RU2183321C1 - Method of determination of content of tartaric acid its salts - Google Patents

Abstract

FIELD: food-processing industry; detection of adulteration of juice and dairy products; analysis of sewage and other contaminants. SUBSTANCE: method consists in drawing sample, clarifying it by settling or filtering and dividing it into two portions. Oxidant is added to first portion and sulfuric acid is added to second portion; then, both portions are subjected to photometric measurement; their optical density E $\genfrac{}{}{0ex}{}{\text{1}}{\text{1}}$ and E $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ , is measured and indicator is added, after which photometric measurement is repeated and optical densities E $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ and E $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ are measured again; content of tartaric acid (C_t.a.) and/or its salts is calculated by the following formula: (C_t.a.) = K(E $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ -E $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ )-(E $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ -E $\genfrac{}{}{0ex}{}{\text{1}}{\text{1}}$ ), where K is proportionally factor. Oxidation of first portion of first portion of sample may be effected by means of hydrogen peroxide or another agent whose standard electrode potential of reduction in acid medium ranges from 1 to 1.8. Ammonium vanadate is used indicator. EFFECT: enhanced accuracy; reduced time of analysis; reduced limit of detection; extended field of application. 8 cl

Description

Technical field
The invention relates to methods for research and analysis of materials using optical means, in particular systems in which a material enters a chemical reaction by observing a color change under the influence of a chemical indicator.

 The invention can be used to determine the presence and concentration of tartaric acid and its salts in any aqueous solutions, in food products, in juice-containing and milk raw materials, and in products made from it. The invention allows to detect and determine the concentration in a solution of any substances containing anion of tartaric acid, that is, both tartaric acid itself and any of its salts (tartrates). The method can also be used to detect falsification of juice and juice drinks with additives of tartaric acid or its salts. In addition, the invention can be used in the chemical industry for the analysis of industrial effluents and commercial samples of tartaric acid and / or its salts - tartrates.

State of the art
A known method for the detection of tartaric acid (SU 185881 A, IPC ⁷ G 01 N 33/02, 10/15/1966). A sample of the studied powder is taken, it is subjected to ultraviolet irradiation, the sample is mixed with molybdenum acid ammonium, ground in a mortar and moistened, by the appearance of a blue or blue-green color, the presence of color is judged on the presence of tartaric acid in the sample.

 This method is applicable only for the separation of tartaric and citric acids in a dry crystalline state, in addition, this method is qualitative and does not provide the possibility of quantitative determination of tartaric acid in any salts and solutions.

 The closest analogue is the method for the detection of tartaric acid ("Tartaric acid in grape juice" - International Federation of Fruit Juice Producers (IFU), IFU Analysis N65, February 1995, p.1-3), including the preparation of a sample consisting of sampling and filtering the analyzed sample, adding sulfuric acid solution to it, performing liquid chromatography, photometric measurement of electromagnetic radiation at a wavelength of 210 nm and determining the content of tartaric acid using the obtained data using calibration solutions or experimentally established dependence of the radiation intensity on tartaric acid concentration.

 The known method has a low accuracy and a high detection limit. For the implementation of the method requires complex expensive equipment, in particular membrane filters for fine cleaning of the sample. This method can be used to determine the concentration of tartaric acid about 500 mg / l, otherwise it is necessary to further dilute the original sample. In addition, the known method does not provide the ability to determine the content of salts of tartaric acid. All this significantly complicates its use and limits the scope of its application.

SUMMARY OF THE INVENTION
The objective of the invention is to develop a method for determining the concentration of tartaric acid in food products, juices and water-juice mixtures, industrial effluents, and other substances containing tartaric acid and / or its salts.

 When implementing the invention, the following technical results can be obtained: accelerating the determination of the concentration of tartaric acid and its salts (tartrates), increasing the accuracy and lowering the detection limit of tartaric acid and / or its salts - tartrates, expanding the scope of the method, expanding the range of determined concentrations without diluting the sample .

These technical results are achieved by the fact that in the method for the detection of tartaric acid, including sample preparation, the separation of the prepared sample into two parts. In the first part, an oxidizing agent is added, in the second, sulfuric acid, by measuring these parts of the sample, the values of their optical density E ₁ ¹ and E ₁ ² are measured, then an indicator is added to them and, second-time photometric measurements, their optical density E ₂ ^{1 is} measured accordingly and E ₂ ² , and the content of tartaric acid (C _VK ) and / or its salts (tartrates) is calculated by the formula: C _VK = K ((E ₂ ² -E ₁ ² ) - (E ₂ ¹ -E ₁ ¹ )) where K is the coefficient of proportionality, determined experimentally, for example, using calibration solutions.

The invention differs from the closest analogue in that the prepared sample is divided into two parts, an oxidizing agent is added to the first one, sulfuric acid is added to the second, photometric measuring these parts of the sample, their optical density values are measured E ₁ ¹ and E ₁ ² , respectively, then added to them indicator and, by photometric measurement a second time, the values of their optical density are measured, respectively, E ₂ ¹ and E ₂ ² , and the content of tartaric acid (C _bk ) and / or its salts is calculated by the formula:
With _VK = K ((E ₂ ² -E ₁ ² ) - (E ₂ ¹ -E ₁ ¹ )),
where K is the calibration coefficient of proportionality, determined experimentally, for example, using calibration solutions.

 Mostly alcoholic or non-alcoholic drinks, including juices or juice-containing drinks, are used as samples.

 When preparing a sample, it is advisable to add activated carbon as a sorbent and then filter or centrifuge it to remove suspended matter and solid impurities.

 It is preferable to use substances with a standard electrode reduction potential in an acidic medium, the value of which lies in the range from 1 V to 1.8 V.

 In particular, hydrogen peroxide and / or iodates and / or bromates and / or dichromates and / or chromates and / or manganates and / or metal permanganates are used as an oxidizing agent.

As an indicator, it is advisable to use ammonium vanadate - NH ₄ VO ₃ .

For photometry, it is advisable to use electromagnetic radiation with a wavelength of 520-580 nm, mainly with a wavelength of 546 ⁺ / - 10 nm.

 The proposed method is based on the fact that the detection of tartaric acid occurs photometrically directly in the juice, and not gravimetrically or chromatographically, as occurs in the framework of known methods. The use of compounds with standard electrode reduction potentials ranging from 1 to 1.8 V as oxidizing reagents is necessary, since substances with a lower electrode potential will not oxidize tartaric acid, and with a higher electrode potential, all the others present in the sample will be oxidized soluble components, for example sugars, fruit acids. The most affordable oxidizing agent is hydrogen peroxide, which forms peroxo-vanadate ions with ammonium vanadate.

 The determination does not interfere with the prevailing amounts of sugar, citric and malic acids present in the sample, due to the selection of conditions under which tartaric acid reacts selectively with vanadate.

 The method does not require complex equipment for implementation. It is easily applicable in the field, in particular without a photometer, simply by visually comparing the color of the zero sample and the detected sample. The difference in color intensity is noticeable when more than 15% grape juice is added to apple juice.

Information confirming the possibility of carrying out the invention
The invention is as follows:
1. Sample preparation.

 To measure the content of tartaric acid, samples of, for example, juice raw materials are pre-mixed with activated carbon, and then filtered and / or centrifuged, removing the flesh and activated carbon that has sorbed interfering compounds.

 A solution of ammonium monovanadate is prepared by dissolving ammonium monovanadate in a solution containing sodium hydroxide and sodium acetate.

 To prepare the oxidizer solution, a 30-50% hydrogen peroxide solution is transferred to a 100 ml flask and adjusted to the mark with a 1-2 M sulfuric acid solution.

 3. Checking the operation of the equipment.

In order to check the operation of the equipment (photometer and microdosers), tartaric acid is determined in its standard solution with a concentration of 2-4 mg / ml. The sample volume is 500-1000 μl. The volume of the test is 3,600 ml. The determination is carried out according to the method described above. Build a graph of the dependence of E on With _VK , which determine the value of K - the proportionality coefficient.

 During normal operation of the equipment, the coincidence of the calculated value with the standard should be within 100 ± 5%.

A certain amount of tartaric acid is based on photometry of the formed complex anion V ^(IV) -V ^(V) during the oxidation of tartaric acid ammonium vanadate in an acidic medium at a wavelength of 546 ± 10 nm.

 Conduct sample preparation. For this, 1-5 g of activated carbon is added to the solution of the analyzed sample of apple juice concentrate with a volume of 10-15 ml and mixed. It is kept for 10-15 minutes without stirring and filtered to obtain a clear, clear, unpainted solution. To 5.0-10.0 ml of this solution add 0.5-2.5 ml of NaOH solution with a concentration of 2-4 M, mix and incubate for 5-10 minutes. Then, 0.5-2.5 ml of 2-4 M HCl is poured and stirred. The resulting solution is divided into two parts and each of the parts is transferred to 1-5 cm thick photometric cuvettes. Thus, two cuvettes are prepared, one of which will be “zero”, in which the first part of the solution is located, i.e. taking into account the color of excess vanadate, passing in an acidic environment into a yellow vanadyl cation.

After that, 0.6-3.0 ml of oxidizing agent is added to the “zero” cuvette containing the first part of the solution and mixed, and 0.6-3.0 ml of sulfuric acid solution with concentration 0 is added to the other cuvette containing the second part of the solution , 1-1.0 M. Mix and measure the values of their optical density E ₁ ¹ and E ₁ ² respectively. The measurement of the optical density of the solution can be carried out at any wavelength in the range of the emission spectrum of 520-580 nm, however, the best results are obtained when using optical radiation with a wavelength of 546 ± 10 nm. After that, 1-5 ml of ammonium vanadate solution is added to the cuvettes. Stirred again and again measure the values of their optical density E ₂ ¹ and E ₂ ² respectively.

The content of tartaric acid With _VK and / or its salts is calculated by the formula:
With _VK = K ((E ₂ ² -E ₁ ² ) - (E ₂ ¹ -E ₁ ¹ )),
where K is the calibration coefficient of proportionality, determined experimentally, for example, using calibration solutions.

To increase the accuracy of determining the content of tartaric acid, the same steps for preparing a sample for analysis are carried out in parallel in a third cuvette containing distilled water, and the optical density of the solution is determined without an indicator (E ₁ ³ ) and with an added indicator - ammonium vanadate (E ₂ ³ ), respectively .

The concentration of tartaric acid With _VK calculated by the formula:
With _VK = K ((E ₂ ² -E ₁ ² ) - (E ₂ ¹ -E ₁ ¹ ) - (E ₂ ³ -E ₁ ³ )).

 The coefficient K is obtained, for example, when calibrating a particular photometer using a series of standard solutions of tartaric acid and / or tartrates.

Recalculate With _VK to 11.2 Vh. The value should be no more than 100 mg / l, which corresponds to the addition of 5% grape juice to apple juice, this value can be neglected within the experimental error. The limit of sustainable detection can be considered 450 mg / l, which corresponds to 15% of grape juice in apple. Values greater than 1000 mg / L indicate gross falsification. Only in this case does the non-characteristic glucose / fructose ratio appear in the apple juice concentrate, which can be measured chromatographically or enzymatically.

 The described method has the following advantages.

 The detection limit is 20-50 mg / l of tartaric acid in the analyzed solution, which corresponds to E = 0.030-0.065 for a 1 cm thick cuvette. With an increase in the cuvette thickness (for example, up to 5 cm), the accuracy and sensitivity of the method proportionally increase.

 The reproducibility of the method is not worse than 3%.

 Accuracy no more than 5%.

 After processing with apple juice reagents, the optical density at a wavelength of, for example, 520-580 nm should not exceed 0.05-0.15 (light color), which corresponds to a normal apple. Large values indicate the falsification of apple juice with tartaric acid.

 The described method has the following advantages.

 Unlike existing methods, the proposed method does not require a complicated sample preparation procedure, the measurement is carried out directly in the juice, the pulp from the juices is removed by conventional filtration.

 All reactions can be carried out directly in the cuvette of the photometer, which speeds up the process and makes it safer in comparison with the methods known today.

 The sensitivity of the method is significantly higher than when determined by enzymatic and / or chromatographic methods for measuring tartaric acid, since under the selected conditions of the method there are practically no interfering elements. Differences between falsified and unfalsified apple juice can be seen with the naked eye, i.e. without the use of any measuring instruments, which makes the method convenient for use in any conditions, even in the field.

Claims (8)

1. A method for detecting tartaric acid, including sample preparation, its photometry and determination of the content of tartaric acid according to the obtained data, characterized in that the prepared sample is divided into two parts, an oxidizing agent is added to the first, and sulfuric acid is added to the second sulfuric acid by photometric measurement of both parts of the sample, respectively their optical density values E and E _{¹ Jan. Feb. ^1,} is then added to them and an indicator, a second fotometriruya, respectively measured values of absorbance ¹ and E ₂ E ₂ ^2, and the content of tartaric acid (P _VC) and / or its salts th calculated by the formula
With _VK = K ((E ₂ ² -E ₁ ² ) - (E ₂ ¹ -E ₁ ¹ )),
where K is the calibration coefficient of proportionality.  2. The method according to p. 1, characterized in that the samples used are alcoholic or non-alcoholic drinks, including juice-containing ones.  3. The method according to any one of paragraphs. 1 and 2, characterized in that when preparing the sample, activated carbon is added as a sorbent to it and then the sample is filtered.  4. The method according to any one of paragraphs. 1-3, characterized in that as the oxidizing agent use substances with a standard electrode potential reduction in an acidic environment in the range from 1 to 1.8 V.  5. The method according to any one of paragraphs. 1-4, characterized in that the oxidizing agent is hydrogen peroxide and / or iodates and / or bromates and / or dichromates and / or chromates and / or manganates and / or metal permanganates.  6. The method according to any one of paragraphs. 1-5, characterized in that the indicator used is ammonium vanadate.  7. The method according to any one of paragraphs. 1-6, characterized in that when photometric use electromagnetic radiation with a wavelength of 520-580 nm. 8. The method according to any one of paragraphs. 1-7, characterized in that when photometric use electromagnetic radiation with a wavelength of 546 ⁺ / -10 nm.