Quantitative nuclear magnetic resonance (qNMR) in combination with metrological weighing is optimised to demonstrate the power of the qNMR measurement method. It is shown that with 1 H-qNMR it is possible to certify the purity of organic reference materials (expressed as mass fraction) with relative expanded uncertainties of \0.1 % for a 95 % confidence interval (k = 2). Following well-defined selection criteria, a set of twelve different chemical compounds is evaluated and certified to serve as internal references for 1 H-qNMR measurements. A series of comparison measurements is made amongst a subset of the selected compounds. The purity of maleic acid is determined by six different 1 H-qNMR measurement series, and all results show full consistency. All the six mean values are covered within the range of ±0.05 %. In two more measurement series, four different nuclei are analysed within the same sample against one calibrator. Even with non-optimised signal intensity ratios and varying signal pattern, a high consistency was obtained. Therefore, the validity and robustness of 1 H-qNMR measurement results are demonstrated. 1 H-qNMR measurement results are directly traceable to a variety of internationally accepted primary reference materials, and therefore, traceability to SI units is obtained. All experiments are performed under ISO/IEC 17025 and ISO Guide 34 accreditation.
The homogeneity of samples intended for metrological intercomparison studies must be granted without ambiguity. This holds equally true for aqueous solutions for which the determination of betweenbottle variations requires measurement techniques with extremely high precision. Therefore measurement series were designed for automated analysis techniques such as titrimetry, optical emission spectrometry and ion chromatography which offer very high precision of results. Between-bottle relative standard deviations (RSD) of at best 0.008% were obtained with titrimetry. With optical emission spectrometry and ion chromatography, between-bottle RSD's of 0.02% and 0.05% were obtained. The contributions from these measurements were included in a conservative approach to the uncertainty budgets of the gravimetrical reference values for the analytes in the samples.
Over the last three years Sigma-Aldrich has built-up a competence centre for CRM (Certified Reference Material) production in Buchs, Switzerland. The new facility is accredited following both ISO/IEC 17025 and ISO Guide 34. The commercial availability of a broad range of different CRMs is of highest importance with respect to the realisation of metrological concepts in practice. This article describes the process of the production and certification of inorganic CRMs of highest quality. This comprises the comprehensive characterisation of the starting materials, the high precision weighing of the compounds, homogenisation and special packaging of these new CRMs.
In this key comparison anion calibration solutions of chloride and phosphate were investigated. The contents of both solutions were about 1 g/kg relative to the anion mass. For the chloride comparison 10 participants provided results by the following three analytical techniques: coulometry, titrimetry and ion chromatography. The phosphate amount content was determined by 10 NMIs whereby the following 6 techniques were applied: ion chromatography, titrimetry, ICP-OES, gravimetry, UV-Vis and ion-exchange followed by coulometry. The following institutes participated in this key comparison:
BAM and PTB (Germany)
BNM-LNE (France)
CENAM (Mexico)
EMPA (Switzerland)
GUM (Poland)
INTEC (Chile)
KRISS (Korea)
NMIJ (Japan)
NRCCRM (China)
SMU (Slovakia)
With one exception all results were found within the range of ±0.25% with respect to the gravimetric value. The variability (RSD) of the results is below 0.1% for both the chloride and the phosphate solution (chloride without CENAM result). Compared to the pilot study CCQM-P32 the results of CCQM-K29 were significantly better. This is especially true for the phosphate comparison.Main text.
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 kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the
CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.