Nuclear quadrupole resonance (NQR) is used as a method for the characterization of cocrystals and crystal polymorphs. 14N NQR spectra of several cocrystals of carbamazepine have been measured together with the 14N NQR spectra of cocrystal formers. The results show that the 14N NQR spectrum of a cocrystal and the 14N NQR spectra of cocrystal formers differ well outside the experimental resolution. It is further described how the NQDR techniques, that have been used to measure the 14N NQR frequencies, can be used to check the homogeneity of a polycrystalline sample and to monitor the stability of a metastable crystal polymorph.
COBISS.SI-ID: 2502244
Nitrogen atoms are present in a number of solid explosives and illicit substances. The nuclear quadrupole resonance (NQR) spectra and spin-lattice relaxation of the nitrogen atomic nucleus N-14 can be used to characterize these compounds and to distinguish between possible crystal polymorphs. After the characteristic N-14 NQR frequencies and spin-lattice relaxation rates in a compound are determined, NQR can be used to detect this compounds and, in case of crystal polymorphs, also to determine the method of preparation. The N-14 NQR frequencies and spin-lattice relaxation rates are measured either by pulse NQR or by nuclear quadrupole double resonance (NQDR) based on magnetic field cycling. Here, we discuss several H-1-N-14 NQDR techniques which can be used to measure the N-14 NQR frequencies and spin-lattice relaxation rates under various experimental conditions. Some characteristic applications of these techniques are presented and discussed in details.
COBISS.SI-ID: 2510948