Caffeine derivative techniques

Spectrophotometric methods for the analysis of caffeine Caffeine is quantified spectrophotometri-cally by measuring the ultraviolet (UV) absorbance at wavelengths between 270 and 280 nm. The major drawback of such methods is the presence of interfering substances. Such interferences can be reduced, but not eliminated, by using derivative techniques. Sample cleanup by various types of columns and background correction procedures is used to purify caffeine before spectrophotometric measurement. For example, in the Levine method, sample cleanup is achieved by a series of acidic and basic Celite columns. This method is adopted by AOAC for the analysis of... 

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

Hills et al. (1991) applied simultaneous supercritical fluid extraction to roasted coffee beans. This technique can be used with or without a derivatizing reagent In a dissociative mechanism, the adsorbed analyte must first desorb from a matrix active site and be dissolved in the supercritical fluid and then react to form the less polar derivative, which favors solvation in the supercritical carbon dioxide. In the associative mechanism, derivatization occurs while the analyte is adsorbed on the active site of the matrix. Reaction with the adsorbed analyte results in the desorption of the non-polar derivative into the supercritical fluid . Thus 2-hexenedioic acid (E.49) was identified for the first time as a native compound (without the use of a derivatizing agent). Benzenic and furanic compounds and caffeine were also identified. 

Abuiijeie, M.A. el-Din, M.S. Mahmoud, LI. Determination of theobromine, theophylhne and caffeine in various food products using derivative UV-spectrophotometric techniques and high-performance liquid chromatography. J.Liq.Chromatogr., 1992, 15, 101-125 [ethyl paraben (IS)]... 

This technique may be used in two distinct ways. The drug may be labeled at a specific site(s) and the mass spectra of metabolites derived from the labeled compound compared with those obtained from the unlabeled drug. Recent examples of this application include reports on the metabolism of oxybutynin,tocainide, and ketamine. Alternatively, a heavy isotope (usually H) is introduced into the metabolite of interest by reaction with a labeled derivatizing reagent. For example, perdeutero-methylation results in a mass difference of 3 daltons between labeled and unlabeled derivatives per methyl group. Structures of metabolites obtained from caffeine and phenytoin have been confirmed by this technique. Tri(deuteromethyl)silylation has been employed in the identification of metabolites of carbamazepine and afloqualone. ... 

Purpose. To extract the active principle, an alkaloid, caffeine, from a native source, tea leaves. Caffeine is a metabolite (a product of the living system s biochemistry) found in a variety of plants. We wtU use ordinary tea bags as our source of raw material. This experiment illustrates an extraction technique often used to isolate water-soluble, weakly basic natural products from their biological source (see also Experiment [llA] for another extraction strategy). The isolation of caffeine win also give you the opportunity to use sublimation as a purification technique, since caffeine is a crystalline alkaloid that possesses sufficient vapor pressure to make it a good candidate for this procedure. In addition, the preparation of a derivative of caffeine, its 5-nitrosalicylate salt, will be carried out. This latter conversion takes advantage of the weakly basic character of this natural product. 

---