Directional selection, definition

The kinetics of OZ formation is entirely different from those discussed before (Fig. 23, C). The initial section of the curves is characterized by the appearance of induction period up to 15 min. These results unambiguously point out that the catalyst direct selectively the process to the oxidation of the isopropyl substituent in the cumene molecule and only after the accumulation of a definite amount of products, which probably block the catalytic surface, the ozone attacs the benzene ring. In this case the order of activity of the samples is just opposite to that of CHP formation, i.e. 5<8<7[Pg.434]

Situation Suppose a (monovalent) ionic species is to be measured in an aqueous matrix containing modifiers direct calibration with pure solutions of the ion (say, as its chloride salt) are viewed with suspicion because modifier/ion complexation and modifier/electrode interactions are a definite possibility. The analyst therefore opts for a standard addition technique using an ion-selective electrode. He intends to run a simulation to get a feeling for the numbers and interactions to expect. The following assumptions are made ... 

Trying to determine which column is ideal for a specific analysis can be difficult with over 1000 different columns on the market [74]. A proper choice implies a definition of parameters such as column material, stationary phase (polarity), i.d., film thickness and column length. Guides to column selection are available [74,75]. The most important consideration is the stationary phase. When selecting an i.d., sample concentration and instrumentation must be considered. If the concentration of the sample exceeds the column s capacity, then loss of resolution, poor reproducibility and peak distortion will result. Film thickness has a direct effect on retention and the elution temperature for each sample compound. Longer columns provide more resolving probe, increase analysis times and cost. 

There are three important aspects of the definition. First, a catalyst may increase or decrease the reaction rate. Second, a catalyst may influence the direction or selectivity of a reaction. Third, the amount of catalyst consumed by the reaction is negligible compared to the consumption of reactants. 

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