An adiabatic demagnetization in the rotating frame (ADRF) criminates between species with overlapping spectra on the differential cross polarization (DCP), or inversion recovery cross basis of their cross polarization times and allows selective polarization (IRCP), technique has been developed to study synresonances to be nulled (2-8). The technique has been varithetic calcium phosphates and bone mineral. ADRF of the protons ously called inversion recovery cross polarization (IRCP) followed by a remagnetization of the phosphorus-31 spins results (4), cross polarization with polarization inversion (CPPI) in an equalization of the dipolar and phosphorus Zeeman nuclear (5), differential cross polarization (DCP) (6), and cross spin temperatures. By shifting the phase of the phosphorus RF by polarization-depolarization (CPD) (7), in the literature. 180Њ during the forward cross polarization it is possible to invert Wu et al. were able to use the DCP technique to suppress the temperature of this reservoir and initiate reverse cross polarizathe dominant phosphate group and hence detect and identify tion. Transient Strombotne-Hahn oscillations were observed on a unique protonated phosphate present in bone mineral ex inverting the temperature. The presence of these oscillations comvivo (6).
plicates the determination of a null point on the basis of cross DCP techniques are usually derived from conventional 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 cross polarization techniques (9, 10) and require the simulta-RF field strength that is slightly smaller than the equivalent Sneous irradiation of the sample at the resonance frequencies spin local dipolar field in order to produce a zero crossing after of the two nuclei. Ideally the magnitudes of both these fields the transient oscillations have decayed. ᭧ 1997 Academic Press
should be much larger than the local dipole-dipole fields in the sample. These large fields are difficult to generate over a large volume, as is required when studying macroscopic objects. In addition, large fields are a problem when applied