CASE with high accuracy data

Mass spectrometry will rarely deliver as much structural information as alternative techniques such as NMR and it is thus unrealistic to expect that one could achieve the success rates of CASE via NMR with MS, even with high accuracy MS data. However, there is still plenty of room for improvement and the development of new methods for accurate data will be a field worth following over the next 10 years. 

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It is important to realize that when graphs are made or numerical analysis is performed to fit data to the rate laws, the points are not without some experimental error in concentration, time, and temperature. Typically, the larger part of the error is in the analytical determination of concentration, and a smaller part is in the measurement of time. Usually, the reaction temperature does not vary enough to introduce a significant error in a given kinetic run. In some cases, such as reactions in solids, it is often difficult to determine the extent of reaction (which is analogous to concentration) with high accuracy. 

Even if the flow conditions of liquids on the microscale are almost laminar and therefore numerical simulations with high accuracy are applicable, there are several reasons for the basic necessity for experimental flow visualization. In most cases, for instance, the exact data of geometries and wall conditions of microchannels and data on chemical media such as diffusion coefficients and reaction rates are unknown. Furthermore, in cases of chemical reactions, the interaction between mass transport and conversion are not calculable to date, especially if simultaneous catalytic processes take place. Therefore, the visualization of microscale flow is a helpful tool for understanding and optimizing microchannels. 

It is often more advantageous to use comparative methods, that is, to work with the mixture of the two compounds in the experiments, which ensures identical experimental conditions for the parallel reactions. The isotope competition method does not require pure isotopic compounds, it can be used even with compounds of natural isotopic composition, and thus it can be applied to the determination of C, N, and 0 isotope effects. However, the isotopic composition must be measured with high accuracy, in the case of stable isotopes usually by mass spectrometry, in the case of radioisotopes by measuring the change in the specific activity. In order to obtain the kinetic isotope effect, one needs to determine the isotopic composition of the test compound, first at the start of the reaction then again after the reaction has taken place to a known extent. The isotope effect can also be obtained from the isotopic analysis of the reaction products. In the latter case, the method of the evaluation of k /k from the experimental data can be found, for example, in the book of Vertes and Kiss (1987). 

Figure 5.6 reports the predicted product yields and their comparison with real values. In this case, Castiglioni (1983) correlation resulted to be the worst, while Volk et al. (2002) and Smith et al. (2006) approaches predicted the yields with high accuracy. Unfortunately, the range of pressure and temperature at which Castiglioni (1983) correlations are reported is lower than those of the available commercial data, and extrapolations were necessary to calculate product yields, which introduces more error. Also, it has to be commented that the data used for this comparison were taken from the work reported by Volk et al. (2002), and that may be the reason for the better predictability observed with their correlation. 

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