Polymorphism in Sulfanilamide: ¹⁴N Nuclear Quadrupole Resonance Study

To demonstrate the selectivity of ¹⁴N nuclear quadrupole resonance (¹⁴N NQR) spectroscopy in chemistry and pharmacy, a study of sulfanilamide polymorphism was undertaken. We studied 3 known polymorphs of sulfanilamide by ¹⁴N NQR. We found at room temperature 2 sets of 3 ¹⁴N NQR transition frequencies, corresponding to 2 different nitrogen sites in the crystal structure for each of 3 polymorphs. We measured the temperature dependence of all quadrupole frequencies ν⁺, ν^-. In each set, only 1 of the 3 ¹⁴N NQR frequencies is enough to characterize the polymorph. Spin-lattice relaxation time (T₁) measurement is supplemental information. We also measured the transition temperature between polymorphs and estimated the ratio of polymorphs after thermal treatment of sample.