Normalized signal intensity

The self-diffusion coefficient measurements were made using the pulsed-gradient spin-echo (PGSE) method which has recently been reviewed (JLL). For a nucleus in an isotropic solution, the PGSE-NMR normalized signal intensity, 1/1q is given by ... 

Figure 11.4. Effect of spin state populations (indicated by the relative thickness of the lines) on NMR signal intensity, (a) Larger than normal excess in lower state, giving enhanced absorption (b) normal slight excess in lower state, giving normal signal intensity (c) saturation, giving zero signal and (d) inverted population (excess in upper state), giving net emission.

Pig. 22. Time dependence ofthe normalized signal intensities of reactant lArl] (m/z 262, black) and product [ArBn] (m/z 226, red) formed in the Pd-catalyzed crosscoupling reaction with BnZnBr in CH3CN at room temperature as determined by ESI mass spectrometry. Results of two experiments with different catalyst loadings are shown (diamond = 100 mol%, triangle = 5 mol% relative to lArl] ). 

So that the results from the delayed-contact and variable-contact data could be compared, they were normalized to give equal signal intensities at a contact time of 0.5 ms (zero delay in the delayed-contact experiment) after the variable-contact data had been adjusted to allow for the fact that full equilibration of proton and polarisation had not quite been reached after 0.5 ms. The difference in normalised signal intensity between the variable-contact and delayed-contact experiments, at a given time point t, is then a measure of the amount of 13C cross-polarising between 0.5 ms and t. 

The most difficult materials to study by NMR microscopy are those with short T2 or T2 relaxation times and/or with low concentrations of the nudear spins, which normally result in poor NMR signal intensities. One possibility for improving the image quality is to adapt the shape and size of the rf coils to the size of the objects in order to achieve the best possible filling factor and therefore the best sensitivity [1]. In addition, methods with short echo or detection times have been developed, such... 

Thorn EMI 9235QB) near the phosphor screen to collect all of the ion signal as the probe laser was tuned over the 0(3Pj) Doppler profile at laser wavelengths of 226.23, 226.06 and 225.65 nm for j = 0, 1 and 2, respectively. The output of the photomultiplier was sent to a boxcar averager gated at the appropriate arrival time. The probe laser power was simultaneously measured with a photodiode in order to normalize the 0(3Pj) signal intensity for fluctuations in laser power. 

Theory tells us that the maximum gain in proton signal intensity is 50%, but normally we are dealing with changes of only a few per cent, and the magnitude of these is dependent on the distance between the irradiated proton(s) and the observed ones the effect is too small to be visible when this distance exceeds about 5 A. 

Of course, it is quite easy to solve the bandwidth needs of proton spectra - they only have a spread over about 20 ppm (8 kHz at 400 MHz). Things get a bit more difficult with nuclei such as 13C where we need to cover up to 250 ppm (25 kHz) spread of signals and we do notice some falloff of signal intensity at the edge of the spectrum. This is not normally a problem as we seldom quantify by 13C NMR. However, it can be a problem for some pulse sequences that require all nuclei to experience 90°... 

Shang et al. [7] studied the effect of different additives (NaAc, NaOH, NaCl, NH4Ac) on analyte signal intensity and they found that the relative intensity of NPEO adduct ions may be enhanced by all additives, but NaAc produced the most abundant adduct ions for the entire ethoxylate series with good reproducibility. Additionally, the intensity of adducts, especially for mono- and diethoxylates was found to depend on reaction time prior to LC-ESI-MS analysis and concentration of NaAc. They recommended 0.5 mM NaAc for normal-phase separation with solvent system toluene-MeOH-water. In reversed-phase systems the highest abundance of sodium adducts for NPEOs ( iEO = 1-10) was observed at concentrations higher than 10 xM, while any further increase in concentration had very low influence on signal intensity [10,11],... 

Transverse relaxation of musculature is relatively fast compared with many other tissues. Measurements in our volunteers resulted in T2 values of approximately 40 ms, when mono-exponential fits were applied on signal intensities from images recorded with variable TE. More sophisticated approaches for relaxometry revealed a multi-exponential decay of musculature with several T2 values." Normal muscle tissue usually shows lower signal intensity than fat or free water as shown in Fig. 5c. Fatty structures inside the musculature, but also water in the intermuscular septa (Fig. 5f) appear with bright signal in T2-weighted images. 

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