Line-shape analysis, solid sample

In the solid, dynamics occurring within the kHz frequency scale can be examined by line-shape analysis of 2H or 13C (or 15N) NMR spectra by respective quadrupolar and CSA interactions, isotropic peaks16,59-62 or dipolar couplings based on dipolar chemical shift correlation experiments.63-65 In the former, tyrosine or phenylalanine dynamics of Leu-enkephalin are examined at frequencies of 103-104 Hz by 2H NMR of deuterated samples and at 1.3 x 102 Hz by 13C CPMAS, respectively.60-62 In the latter, dipolar interactions between the 1H-1H and 1H-13C (or 3H-15N) pairs are determined by a 2D-MAS SLF technique such as wide-line separation (WISE)63 and dipolar chemical shift separation (DIP-SHIFT)64,65 or Lee-Goldburg CP (LGCP) NMR,66 respectively. In the WISE experiment, the XH wide-line spectrum of the blend polymers consists of a rather featureless superposition of components with different dipolar widths which can be separated in the second frequency dimension and related to structural units according to their 13C chemical shifts.63... 

Molecular Weight Dependence of Phase Structure. Similar line shape analysis was performed for samples with molecular weight over a very wide range that had been crystallized from the melt. In some samples, an additional crystalline line appears at 34.4 ppm which can be assigned to trans-trans methylene sequences in a monoclinic crystal form. Therefore the spectrum was analyzed in terms of four Lorentzian functions with different peak positions and line widths i.e. for two crystalline and two noncrystalline lines. Reasonable curve fitting was also obtained in these cases. The results are plotted by solid circles on the data of the broad-line H NMR in Fig. 3. The mass fractions of the crystalline, amorphous phases and the crystalline-amorphous interphase are in good accord with those of the broad, narrow, and intermediate components from the broad-line NMR analysis. 

In the solid state, all interactions contribute to the line shape. The resulting spectrum is usually observed as a very broad line, which in many cases is useless in subtle structural analysis of phosphorus compounds.15 Figure 1A shows a typical 31P NMR spectrum recorded without sample rotation (static spectrum). 

Fig. 8.5. Solid-state N NMR spectra obtained from the oriented [ N]Gly silk fibroin fiber sample. Spectra were observed with the fiber axis both (A) parallel and (B) perpendicular to the magnetic field. The best-fit simulated line shapes are superimposed on the experimental spectra. Parameters for spectral simulation were found from error analysis as a function of ap and Pf(C).

As early as 1997, Taylor et al. [57] demonstrated the gradient separation of corticosteroids in extracts of equine urine and plasma (Figure 10). The sample were purified using solid-phase extraction and automated dialysis, respectively. A reproducibility study revealed that peak broadening occurred only after the analysis of 200 urine extracts. Later, Stead et al. observed that on-line sample concentration could be easily achieved, as longer injection times had minimal influence on peak shape [58]. They demonstrated that the CEC separation of steroids in plasma was superior to HPLC. Several other groups also reported successful CEC separations of drugs and major metabolites in extracts of urine and plasma [59-62],... 

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