Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.15, #1)
The traceability chain in medical laboratories: a long and winding road, the example of HbA1c by Cas Weykamp (pp. 3-7).
In medical laboratories, a metrological basis for quantitation is missing for many tests. This is recognised by the profession and over the last decade the concept of metrological traceability is advocated. However, daily practice is refractable: for many analytes reference measurement procedures are missing and once in place, clinicians obstruct the new units. This wearisome process is described in general terms and illustrated by the specific case of HbA1c. A working group of the scientific division of the IFCC developed a reference system for this key parameter in diabetes management. This system is worldwide accepted as the analytical anchor. However, clinicians objected the new units. A debate of years followed. This urged the international diabetes organisations IDF, EASD and ADA to find a solution to avoid confusion. They came up with a consensus statement, but this compromise—report of HbA1c in three units—was unpractical and not accepted. Finally, decisions were made at a national level: the European Union and Japan will report in the new units, the US in their old national units and an additional unit, the estimated average glucose.
Keywords: Metrology in medical laboratories; HbA1c ; Diabetes
CCQM-P111 study on traceable determination of practical salinity and mass fraction of major seawater components by Steffen Seitz; Petra Spitzer; Richard J. C. Brown (pp. 9-17).
The first part of the study assessed the equivalence of practical salinity measurement results of a slightly diluted seawater sample from the North Atlantic, which were traceable to the SI. The study shows that the practical salinity reference value S RV (here S RV = 34.967) can be determined with a relative standard uncertainty of 3×10−4. This quantifies the uncertainty range, in which long-term comparability of practical salinity measurement results can be guaranteed currently. In the second part of the study, eight laboratories determined the mass fractions of five seawater components to quantify the equivalence of these measurement results. The results were: Na+ (10.726 ± 0.134) g/kg, Mg2+ (1.288 ± 0.018) g/kg, Sr2+ (0.00755 ± 0.00011) g/kg, Cl− (19.360 ± 0.047) g/kg, SO4 2− (2.650 ± 0.025) g/kg. The investigation confirmed the reference composition mass fractions of sodium, magnesium and chloride ions, but it showed a disagreement for strontium and sulphate ions.
Keywords: Practical salinity; Conductivity; SI traceability; Mass fractions of seawater components
An approach to detection capabilities estimation of analytical procedures based on measurement uncertainty by Juan Jiménez-Chacón; Manuel Alvarez-Prieto (pp. 19-28).
Detection capabilities are important performance characteristics of analytical procedures. There are several conceptual approaches on the subject, but in most of them a level of ambiguity is presented. It is not clear which conditions of measurements should be used, and there is a relative lack of definition concerning blanks. Moreover, there are no systematic experimental studies concerning the influence of uncertainty associated with bias evaluation. A new approach based on measurement uncertainty is presented for estimating quantities that characterize capabilities of detection. It can be applied to different conditions of measurement and it is not necessary to perform an additional experiment with blanks. Starting from a modelling process of the combined uncertainty of concentration, it is possible to include in the estimated quantities the effects due to random errors and the uncertainty associated to evaluation of bias. The detection capabilities are then compared with the results obtained using some other relevant approaches. Slightly higher values were obtained with the measurement uncertainty approach due to inclusion of uncertainty associated with bias.
Keywords: Detection limit; Critical concentration; Detection capabilities; Uncertainty modelling; Validation
Purity determination as needed for the realisation of primary standards for elemental determination: status of international comparability by Heinrich Kipphardt; Ralf Matschat; Jochen Vogl; Tamara Gusarova; Michael Czerwensky; Hans-Joachim Heinrich; Akiharu Hioki; Leonid A. Konopelko; Brad Methven; Tsutomu Miura; Ole Petersen; Gundel Riebe; Ralph Sturgeon; Gregory C. Turk; Lee L. Yu (pp. 29-37).
Within the National Metrology Institutes (NMIs) and designated laboratories, an interlaboratory comparison, CCQM-P107, was conducted to verify the degree of international comparability concerning the results of purity analysis. The mass fractions of Ag, Bi, Cd, Cr, Ni, Tl at the lower mg/kg-level in a high purity zinc material were determined, but the real measurand in metrological sense was the sum of the six mass fractions. Homogeneity was investigated by glow discharge mass spectrometry, reference values were obtained using isotope dilution mass spectrometry. Six NMIs participated, contributing eight independent data sets. The agreement amongst the results of the participants, their median and the agreement with the reference values were usually excellent and in almost all cases below the target uncertainty of 30% relative. In this manner, the accuracy of results and the comparability between the participants was demonstrated to be established.
Keywords: Interlaboratory comparison; Purity analysis; High purity metals; CCQM-P107; Zinc
International comparison of the determination of the mass fraction of cadmium, chromium, mercury and lead in polypropylene: the Comité Consultatif pour la Quantité de Matière pilot study CCQM-P106 by Liandi Ma; Liuxing Feng; A. Hioki; K. H. Cho; J. Vogl; A. Berger; G. Turk; S. Macleod; G. Labarraque; W. F. Tong; D. Schiel; C. Yafa; L. Valiente; L. A. Konopelko; C. Quetel; P. Vermaercke; J. V. L. Manzano; M. Linsky; E. Cortés; S. Tangpitayakul; L. Plangsangmas; L. Bergamaschi; R. Hearn (pp. 39-44).
The CCQM-P106 pilot study was organized by the inorganic working group of the Comité Consultatif pour la Quantité de Matière (CCQM) as a feasibility comparison to study the applicability of different analysis methods to the polypropylene sample and test the abilities of the participants for measuring the Cd, Cr, Hg and Pb in polypropylene. National Institute of Metrology P.R. China (NIM) acted as the coordinating laboratory of this pilot study. There were 21 laboratories that submitted the final results. The median values of the mass fraction of Cd, Cr, Hg and Pb were 36.12 mg kg−1 (the median absolute deviation about the median (MADe) = 0.46 mg kg−1), 252.5 mg kg−1 (MADe = 3.4 mg kg−1), 387.0 mg kg−1 (MADe = 10.1 mg kg−1) and 466.2 mg kg−1 (MADe = 8.9 mg kg−1), respectively. Isotope dilution mass spectrometry (IDMS), inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-optical emission spectrometry (ICP-OES), atomic absorption spectrometry (AAS), instrumental neutron activation analysis (INAA) and X-ray fluorescence (XRF) measurement methods were used, and microwave digestion was used by the most of the participants. In general, very good agreement of the results was observed. Moreover, compared to the results of other methods, the results of IDMS still showed less spread amongst laboratories and had a smaller uncertainty. In addition, the results of some analytes used by XRF and INAA also got satisfactory agreement with the median value.
Keywords: Cadmium; Chromium; Mercury; Lead; Polypropylene; CCQM
About acceptance and rejection zones as defined in the EURACHEM/CITAC Guide (2007) “Use of uncertainty information in compliance assessment” by Elio Desimoni; Barbara Brunetti (pp. 45-47).
Considering measurement uncertainty is mandatory in assessing conformance to legal or compositional limits, and specific guidelines are available issued by ASME, ISO and Eurachem/CITAC. However, differences between ISO and EURACHEM/CITAC wordings could induce some perplexities in the most careful readers. Possible problems arise from considering that, before performing a test, it should be decided whether it is to be a test for conformity or a test for non-conformity. This choice could perhaps require some renaming of acceptance/rejection zones as defined in the EURACHEM/CITAC Guide. A tentative solution is discussed in this contribution.
Keywords: Guard band; Acceptance/rejection zones; Inconclusive zone; Tests for conformity; Test for non-conformity
Response to “About acceptance and rejection zones” by Stephen L. R. Ellison; A. Williams (pp. 49-51).
Desimoni and Brunetti raise some questions about the use of Eurachem/CITAC guide, because the Eurachem/CITAC guide does not discuss an ISO recommendation before performing a test, it should be decided whether it is to be a test for conformity or a test for non-conformity. In response, it is pointed out that although this recommendation is not discussed explicitly, it is of necessity covered by the decision rule that describes how the measurement uncertainty will be taken into consideration with regard to accepting or rejecting a product according to its specification and the result of a measurement. In addition, they propose the introduction of an ‘inconclusive’ zone. We do not think that this is necessary, since the Eurachem/CITAC guide takes the view that action on rejection should be covered by the ‘decision rule’ and this can make equivalent provision for confirmation or interpretation.
Keywords: Compliance assessment; Decision rules; Guard band; Acceptance/rejection zones
Comment on “Validation of specificity in doping control: problems and prospects” by Ulrich Flenker; Wilhelm Schänzer (pp. 53-55).
The paper contains a reply to ‘Validation of specificity in doping control: problems and prospects’ by N. M. Faber. Dr. Faber charges the work of anti-doping scientists of the use inappropriate methods. The allegations refer to the procedure of substance identification which according to Dr. Faber is based on subjective criteria (“visual inspection”). We demonstrate that by contrast it represents an objective, logically sound, and clearly defined procedure which strictly follows the logic of scientific reasoning.
Keywords: Substance identification; Validation; Scientific reasoning; Doping control
How IAF and ILAC manage the recognition of Regional Accreditation Groups: the peer evaluation system of IAF and ILAC for Regional Accreditation Groups by Frauke Behrens; Monika Wloka (pp. 57-66).
The peer evaluation of single accreditation bodies in order to sign an Arrangement for Recognition of the international accreditation organizations International Accreditation Forum, Inc. (IAF) and International Laboratory Accreditation Cooperation (ILAC), whether performed by Regional Accreditation Groups or directly by IAF and/or ILAC, is standard practice. The fundamental requirements for such evaluations are well specified in documents. However, the careful evaluation of all their Arrangement members poses an enormous logistic task for IAF and ILAC, and the signatories can be evaluated more thoroughly within their Regional Groups. Hence, IAF and ILAC typically evaluate only the Regional Accreditation Groups and accept all signatories of a Regional Accreditation Group once successfully evaluated by their respective Regional Group. However, the requirements for the evaluation of a Regional Group are extensive, and the evaluation procedure is highly complicated and must be conducted very carefully in order to assure that the results of accreditation can be trusted. This article describes the evaluation procedure used by IAF and/or ILAC for Regional Groups wishing to sign the IAF/ILAC Arrangement. We wish to inform and to aid these Regional Groups setting out for evaluation, and also to build confidence in the IAF/ILAC Arrangements.
Keywords: Accreditation; Arrangement; IAF; ILAC; Peer evaluation; Region