RU2490629C1 - Method of extracting caffeine from aqueous solution - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: to extract caffeine from an aqueous solution, a water-salt solution of caffeine with pH 11.0±1.0 is prepared using saturated potassium carbonate solution as a salting-out agent; caffeine is extracted until establishment of phase equilibrium for 7-10 minutes with a solution of a solvotropic reagent in ethyl alcohol with concentration of 0.85-0.90 mol/dm³ with volume ratio of the water-salt solution of caffeine to the extractant of 5:1; the water-salt phase is separated from the organic phase and analysed by UV spectrophotometry at wavelength of 272 nm. Concentration of caffeine in the aqueous solution is determined from a calibrated curve.

EFFECT: method enables to achieve high coefficient of distribution of caffeine with one-fold extraction with a solution of a solvotropic reagent in ethyl alcohol, and virtually complete extraction of caffeine from the water-salt solution.

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Description

The invention relates to analytical chemistry and pharmaceuticals and can be used to extract purine alkaloids from aqueous media for the purpose of their subsequent determination.

The closest in technical essence and the achieved effect is the sorption of caffeine on supercrosslinked polystyrene [Andreeva E.Yu., Dmitrienko S.G., Yu.A. Zolotov. Sorption of caffeine and theophylline on hypercrosslinked polystyrene. News. Mosk. University. Ser. 2. Chemistry. 2010.V. 51. No. 1].

The technical task of the invention is to develop an extraction system in order to achieve high distribution coefficients of caffeine and its almost complete extraction from aqueous solutions with a hydrophilic solvent using a solvotropic reagent.

The solution of the technical problem of the invention is achieved by the fact that in the proposed method for the extraction of caffeine from aqueous solutions, dibutyl phthalate (DBP) is used as a solvotropic reagent, ethyl alcohol is an extractant, and potassium carbonate is a salting out agent. A solution of DBP in ethanol is prepared with a concentration of 0.8-0.9 mol / dm ³ , caffeine is extracted with this solution from a water-salt solution, which has a pH of 11.0 ± 1.0 due to the use of potassium carbonate as a salting out agent. For this, a sample of pharmacopoeial purity caffeine, taken on an analytical balance, is placed in a 50 cm ³ chemical beaker, dissolved in a small volume (2-3 cm ³ ) of distilled water, after the sample is completely dissolved, the solution is transferred to a 100-volumetric flask cm ³ , adjusted to the mark with a saturated solution of potassium carbonate, extracted caffeine with a solution of DBP in ethanol, for this a solution of DBP in ethanol with a concentration of 0.9 mol / dm ³ is added to the resulting caffeine solution with a volume ratio of water-salt solution caffeine and extractant 5: 1, extracted on a vibratory mixer until interfacial equilibrium is established (7-10 min), after delamination of the system (5-7 min), the water-salt solution is separated from the organic phase and analyzed by UV spectrophotometry, the optical density of water-water is measured saline solution on a UV spectrophotometer in a quartz cuvette with a light-absorbing layer thickness of 1 cm at a wavelength of 272 nm, a graph of the dependence of the optical density of the water-salt solution on the concentration of caffeine is plotted, the concentration of caffeine in the aqueous solution is found from the graph alignment.

Calculate the distribution coefficient (D) and the degree of extraction of caffeine (R,%) by the formulas:

, $$R=\frac{D}{D+f}\cdot 100\%$$

, $$D=\frac{c_o}{c_{\mathrm{at}}}$$

, $$R=\frac{D}{D+f}\cdot \mathrm{one\; hundred}\%$$

,

where c ₀ and c _in are the concentrations of caffeine in the organic and aqueous phases, f is the ratio of the volumes of equilibrium aqueous and organic phases.

The technical result of the invention is to achieve a high distribution coefficient of caffeine (up to 400), almost complete (98.8%) extraction of caffeine from an aqueous solution with a solution of DBP in ethyl alcohol in the presence of potassium carbonate.

The implementation of the method is illustrated by the following example. A water-salt solution of caffeine is prepared, which has a pH of 11.0 ± 1.0 due to the use of a saturated potassium carbonate solution as a salting agent, for which a sample of pharmacopoeial purity caffeine, taken on an analytical balance, is placed in a 50 cm ³ beaker, dissolved in a small volume (2-3 cm ³ ) of distilled water, after complete dissolution of the sample (5 min), the solution is transferred to a 100 cm ³ volumetric flask, adjusted to the mark with a saturated potassium carbonate solution, caffeine is extracted with a solution of DBP in ethanol, for this purpose A solution of DBP in ethanol with a concentration of 0.9 mol / dm ³ is added to the obtained caffeine solution at a 5: 1 ratio of the volume of the water-salt solution of caffeine and extractant; it is extracted on a vibrating mixer to establish interfacial equilibrium (10 min). After delamination of the system (5-7 min), the water-salt phase is separated from the organic phase and analyzed by UV spectrophotometry. The optical density of the water-salt solution is measured on a UV spectrophotometer in a quartz cuvette with a light-absorbing layer thickness of 1 cm at a wavelength of 272 nm, a graph of the dependence of the optical density of the water-salt solution on the concentration of caffeine is constructed, and the concentration of caffeine in the aqueous solution is found on the graph.

The distribution coefficient (D) and the degree of extraction of caffeine after the first extraction (R,%) are calculated by the formulas:

, $$R=\frac{D}{D+f}\cdot 100\%$$

, $$D=\frac{c_o}{c_{\mathrm{at}}}$$

, $$R=\frac{D}{D+f}\cdot \mathrm{one\; hundred}\%$$

,

where c ₀ and c _in - the concentration of caffeine in the organic and aqueous phases; f is the ratio of the volumes of equilibrium aqueous and organic phases.

The concentration of caffeine in an aqueous solution is found according to the calibration graph of the dependence of the optical density of aqueous solutions on the concentration of caffeine.

98.8% of caffeine from its initial content in the analyzed solution passes into the organic phase, while the distribution coefficient is 400.5.

As can be seen from the example, a high distribution coefficient (400.5) and almost complete (98.8%) extraction of caffeine with a solution of DBP in ethanol are achieved, with a 5: 1 ratio of volumes of water-salt solution and extractant and used as a salting out agent potassium carbonate. The duration of the analysis is 30-35 minutes.

When using water-salt solutions of caffeine prepared with a different salting out agent or with the proposed salting out agent, but of a different concentration, as well as using other extractants and phase volume ratios, the degree of extraction of caffeine is much lower than that achieved in the above example.

The proposed method for the extraction of caffeine from aqueous media allows to achieve a high distribution coefficient (up to 400.5) and to achieve almost complete (98.8%) extraction of caffeine from a water-salt solution, characterized by expressivity (analysis time 30-35 min) and can be used in the analysis of aqueous environments containing caffeine.

Claims (1)

The method of extracting caffeine from an aqueous solution, including the preparation of a caffeine solution by dissolving it in a saturated salting out solution, extraction and analysis of the equilibrium aqueous phase, characterized in that a solvent solution of a solvotropic reagent in ethyl alcohol with a concentration of 0.85-0.90 mol is used as an extractant / dm ^3, which is prepared aqueous-salt solution of caffeine with a pH 11.0 ± 1.0 by the application as a salting-out agent of a saturated potassium carbonate solution, extracted caffeine for 7-10 min a reagent solution solvotropnogo that in ethyl alcohol at a volume ratio of the water-salt solution and extracting caffeine 5: 1, water and salt is separated from the organic phase and analyzed by UV spectrophotometry at a wavelength of 272 nm, a calibration curve of the concentration of caffeine found in the aqueous solution.