Contact time experiments

In order to conceive the contributions of the various species to every band, the spectra are deconvoluted. After deconvolution of the recorded spectrum into a sum of Gaussian curves, the different contributing signals can be integrated separately. For quantitative assessment some contact time and cross-polarization criteria have to be met. Optimal conditions are obtained from a variable contact time experiment. Full details have been worked out by Pfleiderer23 and Caravajal et al.21,22 In general, quantitative correlations should only be made for species within one spectrum and not... 

Cera E, Bruno J, Duro L, Eriksen T. (2006) Experimental determination and chemical modelling of radiolytic processes at the spent fiiel/water interface. Long contact time experiments. Swedish Nuclear Fuel and Waste Management Co, TR-06-07. 

When attempting quantitation of a mixture of polymorphs, the first step is to identify which peaks are due to each polymorph, and to select two well-resolved peaks corresponding to the same carbon in each polymorph. A multiple-contact time experiment is then acquired to determine the rates of magnetization transfer (7ch) and decay (Tip) for each form. If these rates are identical in each form, direct integration of the peaks will provide quantitative data, with the relative areas representing the amount of each form present in the mixture. An example of the results of a multiple-contact time experiment is shown in Fig. 2—a plot of the natural logarithm of relative peak area as a function of contact time for neotame forms A and It is clear from this plot that spectra acquired at any contact time will not give equal peak area for both forms. 

Fig. 2 Plot of the results of a multiple-contact time experiment of neotame polymorphic forms A and G showing buildup and decay of magnetization as a function of contact time. (From Ref. l)...

The H- Si cross-polarisation time constants (Ts,h) associated with the Q species of both the 5% V-MCM and the standard MCM-41 calcined samples have been derived from variable-contact-time experiments. These values can be viewed as an indication of how fast the transfer of polarisation from protons to silicons occurs. The value for the 5% V-MCM sample is of the order of 0.15 ms, whereas for the standard sample it is 20 times greater, about 3 ms. 

Oxidation-reduction potential measurements were made with a platinum-calomel electrode system connected to a Beckman Model H-2 pH meter. The buffered bacterial suspensions were similar to those in the dose-contact time experiments. To these suspensions, successive equal aliquots of an ozone solution were added at 1°, and the oxidation-reduction potential was measured in millivolts. 

To obtain additional information about ozone activity at the concentrations of greatest biological interest, oxidation-reduction potentials of buffered bacterial suspensions were determined after addition of various amounts of ozone. It was reasoned that the oxidation-reduction potential at or close to the lethal concentration would exhibit a demonstrable change indicative of the corresponding activity. Figure 2 presents the results of the experiment there is a sharp break in the redox potential at an ozone concentration comparable to the level found to represent the lethal dose in the dosage-contact time experiments. A differential plot of the same data emphasizes this information (Figure 3). 

More information on the chemical structure of bone apatite can be obtained from H—> P CP. First, consider the dependence of peak intensity J(f) on contact time t (also denoted CT) in the conventional variable-contact time experiment (Fig. 11). Such an experiment monitors the CP kinetics, which is very specific for a particular material [12]. There are two models of the CP kinetics, I-T-S and I-S [12]. In this notation, the spin polarization is transferred from spins I to spins S, in our case from protons to P, respectively. 

Figure 24.8 C-NMR CP/MAS spectra with variable contact-time experiment (VCT) (a) SBR, (b) SBR/TiC>2 nanocomposite and (c) SBR/Ti02...

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