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.7, #3)
Uncertainty budgeting at a field laboratory made simple: combining the uncertainty of the field measurement and of the ”stated reference”?
by Paul De Bièvre (pp. 89-89).
Should non-significant bias be included in the uncertainty budget? by A. Maroto; Ricard Boqué; Jordi Riu; F. Xavier Rius (pp. 90-94).
The bias of an analytical procedure is calculated in the assessment of trueness. If this experimental bias is not significant, we assume that the procedure is unbiased and, consequently, the results obtained with this procedure are not corrected for this bias. However, when assessing trueness there is always a probability of incorrectly concluding that the experimental bias is not significant. Therefore, non-significant experimental bias should be included as a component of uncertainty. In this paper, we have studied if it is always necessary to include this term and which is the best approach to include this bias in the uncertainty budget. To answer these questions, we have used the Monte-Carlo method to simulate the assessment of trueness of biased procedures and the future results these procedures provide. The results show that non-significant experimental bias should be included as a component of uncertainty when the uncertainty of this bias represents at least a 30% of the overall uncertainty.
Keywords: Keywords Bias; Uncertainty; Assessment of trueness
Chemical metrology, chemistry and the uncertainty of chemical measurements by John L. Love (pp. 95-100).
Chemical results normally involve traceability to two reference points, the specific chemical entity and the quantity of this entity. Results must also be traceable back to the original sample. As a consequence, any useful estimation of uncertainty in results must include components arising from any lack of specificity of the method, the variation between repeats of the measurement and the relationship of the result to the original sample. Chemical metrology does not yet incorporate uncertainty arising from any lack of specificity from the method selected or the traceability of the result to the original sample. These sources of uncertainty may however have much more impact on the reliability of the result than will any uncertainty associated with the repeatability of the measurement. Uncertainty associated with sampling may amount to 50–1000% of the reported result. Chemical metrology must be expanded to include estimations of uncertainty associated with lack of specificity and sampling.
Keywords: Keywords Metrology; Sampling; Chemical; Specificity; Uncertainty
Metrological role of neutron activation analysis. III. Role of INAA in sampling behavior characterization by W. Tian; Bangfa Ni; Yangmei Zhang; Lei Cao; Pingsheng Wang (pp. 101-105).
The minimum sample size, usually 100 mg or larger, is often the only information given on certificates of existing certified reference materials (CRMs) to describe sampling behavior. This value is not only too large for quality control requirements of microanalysis, but also too general to reflect the strong element-specific nature of the sampling behavior of solid materials. In this paper, the third and final of the series, we explain the need for CRMs with sampling behavior characterized for individual elements and describe the unique role of instrumental neutron activation analysis in sampling behaviour characterization.
Keywords: Keywords Certified reference materials; Quality control; Sampling constant; Instrumental neutron activation analysis
Quality assurance for the analytical data of micro elements in food by Zhengzhi Hu; L. Liu (pp. 106-110).
The micro element content of food is an important quality index due to the action of these elements on human health. In this article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment of the final analytical result, and quality assurance system are briefly described.
Keywords: Keywords Quality assurance; Analytical data; Micro elements; Food testing
Application of isotope dilution mass spectrometry to research of certified reference materials by Mo-tian Zhao; J. Wang; Baikeng Lu; Jianmin Ji; Yanjuan Zhang (pp. 111-114).
This paper briefly describes the method and applications of isotope dilution mass spectrometry(IDMS). Primary standard solutions with various natural isotope abundances were used to certify the concentration of enriched isotope solutions by IDMS. Then these enriched isotopes were used to certify unknown samples by IDMS. Li, K, Mg, Fe, Cu, Ni, Cd, Mo, Pb, etc in CRMs were certified and very good results were obtained in three international comparisons by IDMS.
Keywords: Keywords Isotope dilution mass spectrometry; Ionization enhancing agent; Certified reference material; International comparison
Study of the uncertainty in gravimetric analysis of the Ba ion by Y. Li; Guanghui Tian; Naijie Shi; Xiaohua Lu (pp. 115-120).
The determination of barium by the gravimetric method, in which the precipitation of BaSO4 was formed and weighed, coupled with instrumental measurement of trace constituents was studied. The analyte’s remaining in the filtrate and washes, mechanical loss, contaminants in the precipitate are the main influencing factors of uncertainty. A series of condition tests have been done, to reduce the effect of the factors mentioned above and the optimum test condition was found. The determination was carried out with a strictly defined operational procedure. The trace amounts of barium in the filtrate, washes and mechanical loss were determined by ICP-AES, the chloride occluded in the precipitate was determined by ion chromatography (IC), calculated as BaCl2 and barium, and sodium by FAAS, calculated as Na2SO4. The average mass of barium in the filtrate contributes about 0.06% relative to that of the total barium, in washes about 0.09%, mechanical loss about 0.06%, contaminants of BaCl2 about 0.08% and Na2SO4 about 0.05%. All the trace constituents were determined and corrected on a sample-by-sample basis. Sources of uncertainty were assessed thoroughly. The uncertainty of this combined gravimetric-instrumental method was improved remarkably compared with that of gravimetric method alone. The expanded uncertainty (k =2) is 0.08%.
Keywords: Keywords Gravimetry; Uncertainty; Barium; Traceability
Traceable property values of in-house reference materials by I. Kuselman; Alexander Weisman; Wolfhard Wegscheider (pp. 122-124).
The traceability of in-house reference materials (IHRM) is discussed. It is shown that a systematic error in results of a measured value, specific to a measurement method or to a laboratory developing an IHRM, can be overcome if a comparative approach to IHRM characterization is used. A traceability chain of the value carried by the IHRM to the value carried by the reference material with higher metrological status and sufficiently similar matrix (for example, a certified reference material – CRM according to ISO Guide 30) is helpful in such a case. The chain is realized when the IHRM samples are analysed simultaneously with the CRM samples under the same conditions. This and other traceability chains necessary for the IHRM development are examined as the measurement information sources.
Keywords: Keywords Traceability; Reference materials; Uncertainty estimation; Certification; Comparative approach
Measurement uncertainty: Opinions of the Government, the Accreditation Council and the Candidate accredited laboratory
by R. G. Visser (pp. 124-125).