Selectivity systematic deviations

As a measuring science, analytical chemistry has to guarantee the quality of its results. Each kind of measurement is objectively affected by uncertainties which can be composed of random scattering and systematic deviations. Therefore, the measured results have to be characterized with regard to their quality, namely both the precision and accuracy and - if relevant - their information content (see Sect. 9.1). Also analytical procedures need characteristics that express their potential power regarding precision, accuracy, sensitivity, selectivity, specificity, robustness, and detection limit. 

Assuming, in Table III, that represents exchangeable activity and S2 represents the net inventory of all other mechanisms, a comparison of these model-predicted inventories with those obtained by selective chemical extraction indicates that, while the overall mass balance trends are predicted, agreement in detail of individual extraction inventories with the model-predicted inventories is not always good. The overall mass balance is governed almost totally bv the higher concentration (early time) data. In the case of °Co, inspection of residual plots indicates that, in all cases, the DFO model shows small systematic deviations at early times that account for the mass... 

Control charts are used in many different applications besides analytical measurements. For example, in a manufacturing process, the control limits are often based on product quality. In analytical measurements, the control limits can be established based on the analyst s judgment and the experimental results. A common approach is to use the mean of select measurements as the centerline, and then a multiple of the standard deviation is used to set the control limits. Control charts often plot regularly scheduled analysis of a standard reference material or an audit sample. These are then tracked to see if there is a trend or a systematic deviation from the center-line. 

If regression analysis is used, a warning must be given. The method is purely mechanical and will therefore always yield a result. But if the functions chosen are not appropriate, the curve will show systematic deviations from the straight line of a wavelike character. The procedure must therefore be the following A sufficient number of (x,t) pairs is selected from the experimental material. They are inserted in the chro-nomal and the resulting, usually linear, equations are solved for the constants. 

II. 1 Neutron physical calculations of selected core configurations for burner reactors (CAPRA type) During the determination of the neutronic input data for safety related SAS4A studies systematic deviations in the power distribution for the CAPRA reference core were recognised. The detailed investigations showed that for the more complex types of CAPRA cores more refined calculational treatment is required, i.e. either a fully 3-dimensional diffusion method or even the VARIANT transport method. In the latter case, the considerable influence on control rod worths and on the sodium void effect - especially for configurations with control rods inserted (i.e. not fully withdrawn) - must be studied. 

The ideal value for W is 100%. With the aid of the recovery rate, the complete process can be assessed. If the true value is found, selectivity, accuracy, and robustness for this concentration level and this matrix under the given experimental conditions are proven. To identify a potential matrix influence, the sample matrix to be analyzed (which does not contain the analyte component) is divided into 10 equal sized portions and spiked with concentrated standard solutions, so that the component concentrations in the spiked samples and in the aqueous cahbration standards are the same. The spiked matrix samples are then analyzed with the corresponding analytical method. Ideally, the recovery function is a straight line with a residual standard deviation corresponding to the process standard deviation of the basic analytical method. In case a proportional systematic or constant systematic deviation is the result of the investigation of the matrix influence, the calibration function obtained with aqueous standards cannot be used for data evaluation the standard addition method has to be applied. 

This sensor showed good sensitivity, selectivity, and linear response in the temperature range between 823 K and 873 K [9], though its response systematically deviated from ideal Nerstian values, especially at high temperatures and low CO2 concentrations. Lee et al. [10] investigated the reasons for the non-Nemstian behavior and... 

Fig. 23b points out very clearly the systematic deviation that one would expect in attempting to fit a three-line set of raw data with a single linear regression. One may make use of the distinct nonrandomness of the residuals pattern to identify intersection points in the data set. The intersection points in the residuals pattern of Fig. 23b occur at 300 and 500, exactly the pre-selected apex values for the synthetic data set... 

The N+ relationship, as discussed above, is a systematization of experimental facts. The equation of Scheme 7-4 has been applied to nearly 800 rate constants of over 30 electrophiles with about 80 anionic, neutral, and even cationic nucleophiles covering a range of measured rate constants between 10-8 and 109s 1 (Ritchie, 1978). Only about a dozen rate constants deviated from the predicted values by more than a factor of 10, and about fifty by factors in the range 5-10. It is therefore, very likely that this correlation is not purely accidental. Other workers have shown it to be valid for other systems, e.g., for ferrocenyl-stabilized cations (Bunton et al., 1980), for coordinated cyclic 7r-hydrocarbons (Alovosus and Sweigart, 1985), and for selectivities of diarylcarbenes towards alkenes (Mayr, 1990 Mayr et al., 1990). On the other hand, McClelland et al. (1986) found that the N+ relationship is not applicable to additions of less stable triphenylmethyl cations. 

Under no circumstances should this SOP be construed to supplant or replace the judgement of the medical officers in the selection procedures, who may deviate from these guidelines at their discretion. Deviation from the SOP may also be done in a systematic way... 

Because systematic variations in selectivity with reactivity are commonly quite mild for reactions of carbocations with n-nucleophiles, and practically absent for 71-nucleophiles or hydride donors, many nucleophiles can be characterized by constant N and s values. These are valuable in correlating and predicting reactivities toward benzhydryl cations, a wide structural variety of other electrophiles and, to a good approximation, substrates reacting by an Sn2 mechanism. There are certainly failures in extending these relationships to too wide a variation of carbocation and nucleophile structures, but there is a sufficient framework of regular behavior for the influence of additional factors such as steric effects to be rationally examined as deviations from the norm. Thus comparisons between benzhydryl and trityl cations reveal quite different steric effects for reactions with hydroxylic solvents and alkenes, or even with different halide ions... 

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