Evaluation of Experimental Results

The objective of any review of experimental values is to evaluate the accuracy and precision of the results. The description of a procedure for the selection of the evaluated values (EvV) of electron affinities is one of the objectives of this book. The most recent precise values are taken as the EvV. However, this is not always valid. It is better to obtain estimates of the bias and random errors in the values and to compare their accuracy and precision. The reported values of a property are collected and examined in terms of the random errors. If the values agree within the error, the weighted average value is the most appropriate value. If the values do not agree within the random errors, then systematic errors must be investigated. In order to evaluate bias errors, at least two different procedures for measuring the same quantity must be available. 

A very useful tool in establishing the accuracy and precision of a measurement is a timeline of all the measurements. Very often, a technique will improve over time 

The experimental procedures for obtaining ECD and NIMS data have been described. Examples of the calculations are given for the various classes of molecules. For each group specific test molecules are provided. The aromatic hydrocarbons and aldehydes are Eql(l/lor 1/2) molecules, CS2 is a Eql(2/2) molecule, haloalkanes are DEC(l) molecules, and the halobenzenes and nitromethane are DEC(2) molecules that dissociate via a molecular ion. A graphical procedure for obtaining parameters from ECD data and the calibration of NIMS data using SF6 and nitrobenzene is presented. The use of multiple electron affinities of O2 to define negative-ion states from ECD data is illustrated. A method for the analysis of published NIMS spectra measured at two temperatures reveals the electron affinities of molecules when combined with substitution effects. We then explored the use of precision and accuracy plots and timelines for the evaluation of electron affinities. 

Laramee, J. A. Mazurkiewicz, P. Berkout, V., and Deinzer, M. L. Discrete Electron Capture Negative Ion Mass Spectrometry, in Encyclopedia of Analytical Chemistry, New York Wiley, 2000. 

Stemmier, E. A. and Hites, R. A. Electron Capture Negative Ion Mass Spectra. New York New York, VCH, 1988. 

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For the evaluation of experimental results the use of dimensionless quantities is preferred. 

This exercise will develop your understanding of some of the practical skills involved in acid-base titrations and the processing and evaluation of experimental results. 

It may seem perverse to end such a comprehensive and critical account of the preclinical testing of biopharmaceuticals with ideas that are directed as much at the what and how to investigate as at the ultimate evaluation of experimental results. But, as the depth of the opening quotation subtly suggests, it is essential to consider and reconsider the objectives of toxicity experiments before it is possible to decide the value of their results in permitting safe and effective development of these novel and sometimes surprising products. 

Most electrochemical studies carried out today make use of online computers for control of experiments and for data acquisition and analysis, including the techniques described earlier. Examples of the application of computer evaluation of experimental results include, for instance, pattern recognition [151] and the recording of current-time profiles of the form A(lni)/A(lnt) versus t for mechanistic classification [152] as well as nonlinear regression techniques [153-155]. Efforts have also been made to use knowledge-based systems for the elucidation of reaction mechanisms [156]. 

The boiling point method connected with the evaluation of experimental results according to the method of Motzfeldt et al. (1977) was applied to the determination of vapor pressure of various molten salt systems at a temperature range of 600-1200°C. The most accurate results were, however, obtained by computer fitting of the complete Eq. (7.19) using a sophisticated computer program developed by Hertzberg (1983). 

One problem which may arise in the evaluation of experimental results is that the high-pressure limit may not be attainable with the available experimental techniques, particularly at high temperatures or for small molecules. It is then necessary to obtain by one of the extrapolation methods mentioned in Section 3. We wish to stress that a reliable experimental value for k in such situations can be obtained only if a substantial fraction of the fall-off range near to the high-pressure limit has been investigated, whichever method of extrapolation one uses. This has not been remembered by all authors, but we shall quote in this review Arrhenius parameters, in general, as given in the literature, without corrections. 

One of the most important properties of an analytical method is that it should be free from systematic error. This means that the value which it gives for the amount of the analyte should be the true value. This property of an analytical method may be tested by applying the method to a standard test portion containing a known amount of analyte (Chapter 1). However, as we saw in the last chapter, even if there were no systematic error, random errors make it most unlikely that the measured amount would exactly equal the standard amount. In order to decide whether the difference between the measured and standard amounts can be accounted for by random error, a statistical test known as a significance test can be employed. As its name implies, this approach tests whether the difference between the two results is significant, or whether it can be accounted for merely by random variations. Significance tests are widely used in the evaluation of experimental results. This chapter considers several tests which are particularly useful to analytical chemists. 

The serious problem of arsenie pollution in soils and subsurfaee waters due to mineral dissolution, use of arsenical pesticides, disposal of fly ash, and mine drainage is well known all over the world. Even homogeneous phase speciation of arsenic species in aqueous solutions is very complicated, because this trace element exists in different redox and multistep aeid-base dissociation equilibrium states. A wide range of adsorbents and several methods, such as spectroscopic techniques (FTIR, Raman, X-ray absorption speetra [XAS] extended X-ray absorption fine structure [EXAFS]), elecfrophoresis, in addition to adsorption measurements were used to study the sorption of arsenite and arsenate. Several noteworthy applications of SCMs for evaluation of experimental results are known. One of them is an exeellent example for... 

Evaluation of Experimental Results for the Range of Low and Moderate Phase Flow Ratios Xq at Flooding Point... 

One of the most general treatments of this problem is given by Goldstein and Michalik (1). This treatment has several drawbacks, however. First, it is not possible to introduce corrections for the fact that actual polarizers and analyzers do not work ideally and, secondly, this theory gives only certain special scattering components (V, H, V and H] ) Besides, the assumptions of Goldstein and Michalik are of such a general nature that an evaluation of experimental results in terms of their theory does not lead to more than certain parameter values. Hence this theory is not much used. 

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