Off-resonance effects in (14)N NQR signals from the pulsed spin-locking (PSL) and three-pulse echo sequence; a study for monoclinic TNT.

In NQR detection applications signal averaging by the summation of rapidly regenerated signals from multiple pulse sequences of the pulsed spin-locking (PSL) type is often used to improve sensitivity. It is important to characterise and if possible minimise PSL sequence off-resonance effects since they can make it difficult to optimise detection performance. We illustrate this with measurements of the variation of the decay time T2e and the amplitude of PSL signal trains with pulse spacing and excitation offset frequency for the 870 kHz ν+(14)N NQR line of monoclinic TNT under carefully stabilised temperature conditions.

(14)N NQR, relaxation and molecular dynamics of the explosive TNT.

Multiple pulse sequences are widely used for signal enhancement in NQR detection applications. Since the various (14)N NQR relaxation times, signal decay times and frequency of each NQR line have a major influence on detection sequence performance, it is important to characterise these parameters and their temperature variation, as fully as possible. In this paper we discuss such measurements for a number of the ν+ and ν- NQR lines of monoclinic and orthorhombic TNT and relate the temperature variation results to molecular dynamics.

Nitrogen-14 nuclear quadrupole resonance spectroscopy: a promising analytical methodology for medicines authentication and counterfeit antimalarial analysis.

We report the detection and analysis of a suspected counterfeit sample of the antimalarial medicine Metakelfin through developing nitrogen-14 nuclear quadrupole resonance ((14)N NQR) spectroscopy at a quantitative level. The sensitivity of quadrupolar parameters to the solid-state chemical environment of the molecule enables development of a technique capable of discrimination between the same pharmaceutical preparations made by different manufacturers. The (14)N NQR signal returned by a tablet (or tablets) from a Metakelfin batch suspected to be counterfeit was compared with that acquired from a tablet(s) from a known-to-be-genuine batch from the same named manufacturer.

Variable-pitch rectangular cross-section radiofrequency coils for the nitrogen-14 nuclear quadrupole resonance investigation of sealed medicines packets.

The performance of rectangular radio frequency (RF) coils capable of being used to detect nuclear quadrupole resonance (NQR) signals from blister packs of medicines has been compared. The performance of a fixed-pitch RF coil was compared with that from two variable-pitch coils, one based on a design in the literature and the other optimized to obtain the most homogeneous RF field over the whole volume of the coil. It has been shown from (14)N NQR measurements with two medicines, the antibiotic ampicillin (as trihydrate) and the analgesic medicine Paracetamol, that the latter design gives NQR signal intensities almost independent of the distribution of the capsules or pills within the RF coil and is therefore more suitable for quantitative analysis.

14N quadrupole resonance and 1H T1 dispersion in the explosive RDX.

The explosive hexahydro-1,3,5-trinitro-s-triazine (CH2-N-NO2)3, commonly known as RDX, has been studied by 14N NQR and 1H NMR. NQR frequencies and relaxation times for the three ν+ and ν- lines of the ring 14N nuclei have been measured over the temperature range 230-330 K. The 1H NMR T1 dispersion has been measured for magnetic fields corresponding to the 1H NMR frequency range of 0-5.

Magnetic field-cycling NMR and (14)N, (17)O quadrupole resonance in the explosive pentaerythritol tetranitrate (PETN).

The explosive pentaerythritol tetranitrate (PETN) C(CH(2)-O-NO(2))(4) has been studied by (1)H NMR and (14)N NQR. The (14)N NQR frequency and spin-lattice relaxation time T(1Q) for the nu(+) line have been measured at temperatures from 255 to 325K. The (1)H NMR spin-lattice relaxation time T(1) has been measured at frequencies from 1.

Spectral estimation of irregularly sampled exponentially decaying signals with applications to RF spectroscopy.

The problem of estimating the spectral content of exponentially decaying signals from a set of irregularly sampled data is of considerable interest in several applications, for example in various forms of radio frequency spectroscopy. In this paper, we propose a new nonparametric iterative adaptive approach that provides a solution to this estimation problem. As opposed to commonly used methods in the field, the damping coefficient, or linewidth, is explicitly modeled, which allows for an improved estimation performance.

Quantitative 35Cl nuclear quadrupole resonance in tablets of the antidiabetic medicine Diabinese.

Pulsed (35)Cl nuclear quadrupole resonance (NQR) experiments have been performed on 250-mg tablets of the antidiabetic medicine Diabinese to establish the conditions needed for noninvasive quantitative analysis of the medicine in standard bottles. One important condition is the generation of a uniform radio-frequency (RF) field over the sample, which has been achieved by two designs of sample coil: one of variable pitch, and the other a resonator that has been fabricated from a single turn of copper sheet with a longitudinal gap bridged by tuning capacitors. The results from blind tests show that the number of tablets in a bottle could be predicted to within +/-3%.

Potential of nuclear quadrupole resonance in pharmaceutical analysis.

Nuclear quadrupole resonance is a radio frequency (rf) spectroscopic technique, closely related to NMR, which can be used to detect signals from solids containing nuclei with spin quantum number >1/2. It is nondestructive, highly specific and noninvasive, requires no static magnetic field, and as such is currently used in the detection of explosives and narcotics. Recent technological advances in pulsed NQR methods have shortened detection times, eliminated spurious signals, and enhanced the sensitivity of detection of 14N frequencies, which lie in the low rf range of 0.