Proficiency Testing Schemes Research Articles

Total error in lymphocyte subpopulations by flow cytometry-based in state of the art using Spanish EQAS data.

Flow cytometry analyses of lymphocyte subpopulations (T, B, NK) are crucial for enhancing clinical algorithms and research workflows. Estimating the total error (TE) values for the percentage and absolute number of lymphocyte subpopulations using the state-of-the-art (SOTA) approach with real data from an external proficiency testing (EPT) scheme was performed. A comparison with previously published Biological Variability (BV)-based specifications was carried out. A total of 44,998 results from 86 laboratories over 10 years were analysed and divided into two five-year periods (2012-2016) and (2017-2021). Data come from the IC-1 Lymphocytes scheme of the Spanish External Quality Assurance System (EQAS) GECLID Program. This quantitative scheme includes percentages and absolute numbers of CD3+, CD3+CD4+, CD3+CD8+, CD19+, and CD3-CD56+CD16+ NK cells. The percentage of TE was calculated as: |reported value-robust mean|*100/robust mean for each laboratory and parameter. The cut-off for TE is set at 80 % best results of the laboratories. A significant reduction in the SOTA-based TE for all lymphocyte subpopulations in 2017-2021 was observed compared to 2012-2016. The SOTA-based TE fulfils the minimum BV-based TE for percentages of lymphocyte subpopulations. The parameter with the best analytical performance calculated with SOTA (2017-2021 period)-based TE was the percentage of CD3+ (TE=3.65 %). The values of SOTA-based specifications from external quality assurance program data are consistent and can be used to develop technical specifications. The technological improvement, quality commitment, standardization, and training, reduce TE. An update of TE every five years is therefore recommended. TE assessment in lymphocyte subsets is a helpful and reliable tool to improve laboratory performance and data-based decision-making trust.

Results of the 2020 Genomic Proficiency Test for the network of European Union Reference Laboratory for Antimicrobial Resistance assessing whole-genome-sequencing capacities.

The global surveillance and outbreak investigation of antimicrobial resistance (AMR) is amidst a paradigm shift from traditional biology to bioinformatics. This is due to developments in whole-genome-sequencing (WGS) technologies, bioinformatics tools, and reduced costs. The increased use of WGS is accompanied by challenges such as standardization, quality control (QC), and data sharing. Thus, there is global need for inter-laboratory WGS proficiency test (PT) schemes to evaluate laboratories' capacity to produce reliable genomic data. Here, we present the results of the first iteration of the Genomic PT (GPT) organized by the Global Capacity Building Group at the Technical University of Denmark in 2020. Participating laboratories sequenced two isolates and corresponding DNA of Salmonella enterica, Escherichia coli and Campylobacter coli, using WGS methodologies routinely employed at their laboratories. The participants' ability to obtain consistently good-quality WGS data was assessed based on several QC WGS metrics. A total of 21 laboratories from 21 European countries submitted WGS and meta-data. Most delivered high-quality sequence data with only two laboratories identified as overall underperforming. The QC metrics, N50 and number of contigs, were identified as good indicators for high-sequencing quality. We propose QC thresholds for N50 greater than 20 000 and 25 000 for Campylobacter coli and Escherichia coli, respectively, and number of contigs >200 bp greater than 225, 265 and 100 for Salmonella enterica, Escherichia coli and Campylobacter coli, respectively. The GPT2020 results confirm the importance of systematic QC procedures, ensuring the submission of reliable WGS data for surveillance and outbreak investigation to meet the requirements of the paradigm shift in methodology.

Busulfan Interlaboratory Proficiency Testing Program Revealed Worldwide Errors in Drug Quantitation and Dose Recommendations.

The clinical outcomes of busulfan-based conditioning regimens for hematopoietic cell transplantation (HCT) have been improved by personalizing the doses to target narrow busulfan plasma exposure. An interlaboratory proficiency test program for the quantitation, pharmacokinetic modeling, and busulfan dosing in plasma was developed. Previous proficiency rounds (ie, the first 2) found that 67%-85% and 71%-88% of the dose recommendations were inaccurate, respectively. A proficiency test scheme was developed by the Dutch Foundation for Quality Assessment in Medical Laboratories (SKML) and consisted of 2 rounds per year, with each round containing 2 busulfan samples. In this study, 5 subsequent proficiency tests were evaluated. In each round, the participating laboratories reported their results for 2 proficiency samples (ie, low and high busulfan concentrations) and a theoretical case assessing their pharmacokinetic modeling and dose recommendations. Descriptive statistics were performed, with ±15% for busulfan concentrations and ±10% for busulfan plasma exposure. The dose recommendations were deemed accurate. Since January 2020, 41 laboratories have participated in at least 1 round of this proficiency test. Over the 5 rounds, an average of 78% of the busulfan concentrations were accurate. Area under the concentration-time curve calculations were accurate in 75%-80% of the cases, whereas only 60%-69% of the dose recommendations were accurate. Compared with the first 2 proficiency test rounds (PMID 33675302, October, 2021), the busulfan quantitation results were similar, but the dose recommendations worsened. Some laboratories repeatedly submit results that deviated by more than 15% from the reference values. The proficiency test showed persistent inaccuracies in busulfan quantitation, pharmacokinetic modeling, and dose recommendations. Additional educational efforts have yet to be implemented; regulatory efforts seem to be needed. The use of specialized busulfan pharmacokinetic laboratories or a sufficient performance in busulfan proficiency tests should be required for HCT centers that prescribe busulfan.

National proficiency test for molecular detection of white spot syndrome virus in China, 2021

National Aquatic Animal Disease Surveillance Program (NAADSP) has started since 2007 to conduct nationwide surveillance for the prevalence of major crustacean pathogens in China, including white spot syndrome virus (WSSV). Standard diagnostic procedures and reliable detection capability are critical for ensuring accurate and comparable surveillance results, hence competent authority of China launched annual proficiency test (PT) synchronously to screen competent aquatic clinical diagnostic laboratories to undertake NAADSP. Here we present the results of PT for molecular detection of WSSV in 2021. Six tissue samples containing different WSSV concentrations were provided as blind samples to a total of 170 laboratories nationwide. All the participating laboratories were asked to perform qualitative or quantitative analyses by using standard molecular assays or commercial detection kits. In the qualitative assessments, 86.8% (125/144) of the participants achieved satisfied results by using conventional nested-PCR. Comparing to the strong/medium positive samples, the identification of negative samples and weak-positive samples have been shown to be more challenging. A relatively higher error rates were reported in results of sample S3 and S4. In the quantitative assessments, cycle threshold (Ct) values of real-time PCR submitted by 47 participants had been analyzed by using robust statistical method. The overall satisfied performance was achieved by 74.5% (35/47) of the participants. Acceptable between-laboratories z-score (ZB) and within-laboratory z-score (ZW) was achieved by 93.3% and 91.1%, respectively, in the analysis of the pair of identical samples S6 and S8. WSSV-PT 2021 supplied valuable reference information for selecting competent laboratories to participate in the NAADSP. Furthermore, the national PT scheme in the study provided an effective tool to access the performance of laboratories in molecular tests, and also gathered practical experience for organizing PTs on other emerging crustacean pathogens in the future.

Comparing the Effectiveness of Robust Statistical Estimators of Proficiency Testing Schemes in Outlier Detection

This study investigates the effectiveness of robust estimators of location and dispersion, used in proficiency testing and listed in ISO 13528:2015, in outlier detection. The models utilize (a) kernel density plots, (b) Z-factors, (c) Monte Carlo simulations, and (d) distributions derived from at most two contaminating distributions and one main Gaussian. The simulation parameters cover a wide range of those commonly encountered in proficiency testing (PT) schemes, so the results presented are of fairly general application. We chose a functional sub-optimal solution by grouping and classifying the model settings, resulting in five matrices readily usable for selecting the best robust estimator. Whenever at most half of the distribution of each contaminating population is outside the central distribution, there is only one optimal estimator. For all other cases, the five matrices provide the appropriate robust statistic. The proposed method applies to 95.1% of 144 results for an existing PT for cement. These actual datasets indicate that the Hampel estimator for the mean and the Q-method for the standard deviation provide the most appropriate performance statistic in 86.1% of the cases.

A pilot PT scheme for external assessment of laboratory performance in testing synthetic opioid compounds in urine, plasma, and whole blood

A proficiency testing (PT) scheme was prepared for laboratories engaged in bioanalytical testing for synthetic opioid compounds in urine, plasma, and whole blood. Samples were prepared using compounds included in the Opioid Certified Reference Material Kit (Opioid CRM Kit) developed by the U.S. Centers for Disease Control and Prevention. Laboratories received samples during a 2-year project with each year consisting of two PT events 6 months apart. In the first year (pilot test), participants included 10 public health laboratories throughout the United States. In the second year, the group of laboratories expanded to include clinical and forensic drug testing laboratories, and 12 additional participating labs joined the program. In Year 1, overall detection percentages for the compounds present in the PT samples were 95.5% in Event 1% and 97.2% in Event 2. There were 31 apparent false positives reported in Event 1 and four apparent false positives reported in Event 2. Carryover or contamination in laboratory analytical systems were found to be the most significant causes of the false positive results, and none of the laboratories that reported false positives in Event 1 did so in Event 2. In Year 2, overall detection percentages for the compounds present in the PT samples were 89.5% in Event 3% and 94.8% in Event 4. There was one apparent false positive reported in Event 3 and three apparent false positives reported in Event 4. Improvements in drug detection between the two PT events in each year demonstrated the benefit of PT schemes in identifying and addressing potential deficiencies in laboratory systems.

The use of scanning electron microscopy (SEM) and energy dispersiveX-ray analysis (EDXA) as a measurement tool for EMPs tasks, guidelines

In a variety of European countries SEM/EDXA based methods are widely used for the measurements and judgements relating thereof regarding asbestos analysis. Most of these methods are used also for other fibrous particles, commonly indicated as Elongate Mineral Particles (EMPs).The span of guidelines reflects the broad use of SEM/EDXA as an analytical method. Guidelines regarding air measurements both for ambient and indoor air are well established. These methods are widely used as is shown in a proficiency testing scheme, organized by the British Health and Safety Executive (HSL) with participants from countries all over Europe and some countries from Asia and Africa. For workplaces a similar guideline with a reduced sensitivity is available, allowing measurements in higher dust concentrations. Features of the methods like analytical sensitivity, detection limits and measurement uncertainty are discussed.For material analysis we apply different analytical methods, using SEM/EDXA as a final step. They are different both in sample preparation and sensitivity. Most of the methods are qualitative or “semi-quantitative” and thought for the analysis of commercial asbestos containing products mainly. If quantitative analysis based on EDXA is used for identification other EMPs can be identified as well. An important tool is the morphological impression of the fibers or structures in the SEM in addition.Changes in regulations which may be expected, will modify some of the methods. Especially lowered Threshold Limit Values (TLV's) in occupational air measurements are difficult to achieve.

Evaluation of the 1R6F certified reference cigarette for proficiency testing of mainstream smoke parameters

A goal of the cooperative agreement between the U.S. Food and Drug Administration and the Center for Tobacco Reference Products (CTRP) at the University of Kentucky was to produce a standard reference cigarette for researchers to further tobacco science. The 1R6F certified reference cigarette for analytical testing was developed to be typical of an American blend cigarette. The cigarettes have been used in proficiency testing (PT) schemes under the supervision of the CTRP since 2016 for a variety of parameters. Data were compared from 8 rounds of PT schemes submitted by participating laboratories, which include various international stakeholders comprised of academic institutions, federal research/regulatory laboratories, tobacco product manufacturers, and independent contract testing laboratories. Evaluation of the datasets for harmful and potentially harmful constituents (HPHCs) within the mainstream smoke of the 1R6F certified reference cigarette included tobacco-specific nitrosamines (TSNA), tar, nicotine, and carbon monoxide (TNCO), and Benzo[α]pyrene (BαP). Of the datasets evaluated, less than 5 % resulted in either a warning or alert, and less than 2 % resulted in an alert. Comparisons across multiple PT rounds revealed no significant differences in the consensus means of the tested parameters. Evaluation of data submitted by participating laboratories for multiple proficiency test rounds shows that the 1R6F certified reference cigarette is an acceptable material as a control reference for the analysis of HPHCs which is imperative since some stakeholders may be required to participate in, and receive satisfactory results, from PT for accreditation purposes.

One Health surveillance-A cross-sectoral detection, characterization, and notification of foodborne pathogens.

Several Proficiency Test (PT) or External Quality Assessment (EQA) schemes are currently available for assessing the ability of laboratories to detect and characterize enteropathogenic bacteria, but they are usually targeting one sector, covering either public health, food safety or animal health. In addition to sector-specific PTs/EQAs for detection, cross-sectoral panels would be useful for assessment of the capacity to detect and characterize foodborne pathogens in a One Health (OH) perspective and further improving food safety and interpretation of cross-sectoral surveillance data. The aims of the study were to assess the cross-sectoral capability of European public health, animal health and food safety laboratories to detect, characterize and notify findings of the foodborne pathogens Campylobacter spp., Salmonella spp. and Yersinia enterocolitica, and to develop recommendations for future cross-sectoral PTs and EQAs within OH. The PT/EQA scheme developed within this study consisted of a test panel of five samples, designed to represent a theoretical outbreak scenario. A total of 15 laboratories from animal health, public health and food safety sectors were enrolled in eight countries: Denmark, France, Italy, the Netherlands, Poland, Spain, Sweden, and the United Kingdom. The laboratories analyzed the samples according to the methods used in the laboratory and reported the target organisms at species level, and if applicable, serovar for Salmonella and bioserotype for Yersinia. All 15 laboratories analyzed the samples for Salmonella, 13 for Campylobacter and 11 for Yersinia. Analytical errors were predominately false negative results. One sample (S. Stockholm and Y. enterocolitica O:3/BT4) with lower concentrations of target organisms was especially challenging, resulting in six out of seven false negative results. These findings were associated with laboratories using smaller sample sizes and not using enrichment methods. Detection of Salmonella was most commonly mandatory to notify within the three sectors in the eight countries participating in the pilot whereas findings of Campylobacter and Y. enterocolitica were notifiable from human samples, but less commonly from animal and food samples. The results of the pilot PT/EQA conducted in this study confirmed the possibility to apply a cross-sectoral approach for assessment of the joint OH capacity to detect and characterize foodborne pathogens.

Assay of sodium carbonate

Main textThe CCQM-K173 Assay of Sodium Carbonate key comparison was jointly organized by the Inorganic Analysis (IAWG) and Electrochemical Analysis and Classical Chemical Methods (EAWG) working groups of CCQM to test the abilities of the national metrology institutes (NMIs) to measure the purity or amount content of solid bases. They are important challenges for reference material producers, providers of other measurement services, such as proficiency testing schemes. Evidence of successful participation in formal, relevant international comparisons are needed to support calibration and measurement capability claims (CMCs) made by NMIs and designated institutes (DIs).Nine NMIs participated in this key comparison CCQM-K173. National Institute of Metrology P. R. China (NIM) and Ural Research Institute for Metrology - Affiliated Branch of the D.I. Mendeleyev Institute for Metrology (VNIIM-UNIIM), Russian Federation, acted as the coordinating laboratories of the comparison.The measurement methods used by the participants for measuring the amount content of bases expressed as sodium carbonate were coulometry and titrimetry.In general, good overlap of results was observed, the suitability of coulometry and titrimetry for assay of high purity materials was demonstrated. The majority of results were split in two groups differing from each. This bias was however covered by the stated uncertainty estimates. Various effects have been evaluated that may cause it. However, the reason for the bias has not been identified clearly.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A new methodology for proficiency testing scheme interpretation based on residual analysis

A new methodology for proficiency testing scheme interpretation based on residual analysis

Development and Validation of an UHPLC-MS/MS Method for the Simultaneous Determination of 11 EU-Regulated Mycotoxins in Selected Cereals.

The availability of reliable sensitive multi-analyte methods for unambiguous determination of mycotoxins is crucial for ensuring food and feed safety, considering their adverse health effects and (co-)occurrence in various foods. Accordingly, a multi-mycotoxin confirmatory method for simultaneous determination of 11 mycotoxins regulated in cereals within the European Union (EU) using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) was developed and in-house validated to fit the EU legislation requirements for analytical methods. A simple sample preparation was based on a solid–liquid extraction using a solvent mixture acetonitrile/water/formic acid (79/20/1, v/v/v) and a dilution of raw extract using water/acetonitrile/formic acid (79/20/1, v/v/v) before instrumental analysis. Average recoveries in all three validated cereal crop types (maize, wheat, and barley), spiked at multiple levels, were found acceptable for all analytes when matrix-matched calibration was used, ranging from 63.2% to 111.2% and also showing very good repeatability, with relative standard deviations below 20%. Matrix effect (SSE) evaluation revealed maize as the most complex of the three analyzed cereal matrices, with strong SSE (<50% and >150%) recorded for all 11 analyzed mycotoxins. An additional method verification was performed through successful participation in proficiency testing schemes, with the achieved z-scores generally in the acceptable range of −2 ≤ z ≤ 2. The obtained validation results demonstrated the suitability of the developed confirmatory multi-mycotoxin UHPLC-MS/MS method based on a dilute-and-shoot principle for the simultaneous determination of low concentrations of 11 EU-regulated mycotoxins in cereals, including aflatoxins B1, B2, G1 and G2, deoxynivalenol, fumonisins B1 and B2, zearalenone, T-2 and HT-2 toxins, and ochratoxin A.

A national proficiency scheme for human leucocyte antigen typing by next-generation sequencing

BackgroundAccurate human leucocyte antigen (HLA) typing is essential for solid organ transplantation (SOT) and hematopoietic stem cell transplantation (HSCT). Next-generation sequencing (NGS) is increasingly adopted by clinical laboratories performing HLA typing. To ensure reliable NGS-based HLA typing throughout China, a HLA-NGS proficiency testing (PT) scheme was set up. MethodsA panel of 10 DNA reference materials for 11 HLA loci were distributed to 24 participants. They were asked to submit NGS typing results for at least six loci including HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1, and HLA-DPB1. Information regarding individual laboratory’s sample preparation method, NGS platform, and genotyping software was also collected. ResultsThirteen participants correctly identified HLA alleles in all samples. The total concordance rate for all HLA alleles typed was 99.2% (3390/3420). The overall discordance was 0.2% (3/1440) for Class I, and 1.4% (27/1980) for Class II loci. Further investigation of the typing mistakes pointed to poor sequencing coverage and wrong allele calls. The errors identified reflect the deficient aspect of NGS in HLA typing, which may have implications for quality improvement for relevant laboratories. ConclusionsThe results of this PT underscore the necessity of regular participation in external quality assessment for clinical laboratories that perform HLA-NGS typing.

Application of proficiency testing scheme at determining the tank capacity on the results of laser 3D scanning

A three-level proficiency testing scheme is proposed in the form of the interlaboratory comparisons for the determination of the tank capacity of all possible types calculated by the laboratories’ own software. The proficiency testing scheme will be available to any accredited or non-accredited laboratory worldwide. Each laboratory chooses from the proposed computational tasks what it needs. To protect the confidentiality of the information within the framework of this scheme, all the Participants generate their individual codes, which they indicate in the file name with the results of their calculations.&#x0D; The laboratories are suggested to pass successfully three levels of operation characteristics testing ranked by the increase of the set tasks:&#x0D; 1) calculation of the tanks’ interval capacities without introducing any corrections by their 3D models prepared by the Provider;&#x0D; 2) calculation of the tanks' interval capacities by introducing all necessary corrections by their 3D models prepared by the Provider;&#x0D; 3) calculation of the tanks’ interval capacities by scans that have not been subjected to preliminary preparation by the Provider.&#x0D; To participate in the first level of the proficiency testing, it is necessary to:&#x0D; — download the program of proficiency testing of the first level from the site SE «Ukrmetrteststandart» https://metrology.kiev.ua/ru/mezhlaboratornye-sravneniya;&#x0D; — download files with point coordinates on the tank wall from Google disk Comparison: http://bit.ly/vgsucsm;&#x0D; — calculate interval capacities of the tanks without the introduction of any corrections;&#x0D; — send files with calibration tables of the tanks to the Provider’s e-mail: vgsucsm@gmail.com;&#x0D; — if the submitted data is suitable for analysis, then register and pay for the service;&#x0D; — receive the results of the proficiency testing via your e-mail;&#x0D; — read the publication of the proficiency testing results in the journal «Measurement infrastructure» https://mi-journal-online.org.&#x0D; At the first level of the proficiency testing, the payment is fulfilled only for the registration of the Participant and the execution of the documents on the completion of this level.

Continual Improvement of the Reliability of Next-Generation Sequencing-Based ctDNA Analysis: A Long-Term Comparison of ctDNA Detection in China.

Since circulating tumor DNA (ctDNA) sequencing is increasingly being applied in clinical management of patients with cancer, its testing accuracy has become a matter of serious concern. To address this issue, a long-term ctDNA analysis proficiency testing (PT) scheme for next-generation sequencing (NGS) was launched in China in 2018, serving as an educational tool for assessing and improving the testing quality of NGS-based ctDNA detection. Feedback from participating laboratories across 23 different PT samples containing different variants with varying variant allele frequency was collected between 2018 and 2021. To further show the landscape of changing conditions in accuracy and reliability of NGS-based ctDNA testing, performance was analyzed by evaluating the cfDNA extraction kits, testing panels, target enrichment strategies, and sequencing platforms. During the 4 years, 2745 results reported from 504 laboratories were evaluated. Only 66.3% of results from laboratories were entirely in concordance with the expected results. Nonetheless, along with an increasing number of participating laboratories, the number of errors occurring in laboratories, and the proportion of laboratories that experienced errors both showed a significant downward trend. No obvious differences in the error rates were found regarding the kit manufacturers or sequencing platform. Moreover, the individual performances of the laboratories improved when they participated in more PT scheme rounds. These data demonstrated that the performance of individual Chinese laboratories for NGS-based ctDNA analysis continuously improved over time with participation in PT schemes. However, further care must also be taken in standardized operations and validations.

What Does Your Proficiency Testing (PT) Prove? A Look at Inorganic Analyses, Proficiency Tests, and Contamination and Error, Part I

Trace inorganic analysis is an essential part of analytical testing. In many cases, contamination can alter or skew elemental analysis, which leads to inaccurate results. Another way in which contaminants can alter results in a detrimental fashion is in regard to proficiency testing and laboratory audits. Proficiency testing (PT) is a series or schemes of samples that are intended to assess the performance of individuals or laboratories in specific areas or for specific analytical tests. PT is also designed to be used to improve processes and methods. If contamination and error enter into the analysis process, then the results can be altered, causing the analyst or laboratory to perform poorly in a PT scheme. In this two-part article, we examine the development, rationale, and best practices for PT, including how contamination can enter inorganic samples and how to eliminate or control those sources.

Comparing the Robustness of Statistical Estimators of Proficiency Testing Schemes for a Limited Number of Participants

This study aims at developing models in analyzing the results of proficiency testing (PT) schemes for a limited number of participants. The models can determine the best estimators of location and dispersion using unsatisfactory results as a criterion by combining: (a) robust and classical estimators; (b) kernel density plots; (c) Z-factors; (d) Monte Carlo simulations; (e) distributions derived from the addition of one or two contaminating distributions and one main Gaussian. The standards ISO 13258:2015, ISO 5725:2:1994, and EN ISO/IEC 17043:2010 are the basis of the analysis. The study describes an algorithm solving the optimization problem for (a) Gaussian, bimodal or trimodal distributions; (b) participating labs from 10 to 30; (c) fraction of the contaminating population up to 0.10; (d) variation coefficient of the main distribution equal to 2; (e) equal standard deviations of all the distributions, and provide figures with the optimal estimators. We also developed a generalized algorithm using kernel density plots and the previous algorithm, which is not subject to restrictions (b)–(e) and implemented in the results of a PT for the 28-day strength of cement with 12–13 participants. Optimal estimators’ figures and the generalized algorithm are helpful for a PT expert in choosing robust estimators.

A mathematical model for improving the ion chromatography method by applying external adjustment standards

Ion chromatography (IC) is included in the list of very efficient and fast methods for obtaining results without losses and with the minimization of the human factor.The aim of this paper is to demonstrate the mathematical model for adjusting anion concentrations (NO2– nitrite, NO3– nitrate, Cl- chloride and SO42- sulphate) for water samples by using external standards. The method uses an interpolation and requires a certain number of injections with an external standard (if a single calibration curve is used) or with several external standards (if many calibration curves are used for the same anion). The importance of interpolation is to obtain a theoretical value of the adjustment standard for any sample by reference to the real readings of this external standard.In this study, interpolation works by determining an equation of degree n, covering n interpolations, using the read values of some adjustment standards (eg. AR20-X and AR100-X). The obtained equation can be used later for any injection X , characteristic of a real sample NX, in order to obtain the adjusted areas AR20-X* and AR100-X*.Thus, it becomes possible to calculate the factor f that serves to adjust the areas of the real samples.This strategy demonstrates that the calibration curve can be done quite rarely, and that the results obtained should not be affected by the periodicity of the calibration curve, in compliance with the performance parameters of the method (eg according to Shewhart-type control diagrams and Proficiency Testing (PT) schemes).Even if the results obtained without interpolation follow the recommendations given by US EPA Method 300.0:1993 (the peak area of the adjustment standard does not exceed ± 10% of the area of the adjustment standard read on calibration) and by ISO 10304–1:2007 (the retention time for the anion peaks does not exceed ± 10% in a batch and the minimal resolution for any two investigated peaks of the recorded chromatograms (R) was>1.3), the method performs a continuous adjustment of the sample concentrations to the used calibration curves, providing more relevant results.

Method development and evaluation for the determination of perfluoroalkyl and polyfluoroalkyl substances in multiple food matrices

ABSTRACT A method for the determination of 21 perfluorinated and 10 polyfluorinated alkyl substances (PFAS) was developed for application in different food matrices. Acetonitrile was used as the extraction solvent with solid phase extraction weak anion-exchange (SPE-WAX) clean up, with LC-MS/MS analysis using both surrogate and performance standards to correct for losses during sample preparation and matrix effects. The method has been evaluated in four different matrices (fish, pizza, chicken nuggets and spinach). Originally, the focus was to develop a method for foods commonly thought to be a source of PFASs (e.g. fish). It was expanded to include foods where PFAS exposure would be possible through their presence in grease-proof food packaging (e.g. pizza, chicken nuggets). Vegetables (lettuce) and fruit (tomato) have recently been considered as part of proficiency testing programmes, so the inclusion of some testing in a vegetable matrix (i.e. spinach) was also added to the testing. Limits of quantification ranged from 0.018 ng g−1 (L-PFDS) to 5.28 ng g−1 (FHEA), although method quantification limits for PFBA (12.4 ng g−1), 6:2 PAP (8.96 ng g−1) and 8:2 PAP (3.49 ng g−1) were elevated above instrumental limits owing to their consistent detection in reagent blank samples. PFAS analyses were strongly impacted by matrix, therefore the use of isotopically labelled internal standards was critical to the development of accurate results. The accuracy of the method using numerous proficiency testing schemes or interlaboratory comparison studies has shown the developed method to be successful with z-scores for all concerned analytes in all test matrices remaining within ±2.0, with the exception of PFBA in wheat flour which was −2.4.

Treating children with tuberculosis—Using pharmacometrics to do better

Treating children with tuberculosis—Using pharmacometrics to do better