5 research outputs found
CCQM-K90, formaldehyde in nitrogen, 2 μmol mol− 1 Final report
The CCQM-K90 comparison is designed to evaluate the level of comparability of national metrology institutes (NMI) or designated institutes (DI) measurement capabilities for formaldehyde in nitrogen at a nominal mole fraction of 2 μmol mol−1.
The comparison was organised by the BIPM using a suite of gas mixtures prepared by a producer of specialty calibration gases. The BIPM assigned the formaldehyde mole fraction in the mixtures by comparison with primary mixtures generated dynamically by permeation coupled with continuous weighing in a magnetic suspension balance. The BIPM developed two dynamic sources of formaldehyde in nitrogen that provide two independent values of the formaldehyde mole fraction: the first one based on diffusion of trioxane followed by thermal conversion to formaldehyde, the second one based on permeation of formaldehyde from paraformaldehyde contained in a permeation tube.
Two independent analytical methods, based on cavity ring down spectroscopy (CRDS) and Fourier transform infrared spectroscopy (FTIR) were used for the assignment procedure.
Each participating institute was provided with one transfer standard and value assigned the formaldehyde mole fraction in the standard based on its own measurement capabilities.
The stability of the formaldehyde mole fraction in transfer standards was deduced from repeated measurements performed at the BIPM before and after measurements performed at participating institutes. In addition, 5 control standards were kept at the BIPM for regular measurements during the course of the comparison.
Temporal trends that approximately describe the linear decrease of the amount-of-substance fraction of formaldehyde in nitrogen in the transfer standards over time were estimated by two different mathematical treatments, the outcomes of which were proposed to participants. The two treatments also differed in the way measurement uncertainties arising from measurements performed at the BIPM were propagated to the uncertainty of the trend parameters, as well as how the dispersion of the dates when measurements were made by the participants was taken into account.
Upon decision of the participants, the Key Comparison Reference Values were assigned by the BIPM using the largest uncertainty for measurements performed at the BIPM, linear regression without weight to calculate the trend parameters, and not taking into account the dispersion of dates for measurements made by the participant. Each transfer standard was assigned its own reference value and associated expanded uncertainty. An expression for the degree of equivalence between each participating institute and the KCRV was calculated from the comparison results and measurement uncertainties submitted by participating laboratories. Results of the alternative mathematical treatment are presented in annex of this report
Mass Balance Method for the SI Value Assignment of the Purity of Organic Compounds
A mass
balance method is described for determining the mass fraction of the
main component of a high purity organic material. The resulting assigned
value is established to be traceable to the SI and can be determined
with a small associated measurement uncertainty. Pure organic materials
with values and uncertainties determined in this way are necessary
as primary calibrators of reference measurement systems in order to
underpin the metrological traceability of routine measurement results.
The method has been applied to materials in which the main components
were respectively theophylline, digoxin, 17β-estradiol, and
aldrin. Its performance has been validated in international comparisons
coordinated by the BIPM and is in principle applicable to a wide structural
range of stable, nonvolatile organic compounds. It has been successfully
applied to mass fraction assignments when the main component is present
in the range of (950–1000) mg/g and can achieve associated
standard uncertainties ranging from 0.5 mg/g (for high purity materials
or those containing well-characterized, stable minor components) to
2 mg/g (materials with a significant number or variety of impurities).
It is in principle equally applicable to materials with a smaller
mass fraction content of the main component
Calibration Strategies for FT-IR and Other Isotope Ratio Infrared Spectrometer Instruments for Accurate δ<sup>13</sup>C and δ<sup>18</sup>O Measurements of CO<sub>2</sub> in Air
This
paper describes calibration strategies in laboratory conditions
that can be applied to ensure accurate measurements of the isotopic
composition of the CO<sub>2</sub> in ultradry air, expressed as δ<sup>13</sup>C and δ<sup>18</sup>O on the VPDB scale, with either
FT-IR (in this case a Vertex 70 V (Bruker)) or an isotope ratio infrared
spectrometer (IRIS) (in this case a Delta Ray (Thermo Fisher Scientific)).
In the case of FT-IR a novel methodology using only two standards
of CO<sub>2</sub> in air with different mole fractions but identical
isotopic composition was demonstrated to be highly accurate for measurements
of δ<sup>13</sup>C and δ<sup>18</sup>O with standard uncertainties
of 0.09‰ and 1.03‰, respectively, at a nominal CO<sub>2</sub> mole fraction of 400 μmol mol<sup>–1</sup> in
air. In the case of the IRIS system, we demonstrate that the use of
two standards of CO<sub>2</sub> in air of known but differing δ<sup>13</sup>C and δ<sup>18</sup>O isotopic composition allows standard
uncertainties of 0.18‰ and 0.48‰ to be achieved for
δ<sup>13</sup>C and δ<sup>18</sup>O measurements, respectively.
The calibration strategies were validated using a set of five traceable
primary reference gas mixtures. These standards, produced with whole
air or synthetic air covered the mole fraction range of (378–420)
μmol mol<sup>–1</sup> and were prepared and/or value
assigned either by the National Institute of Standards and Technology
(NIST) or the National Physical Laboratory (NPL). The standards were
prepared using pure CO<sub>2</sub> obtained from different sources,
namely, combustion; Northern Continental and Southern Oceanic Air
and a gas well source, with δ<sup>13</sup>C values ranging between
−35‰ and −1‰. The isotopic composition
of all standards was value assigned at the Max Planck Institute for
Biogeochemistry Jena (MPI-Jena)
Overcoming challenges regarding reference materials and regulations that influence global standardization of medical laboratory testing results
Background Standardized results for laboratory tests are particularly important when their interpretation depends on fixed medical practice guidelines or common reference intervals. The medical laboratory community has developed a roadmap for an infrastructure to achieve standardized test results described in the International Organization for Standardization standard 17511:2020 In vitro diagnostic medical devices - Requirements for establishing metrological traceability of values assigned to calibrators, trueness control materials and human samples. Among the challenges to implementing metrological traceability are the availability of fit-for-purpose matrix-based certified reference materials (CRMs) and requirements for regulatory review that differ among countries. A workshop in December 2021 focused on these two challenges and developed recommendations for improved practices. Discussion The participants agreed that prioritization of measurands for standardization should be based on their impact on medical decisions in a clinical pathway. Ensuring that matrix-based CRMs are globally available for more measurands will enable fit-for-purpose calibration hierarchies for more laboratory tests. Regulation of laboratory tests is important to ensure safety and effectiveness for the populations served. Because regulations are country or region specific, manufacturers must submit recalibration changes intended to standardize results for regulatory review to all areas in which a measuring system is marketed. Recommendations A standardization initiative requires collaboration and planning among all interested stakeholders. Global collaboration should be further developed for prioritization of measurands for standardization, and for coordinating the production and supply of CRMs worldwide. More uniform regulatory submission requirements are desirable when recalibration is implemented to achieve internationally standardized results