PubMed · 14149321
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T KASAI. 1964. [PERSONAL EXPERIENCES WITH VERTIGO].. https://pubmed.ncbi.nlm.nih.gov/14149321/
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The behaviour of di- and tri-fluorinated-ephedrines and -norephedrines has been studied by fast atom bombardment, atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) experiments and compared with that of the unfluorinated analogues. Under all the employed ionisation conditions [MH](+) and [MH-H(2)O](+) species are mainly produced. Both high- and low-energy collisional experiments were performed on the protonated molecules to put in evidence any possible significant differences due to different ionisation methods. Multiple MS/MS experiments, performed by ion trap, allowed establishment of the decomposition pathways at lower activation energy. The data thus obtained indicate that the presence of fluorinated substituents leads to a higher stability of the molecular species, with strengthening of the C(1)-C(2) bond of the molecule and with a lower proclivity to thermally-induced dehydration.
Different strategies for the quantification of partially coeluting optical isomers have been investigated. The methods tested are based on the use of different features as the analytical UV signals: peak heights, perpendicular drop areas, first and second derivatives of the chromatograms, peak areas obtained by deconvolution of the overlapped peaks with data fitting optimization, and a multivariate model (principal component regression, PCR). The amphetamine-derivative drug pseudoephedrine was selected as a model compound. For chromatography, LiChrospher 100 RP18 and a mobile-phase consisting of methanol and a solution of carboxymethyl-beta-cyclodextrin (the chiral selector) were used. The UV detector was set at 215 nm. The accuracy obtained with the tested methods at different degrees of overlapping and at different concentration ratios between enantiomers was evaluated. The results of this study demonstrated that the best option for quantification of partially overlapped UV peaks of enantiomers and to obtain the enatiomeric excess is the use of a PCR model using peak heights, perpendicular drop peak areas and deconvoluted peak areas as the original variables. The predictive ability of the proposed calibration model is of about 2-8 times better (depending on the overlapping degree) than that achieved with the other models tested.
A simple, sensitive, and reliable method using gas chromatography (GC)-mass spectrometry (MS) is developed for the simultaneous determination of ephedrine alkaloids and 2,3,5,6-tetramethylpyrazine (TMP) in Ephedra sinica Stapf. The sample is extracted with ethyl ether and submitted to GC-MS for identification and quantitation without derivatization. The column used for GC is an HP-5 (30.0 m x 250 microm x 0.25 microm, 5% phenyl methyl siloxane), and the carrier gas is helium. The detection limits for ephedrine, pseudoephedrine, and TMP are 0.4 ng 0.7 ng, and 0.02 ng (signal-to-noise ratio of 3), respectively. The reproducibility of the total procedure is proved to be acceptable (RSD < 2%), and the recoveries are above 93%.