Primary Reference Measurement Procedure Research Articles

Comparative analysis and classification of measurement procedures and procedures for transferring of unit of quantity as elements of metrological traceability chain of measurement results

The article analyzes types of measurement procedures and procedures for transferring a unit of quantity, such as: primary reference measurement procedures, reference measurement procedures, calibration procedures, validation procedures, end-user measurement procedures and measurement procedures. The article discusses requirements for developing the presented procedures, their research and approval. The article presents a classification of procedures depending on their place in metrological traceability chain, type of determined metrological characteristics and their application in the field of regulation. Based on the results of the analysis of regulatory documents, a table that describes basic requirements for development and approval of measurement procedures and procedures for transferring a unit of quantity is presented. The article also discusses requirements established for conformity assessment procedures for measurement procedures and procedures for transferring а unit of quantity, such as certification, validation and verification of procedures. The article presents definitions and scope of application for conformity assessment of measurement procedures and procedures for transferring a unit of quantity. Based on the analysis of requirements for conformity assessment of procedures, a flowchart for selecting appropriate conformity assessment procedure is presented. Due to this scheme, laboratories will be able to unambiguously choose one or another conformity assessment procedure to approve the required measurement method or method of transferring a unit of value. In particular, in preparation for accreditation for compliance with the requirements of ISO/IEC 17025-2017 “General requirements for the competence of testing and calibration laboratories.” The proposed scheme of choosing a procedure for conformity assessment of a specific measurement procedure eliminates ambiguity of the requirements of regulatory documents.

Reliable biological and multi-omics research through biometrology.

Metrology is the science of measurement and its applications, whereas biometrology is the science of biological measurement and its applications. Biometrology aims to achieve accuracy and consistency of biological measurements by focusing on the development of metrological traceability, biological reference measurement procedures, and reference materials. Irreproducibility of biological and multi-omics research results from different laboratories, platforms, and analysis methods is hampering the translation of research into clinical uses and can often be attributed to the lack of biologists' attention to the general principles of metrology. In this paper, the progresses of biometrology including metrology on nucleic acid, protein, and cell measurements and its impacts on the improvement of reliability and comparability in biological research are reviewed. Challenges in obtaining more reliable biological and multi-omics measurements due to the lack of primary reference measurement procedures and new standards for biological reference materials faced by biometrology are discussed. In the future, in addition to establishing reliable reference measurement procedures, developing reference materials from single or multiple parameters to multi-omics scale should be emphasized. Thinking in way of biometrology is warranted for facilitating the translation of high-throughput omics research into clinical practices.

Primary Reference Measurement Procedures in the Food Industry: Usage Experience and Development Prospects

This article reviews the usage experience and development prospects of four state primary reference measurement procedures (SPRMPs) created to provide metrological support of measurements in the food and agricultural industries. The SPRMPS certified in 2016–2019 include those of the mass fraction of fat, ash, and carbohydrates in food products and raw materials; of the mass fraction of crude fat (oil content) in oilseeds and related products. The mass fraction of fat, crude fat, and oil content is measured using the Randall method; the mass fraction of ash is determined by the thermogravimetric method; the mass fraction of carbohydrates (total sugar) is defined by iodometric titration. The considered SPRMPs were used to develop reference materials (RMs) for the composition of dairy and meat, egg powder, starch, baby food, oilseeds, related products, and compound feeds. SPRMPs implementation required extending the range of the manufactured RMs for new product groups. High-precision procedures for measuring the mass fraction of fat in liquid dairy products, fish, pastry, confectionery, and pasta products, as well as the mass fraction of lactose in liquid dairy products were developed and certified to describe the characteristics of dairy, pollock fillets, and wheat crackers composition.

Development of Measurement Procedures for the Characterization of Reference Materials for Carbohydrate Composition of Dairy Products

This article studies the development of measurement procedures based on various methods for a comprehensive analysis of the carbohydrate composition of food systems. The basis of the primary reference measurement procedure (PRMP) is the method of iodometric titration based on the ability of iodine to oxidize aldosaccharides to the corresponding uronic acids in an alkaline medium. The accuracy of the PRMP was improved by optimizing the measurement parameters, including the method of high-performance liquid chromatography with refractometric detection (HPLC/RD), and by establishing their possible variation limit based on a multifactorial experiment. The application of the PRMP made it possible to measure the mass fraction of carbohydrates (total sugar) as the sum of the mass fractions of reducing and non-reducing sugars in milk and dairy products, grain and milk products, low-lactose and lactose-free products, including those used for preparing baby food. In order to further detail the carbohydrate composition, highly selective methods were developed for measuring the mass fractions of lactose and galactose by the spectrophotometric (enzymatic) method, and the mass fractions of mono- and disaccharides by the HPLC/RD method in milk and dairy products. It was found that the measurement results of both the total content of carbohydrates and individual mono- and disaccharides in the samples of milk and dairy products obtained by various methods (iodometric titration, HPLC/RD, enzymatic method, refractometry, IR spectroscopy, calculation method) are consistent with each other subject to the stated uncertainties. Thus, the applicability of the developed PRMP in combination with other methods for conducting an in-depth analysis of the carbohydrate composition of milk and dairy products was confirmed. The developed procedures were used to characterize reference materials for the composition of dairy products (3 types), mono- and disaccharides (9 types).

Candidate primary reference measurement procedure for the amount-of-substance content of a complexing agent expressed as EDTA based on the coulometric titration with electrogenerated Hg ions

The primary reference measurement procedure is a method to realize the definition of the quantity without relation to a reference standard of the same quantity. This paper presents a candidate primary reference measurement procedure for the measurement of the amount-of-substance of a complexing agent expressed as ethylenediaminetetraacetic acid (EDTA) based on coulometric titration. Herein, mercury (Hg) was used as the anode because it does not undergo spontaneous oxidation. Furthermore, a 1:1 complex is formed between the electrogenerated Hg2+ ions and EDTA (in the form of Y4−). Although the electrochemical oxidation of Hg may generate Hg2 2+ ion, Hg2 2+ undergoes disproportionation in the presence of EDTA, thereby forming the desired Hg2+ species. The equivalence point occurs at the maximum of the derivative of the theoretical titration curve. As such, the measurement results were obtained by assuming that the maximum of the derivative of the experimental titration curve was the end point. The developed procedure was employed for the measurement of the amount-of-substance content of the complexing agent in EDTA reference material certified at the Slovak Institute of Metrology. The experimental measurements agreed well with the certified value for the reference material within the measurement uncertainty. The candidate procedure will be useful in certifying EDTA reference material and establishing international equivalence of amount content of the complexing agent.

International co-validation on absolute quantification of single nucleotide variants of KRAS by digital PCR.

The precise quantification of KRAS single nucleotide variant (SNV) is critical for the treatment and prognosis of lung and colorectal cancer. Validation of digital PCR (dPCR) as a method for accurate quantification of KRAS SNV has great clinical importance. An international co-validation on absolute quantification of KRAS SNV by dPCR was conducted among three national measurement institutes (NMIs) from China (NIM), South Korea (KRISS), and Japan (NMIJ). A candidate reference material (RM) was provided by NIM and three measurands were reported: copy number concentration (Tc) of KRAS G12A mutation and wild type and KRAS G12A fractional abundance (FA). Homogeneity and stability assessment showed that the study materials provided by NIM were sufficiently homogeneous and stable during the study period. En number performance statistics was used to evaluate equivalence of the study among the three NMIs. All En values for both Tc and KRAS G12A FA≤1 showed good agreement and consistency with the reference value within the expanded uncertainty. This indicates that dPCR with full uncertainty evaluation can serve as a candidate primary reference measurement procedure (PRMP) for the KRAS SNV measurement and value assignment of reference materials.

Preparation of Three New Certified Reference Materials for Food and Environmental Analysis and Certification Using Laboratory Intercomparison as well as Primary Reference Measurement Procedures

Three new reference materials: MODAS-3 Herring Tissue (M-3 HerTis), MODAS-4 Cormorant Tissue (M-4 CormTis), and MODAS-5 Cod Tissue (M-5 CodTis) were prepared and certified on the basis of results of a worldwide intercomparison exercise. Independently of our proven method of establishing the certified and information values, the content of several essential and toxic elements was additionally determined by the use of ratio primary reference measurement procedures (definitive methods) based on radiochemical neutron activation analysis (RNAA) in the case of As, Cd, Co, Cr, Fe, Mo, Se, and U and isotope dilution mass spectrometry (IDMS) in the case of Hg, respectively. Good agreement of the established certified values and the results obtained by ratio primary reference measurement procedures confirmed the validity of the certification procedure. The total number of elements which could be certified amounted to 30, 21, 18 in M-3 HerTis, M-4 CormTis, and M-5 CodTis, respectively. The relative frequency of use of individual analytical techniques in this intercomparison campaign was calculated and discussed. Inductively coupled plasma mass spectrometry (ICP-MS) is now a dominant technique, followed by atomic absorption spectroscopy (AAS), NAA, and emission spectroscopy (ES). The decreasing share of NAA as compared to several earlier intercomparison exercises should be noticed. NAA is the only method in the array of highly sensitive methods of inorganic trace analysis, which is essentially free from blank. The lack of this method in the foreseeable future may be an obstacle in the prospective certification campaigns and may endanger the implementation of quality assurance in trace analysis.

Development of food industry metrological assurance complex

The paper considers the contribution of experts from the Laboratory of Metrology of Moisture Measurement and Reference Materials to the improvement of the food industry metrological assurance system. The information on the results of the development of forty types of reference materials (RM) for the composition of various nutrition, food staples and nutritional supplement in the period 2008-2020 is generalized. The development of each new RM type included preparation of the material, research for its stability and homogeneity, and determination of certified value with the appliance of State primary (GET 173) and secondary (GVET 176-1) standards, as well as primary reference measurement procedures and conducting the interlaboratory experiment for checking the applicability of the RM. The creation in 2008 of GET 173 was accompanied by the development of RMs for the composition of grains and dry milk product. The approval in 2010 of GVET 176-1 allowed to add in the RM the certified value for the mass fraction of nitrogen (protein). As a result of successful participation in comparisons, UNIIM got 6 items of calibration and measurement capabilities on measurements of mass fraction of nitrogen in glycine, milk powder, grain, egg powder, cereal and feed-stuff in the BIPM database. 35 types of RM for the composition of dairy and meat products, egg powder, infant food, oil and starch products together with the development of primary reference measurement procedures for measurement of fat, crude fat, ash and carbohydrates mass fraction were created between 2016 and 2019. Moreover, the RM for the composition of nutritional supplement (glycine, melamine, cystine) and dairy products for metrological assurance of IR-analysers as well as RM for the composition of reconstituted milk were developed for the control of measurement results by the enzyme-linked immunosorbent assay (ELISA). Developed RM were systemized on fields of the appliance of Technical regulations of Customs Union and the sectors of the international food triangle model. These RMs allow providing the measurement uniformity of the identification indicators and the nutritional value of food products and food staples.

Development of primary reference measurement procedure and reference materials for mass fraction of crude fat (oil content) in oilseeds and other products on their base

The article is devoted to development of metrological support for measurements of mass fraction of crude fat (oil content) value which is hard to explain and generalised quality value of oilseeds and produced on their oilseeds residues, cereals and pulses, foodstuff and its components. Results of this value measurement depend on conditions of analysis and testing samples matrix. The problem of insuring of the results compossibility can be solved by the development of primary reference measurement procedure (PRMP) as well as development of related reference materials for transfer of the units to the results of routine measurements. As the basic method was taken modified extractive method - Randall’s method of quantitative extraction of free and chemical or mechanical bound fat from product samples followed by measurement. Development of PRMP included the optimisation of the parameters of the measurement of the possible limits of their variation, as well as evaluating components of the uncertainty of measurement taking into account contributions related to influence on the measurement results of the applied equipment and reagents, equations, measurement, methodological factors, the heterogeneity of samples. The extended uncertainty of the measurement results of the mass fraction of crude fat (oil content) at the coverage coefficient k=2 was 0.15 %, providing a margin of accuracy of the developed PRMP concerning standardised measurement methods from 2.7 to 13.3 times. Comparisons of measurement results of crude fat mass fraction (oil content) in the seeds of: sunflower, soy, rape plant, mustard, flax by PRMP and GOST 10857-64, GOST 32749-2014, GOST 8.597-2010 vindicated the absence of result biases according to PRMP in compare with the routine methods results. Developed PRMP for crude fat (oil content) mass fraction in oilseeds and other products on their base (FR.PR1.31.2019.00009) together with PRMP for mass fraction of ash in nutritive products and food ingredients (FR.PR1.31.2018.00002), and state standards for system of units GET 173-2017, GVET 176-1-2010 was used for characterisation of 14 types of reference materials such as GSO 11268-2019/ GSO 11270-2019; GSO 11279-2019/ GSO 11283-2019; GSO 11284-2019/ GSO 11289-2019.

Use of quantitative 1H and 13C NMR to determine the purity of organic compound reference materials: a case study of standards for nitrofuran metabolites

Comparability of measurement results and their metrological traceability to the International System of Units (SI) are fundamental tools to ensure reliable decisions in the social sphere, commerce, and science. The use of appropriate references in analytical chemistry, such as certified reference materials (CRMs) of high purity substances, is one of the required procedures to obtain traceable measurements. When commercial standards with non-certified purity values are used, traceability must be achieved by determining the purity of the standard using a potential primary reference measurement procedure or other appropriate methods. Quantitative nuclear magnetic resonance (qNMR) is a technique with the potential to be used in primary measurement procedures. This work presents the determination of purity by 1H qNMR for nitrofuran metabolites 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), and 1-aminohydantoin (AHD). Furthermore, a recent qNMR method developed by our group to improve the quantitative performance of measurements using 13C nucleus was used to determine the purity of semicarbazide (SEM) nitrofuran metabolite. Purity values obtained by qNMR for AOZ, AMOZ, and AHD standards were compared to values obtained by the mass balance approach using a suite of analytical methods: Karl Fischer (KF) coulometric titration and thermogravimetry (TG) for the determination of water and residual solvents, gas and liquid chromatography for the determination of impurities structurally related to the metabolites. The results obtained by qNMR and mass balance were consistent.Graphical abstract.

Establishment of primary reference measurement procedures and reference materials for EGFR variant detection in non-small cell lung cancer.

Circulating tumor DNA (ctDNA)-based mutation detection is promising to change the clinical practice of genotype-directed therapy for cancer. A growing number of non-invasive tests for cancer screening and monitoring that involve the detection of ctDNA have been commercialized. Primary reference measurement procedures (PRMPs) and reference materials (RMs) are urgently needed to assess the non-invasive tests. In this study, a PRMP based on digital PCR (dPCR) and ctDNA RMs for quantification of the frequently occurring variant in epidermal growth factor receptor (EGFR L858R, T790M, and 19Del) in non-small cell lung cancer (NSCLC) were established. The candidate dPCR PRMP showed high specificity (false positive rate 0-0.003%), good repeatability (coefficient of variance (CV), 2-3% for 104 copies/reaction), and high interlaboratory reproducibility (3-10%). A good linearity (0.97 < slope < 1.03, R2 ≥ 0.9999) between the measured mutant (MU) value and prepared value was observed for all assays over the fractional abundance (FA) range, between 25% and 0.05%. The limit of quantification (LoQ) was determined to be 34 L858R, 23 T790M, and 34 19Del copies/reaction, corresponding to a FA of 0.2%. An inter-laboratory study of using the EGFR ctDNA RMs and dPCR assays demonstrated that the participating laboratories produced consistent concentrations of MU and wild-type (WT), as well as FA. This study demonstrates that dPCR can act as a potential PRMP for EGFR mutation for validation of NSCLC genotyping tests and ctDNA quantitative tests. The PRMP and RMs established here could improve interlaboratory repeatability and reproducibility, which supports rapid translation and application of non-invasive tests into clinical practice.

The question of metrological traceability of COOMET reference materials. Pt. 2. Reference materials characterization

The concept of reference materials metrological traceability establishment within the framework of Euro-Asian Cooperation of National Metrological Institutions (COOMET) Technical Committee 1.12 “Reference Materials” (TC 1.12) is overviewed. Particular cases of COOMET Reference Materials development are provided. The authors considered approaches to demonstrate a metrological traceability of reference materials with different types of their characterisation, e. g., appliance of national measurement standards, or performance of interlaboratory comparison testing, or usage of primary reference measurement procedure for reference materials characterisation if a state measurement standard for units is absent.

Problems of Ensuring Metrological Traceability of Quality Control Measurement Results for Food Products and Food Raw Materials

The article raises the problem of ensuring metrological traceability of quality and nutritional value measurement results for food products and food raw materials: water (moisture), nitrogen (protein, crude protein), fat, ash and carbohydrate content. The problem under consideration can be solved by applying reference materials of food composition, traceable to state primary measurement standards GET 173-2017 and GET 176-2019 and primary reference measurement procedures (PRMP), for attestation of measurement procedures and accuracy verification of measurement results. The article discusses the results of PRMP development for measuring mass fraction of fat, ash and carbohydrates in food products and food raw materials, and mass fraction of crude fat (oil content) in oilseeds and products based on them. The paper also presents metrological characteristics of reference materials of the composition of dried dairy products, dried grain and dairy-grain cereals for babies, egg powder, freeze-dried meat products, animal feed. The results of the work allow for building a chain of metrological traceability from GET 173-2017, GET 176-2019 and PRMP to routine measurement procedures, thereby ensuring the uniformity of measurements of nutritional value of food products.

Problems of ensuring metrological traceability of measurement results of indicators of quality for food products and food raw materials

The article raises the problem of ensuring metrological traceability of the measurement results of indicators of quality and nutritional value for food products and food raw materials: water (moisture), nitrogen (protein, crude protein), fat, ash and carbohydrates. The problem under consideration can be solved by applying reference materials of food composition, traceable to state primary measurement standards GET 173-2017 and GET 176-2019 and primary reference measurement procedures (PRMP), for attestation of measurement procedures and accuracy checking of measurement results. The article discusses the results of the PRMP development of mass fraction of fat, ash and carbohydrates in food products and food raw materials, as well as mass fraction of crude fat (oil content) in oil crops seeds and products based on them. The paper also presents metrological characteristics of reference materials of composition of dry dairy products, grain-milk dry porridges for nutrition of babies, grain dry porridges for nutrition of babies, egg powder, freeze-dried meat products, animal feed. The results of the work allow for building a chain of metrological traceability from GET 173-2017, GET 176-2019 and PRMP to routine measurement procedures, thereby ensuring the uniformity of measurements of nutritional value of food products.

Development of primary reference measurement procedures for food quality control

The work is about the development of primary reference measurement procedures for food quality control based on the methods of gravimetry, butymetry, photometry, chromatography, spectrometry and others.

The role of NAA in securing the accuracy of analytical results in the inorganic trace analysis

The unique value of the neutron activation analysis (NAA) for analytical quality assurance is demonstrated through its contribution to the certification of the reference materials over the time span of 40 years. Ratio primary reference measurement procedures i.e. definitive methods, based on radiochemical NAA, play an important role in confirming the validity of the certified values established in the international intercomparisons. Real analytical situations where the use of NAA was critical to get accurate results are presented. The dangers associated with the possible non-availability of the NAA in the near future are indicated.

Ratio primary reference measurement procedure (RPRMP) for the certification of chromium content in biological reference materials

Abstract Primary reference measurement procedure for Cr determination in biological samples by radiochemical neutron activation analysis (RNAA) has been elaborated. The procedure is based on quantitative and selective separation of chromium from neutron irradiated sample by column chromatography using MnO2-Resin and determination of 51Cr by γ-ray spectrometry. Quality components have been incorporated into the RNAA method which makes it possible to meet the requirements of the definition of ratio primary reference measurement procedure. The usefulness of the elaborated procedure to assign the certified values for Cr in new certified reference material (CRMs) based on animal tissues is demonstrated. The tentative certified values for Cr have been proposed for: MODAS M-4 Cormorant Tissue and M-5 Cod Tissue CRMs.

Assessment of Digital PCR as a Primary Reference Measurement Procedure to Support Advances in Precision Medicine.

Genetic testing of tumor tissue and circulating cell-free DNA for somatic variants guides patient treatment of many cancers. Such measurements will be fundamental in the future support of precision medicine. However, there are currently no primary reference measurement procedures available for nucleic acid quantification that would support translation of tests for circulating tumor DNA into routine use. We assessed the accuracy of digital PCR (dPCR) for copy number quantification of a frequently occurring single-nucleotide variant in colorectal cancer (KRAS c.35G>A, p.Gly12Asp, from hereon termed G12D) by evaluating potential sources of uncertainty that influence dPCR measurement. Concentration values for samples of KRAS G12D and wild-type plasmid templates varied by <1.2-fold when measured using 5 different assays with varying detection chemistry (hydrolysis, scorpion probes, and intercalating dyes) and <1.3-fold with 4 commercial dPCR platforms. Measurement trueness of a selected dPCR assay and platform was validated by comparison with an orthogonal method (inductively coupled plasma mass spectrometry). The candidate dPCR reference measurement procedure showed linear quantification over a wide range of copies per reaction and high repeatability and interlaboratory reproducibility (CV, 2%-8% and 5%-10%, respectively). This work validates dPCR as an SI-traceable reference measurement procedure based on enumeration and demonstrates how it can be applied for assignment of copy number concentration and fractional abundance values to DNA reference materials in an aqueous solution. High-accuracy measurements using dPCR will support the implementation and traceable standardization of molecular diagnostic procedures needed for advancements in precision medicine.

Traceability to a primary reference measurement procedure (ID-LCMS); A key step in validating the clinical accuracy and safety of hospital blood glucose monitoring systems

ObjectiveA key step in the evaluation of the accuracy of blood glucose monitoring systems (BGMS) is using a comparator method aligned to a high order definitive reference method. We describe how we achieved traceability to an isotope dilution liquid chromatography mass spectrometry (ID-LCMS) method. We used ID-LCMS to evaluate the accuracy and specificity of two hospital BGMS used in China. MethodID-LCMS was used to verify the calibration alignment of the laboratory plasma hexokinase reference method using NIST standard reference material and clinical samples. The ID-LCMS aligned hexokinase method was used to evaluate the clinical accuracy of two BGMS in hospitalized patients. System accuracy was evaluated using Chinese consensus guidelines. BGMS accuracy was also assessed with interference factors known to be present in critically ill patients' blood. ResultsThe laboratory plasma hexokinase reference method was shown to calibrate closely with ID-LCMS. Two BGMS demonstrated good correlation with this reference method. Only one BGMS met the Chinese guidelines. The interference factors didn’t influence this BGMS but adversely affected the clinical accuracy of the other. ConclusionsWe advocate that our IDMS calibration alignment approach for ensuring the accuracy of the glucose reference method should be adopted in evaluations assessing the accuracy of blood glucose monitoring systems.

Commutability Assessment of Candidate Reference Materials for Pancreatic α-Amylase.

Measurement standardization of the catalytic concentration of α-amylase in serum is based on 3 pillars: the primary reference measurement procedure (PRMP), reference laboratories, and suitable certified reference materials (CRMs). Commutability is a prerequisite when using a CRM for calibration and trueness control of routine methods or for value transfer from the PRMP to end-user calibrators of routine methods through a calibration hierarchy. We performed a commutability study with 30 serum pools and 5 candidate reference materials (RMs) for pancreatic α-amylase using an automated version of the PRMP and 5 different routine methods. Four candidate RMs had an artificial matrix, each with a different composition, and 1 candidate RM was based on human serum. Data were analyzed according to a linear regression analysis with prediction interval as described in the Clinical and Laboratory Standards Institute guideline EP30-A and a difference in bias analysis as described in the recommendations of the IFCC Working Group on Commutability. The commutability profile of the 4 candidate RMs with an artificial matrix was variable. Only 1 candidate RM, with human serum albumin in the matrix, showed a good profile like that of the candidate RM based on serum. The comparison of both commutability assessment approaches indicated some differences because of inconclusive results for the difference in bias approach, suggesting a large uncertainty on the commutability assessment. A CRM for pancreatic amylase in an artificial matrix can be commutable for routine methods using the same substrate as the PRMP, but the matrix composition is crucial.