RU2319143C2 - Method of determining aspartic acid in aqueous solution - Google Patents

Abstract

FIELD: analytical methods in food industry.

SUBSTANCE: invention relates to analytical chemistry of organic compounds and is intended for use in development of processes of production of biologically active supplements, polyvitamins, and protein mixtures. Method comprises preparation of aqueous solution of aspartic acid and quantitative determination of acid. More specifically, to aqueous solution of acid, crystalline lithium sulfate is added as desalting agent and then mixture of hydrophilic solvent is added to water-salt solution of acid, said mixture of hydrophilic solvent being prepared from butyl alcohol, acetone, and ethyl acetate. Thereafter, extract is separated and amount of aspartic acid is determined therein with the aid of potentiometric titration technique, which involves plotting differential curve of medium potential vs. volume of titrant and calculating degree of recovery of aspartic acid using suitable formula.

EFFECT: accelerated analytical procedure using safety reagents.

2 tbl, 7 ex

Description

The invention relates to the analytical chemistry of organic compounds and can be used in the development of processes for the production of biologically active food additives, multivitamins, protein mixtures.

The closest in technical essence and the achieved effect is a spectrophotometric method for determining aspartic acid by reaction with ninhydrin [Korenman IM Photometric analysis. Methods for the determination of organic compounds. - M.: Chemistry, 1970. - 344 p.].

The disadvantages of this method is the complexity, the use of a toxic reagent - ninhydrin, the inability to implement the method for determining aspartic acid in an industrial environment.

An object of the invention is to develop an express method for determining the amount of aspartic acid in an aqueous solution using safe reagents, characterized by the simplicity of hardware design.

The technical problem is achieved in that in a method for determining the amount of aspartic acid in an aqueous solution, including sampling, preparation of an aqueous solution of acid, quantitative determination of acid, it is new that a salting agent is added to the aqueous solution of aspartic acid - crystalline lithium sulfate in an amount of 20-25 wt. .% to the amount of an aqueous solution of acid, stirred, to a water-salt solution of acid add a mixture of hydrophilic solvents in a ratio of 10: 1, and the mixture of hydrophilic solvents oil is prepared from 55-55.5 wt.% butyl alcohol, 20-20.5 wt.% acetone and 24-25 wt.% ethyl acetate, the extract is separated, the amount of aspartic acid is determined by potentiometric titration, constructing a differential curve of the variation of the medium’s potential from titrant volume. Find the equivalent volume of titrant spent on titration, then by the formula (1) calculate the mass of aspartic acid in the extract (m _o ) and the corresponding distribution coefficient by the formula (2):

where C is the concentration of titrant, mol / l; V is the titrant volume spent on titration, ml; M is the molar mass of the acid equivalent, g / mol;

The degree of extraction (R,%) of aspartic acid is calculated by the formula (3):

where D is the distribution coefficient of aspartic acid between the mixture of solvents and the water-salt solution, r is the ratio of the equilibrium volumes of the aqueous and organic phases.

The duration of the analysis of the proposed method is 15-20 minutes

The technical result consists in the development of an express method for determining the amount of aspartic acid in an aqueous solution using safe reagents, characterized by the simplicity of hardware design.

The proposed method for determining the amount of aspartic acid in an aqueous solution is carried out according to the following method.

To 20 ml of an aqueous solution of aspartic acid with an initial concentration of 0.1-1 mg / ml add 20-25 wt.% Salting out agent (lithium sulfate). A mixture of hydrophilic solvents is preliminarily prepared, consisting of 55-55.5 wt.% Butyl alcohol, 20-20.5 wt.% Acetone and 24-25 wt.% Ethyl acetate, which is then added to an aqueous salt solution of aspartic acid in an amount of 2 ml. Then it is extracted on a vibrating mixer for 5 minutes (during this time interphase equilibrium is reached), it is held for 1-2 minutes, after the phases are separated, the extract is separated without capturing the aqueous layer, quantitatively transferred to a cell for potentiometric titration and titrated by the acid-base mechanism. As a titrant, a 0.01 mol / L KOH solution in anhydrous ethyl alcohol is used. In non-aqueous titration, a glass electrode serves as an indicator electrode. Preliminary studies have shown that it meets the following requirements: chemical inertness, clarity and reproducibility of the resulting analytical signal. A silver chloride electrode filled with a saturated solution of potassium chloride in ethanol is used as a reference electrode to prevent water from entering the electrode into a non-aqueous solution of the determined acid. Electromotive force is measured on a high-resistance potentiometer.

On the differential curve of potentiometric titration of aspartic acid there is a maximum corresponding to the acid content in the extract. Find the equivalent volume of titrant spent on titration, then by the formula (1) calculate the mass of aspartic acid in the extract (m _o ) and the corresponding distribution coefficient by the formula (2):

where C is the concentration of titrant, mol / l; V is the titrant volume spent on titration, ml; M is the molar mass of the acid equivalent, g / mol;

The degree of extraction (R,%) of aspartic acid is calculated by the formula (3):

where D is the distribution coefficient of aspartic acid between the mixture of solvents and the water-salt solution, r is the ratio of the equilibrium volumes of the aqueous and organic phases.

97-98% of aspartic acid from its content in the initial solution passes into the organic phase. The implementation of the method is illustrated by the following examples.

Example 1

To 20 ml of an analyzed aqueous solution of aspartic acid, 2 ml of a mixture of solvents containing 55 wt.% Butyl alcohol, 20 wt.% Acetone and 25 wt.% Ethyl acetate is added. Extract on a vibratory mixer for 5 minutes. Extraction with a mixture of hydrophilic solvents in the absence of a salting out agent does not lead to the formation of an organic phase, the method is not feasible.

Example 2

To the analyzed solution of aspartic acid add a salting out agent - crystalline lithium sulfate in an amount of 20 wt.%. To 20 ml of a water-salt solution of aspartic acid, 2 ml of a mixture of solvents containing 55 wt.% Butyl alcohol, 20 wt.% Acetone and 25 wt.% Ethyl acetate are added. It is extracted on a vibratory mixer for 5 minutes, the extract is separated without capturing the aqueous layer, quantitatively transferred to a cell for potentiometric titration and titrated with a 0.01 mol / L KOH solution in anhydrous ethyl alcohol. The indicator electrode is a chemically neutral glass electrode. The reference electrode is silver chloride, filled with a saturated solution of potassium chloride in ethyl alcohol. The electromotive force is measured on a high-resistance potentiometer, and a differential curve of potentiometric titration of the dependence of the change in the EMF on the volume of the titrant is built.

On the differential curve of potentiometric titration of aspartic acid there is a maximum corresponding to the acid content in the extract. Find the equivalent volume of titrant spent on titration, then by the formula (1) calculate the mass of aspartic acid in the extract (m _o ) and the corresponding distribution coefficient by the formula (2):

where C is the concentration of titrant, mol / l; V is the titrant volume spent on titration, ml; M is the molar mass of the acid equivalent, g / mol;

The degree of extraction (R,%) of aspartic acid is calculated by the formula (3):

where D is the distribution coefficient of aspartic acid between the mixture of solvents and the water-salt solution, r is the ratio of the equilibrium volumes of the aqueous and organic phases.

97.9% of aspartic acid from its content in the initial solution passes into the organic phase. Achieved almost complete (97-98 wt.% - noy) extraction of aspartic acid, the method is feasible.

Example 3

The analysis is carried out analogously to example 2, but crystalline lithium sulfate in an amount of 25 wt.% Is added to an aqueous solution of aspartic acid. 97.6% of aspartic acid from its content in the initial solution passes into the organic phase. Achieved almost complete (97-98 wt.% - noy) extraction of aspartic acid, the method is feasible.

Example 4

The analysis is carried out analogously to example 2, but crystalline lithium sulfate in an amount of 30 wt.% Is added to an aqueous solution of aspartic acid. After extraction, salting out crystals are precipitated; the method is not feasible.

Example 5

The analysis is carried out analogously to example 2, but crystalline lithium sulfate in an amount of 15 wt.% Is added to an aqueous solution of aspartic acid. 46% of aspartic acid from the initial content in the analyzed solution passes into the organic phase. Almost complete (97-98 wt.% - noy) extraction of aspartic acid is not achieved. The method is not feasible.

Example 6

The analysis is performed as in Example 2, but a three-component mixture of hydrophilic solvents containing 35 wt.% Butyl alcohol, 55 wt.% Acetone and 10 wt.% Ethyl acetate is added to the aqueous salt solution of aspartic acid. 35.4 aspartic acid passes into the organic phase from its content in the initial solution. Almost complete (97-98 wt.% - noy) extraction of aspartic acid is not achieved, the method is not feasible.

Example 7

The analysis was performed as in Example 2, but a three-component mixture of hydrophilic solvents containing 70 wt.% Butyl alcohol, 25 wt.% Acetone and 5 wt.% Ethyl acetate was added to the aqueous salt solution of aspartic acid. 65.5% of aspartic acid from its content in the initial solution passes into the organic phase. Almost complete (97-98 wt.% - noy) extraction of aspartic acid is not achieved, the method is not feasible.

Table 1 shows a comparative characteristic of examples of determination of aspartic acid in an aqueous solution by the present method.

Table 1
Comparative characteristics of examples of determination of aspartic acid in aqueous solution by the present method Example Number The content of salting out agent, wt.% The composition of the extractant, wt.% The degree of extraction of aspartic acid,% butyl alcohol acetone ethyl acetate one - 55 twenty 25 - 2 twenty 55 twenty 25 97.9 3 25 55 twenty 25 97.6 four thirty 55 twenty 25 - 5 fifteen 55 twenty 25 46 6 twenty 35 55 10 80.3 7 70 25 25 5 65.5

As follows from table 1, the positive effect of the proposed method is achieved when the content of the salting out agent is 20-25 wt.%, The use of a three-component mixture of hydrophilic solvents, consisting of 55-55.5 wt.% Butyl alcohol, 20-20.5 wt.% Acetone and 24-25 wt.% ethyl acetate and a volume ratio of a mixture of extractants and a water-salt solution of 1:10.

The proposed method for determining the amount of aspartic acid in an aqueous solution allows to determine aspartic acid in an aqueous solution at a concentration level of 0.1-1 mg / ml (table 2).

table 2
Determination of aspartic acid in extracts obtained by extraction with a mixture of hydrophilic solvents of the claimed composition; n = 4, P = 0.95 The acid content in aqueous solution, mg The acid content in the extract, mg 0.1 0.097 ± 0.18 0.2 0.194 ± 0.11 0.3 2.917 ± 0.20 0.4 0.389 ± 0.23 0.5 0.486 ± 0.18 0.6 0.581 ± 0.13 0.7 0.679 ± 0.21 0.8 0.754 ± 0.15 0.9 0.824 ± 0.12 1,0 0.936 ± 0.13

Claims (1)

A method for determining the amount of aspartic acid in an aqueous solution, including sampling, preparation of an aqueous acid solution, quantitative determination of acid, characterized in that a salting out agent, crystalline lithium sulfate, is added to an aqueous solution of aspartic acid in an amount of 20-25 wt.% To the amount of an aqueous acid solution, mix, to a water-salt solution of acid add a mixture of hydrophilic solvents in a ratio of 10: 1, and a mixture of hydrophilic solvents is prepared from 55-55.5 wt.% butyl alcohol, 20-20.5 wt.% Acetone and 24-25 wt.% Ethyl acetate, the extract is separated, the amount of aspartic acid is determined in it by potentiometric titration, constructing a differential curve of the dependence of the medium potential on the titrant volume, the degree of extraction (R,%) of aspartic acid calculated by the formula R = D100 / D + r, where D is the distribution coefficient of aspartic acid between the mixture of solvents and the water-salt solution, r is the ratio of the equilibrium volumes of the aqueous and organic phases.