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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.10, #6)
Estimation of the uncertainty components associated with the measurement of radionuclides in air filters using γ-ray spectrometry by Marek Makarewicz (pp. 269-276).
This paper discusses and assesses the major sources of uncertainty arising in measurement of radionuclide activity concentrations in air. Besides counting statistics, the main contributors to the overall uncertainty of the activity concentration of long-lived radionuclides are the heterogeneities of the calibration source and the test samples (approximately 4%). In addition, in the case of radionuclides with half-lives of the order of days or shorter, a significant uncertainty results from the variability of the “source term” because the peak concentration of the radionuclide might occur either at the beginning or at the end of the sampling period. For131I (T1/2≈8 days), for instance, the relative standard uncertainty was estimated as 17% owing to this effect. In addition, the uncertainty introduced by the software used for evaluation of the γ-ray spectra is discussed. Details of the uncertainty components, including their assessed probability distributions and degrees of freedom, and the conversion into standard uncertainties are reported in this paper, following the ISO Guide to the expression of uncertainty in measurement. A standard form for documenting and reporting the uncertainty budged is proposed and illustrated with an example.
Keywords: γ-ray spectrometry; Air filters; Aerosol radioactivity; Uncertainty budget; Combined uncertainty
Evaluation of uncertainty sources associated with toxic trace element concentrations in rice by A. K. Ávila; T. O. Araujo; R. M. H. Borges; P. R. G. Couto; M. F. G. Rosias; O. G. F. Rocha; D. S. Vaitsman; V. Dias (pp. 277-282).
Today’s and tomorrow’s globalized world requires the acceptance of each other’s capabilities, competence and metrological traceability of measurements to the International System of Units and thus mutual acceptance of quantitative results. Therefore, mutually and publicly recognized standards and certificates are needed at national and international levels. An important step to attain this ambitious goal is to intensify regional metrological collaboration. The exercises of interlaboratorial comparisons are important as part of a system to guaranty the quality of analysis. To estimate the sources of uncertainty associated with the determination of toxic trace element concentrations in rice and to perform an interlaboratorial comparison, a sample containing cadmium, copper, lead and zinc was distributed to four Brazilian laboratories. The laboratories used atomic emission spectroscopy, graphite furnace atomic absorption spectroscopy and flame atomic absorption spectroscopy. The evaluation of the results provided by the laboratories was made by statistical and graphical methods comparing the results of each laboratory to the certified value.
Keywords: Toxic trace element; Rice; Uncertainties sources
Calibration of UV–vis spectrophotometers for chemical analysis by John F. Clare (pp. 283-288).
The spectrophotometer has become the workhorse for high-throughput routine testing for a wide variety of analytes in chemical and biochemical analysis laboratories. It is important for accuracy and reproducibility in measurement that this instrument is correctly set up and calibrated, a task which is facilitated by an understanding of the principles employed. This presentation reviews the principal issues involved: absorbance calibration, wavelength calibration, and checks for both heterochromatic and isochromatic stray light. Methods and materials for making these checks are compared and discussed.
Keywords: Spectrophotometry; Absorbance calibration; Wavelength calibration; Stray light; Operational qualification
Measurement uncertainty for total ash and acid-insoluble ash determination of Chinese materia medica by Kelvin S. Y. Leung; Kelvin Chan; Angus C. K. Lau; GuangHua Lu (pp. 289-294).
The total ash and acid-insoluble ash contents of Chinese materia medica (CMM) have been widely used as one of the indices to illustrate the quality as well as purity of herbal medicines. Such an approach has also been adopted by many official organizations in writing monographs for pharmacopoeia worldwide. In the present study, a full validation on the methodology was conducted with the inclusion of various commonly encountered matrices in herbs, namely, leaf, flower, fruit, stem and root. The practice ensures method suitability for a wider scope of matrix variation in CMM. Moreover, in order to comply with the technical requirement of International Organization of Standardization 17025 quality assurance system, the concept of measurement uncertainty has also been incorporated in the present study. Measurement uncertainties for total ash and acid-insoluble ash contents have been estimated.
Keywords: Chinese materia medica; Ash; Measurement uncertainty; Validation; Quantitative analysis
A survey of non-conformances raised during accreditation inspections of medical laboratories in South Africa. by Gurdeep Singh Dhatt; David Burnett; Sean Peters; A. W. Van Rijswijk (pp. 295-299).
Under the auspices of the South African National Accreditation System (SANAS) the South African medical laboratory accreditation programme was established in June 1999. This study reports the non-conformances identified during the assessment of 103 medical laboratories in South Africa between September 1999 and December 2001. Laboratories were assessed by SANAS, which is the single accreditation body in the Republic of South Africa. All documentation relating to the assessment of each laboratory was reviewed in detail by the authors to identify the numbers and classification of non-conformances under each of the 25 points of the check list. A total of 862 non-conformances were raised. The top five non-conformances identified were (1) quality management system, (2) test methods, (3) records and (4) quality control and laboratory safety. The deficiencies identified in South African medical laboratories should be viewed in a positive light and promote a culture of continuous quality improvement with appropriate allocation of resources. SANAS should continue to align its requirements and procedures relating to accreditation of medical laboratories with those of their international counterparts with whom mutual recognition agreements/arrangements exist.
Keywords: Accreditation; Medical laboratories; Non-conformances; South Africa; South African National Accreditation System
Further comments on the (miss-)use of r for testing the linearity of calibration functions by D. B. Hibbert (pp. 300-301).
The earlier comments of Dr Huber on the incorrect use of correlation coefficient as a test of linearity of calibration are supported with examples of curved relations leading to apparently acceptable values of r. The discussion of proper statistics that should be used is continued. It is noted that many journals do not allow correlation coefficients to be quoted in defense of linear calibrations.
Recovery revisited by René Dybkaer (pp. 302-303).
During the last decade, various IUPAC documents have presented concepts related to the important ability of a measurement procedure to provide correct quantity values for amount, concentration, or content of a component in a system. The measurement procedure often, but not necessarily, includes one or more separation steps prior to the final instrumental reading. The vocabularies present concepts with some definitions and terms that disagree or are ambiguous, mostly revolving around the term ‘recovery’ and its derivatives. The present proposal consists in defining three concepts with the terms actual quantity, initially estimated quantity, and recovered quantity ratio, where ‘quantity ’ is used in the metrological sense of the international vocabulary of basic and general terms in metrology (BIPM, IEC, IFCC, ILAC, ISO, IUPAC, IUPAP, OIML International vocabulary of basic and general terms in metrology, draft, 3rd edn. BIPM, Sèvres, 2005), not as a synonym of ‘amount’.
Keywords: Actual quantity; Initially estimated quantity; Recovered quantity ratio; Recovery; Recovery factor
Self-implementation of ISO 9001 versus external support: an examination in laboratories involved in chemical measurement by F. Javier Llorens-Montes; Antonia Ruiz-Moreno (pp. 304-307).
The purpose of this research was to study how externalizing the process of implementing ISO 9001 influences the dissemination of cultural values and practices of quality management in laboratories involved in chemical measurement. Employee attitudes and behaviors may be heavily influenced by factors such as the mix of internal workers and consultants in a work group. Some researchers have described cases in which internal workers develop negative work attitudes and behaviors from having to work with consultants and have demonstrated the need to examine the dynamics between internal workers and consultants to understand the influence of ISO 9001 externalization. Three hundred and fifty-nine useful questionnaires were received. The results showed that implementation occurs most successfully through a process of linked internalization. This category involves limiting the labor of the consultant basically to moderate advising, review and internal audit. The laboratory personnel are responsible for developing the documentation of the ISO 9001 system. The implementation process is run by the members and directors of the laboratory.
Keywords: ISO 9000; Quality management; Quality culture; Externalization; Consultants
The Australian perspective by Terry Spencer (pp. 308-314).
This presentation deals with issues of comparability and traceability in food analysis in Australia from several perspectives. This includes the current national (Australian) and increasingly international (Codex) performance-based approach to food analysis. The Australian food regulatory process will be described, particularly those aspects that impact on the analysis of food in a regulatory sense. This section will also describe two areas where specific methods have been mandated in legislation and discuss two case studies where the analytical method has impacted on the elaboration of standards. Other areas to be covered include regulation/requirements relating to supply/availability of reference materials, the use of proficiency testing as a means of ensuring comparability, and, finally, some thoughts on what role BIPM/CCQM may play in the analysis of food.
Keywords: Food analysis; Australian regulations; Reference materials; Proficiency testing
Uncertainty evaluation from Monte-Carlo simulations by using Crystal-Ball software
by A. Gustavo Gonzalez; M. Angeles Herrador; Agustín G. Asuero (pp. 324-324).