A 4-mm Probe for 13C CP/MAS NMR of Solids at 21.15 T

13C CP MAS NMR of halogenated (Cl, Br, I) pharmaceuticals at ultrahigh magnetic fields

“…In this work we report 13 C CP MAS NMR spectra for a number of chlorinated, brominated and iodinated compounds recorded at 21.1 T, the first time such spectra have ever been obtained at this high magnetic field. Indeed, in addition to greatly improved sensitivity, [22] outstanding 13 C NMR spectral resolution can be obtained at this field even in heavily halogenated compounds, as illustrated below. In many cases, essentially pure chemical shift spectra are observed with a resolution nearing that obtainable in liquid-state NMR spectra in solutions.…”

Incorporation of Aluminum in the Calcium Silicate Hydrate (C−S−H) of Hydrated Portland Cements: A High-Field 27Al and 29Si MAS NMR Investigation

“…A significant improvement in resolution of several resonances may be achieved by performing the MAS NMR experiments at a very high magnetic field as a result of the inverse proportionality of the second-order quadrupole interaction with the magnetic field and the increased chemical shift dispersion. Most recently, this has been demonstrated by very high-field 27 Al MAS NMR in the characterization of multiple aluminum environments in zeolite USY, 30 in aluminum orthovanadate, 31 and in an aluminoborate. 32 The advantages of employing very high magnetic fields in 27 Al MAS NMR studies of cementitious materials are illustrated in Figure 2, which compares 27 Al MAS NMR spectra of the central transition for the wPc hydrated for 12 weeks in water recorded at 7.05, 14.09, and 21.15 T. At 7.05 T ( Figure 2a) the spectral region for octahedrally coordinated Al (20 to -10 ppm) includes a narrow centerband at 13.0 ppm and two peaks with lower intensity at 8.6 and 4.0 ppm, which arise from either a second-order quadrupolar line shape from a single 27 Al site or from two different Al species, possessing rather small quadrupole couplings.…”

“…The 27 Al MAS spectra at 14.09 T were obtained in a similar manner for γB 1 /2π ) 50 kHz, γB 2 /2π ) 50 kHz, and a spinning speed of ν R ) 13.0 kHz. At the three magnetic fields, the 27 Al MAS NMR spectrum of the probe itself including an empty zirconia rotor showed a broad resonance of very low intensity. This spectrum was subtracted from the 27 Al MAS NMR spectra of the cement samples prior to the quantitative evaluation of the observed intensities.…”

“…25 This work presents the results of a 29 Si MAS and highfield (14.09 and 21.15 T) 27 Al MAS NMR investigation of the C-S-H resulting from hydration of a white Portland cement (wPc) using water and a 0.3 M aqueous solution of NaAlO 2 . The 27 Al MAS spectra demonstrate that tetrahedral Al in the C-S-H can be distinguished (and quantified) from the resonances for the Al guest ions in the anhydrous alite and belite phases. Quantitative information about Al incorporated in the C-S-H is also obtained by 29 Si MAS NMR for the two series of hydrated wPc by the observation of the Q 2 (1Al) resonance.…”

Impedance matching with an adjustable segmented transmission line

“…Here, the length of the transmission lines can be used to allow the adjustable capacitors to be located remotely from the sample coil, which is often advantageous [9,10]. While adjustable transmission lines have been used in some cases [11], most often commercial capacitors are the adjustable elements. The ''Apex" (A. Palmer) and related commercial designs (Varian Inc.) are based on concentric coaxial capacitors that exhibit some transmission line behavior [12].…”