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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.13, #7)
Scheme and studies of reference materials for volumetric analysis in Japan by Toshiaki Asakai; Mariko Murayama (pp. 351-360).
This paper describes the history and scheme of reference materials and standard solutions for titrimetry in Japan. Titrimetry is one of the most fundamental and precise methods for determination of a constituent, based on the effective purity of reference materials in stoichiometric analysis. It has wide-ranging applications based on titrimetric reactions such as neutralization, redox, chelatometric, and precipitation titration processes, which are used in various analytical fields all over the world. Japanese Industrial Standards (JIS) have played an important role in establishing a stable supply of reference materials for titrimetry since the 1950s. There are several reports of preparations and their determination, including coulometric studies, in order to establish highly reliable reference materials. This paper briefly reviews the schemes and studies of standardization through the provision of reference materials and standard solutions based on JIS, and several applications in other standards.
Keywords: Titrimetry; Volumetric analysis; Stoichiometric standards; Certified reference materials; Japanese Industrial Standards (JIS)
Approaches to uncertainty evaluation based on proficiency testing schemes in chemical measurements by Paola Fisicaro; Soraya Amarouche; Béatrice Lalere; Guillaume Labarraque; Marc Priel (pp. 361-366).
Since the advent of the Guide to the Expression of Uncertainty in Measurement (GUM) founding the principles of uncertainty evaluation, numerous projects have been carried out to develop alternative practical methods when it is impossible to model technical or economical aspects of the measurement process. These methods can use all the experimental data available to the laboratories, such as repeatability, reproducibility, quality-control charts, etc. The studies presented in this paper compare the results obtained by the modelling method from GUM with the uncertainties found by applying alternative methods. They show two examples, one in the field of environmental monitoring, the other in the biomedical field, based on the exploitation of PT schemes results.
Keywords: Uncertainty evaluation; Proficiency testing schemes; Uncertainty in environmental analyses; Uncertainty in biomedical analyses
Strategies implemented at LNE to establish the traceability of environmental measurements by P. Fisicaro; R. Champion; G. Labarraque; B. Lalere; T. Mace; C. Sutour (pp. 367-372).
LNE is actively involved in the development of reference procedures in the domains of organic and inorganic chemistry and in gas analysis. Moreover, production of certified reference materials (CRMs), certification of calibration standards, and providing reference values for proficiency testing schemes (PTS) are fields well settled to ensure the traceability of measurements in environmental monitoring. The paper presents some representative examples of these activities recently realised in our laboratory.
Keywords: Traceability in chemical measurements; Certified reference materials (CRMs); Calibration standards; Proficiency testing schemes (PTS)
Verification of the need for optical purity measurement of chiral pesticide standards as agricultural reference materials by Koichi Saito; Masakazu Yato; Takeshi Ito; Yusuke Iwasaki; Rie Ito; Yasuhiko Matsuki; Hiroyuki Nakazawa (pp. 373-379).
In this study, optical purity measurement was performed on eight kinds of commercially available pesticide, namely, Dimethenamid-P, Dichlorprop-P, Fluazifop-P butyl, Indoxacarb, Metalaxyl-M, Mecoprop-P, Quizalofop-P ethyl, and Uniconazole-P, in both enantiomer and racemate forms. Chiral separation of each pesticide was achieved by using HPLC with a photodiode-array (PDA) detector and a circular dichroism (CD) detector, which were connected in series. The chiral column used for the enantiomeric separation was a normal phase Chiralpak AD-H column. The mobile phase was n-hexane, with various alcohols added as polar modifiers. The study included investigation of the effects on enantiomeric separation of the percentage of alcohol used, the presence or absence of acid in the mobile phase, and the column temperature, and the optimum detection wavelengths of both PDA and CD detectors. Enantiomeric excess (ee) was calculated as an expression of optical purity. As a result, the ee of some pesticides investigated was approximately (over 95%) in accord with the data provided by manufacturers. However, the ee of Indoxacarb, Uniconazole-P, Quizalofop-P ethyl, and Fluazifop-P butyl was in the range 34.1–94.5%. These results suggest that there is a need to conduct optical purity tests, in addition to a chemical purity test, for optically active pesticides.
Keywords: Optical purity measurement; Pesticide standard; Chiral separation; Enantiomeric excess
pH determination on a carbonate buffer by Harned cells of different designs by Igor Maksimov; Masaki Ohata; Susumu Nakamura; Akiharu Hioki; Koichi Chiba; Petra Spitzer (pp. 381-387).
The carbonate solution is one of seven primary standard buffers set recently by the International Union of Pure and Applied Chemistry (IUPAC) recommendations (Buck et al., Pure Appl Chem 74:2169–2200, 2002). The peculiarity of the pH measurement of this buffer in a traditional Harned cell (classic cell) is due to the loss of carbon dioxide with hydrogen flow and the ensuing change of its chemical composition. This results in a continuous increase of the recorded electromotive force (E) of the cell. Therefore, almost all National Metrology Institutes (NMIs) are now using the extrapolation of measured E data to zero time point in order to find the initial pH. The National Metrology Institute of Japan (NMIJ) has developed a different design of Harned cell (NMIJ cell) with compensation of the lost carbon dioxide from the intermediary saturation vessel. The results of the study of the NMIJ cell are presented, together with those of the trilateral NMIJ–PTB–ZMK (NMI of Japan with the NMI of Germany [Physikalisch-Technische Bundesanstalt, PTB] and the German Centre for Measurements and Calibrations [Zentrum für Messen und Kalibrieren GmbH, ZMK]) comparison of pH values for the carbonate solution in different designs of Harned cell.
Keywords: pH; Carbonate buffer; Electrochemical cell; Harned cell
Development of certified reference materials of high-purity volatile organic compounds: purity assay by the freezing-point depression method by Yoshitaka Shimizu; Yoko Ohte; Xinnu Bao; Satoko Otsuka; Yuko Kitamaki; Keiichiro Ishikawa; Toshihide Ihara; Kenji Kato (pp. 389-396).
For accurate measurement of concentrations of substances by instrumental analysis, reliable calibration standards are needed. In Japan, national reference materials are supplied under the national standards dissemination system named the Japan Calibration Service System (JCSS). In JCSS, calibration standards for the analysis of environmental pollutants are supplied. For the traceability to the SI of reference materials for calibration in JCSS, the National Metrology Institute of Japan (NMIJ) is developing high-purity reference materials of volatile organic compounds (VOCs) as NMIJ CRMs. The freezing-point depression method, which has potential as a primary method of measurement, is employed for the determination of property value. In this paper, a development scheme of certified reference materials of high-purity VOCs is described.
Keywords: Certified reference materials; Volatile organic compounds (VOCs); Purity; Freezing-point depression method
Preparation and characterization of organic calibration solutions for development of certified reference materials at the National Metrology Institute of Japan by K. Ishikawa; N. Hanari; Y. Shimizu; T. Ihara; T. Maeda; A. Nomura; T. Yarita; K. Kato; K. Chiba (pp. 397-408).
Certified reference materials (CRMs) are playing an increasingly important role in environmental monitoring in Japan. The National Metrology Institute of Japan (NMIJ)/National Institute of Advanced Industrial Science and Technology (AIST) has been developing CRMs of organic calibration solutions since 2003, and has issued several NMIJ CRMs. The development of these materials was conducted at the NMIJ in cooperation with candidate material producers. The freezing-point depression method was principally adopted for assessment of the purity of starting materials to give reliable certified values. Gas chromatography with flame ionization detection (GC–FID) and/or high-performance liquid chromatography (HPLC), which are based on independent principles and whose levels of accuracy are well evaluated, were applied in combination with other methods to avoid any possible analytical bias. Purity assessment is outlined for two typical examples, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDD) and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDT), which were used as starting materials for a CRM under development. Methods adopted for gravimetric preparation and ampouling of solutions were qualified and optimized to reduce the uncertainties of certified values due to these factors. Furthermore, a new experimental scheme for assessment of stability and preparation variation is proposed for the proper estimation of uncertainties.
Keywords: Certified reference material; Certified value; Calibration solution; Uncertainty; Environmental monitoring
Preparation and certification of creatinine and urea reference materials with certified purity as a traceability source in clinical chemical measurements by Akiko Takatsu; Sakae Eyama; Mika Saeki (pp. 409-413).
Purity certified reference materials (CRMs) are playing a key role in metrological traceability, because they form the basis for many traceability chains in chemistry. Recently, the National Metrology Institute of Japan (NMIJ) has developed two purity CRMs for creatinine (NMIJ CRM 6005-a) and urea (NMIJ CRM 6006-a), because the concentrations of these two compounds are frequently measured in clinical laboratories for monitoring the renal functions. In the certification of purity CRMs, it is essential that the materials have been thoroughly characterized for purity, and the purity should preferably be determined directly by a primary method of measurements. In the development of these two CRMs, we used the purified materials as candidates. The certified values were assigned based on the results of two different methods; acidimetric titration and nitrogen determination by the Kjeldahl method. Since both methods cannot distinguish some impurities from the target compounds, major impurities in the candidate materials were also identified, quantified, and subtracted. These CRMs can provide a traceability link between routine clinical methods and SI units.
Keywords: Certified reference material; Purity; Traceability; Titrimetry; Primary methods; Laboratory medicine
Stability evaluation of alkali metal standard solutions by using precise ion chromatography by Yoshiyasu Yamauchi; Akiharu Hioki (pp. 415-419).
Mass fractions of alkali metal (Li, Na, K, Rb, Cs) standard solutions (1000 mg/kg) were measured with about 0.1% relative standard deviation by improving the method of injection in ion chromatography (IC). This technique was applied to stability testing of the standard solutions. After storage of each alkali metal standard solution for 18 months, an increase of the mass fraction was observed, for all the alkali metal ions, of approximately 0.15% per year at 25 °C and approximately 0.02% per year at 5 °C. The observed increase of the mass fraction can be explained by the weight loss of the solution during storage. The deviation between the mass fraction measured by IC and the preparation mass fraction after correcting the weight loss for solvent evaporation was within ±0.05% for every alkali metal ion. It is concluded that alkali metal standard solutions of 1000 mg/kg are basically stable for more than 18 months under these storage conditions and that correction for evaporation is effective if weight monitoring of each bottle is performed precisely.
Keywords: Stability evaluation; Storage; Alkali metal standard solution; Ion chromatography (IC); High precision; Bracket method
Proficiency testing scheme for the harmonization and comparability of analytical measurements by Yoshito Mitani; Judith Velina Lara-Manzano; Aaron Rodriguez-Lopez (pp. 421-426).
According to the experience of the successful implementation of proficiency tests (PT) by using the certified reference value as the assigned value, a new scheme of evaluation is presented by suggesting the use of the uncertainty associated with the certified value. The technical performance of laboratories is evaluated by the parameter quadratic mean error (QME), which is the square root of the sum of the square of the bias and that of the standard deviation of the laboratory. This parameter is considered as the estimate of the measurement uncertainty of the laboratory and is compared to the uncertainty (U) associated with the certified value provided by an NMI. Considering that the calibration and measurement capability, known as the CMC, is recognized among NMIs, the ratio QME/U enables us to compare the PT relative to the CMC of an NMI, and, consequently, to any other comparison results based on the CMC of signatories of the mutual recognition arrangement (MRA) of the International Committee of Weights and Measure (CIPM).
Keywords: Proficiency test (PT); Quadratic mean error (QME); Relative QME (QMER); Calibration and measurement capability (CMC); Traceability; Comparability