CP/MAS NMR at high speeds and high fields

Jakobsen, Hans J.; Daugaard, Preben; Langer, V.

doi:10.1016/0022-2364(88)90211-9

Cited by 36 publications

(29 citation statements)

References 4 publications

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“…The total integrated area of CP spectra was 0.42-0.49 of that observed for the corresponding BD spectra (i.e., CP enhancement was < 0.5 compared to a theoretical maximum of 4). The discrepancy is even larger, as CP efficiency is reduced at high spinning speeds (Jakobsen et al, 1988), and the compensating ramped-amplitude technique (RAMP) was not available on our equipment (Preston, 2001). For three other chars derived from wood in wildfires, we found that CP efficiency at 8000 Hz was 0.57-0.73 of that at 4700 Hz (unpublished results).…”

Section: Cp Efficiency For Charsmentioning

confidence: 88%

“…The areas were corrected for the SSB of the aromatic signal, by assuming equal intensity for both sidebands (Preston, 2001). The spinning speed of 8000 Hz was chosen as a compromise between reduction of SSBs vs. the loss of CP efficiency with increasing spinning speeds (Jakobsen et al, 1988). For intensity comparisons (CP vs. DD spectra with 8000 scans; CP vs. BD 720 scans) spectra were plotted in the absolute intensity mode using the Aspect computer.…”

Section: Effects Of Charringmentioning

confidence: 99%

See 1 more Smart Citation

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

Czimczik

Preston

Schmidt

et al. 2002

Organic Geochemistry

253

161

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Section: Cp Efficiency For Charsmentioning

confidence: 88%

Section: Effects Of Charringmentioning

confidence: 99%

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

Czimczik

Preston

Schmidt

et al. 2002

Organic Geochemistry

253

161

View full text Add to dashboard Cite

“…For a few samples, spectra were also recorded on Varian VXR-400S (9.4 T) and VXR-500 (11.7 T) spectrometers for comparison of the quadrupolar coupling parameters and chemical shift data determined at the lower (7.1 T) magnetic field strength. All spectrometers employed homebuilt high-speed spinning MAS probes of double air-bearing design (Jakobsen et aL, 1988a) for 7 mm o.d. (220-#1 sample volume) or 5 mm o.d.…”

Section: Zai and 29si Mas-nmr Spectroscopymentioning

confidence: 99%

“…These high spinning speeds ensured efficient suppression of dipolar interactions with abundant spin I = 1/2 nuclei (1H) and paramagnetic sites or ions. Furthermore, the intensities of interfering spinning sidebands for the central 27A1 transition were reduced and the quality of the experimental spectra greatly improved (Jakobsen et al, 1988a). Zirconia (PSZ-700 HP) 7-ram rotors and a spinning speed of 7.2 kHz were used for 29Si observation and Si3N4 7-ram rotors with a speed of 9-10 kHz for the 27A1 MAS experiments.…”

Section: Zai and 29si Mas-nmr Spectroscopymentioning

confidence: 99%

“…The magic angle was set by observing the rotational echoes in the FID of the 79Br resonance for KBr (Frye and Maciel, 1982) in a dynamic mode. For the 27A1 MAS experiments, the magic angle was checked and set accurately in the same manner using the 27A1 resonance for a sample of hydrated calcium aluminate cement (Ca~A1206" 6D20; Jakobsen et al, 1988a).…”

Section: Zai and 29si Mas-nmr Spectroscopymentioning

confidence: 99%

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Diagenetic Structural Transformations in North Sea Jurassic Illite/Smectite

Lindgreen

1991

Clays and clay miner.

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Abstract--The Kimmeridgian-Volgian(-Ryazanian) claystone is the principal oil source rock in the troughs of the North Sea. Randomly (R0) ordered mixed-layer illite/smectite (US) appears to have transformed to RI-(IS) or R3-(ISII) ordered simultaneously with oil generation. The proportion of illite layers in I/S increased to 95% d,aring diagenesis in these claystones. Exceptions are three samples of I/S of probably bentonitic origin; these have apparently changed during diagenesis to R0-0rdered I/S containing 40-50% illite layers. Fine fractions of the claystones dominated by I/S were analyzed by ZTAl and 29Si magic-angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, ~TFe Mrssbauer spectroscopy, and X-ray powder diffraction (XRD), and for total chemical composition. Si/AI ratios determined from MAS-NMR agree closely with those calculated from total chemical analysis; however, tetrahedral and octahedral AI occupancies were most accurately determined by NMR. An increase in the percentage of illite layers and in the ordering of the I/S was accompanied by fixation of K ~ and NH4 + in the I/S, by tetrahedral AIfor-Si substitution, and by octahedral Al-for-(Mg + Fe) substitution, resulting both in an increase of charge in the 2:1 layers and in a migration of charge from octahedral to tetrahedral sheets. The I/S of probably bentonitic origin had a larger tetrahedral and a smaller octahedral charge than expected from its content of illite layers. MAS-NMR showed a significantly higher content of tetrahedral AI (most likely in smectitic sites) than expected from the percentage ofillite layers calculated from XRD. Correspondingly, XRD of K+-saturated and glycolated specimens showed that several smectite layers possessed a significant charge. A constant b-dimension of the I/S and the presence of a significant charge in the smectite layers suggest that a transformation of smectite to illite layers in the I/S by tetrahedral Al-for-Si substitution followed by interlayer cation fixation and interlayer contraction is the most probable genesis for the I/S investigated.

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Determination of enantiomeric purity from solid‐state ³¹P MAS NMR of organophosphorus compounds

Andersen

Bildsøe

Jakobsen

1990

Magnetic Reson in Chemistry

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Phosphorus-31 Magic-Angle Spinning (MAS) NMR is shown to be an extremely useful and accurate method for the determination of the enantiomeric purity for chiral organophosphorus compounds. "P and "C chemical shielding tensors in racemic and enantiomeric crystals of organophosphorus compounds vary because of different crystal symmetries. This implies that solid-state 31P (13C) MAS spectra of an enantiomerically impure sample reveal separate signals from the racemic and enantiomer crystallites. Simple integration (or deconvolution) of the MAS NMR signals can thus be used to determine the enantiomeric purity of the sample. For organophosphorus compounds the application of this technique to 31P MAS NMR is of particular interest due to the high sensitivity and large shielding anisotropy of the 31P nucleus. KEY WORDS 31P MAS NMR Enantiomeric purity

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CP/MAS NMR at high speeds and high fields

Cited by 36 publications

References 4 publications

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

Diagenetic Structural Transformations in North Sea Jurassic Illite/Smectite

Determination of enantiomeric purity from solid‐state ³¹P MAS NMR of organophosphorus compounds

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CP/MAS NMR at high speeds and high fields

Cited by 36 publications

References 4 publications

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

Diagenetic Structural Transformations in North Sea Jurassic Illite/Smectite

Determination of enantiomeric purity from solid‐state 31P MAS NMR of organophosphorus compounds

Contact Info

Product

Resources

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Determination of enantiomeric purity from solid‐state ³¹P MAS NMR of organophosphorus compounds