Solvent resonance

The same principles apply to couplings from spins with/> 1/2, where these are not seriously affected by relaxation. Figure Bl.l 1.4 illustrates a connnon case. The solvent resonance at 30 ppm is a 1 3 6 7 6 3 1... 

Figure 3.30. (a) UV-vis absorption spectra of the HPAA product (solid line) and the HPDP substrate (dash line) in a H20/MeCN (1 1) mixed solvent, (b) Picosecond time-resolved resonance Raman (ps-TR ) spectra of HPDP obtained with a 267 nm pump and 200 nm prohe wavelengths in a HjO/MeCN (1 1) mixed solvent. Resonance Raman spectrum of an authentic sample of HPAA recorded with 200 nm excitation is displayed at the top. (Reprinted with permission from reference [49]. Copyright (2006) American Chemical Society.)... 

SFC-NMR was used for the separation and identification of a mixture of five vitamin A acetate isomers using supercritical CO2 as the eluent [74], An advantage pointed out in this report is the lack of a solvent resonance, eliminating the need for solvent suppression and allowing unrestricted observation of the entire... 

Figure 6.36 500 MHz H NMR spectra obtained during a stop-flow LC-NMR experiment on a 1 mg injection of a crude sample of a drug compound, (a) LC chromatogram, (b) spectram corresponding to the parent bulk drug compound acquhed for 64 transients and (c) to the impurity peak RRT 0.87 (—3% by area), acquhed for 1024 transients. NOESY-type presaturation was used to suppress the solvent resonances. Bruker DRX500 H/ C 4-mm z-gradient probe with a 120 pi active cell volume.

Fig. 10. Proton NMR spectra at 220 Me of cyanoferriporphin and porphin zinc(II). The lines between —4.5 and —9.5 ppm correspond to the solvent resonances and their spinning side-bands...

The use of pyridine as solvent dramatically alters the spectral properties of the iron complex of octamethylcorrole. Such a spectrum is reported in Fig. 20 and pertinent data in Table 12. The three resonances (A-C) observed at low field have been attributed to the methyl substituents, the fourth resonance probably being located in the diamagnetic region obscured by the solvent resonances. 

The position of the solvent resonances depend on pH, solvent compositions and temperature. Especially in gradient separations the exact solvent composition in which the sample is dissolved is unknown. In addition, variation in the solvent position (which also depends on variations in other parameters) is strong. Depending on the absolute composition and temperature, a solvent change of 1 % can already shift the acetonitrile signal by more than 15 Hz. The complexity of the dependency of the solvent signals on the conditions makes it absolutely necessary to adjust the parameters for each sample individually. The adjustment procedure consists of the following steps ... 

The simplest of these is continuous-flow detection, but this is usually only practical when using H or 19F NMR for detection unless isotopically enriched compounds are available. However, there are examples of HPLC-NMR studies using 2H and 31P NMR detection in the drug metabolism field. Where continuous-flow NMR detection is used for gradient elution, the NMR resonance positions of the solvent peaks shift with the changing solvent composition. For effective solvent suppression, these solvent resonance frequencies must be determined as the chromatographic run proceeds. 

Not evaluated. Not evaluated due to overlap with solvent resonance. 

Solvates (hydrates) Same as for true polymorphs 0.5-2 Unique solvent resonances, shifted drug resonances, solvent mobility may be assessed 0.5-5 Solvent bands and shifted absorption bands due to H-bonding interactions 5-10... 

Isomorphic desolvates Substantial overlap of diffraction pattern (poorly distinguished) 0.5-2 Solvent resonances disappear. Drug resonances shift significantly relative to X-ray 0.5-5 Solvent bands disappear, chug bands shifted, highly similar to parent solvate spectra 5-10... 

Fig. 2. 13C Gel-phase NMR spectra of modified polystyrene-2%-co-DVB in CDCI3 at 75 MHz. (a) Merrifield resin (b) epoxy alcohol bound polymer at room temperature (c) epoxy alcohol bound polymer at 50°C (d) model compound in solution. The solvent resonance is marked with an asterisk. (Reproduced from Shapiro and Gounarides4 with permission.)...

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