RU2249818C2 - Protein content determination method - Google Patents

Abstract

FIELD: analytical methods in food industry.

SUBSTANCE: invention relates to analyzing various objects for content of proteins in a series of food processing industry branches, in particular in dairy industry. Method comprises providing analytical medium with electrochemically active components, to which protein-containing test sample is added, then measuring potential of indicator electrode, and determining content of proteins therethrough when compared to calibration graph. Novelty resides in using, as analytical medium, alkali solution containing hydroxyl and copper(II) ions at weight ratio 76-119 and measurement of potential is performed is performed on copper indicator electrode at copper(II) ion-to-protein weight ratio 0.156-6.97.

EFFECT: simplified procedure and increased measurement accuracy.

18 ex

Description

The invention relates to methods for analyzing various objects for the content of proteins in them and can be used in a number of branches of the food industry, in particular the dairy, as well as in the analysis of other biological systems.

There are various methods for determining the protein content, for example, ultrasonic, spectral, refractometric, etc. [Bruslavsky L.P., Fetisov E.A., Shidlovskaya V.P. Instruments for monitoring the composition and quality of milk. The dairy industry, No. 1, 1998, p.22-23].

There is also a potentiometric method for determining proteins using enzyme electrodes, based on the fact that as a result of the reaction of a substance with an enzyme, products are formed (hydrogen ions, ammonium, hydrogen peroxide, etc.), to which one or another indicator electrode is sensitive [Nikolsky B.P., Materova E.A. Ion-selective electrodes. - L .: Chemistry, 1980 .-- 240 p., Ill. (p.126-140). Morph V. Principles of work of ion-selective electrodes and membrane transport: Per. from English - M: Mir, 1985. - 280 p., Silt (p. 265-269)]. By measuring the potential of such an electrode in a solution with an unknown protein content, the protein content is found from a previously constructed calibration schedule.

A common drawback of potentiometry using enzyme electrodes is the complexity of their manufacture, associated, in particular, with the need to fix the enzyme on the surface of the ion-selective electrode (immobilization), the complexity of isolation and purification of the enzyme, and the large instability of the readings over time.

The purpose of the invention is to simplify the methods of determination and increase the reliability of measurements.

Implementation of the proposed method is as follows.

An analytical medium with electrochemically active components is created, a sample analyzed for proteins is introduced into it, the potential of the incentive electrode relative to the reference electrode is measured, and the amount of proteins is determined from the potential value by means of a calibration graph.

A distinctive feature of the proposed method is that, as an analytical medium, an alkaline solution containing hydroxyl ions and copper (II) ions with a mass ratio of 76-119 is used, and the potential is measured on a copper indicator electrode with a mass ratio of copper (II) ions to proteins 0.156 - 6.97.

The proposed method compares favorably with the prototype in its simplicity, since it is not necessary to specially prepare the enzyme, purify it, fix it on the surface of the ion-inactive electrode, and periodically re-calibrate the electrode due to the natural aging of the enzyme. The latter fact is especially unpleasant, since it significantly affects the reliability of measurements.

The results of the measurements are demonstrated by the following examples on a series of standard milk samples, the protein content of which was determined by the formal method and was 2.50% at a milk density of 1.028 g / ml.

составляет 119. В раствор погружают на глубину 30 мм медный электрод, выполненный в виде стержня диаметром 1,8 мм и длиной около 100 мм, рабочую часть которого предварительно кратковременно протравливают в 3 М растворе соляной кислоты, тщательно промывают водопроводной и дистиллированной водой, остатки которой удаляют фильтровальной бумагой. Закрепляют медный электрод в штативе и подключают его проводником к клемме измерительного электрода датчика ДЛ-01. В стакан с анализируемым раствором помещают электролитический ключ, который через промежуточный сосуд с насыщенным раствором хлорида калия соединяют электролитически с насыщенным хлорсеребряным электродом сравнения, вмонтированным в датчик. Кабель датчика подключают к потенциометру, в качестве которого выступает рН-метр рН-340. Производят измерение потенциала медного электрода после его стабилизации по истечении 3-5 минут при температуре раствора 25°С, который составляет -295 мВ.Example 1. In a 50 ml glass beaker 20.0 ml of a 2.00 M aqueous solution of sodium hydroxide, 0.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L are pipetted into a measured pipette, the mixture is thoroughly mixed until homogeneous. The ratio of the mass of hydroxyl ions to the mass of ions of Cu ²⁺

is 119. A copper electrode made in the form of a rod with a diameter of 1.8 mm and a length of about 100 mm is immersed to a depth of 30 mm, the working part of which is pre-etched briefly in a 3 M hydrochloric acid solution, thoroughly washed with tap and distilled water, the rest of which removed with filter paper. Fix the copper electrode in a tripod and connect it with a conductor to the terminal of the measuring electrode of the DL-01 sensor. An electrolytic key is placed in a glass with the analyzed solution, which is connected through an intermediate vessel with a saturated solution of potassium chloride electrolytically to a saturated silver chloride reference electrode mounted in the sensor. The sensor cable is connected to a potentiometer, which is a pH meter pH-340. The potential of the copper electrode is measured after it is stabilized after 3-5 minutes at a solution temperature of 25 ° C, which is -295 mV.

Then the electrode is removed from the solution, washed, etched in acid, washed again in tap and distilled water, and its residues are removed with filter paper. 0.50 ml of milk is pipetted into the glass with the solution, which corresponds to 0.0128 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode and the electrode potential is measured after it is stabilized after 3-5 minutes at a solution temperature of 25 ° C, which is -337 mV.

Example 2. In another 50 ml glass beaker, add 20.0 ml of a 2.00 M aqueous sodium hydroxide solution, 0.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L into a 50 ml measuring pipette, mix thoroughly until homogeneous . Then, 1.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0257 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in Example 1, and the electrode potential is measured after it stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -364 mV.

Example 3. In a third 50 ml glass beaker, add 20.0 ml of a 2.00 M aqueous solution of sodium hydroxide, 0.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L into a 50 ml measuring pipette, mix thoroughly until homogeneous . Then, 1.50 ml of milk is introduced into the indicated solution, which corresponds to 0.0385 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in Example 1, and the electrode potential is measured after it stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -395 mV.

Example 4. In a fourth 50 ml glass beaker, add 20.0 ml of a 2.00 M aqueous sodium hydroxide solution, 0.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L to a 50 ml measuring pipette, mix thoroughly until homogeneous . Then, 2.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0514 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in Example 1, and the electrode potential is measured after it stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -405 mV.

Using the experimental data of examples 1-3, a calibration graph is constructed in the coordinates: the mass of proteins is the electrode potential, which fit on a straight line (the experimental values of example 4 do not fit on this straight line). Then, under the conditions of the experiments described in example 1, in a copper-alkaline solution contribute:

0,87;- 0.25 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -313 mV, and the mass of proteins is determined from the calibration graph, which is 0.0064 g, which is calculated on the percentage of proteins in the analyzed sample is 2.5% when the ratio of the mass of Cu ²⁺ to the mass of proteins in the sample

0.87;

в образце 0,156.- 1.40 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -392 mV, and the mass of proteins is determined from the calibration graph, which is 0.0360 g, which is calculated in terms of the percentage of proteins in the analyzed sample is 2.5% with a ratio

in sample 0.156.

составляет 81. В раствор погружают на глубину 30 мм медный электрод, выполненный в виде стержня диаметром 1,8 мм и длиной около 100 мм, рабочую часть которого предварительно кратковременно протравливают в 3 М растворе соляной кислоты, тщательно промывают водопроводной и дистиллированной водой, остатки которой удаляют фильтровальной бумагой. Закрепляют медный электрод в штативе и подключают его проводником к клемме измерительного электрода датчика ДЛ-01. В стакан с анализируемым раствором помещают электролитический ключ, который через промежуточный сосуд с насыщенным раствором хлорида калия соединяют электролитически с насыщенным хлорсеребряным электродом сравнения, вмонтированным в датчик. Кабель датчика подключают к потенциометру, в качестве которого выступает рН-метр рН-340. Производят измерение потенциала медного электрода после его стабилизации по истечении 3-5 минут при температуре раствора 25°С, который составляет -305 мВ.Example 5. In a 50 ml glass beaker, add 20.0 ml of a 4.00 M aqueous sodium hydroxide solution, 1.50 ml of an aqueous solution of copper sulfate with a Cu concentration of ²⁺ 0.176 mol / L into a 50 ml measuring pipette, and the mixture is thoroughly mixed until homogeneous. The ratio of the mass of hydroxyl ions to the mass of ions of Cu ²⁺

is 81. A copper electrode made in the form of a rod with a diameter of 1.8 mm and a length of about 100 mm is immersed to a depth of 30 mm, the working part of which is first etched briefly in a 3 M hydrochloric acid solution, thoroughly washed with tap and distilled water, the rest of which removed with filter paper. Fix the copper electrode in a tripod and connect it with a conductor to the terminal of the measuring electrode of the DL-01 sensor. An electrolytic key is placed in a glass with an analyzed solution, which is connected through an intermediate vessel with a saturated solution of potassium chloride electrolytically to a saturated silver-silver reference electrode mounted in the sensor. The sensor cable is connected to a potentiometer, which is a pH meter pH-340. The potential of the copper electrode is measured after it is stabilized after 3-5 minutes at a solution temperature of 25 ° C, which is -305 mV.

Then the electrode is removed from the solution, washed, etched in acid, washed again in tap and distilled water, and its residues are removed with filter paper. 0.50 ml of milk is pipetted into the glass with the solution, which corresponds to 0.0128 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode and the electrode potential is measured after it is stabilized after 3-5 minutes at a solution temperature of 25 ° C, which is -315 mV.

Example 6. In another 50 ml glass beaker, add 20.0 ml of a 4.00 M aqueous sodium hydroxide solution, 1.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / l into a 50 ml measuring pipette, mix thoroughly until homogeneous . Then, 1.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0257 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1, 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -347 mV.

Example 7. In a third 50 ml glass beaker, add 20.0 ml of a 4.00 M aqueous solution of sodium hydroxide, 1.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L to a 50 ml measuring pipette, and the mixture is thoroughly mixed until homogeneous . Then, 1.50 ml of milk is introduced into the indicated solution, which corresponds to 0.0385 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1, 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -365 mV.

Example 8. In a fourth 50 ml glass beaker, add 20.0 ml of a 4.00 M aqueous sodium hydroxide solution, 1.50 ml of an aqueous solution of copper sulfate with a concentration of Cu ²⁺ 0.176 mol / l in a 50 ml measuring pipette, mix thoroughly until homogeneous . Then, 2.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0514 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is prepared beforehand, as in examples 1 and 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -393 mV.

According to the experimental data of examples 5-8, a calibration graph is constructed in the coordinates: the mass of proteins is the potential of the electrode, which fit directly. Then, under the conditions of the experiments described in example 5, in a copper-alkaline solution contribute:

2,62;- 0.25 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -315 mV, and the mass of proteins is determined from the calibration graph, which is 0.0064 g, which is calculated on the percentage of proteins in the analyzed sample is 2.5% when the ratio of the mass of Cu ²⁺ to the mass of proteins in the sample

2.62;

в образце 0,363.- 1.80 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -380 mV, and the mass of proteins is determined from the calibration graph, which is 0.0463 g, which is calculated on the percentage of proteins in the analyzed sample is 2.5% with respect to

in sample 0.363.

составляет 102. В раствор погружают на глубину 30 мм медный электрод, действуя далее согласно примерам 1, 5. Производят измерение потенциала медного электрода после его стабилизации по истечении 3-5 минут при температуре раствора 25°С, который составляет -345 мВ.Example 9. 22.5 ml of a 6.00 M aqueous solution of potassium hydroxide, 2.00 ml of an aqueous solution of copper sulphate with a concentration of Cu ^{2+ of} 0.176 mol / L are added into a 50 ml glass beaker, the mixture is thoroughly mixed until homogeneous. The ratio of the mass of hydroxyl ions to the mass of ions of Cu ²⁺

is 102. A copper electrode is immersed to a depth of 30 mm, proceeding further according to examples 1, 5. Measure the potential of the copper electrode after it stabilizes after 3-5 minutes at a solution temperature of 25 ° C, which is -345 mV.

Then the electrode is removed from the solution, washed, etched in acid, washed again in tap and distilled water, and its residues are removed with filter paper. 0.50 ml of milk is pipetted into the glass with the solution, which corresponds to 0.0128 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is mixed into the solution, then the copper electrode and the electrode potential is measured after it is stabilized after 3-5 minutes at a solution temperature of 25 ° C, which is -362 mV.

Example 10. In another 50 ml glass beaker, add a pipette 22.5 ml of a 6.00 M aqueous solution of potassium hydroxide, 2.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / l, the mixture is thoroughly mixed until homogeneous . Then, 1.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0257 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1, 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -375 mV.

Example 11. In a third 50 ml glass beaker, a pipette of 22.5 ml of a 6.00 M aqueous solution of potassium hydroxide, 2.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L is added, the mixture is thoroughly mixed until homogeneous . Then, 1.50 ml of milk is introduced into the indicated solution, which corresponds to 0.0385 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1, 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -395 mV.

Example 12. In a fourth 50 ml glass beaker, a pipette of 22.5 ml of a 6.00 M aqueous solution of potassium hydroxide, 2.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L is added, the mixture is thoroughly mixed until homogeneous . Then, 2.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0514 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1 and 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -422 mV.

According to the experimental data of examples 9-12, a calibration graph is constructed in the coordinates: the mass of proteins is the potential of the electrode, which fit directly. Then, under the conditions of the experiments described in example 9, in a copper-alkaline solution contribute:

3,48;- 0.25 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -352 mV, and the mass of proteins is determined from the calibration graph, which is 0.0064 g, which is calculated on the percentage of proteins in the analyzed sample is 2.5% when the ratio of the mass of Cu ²⁺ to the mass of proteins in the sample

3.48;

в образце 0,482.- 1.80 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -380 mV, and the mass of proteins is determined from the calibration graph, which is 0.0463 g, which is calculated on the percentage of proteins in the analyzed sample is 2.5% with a ratio

in sample 0.482.

составляет 76. В раствор погружают на глубину 30 мм медный электрод, действуя далее согласно примерам 1, 5. Производят измерение потенциала медного электрода после его стабилизации по истечении 3-5 минут при температуре раствора 25°С, который составляет -365 мВ.Example 13. In a 50 ml glass beaker, add 20.0 ml of a 10.00 M aqueous solution of sodium hydroxide, 4.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ²⁺ 0.176 mol / L in a 50 ml measuring pipette, and the mixture is thoroughly mixed until homogeneous. The ratio of the mass of hydroxyl ions to the mass of ions of Cu ²⁺

is 76. A copper electrode is immersed to a depth of 30 mm, proceeding further according to examples 1, 5. Measure the potential of the copper electrode after it stabilizes after 3-5 minutes at a solution temperature of 25 ° C, which is -365 mV.

Then the electrode is removed from the solution, washed, etched in acid, washed again in tap and distilled water, and its residues are removed with filter paper. 1.00 ml of milk is pipetted into the glass with the solution, which corresponds to 0.0257 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode (as in examples 1, 5) and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -383 mV.

Example 14. In a 50 ml glass beaker 20.0 ml of a 10.00 M aqueous solution of sodium hydroxide, 4.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L are pipetted into a uniform pipette, the mixture is thoroughly mixed until homogeneous. Then, 2.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0514 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1 and 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -403 mV.

Example 15. In a 50 ml glass beaker 20.0 ml of a 10.00 M aqueous solution of sodium hydroxide, 4.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L are pipetted into a uniform pipette, the mixture is thoroughly mixed until homogeneous. Then, 3.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0771 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is prepared beforehand, as in examples 1 and 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -421 mV.

According to the experimental data of examples 13-15, a calibration graph is constructed in the coordinates of the mass of proteins — the potential of the electrode, which fit directly. Then, under the conditions of the experiments described in example 13, in a copper-alkaline solution contribute:

6,97;- 0.25 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -372 mV, and the mass of proteins is determined from the calibration graph, which is 0.0068 g, which exceeds the actual protein mass of 6.2% , and in terms of the percentage of proteins in the analyzed sample, it is 2.65% when the ratio of the mass of Cu ²⁺ to the mass of proteins in the sample

6.97;

в образце 0,697.- 2.50 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -380 mV, and the protein mass is determined from the calibration graph, which is 0.069 g, which exceeds the actual weight of proteins by 7.8%, and in terms of pa, the percentage of proteins in the analyzed sample, it is 2.68% with the ratio

in sample 0.697.

составляет 43. В раствор погружают на глубину 30 мм медный электрод, действуя далее согласно примерам 1,5. Производят измерение потенциала медного электрода после его стабилизации по истечении 3-5 минут при температуре раствора 25°С, который составляет -342 мВ.Example 16. In a 50 ml glass beaker 20.0 ml of a 10.00 m aqueous solution of sodium hydroxide, 7.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L are pipetted into a uniform pipette, the mixture is thoroughly mixed until homogeneous. The ratio of the mass of hydroxyl ions to the mass of ions of Cu ²⁺

is 43. A copper electrode is immersed in a solution to a depth of 30 mm, acting further according to examples 1.5. The potential of the copper electrode is measured after it is stabilized after 3-5 minutes at a solution temperature of 25 ° C, which is -342 mV.

Then the electrode is removed from the solution, washed, etched in acid, washed again in tap and distilled water, and its residues are removed with filter paper. 1.00 ml of milk is pipetted into the glass with the solution, which corresponds to 0.0257 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode (as in examples 1, 5) and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -356 mV.

Example 17. In a 50 ml glass beaker, add 20.0 ml of a 10.00 M aqueous solution of sodium hydroxide, 7.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L into a 50 ml measuring pipette, and the mixture is thoroughly mixed until homogeneous. Then, 2.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0514 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is previously prepared, as in examples 1, 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -365 mV.

Example 18. In a 50 ml glass beaker, add 20.0 ml of a 10.00 M aqueous solution of sodium hydroxide, 7.00 ml of an aqueous solution of copper sulfate with a concentration of Cu ^{2+ of} 0.176 mol / L into a 50 ml measuring pipette, and the mixture is thoroughly mixed until homogeneous. Then, 3.00 ml of milk is introduced into the indicated solution, which corresponds to 0.0771 g of proteins, the mixture is thoroughly mixed until homogeneous, the electrolytic key is placed in the solution, then the copper electrode is prepared beforehand, as in examples 1 and 5, and the electrode potential is measured after its stabilization after 3-5 minutes at a solution temperature of 25 ° C, which is -371 mV.

According to the experimental data of examples 16-18, a calibration graph is constructed in the coordinates: the mass of proteins is the potential of the electrode, which fit directly. Then, under the conditions of the experiments described in example 16, in a copper-alkaline solution contribute:

12,2;- 0.25 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -338 mV, and the protein mass is determined from the calibration graph, which is 0.0077 g, which exceeds the actual weight of proteins by 20.3% , and in terms of the percentage of proteins in the analyzed sample, it is 3.0% with the ratio of the mass of Cu ²⁺ to the mass of proteins in the sample

12.2;

в образце 1,22.- 2.50 ml of milk, the mixture is thoroughly mixed, the electrode potential is measured, ceteris paribus, which is -370 mV, and the mass of proteins is determined from the calibration graph, which is 0.077 g, which exceeds the actual weight of proteins by 20.3%, and in terms of the percentage of proteins in the analyzed sample, it is 3.0% with the ratio

in sample 1.22.

As follows from the above examples, the proposed method allows the determination of the quantitative content of proteins in the analyzed samples potentiometrically under the conditions indicated in the distinctive part of the description. Moreover, it is much simpler than the prototype, since it does not require additional procedures for obtaining the enzyme, securing it to the ion-selective electrode, periodic calibration of the electrode due to aging of the enzyme, which also increases the reliability of the determination results by the proposed method.

Claims (1)

A method for determining the protein content, including creating an analytical environment with electrochemically active components, introducing into it a sample analyzed for protein content, measuring the potential of the indicator electrode relative to the reference electrode and determining the value of the amount of proteins by means of a calibration graph, characterized in that the analytical environment is used alkaline solution containing hydroxyl ions and copper (II) ions with a mass ratio of 76 ÷ 119, and measuring the potential by the indicator on the copper electrode at a weight ratio of copper ion (II) to proteins of 0.156 ÷ 6.97.