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.11, #11)
Metrological traceability: I make it 42; you make it 42; but is it the same 42? by D. Brynn Hibbert (pp. 543-549).
The paper reproduces a talk given at a 2-day symposium on quality assurance in chemistry held in Brisbane, Australia in 2005. Intended for an audience of analysts in the field, the theme of the symposium drew inspiration from the series of books by Douglas Adams “The Hitchhiker's Guide to the Galaxy”. An introduction to basic concepts of metrological traceability is followed by a discussion of practical steps to ensure metrological traceability of field measurement results. The relationship between metrological traceability and comparability of measurement results is discussed. To achieve metrological traceability in the field, the use of appropriate certified reference materials for calibration is recommended. Examples of atmospheric carbon dioxide and roadside breathalyzer measurements are given.
Keywords: Metrological traceability; Measurement uncertainty; CRM; Reference materials
Low-frequency noise in analytical soil measurements by Petras Serapinas; Jadvyga Lubytė (pp. 550-553).
Fourier analysis of the real-time quality-control charts for colorimetric, photometric, and pH soil measurements shows 1/f n (n=1±0.05) noise intensity dependence on frequency, in correspondence to the earlier test for atomic absorption measurements. In addition, the prevailing character of the sample preparation in the general noise frequency dependence is clearly demonstrated. Some important analytical problems are addressed where knowledge of the specific character of the time variation in the analytical data sets is essential.
Keywords: Metrology in chemistry; Noise; Uncertainty; Reproducibility; Quality-control chart
Equipment qualification and its application to conductivity measuring systems by John J. Barron; Colin Ashton (pp. 554-561).
It is only possible to obtain analytical results that are suitable for their intended purpose if the equipment used is capable of producing measurements of the required quality. To ensure that this requirement is met, analysts should define the performance criteria required from the instruments, ensure that only suitable instruments are selected for analytical measurements, and confirm that these instruments continue to meet these criteria for their entire operational life. This process should be conducted on a formal, documented basis, known as equipment qualification. In addition to describing the key elements of equipment qualification for all analytical instruments, this paper gives specific guidance on its application to conductivity systems that has never previously appeared in the literature. The benefits of performing equipment qualification are highlighted and guidance is given on the selection of control standards and why the equipment vendor performing stages of equipment qualification can be of benefit to the user. The relationship between equipment qualification and method validation is discussed, including how these activities play a major role in determining the quality control measures that should be applied to routine analysis.
Keywords: Equipment qualification; Conductivity; User requirement specification; Design qualification; Installation qualification; Operational qualification; Performance qualification
Estimating the measurement uncertainty in forensic breath-alcohol analysis by Rod G. Gullberg (pp. 562-568).
The evidentiary weight attributed to forensic breath alcohol results in drunk-driving prosecutions requires that measurement uncertainty be established and shown to be fit-for-purpose. The principal components contributing to breath alcohol measurement uncertainty include: (1) biological/sampling, (2) instrumental, (3) traceability and (4) the water/air partition coefficient for control standards. Employing duplicate breath results from over 92,000 subjects to estimate the biological/sampling component and assuming reasonable forensic values for the other components, the combined and expanded uncertainty is determined for a practical example. The combined uncertainty for an unbiased single determination breath alcohol measurement was: $$S_{Y_{{
m Corr}}} = 0.0038,{
m g}/210,{
m L}$$ . Employing the expanded uncertainty (k = 2.58), the 99% confidence interval for a mean breath alcohol concentration of 0.0935 g/210 L was 0.0866 to 0.1004 g/210 L. The proportion of combined uncertainty associated with each component was determined to be: biological/sampling 73%, analytical 10%, traceability 13% and water/air partition coefficient 4%. These are forensically acceptable estimates and demonstrate fitness-for-purpose of breath alcohol measurement when employing appropriate elements of quality control.
Keywords: Measurement uncertainty; Forensics; Breath alcohol
Evaluation of analytical instrumentation. Part XIX CHNS elemental analysers (pp. 569-576).
The reports of this series tabulate a number of features of analytical instruments that should be considered when making comparison between various systems. Scoring these features in a rational manner allows a scientific comparison to be made between instruments as an aid to selection. This is the XIXth report of the series and deals with CHNS elemental analysers.
Keywords: CHNS analysers; Instrumentation; Overview; Evaluation
Local comparability of proficiency testing results: determination of concrete slump and compressive strength values by Liat Kimhi; Chaim Zlotnikov; Ilya Kuselman (pp. 577-583).
A proficiency testing (PT) scheme is developed for comparability assessment of results of concrete slump and compressive strength determination. The scheme is based on preparing of a test portion/sample of a concrete in-house reference material (IHRM) at a reference laboratory (RL) in the same conditions for every PT participant. Therefore, in this scheme IHRM instability is not relevant as a source of measurement/test uncertainty, while intra- and between-samples inhomogeneity parameters are evaluated using the results of RL testing of the samples taken at the beginning, the middle and the end of the PT experiment. The IHRM assigned slump and compressive strength values are calculated as averaged RL results. Their uncertainties include the measurement/test uncertainty components and the components arising from the material inhomogeneity. The test results of 25 PT participants were compared with the IHRM assigned values taking into account both the uncertainties of the assigned values and the measurement/test uncertainties of the participants. Since traceability of the IHRM assigned values to the international measurement standards and SI units cannot be stated, local comparability of the results is assessed. It is shown, that comparability of the slump and compressive strength determination results is satisfactory, while uncertainty evaluation for slump results requires additional efforts.
Keywords: Comparability; Proficiency testing; Concrete; Slump; Compressive strength
Determination of POPs in environmental matrices – proficiency tests for Polish laboratories by Piotr Konieczka; Thomas P. J. Linsinger; Jacek Namieśnik (pp. 584-589).
Thirty Polish laboratories participated in proficiency tests (PT) for determination of persistent organic pollutants – POPs (PCBs – polychlorinated biphenyls, PAHs – polyaromatic hydrocarbons and pesticides) in solid environmental matrices (sediments, soil). Participants used their in-house method. The aim of the exercises was to obtain information about the “state of the art” of POPs analysis in environmental samples. The CV (coefficient of variation) of analytical results submitted varied from 45 to 65%, with an outlier rate 2 to 7%. The averages of results for all analytes were in good agreement with reference values. Statistical treatment of results was made. Comparison of the each result with the certified values characterizing the material has been done. Additionally, z-scores were calculated taking into account the uncertainty of a certified value and the acceptable deviation from the certified value in the range of −20% to +10% (in accordance with recommendations in the newest directives of European Union (EU) [1]); For rejecting outliers Hampel test has been applied.
Keywords: Proficiency test; Polychlorinated biphenyls; Polyaromatic hydrocarbons; Pesticides; River sediment; Soil; Gas chromatography
The role of proficiency testing in the detection and resolution of calibration bias in the LeadCare® blood lead analyzer; limitations of peer-group assessment by Noel V. Stanton; Tracy Fritsch; Ciaran Geraghty; Mary Frances Verostek; Bruce Weiner; Patrick J. Parsons (pp. 590-592).
Following implementation of the CLIA ‘88 laboratory regulations, the primary role of proficiency testing (external quality assessment, PT) in the U.S. has been widely viewed as one of assuring regulatory compliance. PT can also be an effective tool for detecting widespread analytical problems, subject to limitations based on the method of PT assigned value determination. A recent case study describes the role of two PT programs in detecting and resolving a calibration bias in the LeadCare blood lead analyzer, and illustrates the limitations of peer-group target determination in fulfilling that PT role.
Keywords: Proficiency testing; Blood lead; Target determination
Maximum permissible day-to-day imprecision and ISO 15189
by Xavier Fuentes-Arderiu; Raül Rigo-Bonnin (pp. 593-594).