to the assessment of MU. For INR, MU was estimated in a bottom-up approach using reference thromboplastin and certified plasmas. Top-down approaches resulted in MUs between 3.3% and 21.3% for each measurand. In the bottom-up approach, MUs of INR values ranged from 10.9% to 26.4% and showed an upward trend as INR increased. In this study, we were successful in quantifying MU of coagulation assays using practical methods. Our results demonstrated that top-down and bottom-up approaches were adequate for coagulation assays. However, some assays showed significant biases against international standards; therefore, standardization would be necessary to ensure more reliable patient results.

Islet Autoantibody Standardization Program 2018 Workshop: Interlaboratory Comparison of Glutamic Acid Decarboxylase Autoantibody Assay Performance.

The Islet Autoantibody Standardization Program (IASP) aims to improve the performance of immunoassays measuring type 1 diabetes (T1D)-associated autoantibodies and the concordance of results among laboratories. IASP organizes international interlaboratory assay comparison studies in which blinded serum samples are distributed to participating laboratories, followed by centralized collection and analysis of results, providing participants with an unbiased comparative assessment. In this report, we describe the results of glutamic acid decarboxylase autoantibody (GADA) assays presented in the IASP 2018 workshop. In May 2018, IASP distributed to participants uniquely coded sera from 43 new-onset T1D patients, 7 multiple autoantibody-positive nondiabetic individuals, and 90 blood donors. Results were analyzed for the following metrics: sensitivity, specificity, accuracy, area under the ROC curve (ROC-AUC), partial ROC-AUC at 95% specificity (pAUC95), and concordance of qualitative and quantitative results. Thirty-seven laboratories submitted results from a total of 48 different GADA assays adopting 9 different formats. The median ROC-AUC and pAUC95 of all assays were 0.87 [interquartile range (IQR), 0.83-0.89] and 0.036 (IQR, 0.032-0.039), respectively. Large differences in pAUC95 (range, 0.001-0.0411) were observed across assays. Of formats widely adopted, bridge ELISAs showed the best median pAUC95 (0.039; range, 0.036-0.041). Several novel assay formats submitted to this study showed heterogeneous performance. In 2018, the majority of the best performing GADA immunoassays consisted of novel or established nonradioactive tests that proved on a par or superior to the radiobinding assay, the previous gold standard assay format for GADA measurement.

A higher order method for the determination of total phosphorus in human serum

Phosphorus is an essential element in the human body and an important clinical biomarker in serum. However, the lack of reference method that is traceable to the International System of Units and matrix-matched certified reference material (CRM) pose a major challenge in the assessment of the accuracy of phosphorus measurements. A higher order measurement procedure for total phosphorus in human serum by standard addition method using high-resolution sector field inductively coupled plasma mass spectrometry was established. In this method, germanium and gallium are used as internal standards. The accuracy of the measurement was evaluated by comparing the results with the certified values of Trace Elements in Tea Leaf Powder (NMIJ CRM 7505-a) and Trace Elements in Milk Powder (NMIJ CRM 7512-a), as well as the reference value of Electrolytes in Frozen Human Serum (NIST SRM 956d). This method had also been applied in an international interlaboratory comparison (CCQM-K139 Elements in Human Serum). The results of this comparison showed that this method is comparable with the methods used by other established national metrology institutes or designated institutes. In addition, the first human serum reference material that is certified for total phosphorus was produced. This reference material is valuable for method development as well as the assessment of the accuracy of phosphorus measurements in clinical laboratories (as quality control).

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison.

This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practical guidance for standardized passive sampling, and advance the use of passive sampling in regulatory decision making by increasing confidence in the use of the technique. The study was performed by a consortium of 11 laboratories and included experiments with 14 passive sampling formats on 3 sediments for 25 target chemicals (PAHs and PCBs). The resulting overall interlaboratory variability was large (a factor of ∼10), but standardization of methods halved this variability. The remaining variability was primarily due to factors not related to passive sampling itself, i.e., sediment heterogeneity and analytical chemistry. Excluding the latter source of variability, by performing all analyses in one laboratory, showed that passive sampling results can have a high precision and a very low intermethod variability (<factor of 1.7). It is concluded that passive sampling, irrespective of the specific method used, is fit for implementation in risk assessment and management of contaminated sediments, provided that method setup and performance, as well as chemical analyses are quality-controlled.

The reproducibility of corrosion testing in supercritical water—Results of an international interlaboratory comparison exercise

A major challenge in supercritical water-cooled reactor development is the lack of a consistent alloy database. An international interlaboratory comparison test was organized to study the reproducibility of weight change data obtained for identical alloys under similar conditions in different facilities. This paper presents the test procedures, conditions, results, and additional characterization data. More variation in weight change was observed than expected. The scatter was small within the same laboratory, but large between different laboratories. Much of this variation appears to be attributable to differences in test facilities. The data generally agree on the relative ranking of the corrosion resistance.

A review on the determination of isotope ratios of boron with mass spectrometry.

The present review discusses different mass spectrometric techniques-viz, thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), and secondary ion mass spectrometry (SIMS)-used to determine 11 B/10 B isotope ratio, and concentration of boron required for various applications in earth sciences, marine geochemistry, nuclear technology, environmental, and agriculture sciences, etc. The details of the techniques-P-TIMS, which uses Cs2 BO2+ , N-TIMS, which uses BO2- , and MC-ICPMS, which uses B+ ions for bulk analysis or B- and B+ ions for in situ micro-analysis with SIMS-are highlighted. The capabilities, advantages, limitations, and problems in each mass spectrometric technique are summarized. The results of international interlaboratory comparison experiments conducted at different times are summarized. The certified isotopic reference materials available for boron are also listed. Recent developments in laser ablation (LA) ICPMS and QQQ-ICPMS for solids analysis and MS/MS analysis, respectively, are included. The different aspects of sample preparation and analytical chemistry of boron are summarized. Finally, the future requirements of boron isotope ratios for future applications are also given. Presently, MC-ICPMS provides the best precision and accuracy (0.2-0.4‰) on isotope ratio measurements, whereas N-TIMS holds the potential to analyze smallest amount of boron, but has the issue of bias (+2‰ to 4‰) which needs further investigations. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 36:499-519, 2017.

First international inter-laboratory comparison of high-pressure CH4, CO2 and C2H6 sorption isotherms on carbonaceous shales

An inter-laboratory study of high-pressure gas sorption measurements on two carbonaceous shales has been conducted in order to assess the reproducibility of the sorption isotherms and identify possible sources of error. The measurements were carried out by seven international research laboratories using either in-house or commercial sorption equipment (manometric and gravimetric methods). Excess sorption isotherms for methane, carbon dioxide and ethane were measured at 65°C and at pressures up to 25MPa on two organic-rich shales in the dry state. The samples used in this study were taken from immature Posidonia shale (Germany) and over-mature Upper Chokier Formation (Belgium). Their total organic carbon (TOC) contents were 15.1% and 4.4% , respectively, and their vitrinite reflectance (VRr) values 0.5% and 2.0%.The objective of this study was to assess the reproducibility of sorption isotherms among laboratories each following their own measurement and data reduction procedures. All labs were asked to follow a predefined sample drying procedure prior to measurement in order to minimize any effects related to moisture. The reproducibility of the methane excess sorption isotherms was better for the high-maturity shale (within 0.02–0.03mmol/g) than for the low-maturity sample (up to 0.1mmol/g), similar to observations in earlier inter-laboratory studies on coals. The reproducibility for CO2 and C2H6 sorption isotherms was satisfactory at pressures below 5MPa, however, the results deviate considerably at higher pressures. Anomalies in the shape of the excess sorption isotherms were observed for CO2 and C2H6 and these are explained as being due to high sensitivity of gas density to temperature and pressure close to the critical point as well as from a limited measurement accuracy and possibly uncertainty in the equation of state (EoS).The low sorption capacity of carbonaceous shales (as compared to coals and activated carbons) sets very high demands on the accuracy of pressure and temperature measurement and precise temperature control. Furthermore, the sample treatment, measurement and data reduction procedures must be optimized in order to achieve satisfactory inter-laboratory consistency and accuracy. Systematic errors must be minimized first by calibrating the pressure and temperature sensors to high-quality standards. Blank sorption measurements with a non-sorbing sample (e.g. stainless steel) can be used to identify and quantitatively account for measuring artifacts resulting from unknown residual systematic errors or from the limited accuracy of the EoS. The possible sources of error causing the observed discrepancies are discussed.

A Recent Development in Creep-Fatigue Testing

Procedures for the assessment of components subject to cyclic loading at high temperatures require material property input data that characterize the creep-fatigue deformation response and resistance to cracking. For many years, there was no testing standard or code of practice to ensure that such information was generated in a uniform way. This was mainly because the creep-fatigue test data requirements for organizations in various industrial sectors appeared to be so different that the need for standardization was questioned. In the mid-2000s, it was recognized that even though it would make no sense to be prescriptive about such details as cycle shape, there were many aspects of creep-fatigue testing for which guidance would be beneficial to ensure acceptable uniformity in deformation and endurance data generation. In response to this realization, the state of the art relating to creep-fatigue interaction was extensively reviewed by an international group of specialists, and the generated knowledge base was used to underpin a new ASTM testing standard, ASTM E2714-09. The gathered knowledge is reviewed. There is a requirement for all ASTM standards to include a precision and bias statement, and an international interlaboratory creep-fatigue test comparison activity was facilitated to form the basis of this section of ASTM E2714-09. An integral part of the guidance given in the new standard is the recommendation for post-test metallurgical inspection and the way in which this information can be used to give added value to creep-fatigue crack initiation endurance results. The evidence gathered from this study is also examined.

Empirical insights and considerations for the OBT inter-laboratory comparison of environmental samples

Organically bound tritium (OBT) is an important tritium species that can be measured in most environmental samples, but has only recently been recognized as a species of tritium in these samples. Currently, OBT is not routinely measured by environmental monitoring laboratories around the world. There are no certified reference materials (CRMs) for environmental samples. Thus, quality assurance (QA), or verification of the accuracy of the OBT measurement, is not possible. Alternatively, quality control (QC), or verification of the precision of the OBT measurement, can be achieved. In the past, there have been differences in OBT analysis results between environmental laboratories. A possible reason for the discrepancies may be differences in analytical methods. Therefore, inter-laboratory OBT comparisons among the environmental laboratories are important and would provide a good opportunity for adopting a reference OBT analytical procedure. Due to the analytical issues, only limited information is available on OBT measurement. Previously conducted OBT inter-laboratory practices are reviewed and the findings are described. Based on our experiences, a few considerations were suggested for the international OBT inter-laboratory comparison exercise to be completed in the near future.

Characterization of the NIST shellfish Standard Reference Material 4358

A new shellfish Standard Reference Material 4358 was developed by the National Institute of Standards and Technology through an international interlaboratory comparison that involved twelve laboratories-participants from nine countries. The results from the participants were statistically evaluated, and the most robust certified values were based on the median of laboratories’ reported means and the uncertainties derived using the bootstrap method. Massic activity certified values were established for fourteen radionuclides, five activity ratios, and informational massic activity values for eight more radionuclides and two activity ratios.

Analysis of Thermal-Conductivity Measurement Data from International Comparison of National Laboratories

For the first time under the auspices of the Bureau International des Poids et Mesures (BIPM), seven national metrology institutes (NMIs) participated in an international interlaboratory comparison on thermal-conductivity measurements by the guarded hot-plate method. Measurements were conducted successively by all participants on the same set of specimens of insulating materials (mineral wool and expanded polystyrene) at temperatures ranging from 10 °C to 40 °C, according to the International Standard ISO 8302. This protocol aims to minimize issues of material variability by circulating the same pairs of specimens among the laboratories following the strict format of a round-robin test program. This comparison is a pilot study which is intended as a first stage for future key comparisons between NMIs. The descriptive analysis of obtained results shows good agreement between laboratories for the mineral wool (MW) specimens and the thicker specimens of expanded polystyrene (EPS), with relative deviations within the uncertainties of measurement. A positive drift of thermal-conductivity values, which has appeared progressively during the comparison process, seems to be correlated with the size of the metering area of the guarded hot plates used. A statistical analysis was applied to repeated thermal-conductivity measurements at 23 °C, to identify anomalous and outlying data, to assess the within- and between-laboratory variability, and to evaluate the participant laboratories’ performance.