Crystallization of an amorphous solid studied by nuclear quadrupole double resonance

Nuclear quadrupole double resonance (NQDR) is proposed as a method for quantitative observation of crystallization of amorphous solids. NQDR signals from amorphous and crystalline parts of a sample may be separated. The intensity I of the NQDR signal from the crystalline part of the sample is proportional to its mass. With increasing time the amorphous phase in the sample transforms to the crystal phase and the intensity I approaches its limiting value I-0 corresponding to the complete transformation to the crystal phase. The ratio I/I-0 is equal to the mass fraction of the crystalline part of the sample. The same experimental method can be used to determine the mass fraction of a given crystal polymorph in a mixture of crystal polymorphs. As an example we studied crystallization of amorphous nifedipine at 100 degrees C. The results of the NQDR study are compared to the published results of other studies. (c) 2013 Elsevier B.V. All rights reserved.