Harmonized guidelines for internal quality control in analytical chemistry laboratories (Technical Report)

Cardoso A.R., Schmidt J.S., Maraschin A.J., de Andrade D.C., Albano F.D., Bernardes E.M., Rübensam G., Barp G.B., Rodrigues N.P., de Oliveira Y.F., Vazquez J.C., Vecchia F.D.

The use of reference materials (RMs) and certified reference materials (CRMs) is essential to guarantee the reliability of measurement procedures ‐ a major factor motivating the efforts of the geoanalytical community. This work quantifies trends and patterns in the scientific literature concerning RMs and CRMs in geochemistry for specific timespans, with the aim of evaluating historical developments, research fields, geographic shifts of research centres, and current trends. The Scopus database was surveyed for peer‐reviewed full‐texts (14,201 documents), which were subsequently exploited for statistical description, bibliometric mapping and cluster analysis. Mineral exploration and trace element geochemistry stimulated early research, whereas environmental subjects have grown in importance mainly since the year 2000. International standardisation was coincident with an increase of publications covering CRMs and geochemistry, and is thought to reflect the impact of ISO guidelines in this scientific activity. Other factors include investments in research facilities, creation of specialised geoanalytical journals and organisation of international meetings. The analysis shows that RMs are typically used for petrogenetic research topics, whereas CRMs are equally important for environmental sciences, chemistry and geosciences. Environmental sciences are mostly concerned with anthropogenic contamination of ecosystems by heavy metals, whereas geological interest is mainly driven by isotope geochemistry. Scientific frontiers in geoanalytical research comprise microanalytical methodologies, unconventional isotopes, rare earth elements and environmental monitoring. New trends in CRM applications also include biogeochemistry and radionuclides.

Alvarez-Prieto M., Páez-Montero R.

Sometimes, analytical laboratories receive requests with a small number of determinations and/or samples or outside the typical scope of analytical services. As a result, they may not have historical data on the performance of the required analytical procedures and/or appropriate reference materials. Under these conditions, it is difficult or uneconomical to use traditional quality control charts. This is the so-called start-up problem of these charts. Quesenberry’s Q charts are appropriate in these situations because they do not require a prior training phase. In the first part of this series of publications, the fundamentals and the algebraic expressions of the Q charts were presented for the individual measurements for the mean (four cases) and for the variance (two cases). This experimental study was carried out with data from quality control of mass fractions of Co in a serpentinite CRM and SiO2 in a laterite CRM, by ICP-OES. The performance of Q charts is discussed in two situations: when the analytical process showed a clear systematic error from the beginning and when small shifts in mean and variance occurred simultaneously. In the first situation, performances of Q charts for the mean depended on the case: two of them were very sensitive even in the short run and the other two were insensitive and useless. In the second situation, the Q charts showed delayed alarms, but with a comparable behavior to the chart for individual measurements and the moving range of two. EWMA charts associated to Q charts were an excellent complement.

Miyake D., Kanaya S., Ono N.

Abstract Background Reproducibility has been well-studied in the field of food analysis; the relative standard deviation is said to follow the Horwitz curve with certain exceptions. However, little systematic research has been done on predicting repeatability or intermediate precision. Objective We developed a regression method to estimate within-laboratory standard deviations using hierarchical Bayesian modeling and analyzing duplicate measurement data obtained from actual laboratory tests. Methods The Hamiltonian Monte Carlo method was employed and implemented using R with Stan. The basic structure of the statistical model was assumed to be a chi-squared distribution, the fixed effect of the predictor was assumed to be a nonlinear function with a constant term and a concentration-dependent term, and the random effects were assumed to follow a lognormal distribution as a hierarchical prior. Results By analyzing over 300 instances, we obtained regression results that fit well with the assumed model, except for moisture, which was a method-defined analyte. The developed method applies to a wide variety of analytes measured using general principles, including spectroscopy, GC, and HPLC. Although the estimated precisions were within the HorRat(r) criteria, some cases using high-sensitivity detectors, such as mass spectrometers, showed standard deviations below that range. Conclusion We propose utilizing the within-laboratory precision predicted by the model established in this study for internal quality control and measurement uncertainty estimation without considering the sample matrices. Highlights Performing statistical modeling on data from double analysis, which is conducted as a part of internal quality controls, will simplify the estimation of the precision that fits each analytical system in a laboratory.

Chuparina E.V., Belogolova G.A., Baenguev B.A., Sokolnikova J.V., Zarubina O.V.

AbstractThe study of nonstandard samples wherein their element compositions differ from those of routine samples motivates analysts to look for new methodological approaches. To determine the high concentrations of Cr, Ni, Cu, Zn, As, and Pb in polluted plants, the authors applied wavelength dispersive x‐ray fluorescence (WDXRF), using three calibration strategies in comparison. The following sets of calibration samples were tested: available plant and biological CRMs; synthetic samples; and “house reference materials” (HRMs). The synthetic samples were prepared, adding small portions of the loose sediment CRMs to a plant CRM. The polluted plant samples, analyzed by atomic absorption spectrometry and inductively coupled plasma mass spectrometry, were used as HRMs to construct the calibration curves and validate XRF results. It was ascertained that all three calibration strategies can be used to quantify above elements in contaminated plants, providing different precision of WDXRF results. The calibration procedure with HRMs has provided the least errors in the element determinations. Calibration with synthetic samples causes larger errors due to some differences in chemical compositions between calibration and analyzed samples as well as due to probable errors in the synthetic sample preparation. The calibration with plant and biological samples is of limited applicability in XRF of contaminated plants by reason of narrow content ranges of some elements.

Nigro M., Žagar K., Vreča P.

Water is pivotal for human societies’ sustainability and resilience. Isotope hydrology and hydrogeology research plays an important role in understanding and managing water resources. Reliable scientific results hinge on high-quality data. Preventing water sample evaporation is essential for accurate isotopic analysis. In this study, the impacts on the quality of isotopic data were tested for the storage of water samples and the repetitive opening of a laboratory reference material (LRM) sub-sample replica during daily operation. Twenty 15 mL water samples were stored in high-density polyethylene (HDPE) bottles at room temperature and humidity to simulate storage conditions. One 60 mL water sample was collected from the same starting batch to simulate the LRM sub-sample. Each 15 mL sample was analysed once over 80 days for the isotopic composition of oxygen (δ18O) and hydrogen (δ2H). The 60 mL sample was repeatedly analysed in the same period. The data were tested to identify shifts in the isotopic composition induced by evaporative processes. The main results of the work are the following: (i) storage of the 15 mL water samples did not cause detectable evaporation in the testing period; (ii) the 60 mL δ18O values showed evidence of evaporation as proved by the positive shift of the isotopic data; (iii) the repetitive opening of the 60 mL sample was the main cause of evaporation; (iv) five openings can already cause detectable isotopic enrichment. Careful manipulation and frequent replacement of the LRM are thus necessary to prevent deterioration of the quality of the analyses.

Alvarez-Prieto M., Páez-Montero R.S.

Sometimes analytical laboratories receive requests with a small number of determinations and/or a small number of samples, or outside the typical scope of analytical services. As a result, they may not have historical data on the performance of analytical processes and/or appropriate reference materials. Under these conditions it is difficult or uneconomical to use traditional or classic quality control charts. This is the so-called start-up problem of these charts. The Q charts seem appropriate charts under these conditions because they do not need any prior training or study phase. The fundamentals and the algebraic expressions of Q charts for the mean (four cases) and for the variance (two cases) are offered. This experimental study of Q charts for individual measurements was done with data from quality control for the evaluation of mass fraction of Ni and Al2O3 in a laterite CRM by ICP-OES. The performance of these Q charts is discussed where the analytical process is in the state of statistical control and in the presence of outliers at the start-up. In the first situation performance of Q charts are quite satisfactory and they behave properly. When outliers are collected at the beginning, the deformation of some charts is evident or the charts become useless. Severe outliers will corrupt the parameter estimates and the subsequent plotted points, or the charts will become insensitive and useless. The practitioner should take extreme care to assure that the initial values are obtained in the state of statistical control to have adequate sensitivity to detect parameter shifts.

Li A., Abrahim A., Islam M., Mejías E., Hafizati Abdul Halim N., Frew R., Vlachou C., Kelly S.D.

One of the most common types of adulteration of honey involves the addition of invert sugar syrups. A new method was developed to measure the stable isotope ratios of carbon and carbon-bound non-exchangeable (CBNE) hydrogen from specific molecular positions in fructose and glucose in honey. This was achieved through periodate oxidation of the sugars to produce formaldehyde, followed by reaction with ammonia to form hexamethylenetetramine (HMT). The preparation was simplified, optimized, and validated by isotopic analysis of replicate syntheses of HMT from fructose, glucose, sugar syrup and a representative authentic honey sample. The optimized method had a repeatability standard deviation from 1.5‰ to 3.0‰ and from 0.1‰ to 0.4‰ for δ2H and δ13C, respectively. This methodology has advantages over alternative isotopic methods, for measuring CBNE hydrogen isotope ratios in sugars, in terms of time, sensitivity and operability and offers a complementary method to differentiate authentic honey from invert sugar syrups.

Fernandes É., Barros M., Pires P.

AbstractThe purpose of this study was to evaluate the applicability of an alternative analytical technique to the reference method for phosphorus detection in meat and meat products established by ISO 2294:1974, revised by ISO 23776:2021. When an analytical method is modified or a new one is developed and implemented, it should be validated before being accepted for routine determinations. Furthermore, it is necessary to demonstrate that the new or alternative method has good performance characteristics in comparison with the reference method. Therefore, a comparison of the performance of the alternative and the reference method should be made. In the present study, a statistical evaluation of the calibration model of the alternative method was made with data from interlaboratory studies made in five consecutive years using fifty analyses of meat and meat products. The statistical parameters evaluated over time for the calibration curve were the y-intercept and slope; correlation and linearity; analytical limits: detection and quantification; working range; and accuracy (precision and trueness). In the interlaboratory tests, the results obtained by the alternative analytical method were compared with those obtained by the reference method, and their performance in these tests was also evaluated. The results obtained by the alternative method indicated better accuracy than the reference method due to lower relative errors, more precision, and a good trueness evaluation through lower absolute values of the z-score. The study demonstrated that the phosphorus alternative method is applicable for the determination of total phosphorus in the matrix of meat and meat products.

Tsuchiyama T., Ito Y., Taniguchi M., Katsuhara M., Miyazaki H., Kamijima M.

High urinary levels of dialkylphosphates (DAPs), which are common structures of organophosphate pesticides (OPs), have been associated with several adverse health outcomes in human biomonitoring studies. Previous studies have indicated that dietary OP exposure and ingestion of environmentally degraded DAP, which is inactive with acetylcholinesterase, can lead to an increase in urinary DAP levels in the general population. However, the specific food sources contributing to the intake of OPs and DAPs have not been identified. In this study, we analyzed the levels of OPs and preformed DAPs in various food items. DAP levels were markedly high in certain fruits, such as persimmon, apple juice, kiwi, and mandarin. In contrast, only moderate levels of OPs were detected in these foods. Furthermore, the levels of OPs and DAPs were positively associated with vegetables, whereas no such association was observed in fruits. Increased consumption of certain fruits presumably leads to a marked increase in urinary DAP levels in individuals despite limited exposure to OPs, resulting in reduced reliability of urinary DAPs as a marker of OP exposure. Therefore, the possible effects of dietary habits and the resulting intake of preformed DAPs should be considered when interpreting biomonitoring data of urinary DAPs. Additionally, DAP levels in most organic foods were much lower than those in conventional foods, suggesting that the reduction in urinary DAPs by organic diet intervention may be mainly attributed to the reduced intake of preformed DAPs rather than reduced exposure to OPs. Therefore, urinary DAP levels may not be suitable indicators for evaluating ingested OP exposure.

Guo J., Kufer R., Li D., Wohlrab S., Greenwood-Goodwin M., Yang F.

Gemenetzis E.G., Alygizakis N.A.

An HPLC method with UV detector was developed for the determination of DEHP phthalate ester in the alcoholic beverage “Ouzo”. Phthalate esters are added to plastic packaging for food and beverages to increase flexibility, transparency, strength, and longevity. When these substances come into contact with food or beverages, they can lead to the migration of phthalate residues into the product. This paper presents a two-step process involving extraction of the sample with hexane and separation of the phthalates by HPLC. The method was validated for specificity, linearity, limit of quantification, accuracy, precision, range, and ruggedness. The linear range is 0.3–1.5 mg/L DEHP, with a lower limit of quantification of 0.06 mg/L. The precision study showed acceptable RSD values, and the working range is 0.3 to 1.5 mg/L DEHP. The relative standard uncertainty of DEHP determination in Ouzo was ±8%. The results show that the in-house method is suitable, reliable, and fit-for-purpose.

Schilhabel A., Szczepanowski M., van Gastel-Mol E.J., Schillalies J., Ray J., Kim D., Nováková M., Dombrink I., van der Velden V.H., Boettcher S., Brüggemann M., Kneba M., van Dongen J.J., Langerak A.W., Ritgen M.

Detection of patient- and tumor-specific clonally rearranged immune receptor genes using real-time quantitative (RQ)-PCR is an accepted method in the field of precision medicine for hematologic malignancies. As individual primers are needed for each patient and leukemic clone, establishing performance specifications for the method faces unique challenges. Results for series of diagnostic assays for CLL and ALL patients demonstrate that the analytic performance of the method is not dependent on patients’ disease characteristics. The calibration range is linear between 10-1 and 10-5 for 90% of all assays. The detection limit of the current standardized approach is between 1.8 and 4.8 cells among 100,000 leukocytes. RQ-PCR has about 90% overall agreement to flow cytometry and next generation sequencing as orthogonal methods. Accuracy and precision across different labs, and above and below the clinically applied cutoffs for minimal/measurable residual disease (MRD) demonstrate the robustness of the technique. The here reported comprehensive, IVD-guided analytical validation provides evidence that the personalized diagnostic methodology generates robust, reproducible and specific MRD data when standardized protocols for data generation and evaluation are used. Our approach may also serve as a guiding example of how to accomplish analytical validation of personalized in-house diagnostics under the European IVD Regulation.

Ambrus Á., Szenczi-Cseh J., Doan V.V., Domak Z., Gönczöl T., Lörincz A., Miklós G., Nagy A., Szemanné-Dobrik H., Vásárhelyi A.

The development of quality requirements for the analyses of chemical contaminants is reviewed from the formation of the first association of analytical chemists in 1884. Without attempting to give complete coverage, it is shown that the elaboration of quality systems is commanded by the needs of the industry and international trade. Progress along the line of the initial inter-laboratory comparison, methods validated with collaborative tests, and development of internationally harmonized guidelines and protocols to perform complex studies aiming to improve the accuracy and reliability of the results facilitate international trade, and protect consumer health, as well as the environment. The international cooperation for limiting the replication of various (e.g., analytical, toxicological) tests is promoted by multilateral agreements that are also supported by legal obligations. Notwithstanding, the rapid development of requirements and guidance documents provides only the frame for obtaining accurate, defendable results. The production of such results is the duty of the laboratory management, analysts, and study personnel who play the decisive role and bear full responsibility for the samples analyzed.

Thakur D., Dubey N.P., Singh R.