Method uncertainty

Important part of validation procedure is prognosis (on basis of Phai macopoeial requirements and results of inter-laboratory trials) of sample preparation, final analytical operation and total uncertainties. It enables to forecast method uncertainty in control laboratories. 

For most of the methods mentioned above the method uncertainty - important for the expression of material homogeneity, better inhomogeneity - is influenced by different analytical steps such as digestion, and/or extraction, derivatization, separation etc., that are often required to achieve the final result. This consequently increases the method uncertainty. 

Author Conversion concept Sought quantity Measurands Theory of method Verification method Uncertainty analysis... 

Keywords Gamma-ray spectrometry Pulser method Uncertainty Traceability... 

The failure of the definition to stipulate a limitation of range of the relevant quantity for a traceability statement might become a serious problem. Measurement methods, uncertainties and relative capabilities vary greatly over the range of values of a quantity. 

Present-day analytical laboratories are increasingly under pressure to supply objective evidence of their technical competence, of the reliability of their results and performance, and to seek formal certification or accreditation. This pressure may come from the laboratory s customers (e.g., industry and national bodies) but may also be due to scientific considerations. A QM system in place, validation of methods, uncertainty evaluation, the use of primary standards and CRMs, participation in ILCs, and PT, all serve to assure and demonstrate the quality of measurements. Compared to, say, 30 years ago, the stability of the equipment now available is much improved, and a greater range of RMs for method validation and calibration is accessible. Nevertheless, to achieve mutual (international) acceptance of various bodies of evidence for QA activities, a number of protocols have been developed. The most widely recognized protocols used in chemical measurements and testing are the ISO Guide 9000 2000, ISO/IEC 17025 2005, and OECD Guidelines for GLP, as well as its national and sector equivalents. 

U. Kurfurst, Consideration of the uncertainty in the CRM value with the analysis of solid materials using atomic spectrometry. Part 1. Evaluation and benefit of method uncertainty using certified reference materials, Accred. Qual. Assur., 3 (1998), 406-411. 

Method uncertainty, s , The standard deviation associated with a measurement method a factor, with the sampling standard deviation, in determining the overall standard deviation of an analysis. Michaelis constant A collection of constants in the rate equation for enzyme kinetics a measure of the dissociation of the enzyme-substrate complex. 

Sampling loop A small piece of tubing used in chromatography that has a sampling valve to inject small quantities of sample. Sampling uncertainty, Sj The standard deviation associated with the taking of a sample a factor—with the method uncertainty—in detemiining the overall standard deviation of an analysis. 

Random and systematic errors are characteristics of the method, not the values. Random errors can be determined by repeating the experiment. Systematic errors can only be determined by comparisons of values determined by different methods. Uncertainties can be estimated from precision and accuracy plots if it is assumed that there are only random errors. The Ea of the d and f block elements, electronegativities, and work functions of the elements will be evaluated in this chapter using this procedure. 

Because of the imposed potential variation, the potentiodynamic technique presents similar uncertainties as the galvanostatic method. Possible desorption of the adsorbate, owing to potential change, can complicate the results. Oxide formation in certain potential regimes may be more important in the potentiodynamic than in the galvanostatic method. Uncertainties from potential and concentration variations within porous electrocatalysts can be... 

The real difficulties remain in the determination of U. It is relatively simple to determine the method uncertainty of nondestructive analysis as repeated measurements can be performed on the same sample [39]. It is far more difficult with destructive methods and in particular in organic trace analysis. In the latter case, all the steps in the procedure rarely allow one to achieve a repeatability with a relative standard deviation of less than several percent. The methods often require a large sample intake as samples of a few milligrams are not easy to handle in extraction systems. 

Establish the test method uncertainty on n experiments in the most repeatable way (see 4.3.1.1) ... 

The homogeneity has been verified at the level of intake of 0.25 g. The method uncertainty was measured by seven replicate analysis of dissolutions of a coal CRM (NBS 1632a). F and Cl were determined by ion chromatography after oxygen combustion and absorption in water cooled in ice. No in-homogeneity was detected for fluorine. For Cl, a significant difference between the CV of the method and the CV between-bottles was demonstrated the very low Cl content led to a large uncertainty of measurements which could, however, not explain the differences observed in the within- and... 

Finally, it should be noted that in many cases where < 0, is determined by the capacity method uncertainty arises, which is related to the frequency dependence of Mott-Schottky plots. (In particular, the frequency of the measuring current is increased in order to reduce the contribution of surface states to the capacity measured.) As the frequency varies, these plots, as well as the plots of the squared leakage resistance R vs. the potential (in the electrode equivalent circuit, R and C are connected in parallel), are deformed in either of two ways (see Figs. 6a and 6b). In most of the cases, only the slopes of these plots change but their intercepts on the potential axis remain unchanged and are the same for capacity and resistance plots (Fig. 6b). Sometimes, however, not only does the slope vary but the straight line shifts, as a whole, with respect to the potential axis, so that the intercept on this axis depends upon the frequency (Fig. 6a). 

Contaminants contained rather than destroyed or detoxified Increase in volume of material following treatment Some processes produce heat which can cause gaseous emissions Quality assurance measures needed, especially for in situ methods Uncertainties over long term performance, especially with organic contaminants... 

To provide as complete a model of the thermochemistry of zirconium as possible, the reviewers adopted the following approach each experiment is evaluated, reviewed, and, if necessary and possible, the results are recalculated to be consistent with other experimental conclusions and the SIT model (Appendix A). Uncertainties are assigned at this point, subjectively, if necessary. These results, with their associated uncertainties, are accepted if there is no clear reason to reject them and such data are reported in Chapter V. Accepted results are used in the determination of the relevant thermodynamic parameter or to confirm a parameter derived by other methods. Uncertainties assigned at the review stage and associated with the extrapolation to the 7=0 standard state are propagated (Appendix C), to the extent possible, throughout the procedure and the final recommended results with the associated uncertainties are given in Chapter III. In some cases, uncertainties are derived from a sensitivity analysis of the... 

The homogeneity was verified by repeated determinations of total As, arsenobetaine and DMA. The total As content was determined by HG-QFAAS after microwave assisted digestion, whereas DMA was determined by HPLC-ICP-MS. The within-bottle homogeneity was assessed by 10 determinations in each of two bottles, and the between-bottle homogeneity was evaluated by two determinations out of each 20 bottles the method uncertainty was evaluated by five replicate determinations of a digest or extract solution. The within- and between-bottle CV ranged from 0.5 to 1.2% for total As, from 2.1 to 5% for arsenobetaine, and from 7.1 to 10.6% for DMA, which was comparable to the method uncertainty (respectively 2.6, 3.1 and 6.8%) therefore, no inhomogeneity was suspected at a level of 0.3 g for total As and 1 g for As species, and the material was considered to be suitable for use as a CRM. 

Table I presents a summary of the results of the KENO-IV Monte Cario nuclear criticality calculations for the facilities and accidents considered. It. should be noted that the KENO-IV results given in Table I must be adjusted upward by adding the method uncertainty (U) (Reb. 5, 6). U is obtained using the formula U = [(K S ) + (KjSj) , where K is the one-sided 95-95 tolerance limit factor of the benchmaiik criticality calculations, S is the standard deviation of the benchmark calculations, Kj ( I -7) is the onesided 95-95 tolerance limit factor for the inidividual KENO calculations performed in this study, and S2 is the standard demtion of the individual KENO.calculation. U is thus composed of two parts. The first (K S ) is due to the spread in the individual values of keff calculated for the benchmark criticals. The seepnd (KiS is due to the statistics of the specific KENO calculation, wtuchi results from the fact that less than an infinite sample of neutron historic is calcula. There is a 95% probability with 95% confidence that the true k-effective will be less than or equal to the adjusted value given in Table I.

In addition to the adjustment of the KENO-IV results by the method uncertainty, the calculated keff for the lag storage pit must also be adjusted upward approximately 0.03 Ak to account for the fact that the water-filled spaces in the fuel assembly, which result from the removal of instrumentation and control rods, were not represented explicitly in the calculational model. The 0.03 Ak correction factor is based on independent KENO-IV calculations performed by the Westinghouse Nuclear Fuel Division. 

Solute First author Reference Code for Appendix Concentration Temperature (K) Pressure (MPa) Method Uncertainty (%)... 

The SRM 2100 results are reassuring in the sense that they are extraordinarily consistent and independent of test method. Claims of ceramic fracture toughness measurements that were accurate and precise to within a few percent were unheard of in the 1980 s and early 1990 s. It would seem that the experimental errors now have been wrung out of the individual test methods to the extent that the methods are reliable and the test method uncertainties are of the order of a few percent. The scatter of the SRM data base (Table 6) is smaller than the scatter in the VAMAS round robin (Table 1). This is not surprising since the round robin scatter included material variability, within-laboratory test method uncertainty, plus the between-laboratory method uncertainties. 

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