2.6. 13C Cross-polarization, magic-angle spinning, solid-state NMR
The 13C cross polarization magic spinning solid-sate NMR
experiment was set up according to the R.E. Taylor’s method
[23]. All 13C CP MAS ssNMR experiments were performed on the
600 MHz 89 mm wide-bore Bruker Advance III spectrometer
equipped with a 4 mm HXY solid-state MAS probe set up with
two of the channels were configured for 1H and 13C. A reduced volume
rotor (50 lL) was utilized and the active volume mapped to
ensure that the active coil volume entirely contained the sample
volume. Based on these findings, prior to the addition of pre-dried
samples, polytetrafluoroethylene (10 mg) was added into the
bottom of the rotor in addition to a Teflon plug being positioned
above the sample. The rotor was weighed before and after the
addition of samples. The conditions for 13C CP MAS ssNMR were
as follows: 4096 scans, spinning rate of 12.5 KHz, acquisition time
of 0.02 s, and temperature of 278 k. A quantitative calibration
curve was made based on peak integrals (157-142 ppm) for a series
of high purity lignin samples of varying mass.