HR-MAS NMR

TLC plates are of particular interest as substrates for spectroscopy (i) as a storage device for offline spectroscopic analysis (ii) for efficient in situ detection and identification and (iii) for exploitation of spectroscopic techniques that cannot be used in HPLC. Thin-layer chromatography combined with HR MAS (NMR) can be used for compound identification without the need for elution from the stationary phase [413]. Recently also TLC-XRF was found suitable for in situ TLC imaging of elements [414]. The combination... 

Fig. 1.25 Gel-phase H HR-MAS NMR spectrum of resin containing pyridyl ligand (3) and the enol ether side-product (13).

NMR spectroscopy [225]. The measurement of enantiomeric excesses of supported substrates has also been achieved by HR-MAS NMR [226]. 

P. Rousselot-Pailley, D. Maux, J. M. Wieruszeski, J. L. Aubagnac, J. Martinez and G. Lippens, Impurity detection in solid-phase organic chemistry Scope and limits of HR MAS NMR,... 

J. S. Fruchart, G. Lippens, C. Kuhn, H. Gras-Masse and O. Melnyk, Solid-phase enolate chemistry investigated using HR-MAS NMR spectroscopy, J. Org. Chem., 2002,67, 526-532. 

B. Combourieu, J. Inacio, A. M. Delort and C. Forano, Differentiation of mobile and immobile pesticides on anionic clays by 1H HR MAS NMR spectroscopy, Chemical Communications, 2001, 2214-2215. 

A. J. Simpson, W. L. Kingery, D. R. Shaw, M. Spraul, E. Humpfer and P. Dvortsak, The application of H HR-MAS NMR spectroscopy for the study of structures and associations of organic components at the solid-aqueous interface of a whole soil, Environ. 

Shintu, L., Caldarelli, S., and Franke, B. M. (2007). Pre-selection of potential molecular markers for the geographic origin of dried beef by HR-MAS NMR spectroscopy. Meat Sci. 76, 700-707. 

Figure 3.5. (A) JH NMR spectrum of the Brooksville fulvic acid (BFA) dissolved in d6-DMSO and (B) HR-MAS NMR spectrum of the BFA-clay complex swollen in g 6-DMSO. Inset shows that lower abundance aromatic species are present in the spectrum in part B. Reprinted from Simpson, A. I, Simpson, M. I, Kingery, W. L., Lefebvre, B. A., Moser, A., Williams, A. I, Kvasha, M., and Kelleher, B. R (2006). The application of 1H high-resolution magic-angle spinning NMR for the study of clay-organic associations in natural and synthetic complexes. Langmuir 22,4498 1503, with permission from the American Chemical Society.

Structural studies of whole soils and sediments by NMR have been limited to solid-state and HR-MAS NMR techniques due to the limited solubility of whole samples. Although solid-state spectra are typically less resolved than those acquired using... 

Figure 15.7. XH HR-MAS NMR of a forest soil. (Top) Sampled and analyzed as is after the addition of 10 pi of D20 as a lock signal. Resonances in the top spectrum are those that are in contact with water, and thus at the soil-water interface. (Bottom) Same sample as top, but freeze-dried and swollen in DMSO-d6. Note that DMSO is an excellent swelling solvent and penetrates into both the polar and hydrophobic domains in NOM (Simpson et al.,2001b). See color insert.

HR-MAS NMR spectroscopy. Applications to whole soils (Simpson et al., 2001b) are discussed in Section 15.3.3, and applications to organo-mineral interactions (Simpson et al., 2006b) are covered in Section 15.4.3. 

Figure 15.15. ll HR-MAS NMR spectra of a whole soil swollen in D20 and doped with trifluralin (A). II HR-MAS spectra whole soil swollen in D20 (B). For C-III and C-IV, dashed lines indicate the unbound trfluralin while solid lines with brackets indicate the bound trifluralin. protons II are masked by the ahphatic signals from the soil. Reprinted from Simpson, A. J., Kingery, W. L., Shaw, D. R., et al. (2001b).The apphcation of H HR-MAS NMR spectroscopy for the study of structures and associations of organic components at the solid—Aqueous interface of a whole soil. Environ. Sci. Technol. 35, 3321-3325, with permission from the American Chemical Society. 

NMR can provide detail regarding the types of NOM structures that are preferentially sorbed to mineral surfaces in soils and sediments. Simpson et al. (2006b) used H liquid-state and HR-MAS NMR methods to study the sorption of model compound mixtures to calcium-saturated montmorillonite. The model compound mixture included one representative compound from each of the following structural classes sugars, lignin, peptides, and long-chain aliphatics. After sorption, the supernatant was analyzed by liquid-state NMR and the organo-mineral complex... 

Figure 15.19. H liquid-state NMR spectra of peat humic acid (PHA) that did not sorb to clay minerals (material remaining in the supernatant) and H HR-MAS NMR spectra of sorbed peat humic material to kaolinite and montmorillonite. The signal from DMSO-d6 is labeled with an asterisk. Reprinted from Feng, X. J., Simpson, A. X, and Simpson, M. X (2006). Investigating the role of mineral-bound humic acid in phenanthrene sorption. Environ. Sci. Technol. 40,3260-3266, with permission from the American Chemical Society.

Deshmukh, A. P., Simpson, A. J., and Hatcher, P. G. (2003). Evidence for cross-linking in tomato cutin using HR-MAS NMR spectroscopy. Phytochemistry 64,1163-1170. 

Kelleher, B. E, Simpson, M. J., and Simpson, A. J. (2006). Assessing the fate and transformation of plant residues in the terrestrial environment using HR-MAS NMR spectroscopy. Geochim. Cosmochim. Acta 70,4080 094. 

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