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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.10, #4)
Meeting future needs for metrological traceability—a physicist’s view by L. R. Pendrill (pp. 133-139).
Metrological traceability of measurement results provides the comparability needed for reliable measurement in almost every aspect of our daily life, ranging from fundamental science, through health and safety to global trade. From the author’s (a physicist) perspective and understanding of recent literature, measurements in chemistry compare the “amount of analyte”, are often made “indirectly”, are sometimes “not fully traceable to the SI”, and metrological traceability is perhaps “not always the major concern of the practising analytical chemist”. The present article examines which of these views are typically “chemical”, and which are common to both the physicist and the chemist. Much can be gained by formulating a common understanding of basic concepts of traceability of measurement results in meeting ever-increasing demands for comparability of measurement results in both traditional as well as new areas of technology and societal concern.
Keywords: Measurement; Traceability; Comparability; Chemistry; Physics
A statistical strategy for discouraging collusion in split-level proficiency testing schemes by Weiping Wang; Jiang Zheng; Daniel W. Tholen; Zhijun Cao; Xingan Lu (pp. 140-143).
A statistical strategy for discouraging collusion in split-level proficiency testing schemes was developed. When the samples are randomly labeled, the difference in the analyte levels in the two samples can be designed to maximize the probability of detecting collusion when it occurs, so that participants who colluded cannot easily receive satisfactory assessments. This favors providing convictive assessments of participants’ proficiency and giving the participants a level playing field.
Keywords: Discourage collusion; Proficiency testing; Statistical strategy
Is odd-even effect reflected in detection limits? by Surendra P. Verma; E. Santoyo (pp. 144-148).
It is observed for the first time from an extensive compilation that the detection limit ratios for odd/even atomic number neighbour elements are generally less than 1 for nearly all-stable elements of the periodic table (most are even less than 0.5), which is very similar to the odd-even effect in cosmic abundances. This systematic behaviour of detection limits can be explained by a simple relationship with physicochemical and environmental-geological factors. We propose that such a behaviour should be used in future as a fundamental criterion to evaluate the highly variable detection limit data for all chemical elements by a given analytical technique and the estimation of detection limits should be based on at least 30 or more measurements.
Keywords: Detection limit; Trace elements; Sensitivity; ICP-MS
Uncertainty evaluation from Monte-Carlo simulations by using Crystal-Ball software by A. Gustavo Gonzalez; M. Angeles Herrador; Agustín G. Asuero (pp. 149-154).
The first Supplemental Guide to the current edition of the Guide to the expression of uncertainty measurement (GUM) deals with the propagation of distributions, and emphasizes the use of Monte-Carlo Simulation (MCS) for estimating the uncertainty of measurands. In order to carry out MCS we need computer programs for generating pseudo-random numbers and for solving numerically the integral equations arising when simulating the values of the specification variables with a given probability density function (PDF). Crystal-Ball commercial software is very suitable for performing MCS and to estimate the expanded uncertainty for the measurand. The use of Crystal-Ball is illustrated with two working examples dealing with specification models of non-linear features and with correlated variables (such as the slope and intercept of calibration straight lines), respectively.
Keywords: Propagation of distributions; Monte-Carlo simulation; Measurement uncertainty
Evaluation of analytical instrumentation. Part XVII. Instrumentation for inductively coupled plasma emission spectrometry
(pp. 155-159).
Evaluation of analytical instrumentation. Part XVIII. Differential scanning calorimetry
(pp. 160-163).
Design and preliminary evaluation of a procedure for the sampling of incoming bulk raw materials in a feedstuff factory by José Antonio Moure-Alonso; Manuel Aboal-Somoza; Pilar Bermejo-Barrera (pp. 164-171).
The sampling procedure currently applied in a feedstuff factory for incoming raw materials was compared with another sampling method (designed by the authors). The commodities considered were maize, soya and barley, and the sampling protocols were evaluated on the basis of the results obtained when samples taken by both methods were analyzed for moisture and specific gravity. The differences observed in the results obtained from samples collected by both sampling procedures were not statistically significant (two-sided t-test, α=0.05) and hence the validity of the current method was confirmed. However, the results showed that the raw materials become stratified during travel from origin to factory, and this must be taken into account. To improve the current sampling protocol, the points where samples have to be taken must be specified.
Keywords: Sampling procedure; Raw material; Feedstuff; Stratification
Validation of analytical methods used for determination of nitrate in soil by V. Kmecl; J. Sušin; L. Zupančič-Kralj (pp. 172-176).
The standard method (ISO/DIS 14255) and the quick test were used for determination of nitrate in soil. We validated both methods using parameters such as accuracy, reproducibility within 1 day and between days, limit of detection and limit of quantification. The accuracy of the results was determined using the analysis of samples from the international interlaboratory scheme WEPAL. The accuracy of the standard method was good, while for the quick test the results were not accurate. The standard method showed a solid reproducibility of measurement results (in 1 day, relative standard deviation, RSD=0.2%; between days, RSD=0.8%). The quick test gave poorer results (in 1 day, RSD=6%; between days, RSD=7%). We tried to established the compatibility of both methods on real soil samples and we were satisfied to obtain the correlation coefficient 0.98 using the regression straight line. The analyses with the quick field instrument are much simpler and cheaper than the standard laboratory analyses and can be used for advising on nitrogen fertilisation.
Keywords: Nitrogen; Validation; Segmented flow analyser; Quick field instrument