Polymorphism in Sulfanilamide: N Nuclear Quadrupole Resonance Study.

To demonstrate the selectivity of N nuclear quadrupole resonance (N NQR) spectroscopy in chemistry and pharmacy, a study of sulfanilamide polymorphism was undertaken. We studied 3 known polymorphs of sulfanilamide by N NQR. We found at room temperature 2 sets of 3 N NQR transition frequencies, corresponding to 2 different nitrogen sites in the crystal structure for each of 3 polymorphs.

(14) N nuclear quadrupole resonance study of piroxicam: confirmation of new polymorphic form V.

A new polymorphic crystal form of piroxicam was discovered while preparing crystalline samples of piroxicam for (14) N nuclear quadrupole resonance (NQR) analysis. The new crystal form, designated as V, was prepared by evaporative recrystallization from dichloromethane. Three known polymorphic forms (I, II, and III) were also prepared.

A miniaturized NQR spectrometer for a multi-channel NQR-based detection device.

A low frequency (0.5-5 MHz) battery operated sensitive pulsed NQR spectrometer with a transmitter power up to 5 W and a total mass of about 3 kg aimed at detecting (14)N NQR signals, predominantly of illicit materials, was designed and assembled. This spectrometer uses a standard software defined radio (SDR) platform for the data acquisition unit.

¹⁴N nuclear quadrupole resonance study of polymorphism in famotidine.

(14)N nuclear quadrupole resonance (NQR) in two known polymorphs of famotidine was measured. At room temperature, seven quadrupolar sets of transition frequencies (ν(+), ν(-), and ν(0)) corresponding to seven different nitrogen sites in the crystal structure of each of the two polymorphs were found. This confirms the expected ability of NQR to distinguish polymorph B from its analog A.

Zeeman shift--a tool for assignment of 14N NQR lines of nonequivalent 14N atoms in powder samples.

The use of Zeeman perturbed 14N nuclear quadrupole resonance (NQR) to determine the ν+ and ν-14N lines in polycrystalline samples with several nonequivalent nitrogen atoms was investigated. The 14N NQR line shift due to a weak external Zeeman magnetic field was calculated, assuming isotropic distribution of EFG tensor directions. We calculated the broad line distribution of the ν+ and ν- line shifts and experimentally confirmed the calculated Zeeman field dependence of singularities (NQR peaks) in cyclotrimethylenetrinitramine (RDX) and aminotetrazole monohydrate (ATMH).

Capacitor-based detection of nuclear magnetization: nuclear quadrupole resonance of surfaces.

We demonstrate excitation and detection of nuclear magnetization in a nuclear quadrupole resonance (NQR) experiment with a parallel plate capacitor, where the sample is located between the two capacitor plates and not in a coil as usually. While the sensitivity of this capacitor-based detection is found lower compared to an optimal coil-based detection of the same amount of sample, it becomes comparable in the case of very thin samples and even advantageous in the proximity of conducting bodies. This capacitor-based setup may find its application in acquisition of NQR signals from the surface layers on conducting bodies or in a portable tightly integrated nuclear magnetic resonance sensor.

Application of 14N NQR to the study of piroxicam polymorphism.

A study was conducted to test the capability of the (14)N nuclear quadrupole resonance (NQR) method to discriminate qualitatively and quantitatively among different forms of piroxicam. Samples of commercial piroxicam form I and its monohydrate were obtained on the local market. Additionally, samples of form I and II were prepared by recrystallization in 1,2-dichloroethane and ethanol, respectively.