Novel uses of organized media in chemical analysis
Spino, Larry Angelo
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Micelles and cyclodextrins have been utilized for years in a variety of chemical analysis techniques. This work considers some modern applications of micelles and cyclodextrins in chemical analysis. Micellar and cyclodextrin mobile phases (pseudophases) were used in liquid chromatography (LC). Cyclodextrin mobile phases were used in microcolumn LC for separating optical isomers of racemic nicotine and eight other racemic analogues of nicotine. This was the first reported facile and direct separation of these racemates. Synchronous luminescence was used as the detection method for liquid chromatography to identify polynuclear aromatic components that co-elute in the course of a LC separation. As many as five compounds could be identified from a single chromatographic peak. Several scans can be made easily for every eluting peak, however, a single scan is sufficient to produce a complete synchronous luminescence spectra of a complex mixture. The micellar matrix served as the mobile phase and produced an enhancement effect on the luminescence signals. Equations were derived which allow one to determine alphacyclodextrin: substrate complex stoichiometries as well as primary and secondary binding constants by using LC retention values. An equation was also derived which describes the binding of a monoprotic species in which either its ionized or unionized form could bind to one or two cyclodextrin molecules. Becaused multiple binding constants are difficult to evaluate graphically, a non-linear least squares computer program was utilized. The approach works equally well forthe determination of binding cqnstants in micellar media. Resonance enhancement of Raman signals requires excitation on an absorption band of a molecule. This frequently produces background fluorescence from which it is difficult or impossible to extract a vibrational spectrum. Carrying out the resonance Raman analysis in certain dilute aqueous micellar solutions allows one to circumvent the luminescence problem in many cases. Several difÃerent micellar effects can be used simultaneously to enhance Raman signals relative to the background. Both the laser excitation line and the micellar system must be properly chosen so as to produce the best signal to noise ratio. The first examples of micelle mediated resonance Raman analysis of fluorescent compounds using UV and visible laser excitation was shown. Obtaining resonance Raman spectra from thin-layerchromatography plates was also demonstrated.