ADRF differential cross polarization spectroscopy of synthetic calcium phosphates and bone mineral

An adiabatic demagnetization in the rotating frame (ADRF) differential cross polarization (DCP), or inversion recovery cross polarization (IRCP), technique has been developed to study synthetic calcium phosphates and bone mineral. ADRF of the protons followed by a remagnetization of the phosphorus-31 spins results in an equalization of the dipolar and phosphorus Zeeman nuclear spin temperatures. By shifting the phase of the phosphorus RF by 180 degrees during the forward cross polarization it is possible to invert the temperature of this reservoir and initiate reverse cross polarization. Transient Strombotne-Hahn oscillations were observed on inverting the temperature. The presence of these oscillations complicates the determination of a null point on the basis of cross polarization times. It is necessary to shift the phase of the RF only after a Zeeman spin temperature can be defined, and to use an RF field strength that is slightly smaller than the equivalent S-spin local dipolar field in order to produce a zero crossing after the transient oscillations have decayed.