Potential of Nuclear Quadrupole Resonance in Pharmaceutical Analysis

Chemistry Department, King's College, Strand, London WC2R 2LS, United Kingdom.
Analytical Chemistry (Impact Factor: 5.64). 08/2005; 77(13):3925-30. DOI: 10.1021/ac0503658
Source: PubMed


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 0.4-6 MHz, encouraging a wider range of "real world" applications. This Perspective highlights some of the advantages of NQR, the applications in which it could be used, such as the quantification of pharmaceuticals and the identification of polymorphs. Other roles could include detection, analysis, and quality control of pharmaceuticals at all stages of manufacture. Finally, recent advances which enhance even further the sensitivity of detection will be discussed.

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    • "The PSL sequence consists of This work was supported in part by the European research council (ERC, Grant agreement n. 261670), the Swedish Research Council, and Carl Trygger's foundation. a series of refocusing pulses phase shifted by 90 • relative to the first preparatory pulse θ p 0 • [2] [6]. The RF pulses applied at equal time intervals, 2τ , refocus the transverse NQR magnetization, forming a train of M echoes as illustrated in Figure 1. "
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    • "The technique is related to both nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). Unlike NMR and MRI, NQR does not require a large static magnetic field to split the energy levels of the nucleus, making it attractive as a noninvasive technique for detecting explosives in landmines and unexploded ordnance [1]–[5] or screening baggage for narcotics and explosives at airports [6], as well as a relatively inexpensive analytical technique for the structural characterization of various compounds [7], [8]. NQR signals are acquired by applying pulsed RF radiation to the sample, which drives transitions between the quadrupolar energy levels, and then measuring the responses. "
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