Rapid simultaneous determination of alkylxanthines by CZE and its application in analysis of pharmaceuticals and food samples

A novel electrochemical analysis of the legal psychoactive drug caffeine using a zeolite/MWCNT modified carbon paste sensor

Caffeine (Caf) is a natural central nervous system stimulant categorized by the US Food and Drug Administration as a safe drug and its maximal amount in soft drinks has been approximately determined to be lower than 200 mg L⁻¹.

Electrochemical Determination of Caffeine Content in Ethiopian Coffee Samples Using Lignin Modified Glassy Carbon Electrode

Lignin film was deposited at the surface of glassy carbon electrode potentiostatically. In contrast to the unmodified glassy carbon electrode, an oxidative peak with an improved current and overpotential for caffeine at modified electrode showed catalytic activity of the modifier towards oxidation of caffeine. Linear dependence of peak current on caffeine concentration in the range 6 × 10^-6 to 100 × 10^-6 mol L^-1 with determination coefficient and method detection limit (LoD = 3 s/slope) of 0.99925 and 8.37 × 10^-7 mol L^-1, respectively, supplemented by recovery results of 93.79-102.17% validated the developed method. An attempt was made to determine the caffeine content of aqueous coffee extracts of Ethiopian coffees grown in four coffee cultivating localities (Wonbera, Wolega, Finoteselam, and Zegie) and hence to evaluate the correlation between users preference and caffeine content. In agreement with reported works, caffeine contents (w/w%) of 0.164 in Wonbera coffee; 0.134 in Wolega coffee; 0.097 in Finoteselam coffee; and 0.089 in Zegie coffee were detected confirming the applicability of the developed method for determination of caffeine in a complex matrix environment. The result indicated that users' highest preference for Wonbera and least preference for Zegie cultivated coffees are in agreement with the caffeine content.

Capillary electrophoresis separation of aminoalkanol derivatives of 1,7-dimethyl-8,9-diphenyl-4-azatricyclo[5.2.1.0(2,6)]dec-8-ene-3,5,10-trione as potential anticancer drugs

The purpose of this study, the direct separation of aminoalkanol derivatives I and II of 1,7-dimethyl-8,9-diphenyl-4-azatricyclo[5.2.1.0(2,6) ]dec-8-ene-3,5,10-trione, which was found in earlier studies as potential anticancer drugs, were performed. Capillary electrophoresis offers the possibility of fast, cheap, and reproducible separations for compounds I and II. In this paper, the simultaneous separation of I and II by capillary zone electrophoresis has been achieved within 8 min by use of 50 mM phosphate buffer of pH 2.5. Analysis of the two compounds in the serum plasma standards was conducted. Limits of detection of I and II by UV absorbance at 200 nm were achieved in the range of 156.3-156.6 ng/mL. The method was validated for linearity, accuracy, precision, limits of detection, and quantification. The calibration equation revealed a good linear relationship (r(2) = 0.998-0.999). Sufficient recovery was observed in the range of 96.3-99.5%. The method showed good reproducibility with intra- and interday precision of 0.97 and 1.76%, respectively. The quantification limits for the compounds were in the range of 477.0-479.8 ng/mL. The proposed method was applied to the analysis of real serum samples.

Determination of caffeine in coffee products by dynamic complexation with 3,4-dimethoxycinnamate and separation by CZE

A method based on the formation of pi-complexes with chlorogenate-like species was proposed for the determination of caffeine in regular (nondecaffeinated) and decaffeinated coffee. Both caffeate and 3,4-dimethoxycinnamate were able to transform caffeine--a neutral species in aqueous solutions--into an anionic species. The usage of 3,4-dimethoxycinnamate in the running electrolyte is advantageous, because of its greater chemical stability and the improved resolution of the peaks of caffeine, theobromine, and theophylline. Negative peaks were registered with a capacitively coupled contactless conductivity detector when solutions of these alkylxanthines were analyzed with a BGE composed of 20 mmol/L 3,4-dimethoxycinnamic acid and pH adjusted to 8.5 with Tris. This behavior was expected, because the complex is larger and thus should move slower than the free anion. Caffeine was determined in ground and instant coffee with precision and accuracy that meet Brazilian norms about such products. The LOD was estimated as 33 mg/L, which corresponds to 0.8 and 0.3 mg of caffeine per gram of dry instant coffee and ground coffee, respectively. For the case of decaffeinated coffee, ten times preconcentration with dichloromethane was carried out to allow the quantitation of caffeine, which should not exceed the concentration of 1 mg/g in dry matter.