Magnetic Resonance Reproducibility-Based

Mansour et al. [46] developed a simple, rapid efficient quantitative proton magnetic resonance method for the determination of mefenamic acid in Ponstan capsules. The method is based on a comparison between the sum integrals of the two methyl singlets of mefenamic acid and that integral of the sharp singlet of / -methoxybenzylidenemalononitrile (internal standard). The method gave accurate and reproducible results. 

Figure 2 NMR spectra from the brain of a healthy 43 year old male human volunteer. The upper spectrum is from the cerebellum and the lower spectrum is from the occipital cortex. The spectrum was measured at 170 MHz using a 4T magnet with a 15 cm diameter semi-volume coil. Localization was achieved using a pulse sequence based on the STEAM method with a nominal volume of 27 mL. Water peak suppression used selective Gaussian pulses. Cho - choline groups, Cr - creatine, NAA - N-acetylaspartate. Reproduced with permission from Seaquist ER and Gruetter R (1998) Identification of a high concentration of scyllo-inositol in the brain of a healthy human subject using and NMR. Magnetic Resonance in Medicine 39 313-316.

The aromaticity of five-membered rings with two or more heteroatoms was discussed in detail in earlier reviews.52 100 111 In a comprehensive survey on the quantitative measurements of aromaticity,112 it has been shown that basicity-based quantification of aromaticity gave more reproducible resonance energies than other methods, such as heats of formation, ring currents, magnetic susceptibilities, and theoretical indices. 

Until now most efforts in the development of miniaturized analyzers are based on the use of photometric and electrochemical detection. During the workshop many examples will be given. It can be easily shown that miniaturizing the devices with respect to diameters of channels, injected volumes, etc. asks for a more than proportional reduction in the detector volume [6]. In this respect the important development of (ultra-) microelectrodes has to be mentioned. Because electrochemical techniques, but also optical ones like surface plasmon resonance, are essentially based on surface phenomena they are critically dependent on the condition of the sensing surfaces. As these surfaces can often easily be affected in an irreversible way, extreme care in handling is required to get reproducible results. The search for other techniques related to bulk properties of the samples should therefore be continued. These may comprise optical as well as magnetic or enthalpimetric principles. 

Figure 5.2 Examples of mass spectra collected under high-mass resolution conditions over (a) the 55.90-56.10 miq range from a Silicon wafer on a Time-of-Flight (TOF)-based SIMS instrument (Supplied by Physical Electronics), (b) the 39.962-39.966 mIq range from an Adularia mineral sample on two different IMS-1280 Magnetic Sector-based SIMS instruments (care of Cameca), and (c) the 368-372 m/q range from a rat brain section on a TOF-based SIMS instrument in imaging mode (this affects mass resolution as covered in Section 5.3.2.1.2) overlaid with that from a Fourier Transform-Ion Cyclotron Resonance (FT-ICR)-based SIMS instrument. Reproduced with permission from Smith et al. (2013) Copyright 2013 Springer.

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