Method of determining sodium thiosulphate in solutions

FIELD: chemistry.

SUBSTANCE: invention relates to analytical chemistry and can be used in a system for monitoring content of sodium thiosulphate in solutions. The method of determining sodium thiosulphate in solutions is characterised by adding an analysed sample into a reaction vessel containing a corresponding amount of photogenerated iodine, obtained by blowing with air for 1-2 minutes and irradiating the reaction mixture with a stabilised light source, the mixture consisting of 0.5 M potassium iodide solution, an acetate buffer solution with pH 5.6 and a sodium eosinate sensitising agent, by detecting change in current in a cell and upon achieving constant current, re-blowing the reaction mixture with air for 2-3 minutes and re-irradiating with the stabilised light source until achieving the initial amount of iodine in the vessel, measuring the iodine generation time spent on achieving the decrease thereof, determining the amount of sodium thiosulphate from a calibration curve from the change in current and generation time.

EFFECT: invention provides a simple method of determining sodium thiosulphate in solutions and avoids use of expensive equipment.

10 tbl, 5 dwg

 

The invention relates to analytical chemistry and can be used in the system of control over the content of sodium thiosulfate in solution.

The issues of quality control and standardization of medications increase its relevance in the present time in connection with the General increase in the number registered in Russia medicines: over the past five years from 3.5 to 13.5 thousand thousand coming usually from different manufacturers [E. V. Degterev the Analysis of drugs in research, manufacturing and quality control / E. V. Degterev / ROS. chem. W. - 2002. - Vol. XLVI, No. 4. - P. 43-51].

The purity control of drugs, according to the rules of GLP, conducted in three areas: authentication, analysis of purity and quantitative determination of active substance. For analytical control of purity of drugs at the production stage it is advisable to use a simple but robust and capable of rapid analysis techniques. Despite the fact that at the present time to determine the active ingredient in drugs greatest application was received by instrumental methods, has not lost its value and titrimetric (volumetric), the advantages of which is the ease of execution, the possibility of introducing new titrants and indicators, as well as the development of new methods of determination. According to Th�darstvennoy Pharmacopoeia (GF), for the determination of sodium thiosulfate greatest application was received by the iodometric method [Arzamastsev A. P. Analysis of pharmaceutical mixtures / A. P. Arzamastsev, V. M. Pechennicov, V. L. Dorofeyev, E. N. Aksenov / M: satellite Company +. - 2000. - 275 p.], the main disadvantage is the need for standardization of the titrant, difficulty of storage and conducting routine analysis. To eliminate these shortcomings allows the application of instrumental methods for the determination of sodium thiosulfate.

Known photometric method determination of sodium thiosulfate based on recovering his borhydride potassium to sulfide, the interaction of the latter with N,N-dimethyl-n-phenylenediamine in the presence of ferric salts [GOST 25063.1-81 photographic Materials. Method for the determination of thiosulfate, the USSR State Committee on standards. Moscow. - 1982. - S. 7].

Formed form the final reaction is unstable and liable to break under the action of the oxygen of the air, which ultimately reduces the reproducibility of the results obtained.

A known method for the quantitative determination of sodium thiosulfate iodometric method, which was based on the reaction of its interaction with iodine [G. A. Melentyev, L. A. Antonova. Pharmaceutical chemistry. M.: Medicine. - 1986. - S. 91, the international Pharmacopoeia (third and�creation). - T. 3. Specification for quality control of pharmaceutical preparations. The world health organization. Geneva. - 1990. - p. 236].

The main disadvantage of the proposed method is the need for standardization of the titrant, strict compliance with the conditions of its storage.

The known method of determination of sodium thiosulfate in proyavlyaya-fixation solution, comprising administering to analyze the sample at pH=8,1-8,3 formalin, acidification of the solution, the introduction of iodine and subsequent titration of the excess iodine with standard sodium thiosulfate solution, with the aim of increasing the accuracy of the analysis in the presence of sodium sulfite, caustic soda, hydroquinone and methylpentane, formalin is injected in a ratio with the sample, is equal to 0.7 to 0.9:1, and the acidification is carried out with sulfuric acid to pH=1,1-1,3. SU 548808 IPC CL.2G01N 31/16, C01B 17/64, publ. 28.02.77.

However, this method is used to determine sodium thiosulfate in proyavlyaya-fixing solution, and when the determination in pharmaceuticals, it is not applied. The main disadvantage is the need for standardization of the titrant and application in routine analysis.

The closest to the claimed invention is a coulometric method for the determination of sodium thiosulfate based on the interaction of the electrogenerated iodine at a pH of 1.2 with a defined substance [Abolina �.G. New aspects of the galvanostatic kulonometrii in pharmaceutical analysis. The dissertation on competition of a scientific degree of the doctor of pharmaceutical Sciences. - Moscow, all-Russian research Institute of medicinal and aromatic plants (VILAR)RAAS, 2012. - 49 p.].

The disadvantage of the considered method of determining the complexity of the hardware design.

The object of the present invention is to provide a rapid and reliable method for determining the sodium thiosulfate in the solution.

The technical result of the claimed invention is:

- to simplify the method of determining through use as a titrant photogenerated iodine, while maintaining accuracy and detection limit;

- no expensive equipment.

This is achieved by a method of determination of sodium thiosulfate in solution, characterized by the introduction of the sample into the reaction vessel containing the corresponding amount of photogenerated iodine, obtained by blowing 1-2 minutes of air and radiation, stable light source, the reaction mixture consisting of 0.5 M solution of potassium iodide, acetate buffer solution with pH 5, 6 and sensitizer of eosint sodium, the recording of change of current in the cell and upon reaching its persistence p�repeated blowing of the reaction mixture in air for 2-3 minutes and re-irradiation stable light source to achieve the initial amount of iodine in the vessel, fixation time of generation of iodine spent on the completion of his loss, determining the amount of sodium thiosulfate on calibration schedule on the change of current and the generation time.

The essence of the claimed invention consists in that in the cell there is a change in the amount of iodine in a result of chemical interaction of sodium thiosulfate with the titrant, which leads to a decrease of current in an amperometric circuit. After reaching the constancy of the current in an amperometric circuit absorbing the solution was again flushed with air for 1-2 minutes, re-irradiated by the light before reaching the initial amount of iodine in the vessel and measured the generation time, who had gone to replenish loss of iodine. The absorption solution in the cell was replaced after running 20-30 tests. The amount of sodium thiosulfate in the sample was determined by analysis of calibration graphs. Cm. Fig. 1, 2. The results of determination are shown in tables 1, 2. The reliability of the obtained results was confirmed by the additives and iodometric method recommended by the STATE pharmacy [international Pharmacopoeia (third edition). - T. 3. Specification for quality control of pharmaceutical preparations. The world health organization. Geneva.- 1990. - p. 236].

Method recommended by the STATE pharmacy, volume, requires more drugs�and, the need for standardization of the titrant, the visual fixation point of equivalence and, consequently, leads to an increase in the time unit definition and low reproducibility. The proposed method is automated, eliminating the presence of a visual error, does not require expensive equipment, it can be used in conventional analytical laboratories.

Implementation of the method given in example 1.

Example 1. To implement the method using a sodium thiosulfate solution for injection (JSC "EXA" Stavropol, Staromarievskoe road 9 G, series 090313).

1 ml solution for injection quantitatively transferred to volumetric flask of 250 and was adjusted to the mark with bidistilled water. The working solution of the analyzed sample was obtained by repeated dilution 200 times.

In a vessel for titration (Fig.3) was placed 40 ml of 0.5 M solution of potassium iodide, 10 ml of a solution of eosint sodium, 20 ml of acetate buffer solution with a pH of 5.6. To obtain photogenerated iodine cell was purged for 1-2 minutes air and irradiated with a stabilized light source. Iodine is generated at a speed 2,53·10-7mmol/s to the content of his 4·10-4mmol. On the concentration of the titrant was measured by the change of the current in the circuit amperometric cell. After generation of iodine disconnected history�nick light and injected 1 ml of the working solution, while fixing the change of the readings of the galvanometer. After reaching a constant current, the cell was again flushed with air for 2-3 minutes, repeatedly irradiated by the light before reaching the initial amount of iodine in the vessel and measured the generation time required to compensate for the loss of iodine.

For further definitions of the solution in the vessel for titration, again irradiated by the light generating in it a certain amount of iodine. The same absorption solution allows 10-20 definitions. The content of sodium thiosulfate was determined by analysis of calibration graphs obtained for the standard solutions (Fig.1, 2). The accuracy of the results was controlled by the standard method and by the method of additives. The results of the determination of sodium thiosulfate in the solution for injection are presented in tables 1, 2, 3.

Fig.1. A graph of the change of current from the amount determined by sodium thiosulfate (ΔΔn=5,0337 m; R2=1)

Fig.2. A graph of the change of current from the amount determined by sodium thiosulfate (ΔΔτ=3,1328 m; R2=1)

Fig.3. Installation for the titration of substances photogenerated iodine: 1 - vessel for titration; 2 - light source; 3 - solar filter; 4 - magnetic stirrer; 5 - magnet; 6 - electrodes; 7 - current source; 8 - the voltage divider; 9 - galvanometer; 10 - �Altmer.

The results of the determination of sodium thiosulfate, found a photochemical method for the generation time (table.1) and the change of the current (tab.2) are consistent with each other and with results obtained by standard methods [G. A. Melentyev, L. A. Antonova. Pharmaceutical chemistry. M.: Medicine. - 1986. - S. 91, the international Pharmacopoeia (third edition). - T. 3. Specification for quality control of pharmaceutical preparations. The world health organization. Geneva. - 1990. - p. 236]. The lower limit for the determination of sodium thiosulfate is 0.2 µg for amperage and 0.32 μg at the time of generation of the iodine absorption cell.

Table 1
The results of the determination of sodium thiosulfate in the solution for injection, was found in generation time (n=5, p=0,95)
The analyzed sampleEntered, ugΔΔτ,Found, µgSr, %Found in mg/ml
Photochemical methodSr, %by STATE pharmacySolution for injection sodium thiosulfate0,018,75,98±0,305,0299,0±14,64,9299,0±15,05,0
5,034,410,98±30,423,8299,0±14,64,9300,0±15,05,0
10,0A 50.115,97±0,452,8298,5±14,64,9299,5±15,05,0
0,018,86,01±0,305,0300,5±14,54,8299,7±14,54,8
5,034,511,01±0,423,8300,5±14,54,8299,5±14,5/td> 4,8
10,0A 50.115,97±0,452,8298,5±14,54,9299,0±14,54,8

Table 2
The results of the determination of sodium thiosulfate in the solution for injection, was found in the change of the current (n=5, p=0,95)
The analyzed sampleEntered, ugΔΔn, AffairsFound, µgSr, %Found in mg/ml
Photochemical methodSr, %by STATE pharmacySr, %
Solution for injection sodium thiosulfate0,030,05,95±0,305,0297,5±14,64,9299,0±15,0 5,0
5,055,210,95±0,433,9297,5±14,64,9300,0±15,05,0
10,080,315,93±0,473,0296,5±14,75,0299,5±15,05,0
0,030,15,97±0,305,0298,5±14,64,9299,7±14,54,8
5,055,3Representation stands at 10.97±0,433,9298,5±14,64,9299,5±14,54,8
10,080,515,97±0,472,9298,5±14,64,9299,0±14,54,8

Conducted validation assessment meth�Dickie photochemical determination of sodium thiosulfate in solution for injection in terms of specificity, linearity and analytical area of methodology, accuracy and reproducibility. The specificity was estimated by the method "introduced - found", showed no influence of auxiliary substances (tab.1, 2) on the determination of sodium thiosulfate in solution for injection. The dependence between the change of the current (generation times) in the circuit amperometric installation and mass of sodium thiosulfate is linear, the value of the linear correlation coefficient is 1.0000. The accuracy and reproducibility was assessed by comparing the obtained results with the reference values. Statistical processing 7 definitions (tab.3) showed that the relative standard deviation is 0.3.

The reference value of the content of sodium thiosulfate (300 mg/ml) lies within the confidence interval of the mean value (298,7±0,340 on amperage and 298,9±0,278 at generation time), therefore, a systematic error is absent. Method of photochemical titration gives the correct results. The technique is valid in terms of specificity, linearity and analytical area of methodology, accuracy and reproducibility. The relative error of the mean photochemical determination of sodium thiosulfate in the solution for injection is 0.4%.

Table 3
Metrological characteristics of methods for photochemical determination of sodium thiosulfate in solution for injections (p=0,95)
The analyzed samplePhotochemical methodby STATE pharmacy
at generation timeto change the amperage
Found, mg/mlMetrological characteristicsFound, mg/mlMetrological characteristicsFound, mg/mlMetrological characteristics
Solution for injection sodium thiosulfate299,0XCP=298,9298,5XCP=298,7299,5XCP=299,7
299,0ΔCP=0,3299,0ΔCP=0,3300,0ΔCP=0,
299,0Sx=0,2236298,5Sx=0,2739299,5Sx=0,2550
299,0Sr=0,001299,0Sr=0,001299,7Sr=0,001
298,5εCP=0,28%298,5εCP=0,34%300,0εCP=0,32%

Photogenerated iodine can be used to standardize the sodium thiosulfate solution. The implementation of the method shown in example 2.

Example 2. To implement the method of preparing an aqueous solution of sodium thiosulfate. For this 0,5000 g of sodium thiosulfate (h. e. a.) quantitatively transferred to volumetric flask of 250 ml and the volume was adjusted to the mark with bidistilled water. The working solution (2 μg/ml) were repeated 1000 times dilution.

Further identification was carried out according to the above procedure. The results of determination are shown in tables 4, 5.

The results of the determination of sodium thiosulfate, found a photochemical method in time g�the generation (tab.4) and the change of the current (tab.5), are consistent with each other and with results obtained by standard methods [G. A. Melentyev, L. A. Antonovaeronautical chemistry. M.: Medicine. - 1986. - S. 91. The international Pharmacopoeia (third edition). - Vol. 3 Specification for quality control of pharmaceutical preparations. The world health organization. Geneva. - 1990. - p. 236]. The relative standard deviation in the determination of sodium thiosulfate to 18.0 micrograms not exceed 5,00%

Table 5
The results of the determination of sodium thiosulfate in aqueous solution, was found to change the current (n=5, p=0,95)
Introduced sodium thiosulfateΔn, AffairsΔΔn, AffairsFound in mcg
Photochemical methodSr, %by STATE pharmacy,Sr, %
V, mlmNa2S2O3,mcg
0,00,02,0----
1,02,011,99,91,98±0,105,11,98±0,115,6
2,04,022,020,03,98±0,184,54,00±0,184,5
3,06,032,130,16,00±0,183,06,00±0,183,0
4,08,041,939,97,94±0,243,07,98±0,243,0
5,010,0 52,550,29,96±0,282,810,0±0,282,8
6,012,062,860,812,06±0,332,711,96±0,332,8
7,014,072,270,213,94±0,382,714,00±0,382,7
8,016,082,180,115,92±0,442,815,90±0,442,8
9,018,092,590,517,98±0,492,717,90±0,492,7

Table 4
The result� determination of sodium thiosulfate in aqueous solution, was found in generation time (n=5, p=0,95)
Introduced sodium thiosulfateΔτ,ΔΔτ,Found in mcg
Photochemical methodSr, %by STATE pharmacySr, %
V, mlmNa2S2O3,mcg
0,00,01,5-----
1,02,07,66,11,95±0,105-11,98±0,115,6
2,04,024,012,5 3,97±0,174,34,00±0,184,5
3,06,020,218,75,97±0,183,06,00±0,183,0
4,08,026,525,07,97±0,232,97,98±0,243,0
5,010,032,9Of 31.410,03±0,272,710,0±0,282,8
6,012,039,237,7A 12.03±0,332,711,96±0,332,8
7,014,045,443,914,00±0,372,614,00±0,38 2,7
8,016,051,750,216,00±0,452,815,90±0,442,8
9,018,057,856,317,95±0,482,717,90±0,492,7

Replacement of the aqueous organic solvent results in change of the conditions of generation of iodine, which affects the results of the determination of sodium thiosulfate.

Was originally calibrated setting in the presence of ethyl alcohol, acetone and acetic acid. To do this, we measured the readings of the galvanometer in the absence and in the presence of solvents upon the addition of iodine solution from microburette in the system containing 40 ml of a 0.5 M solution of potassium iodide, 20 ml of acetate buffer solution with a pH of 5.6. The results of the determination are presented in table.6 and in Fig.4.

Table 6
The dependence of the readings of the galvanometer on the concentration of iodine in the presence of organic solvents ( CI21·10-4M)
Introduced iodineThe indications of the galvanometer, n
V, mlWith·104mmolH2Oorganic solvents
C2H5OHCCl4CH3COOH
0,00,00,0000,0
0,40,419,916,014,820,0
0,60,632,024,122,132,0
0,80,842,032,029,542,0
1,01,051,039,837,051,0
1,51,574,060,055,574,0
2,02,0100,079,873,5100,0

Fig.4. The dependence of the readings of the galvanometer on the concentration of iodine in aqueous solution (1) and in the presence of 0.02 mmol of ethanol (2), carbon tetrachloride (3) and acetic acid (4).

From the data presented in table.6 and in Fig.4 it follows that the scale of the galvanometer iodine in aqueous solutions and in the presence of acetic acid equal to (2.0·10-6mmol/div), indicating the absence of a chemical reaction between the solvent and reagent.

The price of division of the scale of the galvanometer iodine in the presence of ethanol is 2.5·10-6mmol/div, and in the presence of carbon tetrachloride is 2.7·10-6mmol/div. Thus in these solvents there is a linear relationship between the readings of the galvanometer and the iodine concentration. The decrease in sensitivity�enosti can be associated with partial oxidation of ethanol and evaporation of carbon tetrachloride.

Introduction glacial acetic acid used as the solvent in the solution can cause a change in pH, leading to changes in the generation rate of iodine. The authors recommended that photogeneration of iodine at optimum pH 5÷9 [Dodin E. I. Photochemical analysis / E. I. Dodin. M.: Metallurgy. 1979. - P. 54], which is created by using acetate buffer solution.

Study of the effect of acetic acid on the change in buffer capacity of a solution containing 40 ml of 0.5 M solution of potassium iodide, 20 ml of acetate buffer solution with a pH of 5.6 are given in table.7.

Table 7
The dependence of the pH meter from the amount of acetic acid introduced into the reaction mixture
Entered acetic acid, mmol0,0050,0100,0200,1000,2000,3000,400
pHIs 5.585,575,54Levels lower than the 5.375,225,11 Of 5.02

The data obtained indicate that when the concentration of acetic acid is less than 0,200 mmol pH of the solution remains substantially constant. Consequently, the use of acetic acid as the solvent should not affect the speed of generation of iodine (table.8, Fig.5).

Table 8
The dependence of the readings of the galvanometer from the time of generation of iodine in different concentrations of acetic acid
The generation time of iodine τ, sThe indications of the galvanometer when the concentration of acetic acid in solution, mmol
0,000,020,20
0000
10161615
20323231
30484848
646463
50808079

Fig.5. The dependence of the readings of the galvanometer from the generation time of iodine in the absence (1) and in presence (2) of acetic acid.

The data obtained show that the rate of generation of iodine in aqueous solution and in the presence of acetic acid the same (2,53·10-7mmol/s), which again confirms the absence of chemical reactions. Thus, acetic acid can be used as the solvent for the transfer of an analyte in a solution.

The use of acetic acid for the transfer of sodium thiosulfate to the solution made in example 3.

Example 3. To implement the method using an aqueous solution of sodium thiosulfate. For this 0,5000 g of sodium thiosulfate (h. e. a.) quantitatively transferred to volumetric flask of 250 ml, containing 10 ml of glacial acetic acid and the volume was adjusted to the mark with bidistilled water. The working solution (2 μg/ml) were repeated 1000 times dilution.

Further identification was carried out according to the above procedure. The results of determination are shown in tables 9, 10.

4,0
Table 9
The results of the determination of thiosulfate sodium acetate in the medium, was found in the change of the current (n=5, p=0,95)
Introduced sodium thiosulfateΔn, AffairsΔΔn, AffairsFound in mcg
Photochemical methodSr, %by STATE pharmacySr, %
V, mlmNa2S2O3,mcg
0,00,02,0----
2,04,022,020,03,98±0,184,53,97±0,184,5
8,042,040,07,96±0,253,17,90±0,243,0
6,012,062,460,411,98±0,332,811,96±0,332,8
8,016,082,080,015,90±0,442,815,90±0,442,8

Table 10
The results of the determination of thiosulfate sodium acetate in the medium, was found in generation time (n=5, p=0,95)
Introduced sodium thiosulfateΔτ,ΔΔτ,Found in mcg
Photochemical methodSr, % by STATE pharmacySr, %
V, mlmNa2S2O3,mcg
0,00,01,5-----
2,04,024,012,53,97±0,174,34,00±0,184,5
4,08,026,525,07,97±0,243,07,98±0,243,0
6,012,039,0A 37.511,96±0,322,711,96±0,332,8
8,0/td> 16,051,550,015,95±0,442,815,90±0,442,8

From the data table.9, 10 it follows that the results obtained are characterized by good reproducibility. The relative standard deviation in the determination of sodium thiosulfate in acetic acid-water medium does not exceed 5.0 per cent. Therefore, acetic acid can be used as the solvent for the quantitative determination of sodium thiosulfate.

Thus, the proposed photochemical method for the determination of sodium thiosulfate in solution rapid, does not require expensive equipment, it can be used in conventional analytical laboratories.

Method of determination of sodium thiosulfate in solution, characterized by the introduction of the sample into the reaction vessel containing the corresponding amount of photogenerated iodine, obtained by blowing 1-2 minutes of air and radiation, stable light source, the reaction mixture consisting of 0.5 M solution of potassium iodide, acetate buffer solution with pH 5.6 and sensitizer of eosint sodium, the recording of change of current in the cell and upon reaching its persistence repeat�rim by blowing the reaction mixture with air for 2-3 minutes and re-irradiation stable light source to achieve the initial amount of iodine in the vessel, fixation time of generation of iodine spent on the completion of his loss, determining the amount of sodium thiosulfate on calibration schedule on the change of current and the generation time.



 

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FIELD: medicine.

SUBSTANCE: sample is applied on a paper filter, and standard calibration solutions of metronidazole in the concentration range of 10-100 mcl are radially applied on the same filter. The filter is processed with a developing agent containing 5% potassium hydroxide and acetone taken in ratio 2:1 and thermostated at 100°C until coloured spots are visible. A colour intensity of the sample spot is compared to the colour of the spot colour of the reference calibration solutions to determine the metronidazole concentration in the analysed sample.

EFFECT: method enables the fast and reliable monitoring of the metronidazole content and the timely correction of the therapeutic process.

3 ex

FIELD: medicine.

SUBSTANCE: invention refers to medicine, namely to studying and analysing medical preparations, and can be used for standardising herbal raw materials. A method for identification and qualitative measurement of chlorophyll, carotinoids and hydroxycinnamic acids in a combination in great nettle leaves involves a 1-hour fractional extraction, 30 min each of the ground raw material having a particle size of 1.0 mm on a water bath at a temperature of 100°C with 70% ethanol in a ratio of the herbal raw material to the extractant of 1:100, the combination of the extracts and reduction to 100 ml with a solvent, dilution of the prepared solution in a ratio of 2:25 in 96% ethanol, measuring an optical density of the solution in relation to 96% ethanol at maximum absorption 328±1 nm, 442±1 nm and 667±1 nm, calculation of the total content of hydroxycinnamic acids equivalent to chlorogenic acid, carotinoids equivalent to violaxanthin and chlorophyll in the percentage equivalent to an absolute dry mass of the raw material by formulas.

EFFECT: method provides availability, simplicity, efficiency and low error of measurement.

3 dwg, 1 ex

FIELD: chemistry.

SUBSTANCE: method of determining fat-soluble vitamins A, D2, E and β-carotene which are present at the same time includes separating the fat-soluble vitamins from a substance by extraction with 96% ethanol, separating the alcohol extract of vitamins using a separating funnel, successive chromatography using Sorbfil PTSKH-P-A silica gel plates on a polymer substrate using two eluents with a different range, time of saturating the chamber with eluent vapour of 20 minutes and elution time of 55 min; drying the plates at temperature not lower than 80°C in a temperature-controlled chamber for 3-5 min, treating the plates with a developer - 5% alcohol solution of phosphatomolybdic acid; according to the invention, the eluents used are hexane:chloroform (19:1) and hexane:chloroform (3:1), and detection of the chromatographic zone of β-carotene is carried out before treating the plates with a developer in day light.

EFFECT: simpler and faster process of determining fat-soluble vitamins.

10 dwg, 3 ex

FIELD: chemistry.

SUBSTANCE: in order to extract iron (III) from water solutions diphenylguanidine (DPG) is applied as the first organic reagent. As the second organic reagent, salicylic acid (SA) is applied, and as solvent of organic phase chloroform is applied. In organic phase complex with molar component ratio DPG: Fe3+:SA, equal 1:1:1, is extracted. Process of iron (III) extraction is carried out at medium acidity pH=1.5-2.5 with the following detection of iron (III) by trimetric method.

EFFECT: invention makes it possible to increase selectivity and simplify process of extraction and detection of iron from water solutions.

2 cl, 5 dwg, 1 ex

FIELD: chemistry.

SUBSTANCE: method of determining concentration of grafted amino groups on the surface of mineral filling agents includes preparation of acetylating solution by mixing initial components, its addition to weighed portion of modified mineral filler sample, exposure for quantitative realisation of reaction, titration with alkali solution in presence of indicator, calculation of concentration of amino groups by difference of results of idle titration and sample titration. As acetylating solution used is 0.5-0.6 M solution of acetic anhydride in mixed solvent dichloroethane-pyridine in ratio from 0.5:1-2:1, which contains 0.025-0.15 mol/l of chloric acid as catalyst. 0.5-0.6 M of acetylating solution in mixed solvent, containing chloric acid, is added to weighed portion of modified mineral filler, ratio of weighed portion of sample weight to volume of acetylating solution constitutes 1:4-1:5, after which it is exposed and hydrolysing mixture, consisting of dimethylformamide, pyridine, water, taken in ratio 6:3:1 respectively, is added. After that, obtained mixture is centrifuged to separate residue.

EFFECT: simplification and extension of assortment of analysed materials, containing grafted amino groups on the surface of mineral fillers.

13 ex, 1 tbl

FIELD: chemistry.

SUBSTANCE: method involves potentiometric titration of a sample with complexon (III) with an indicator electrode made of bismuth metal with a buffer solution at pH 4.1-9.0.

EFFECT: easier, more accurate and safer analysis.

2 tbl, 1 dwg

FIELD: chemistry.

SUBSTANCE: method of determining copper involves direct potentiometric titration of complexon (III) at pH 4.1-9.0 with an indicator electrode of bismuth metal in an acetate buffer solution. The invention enables to determine copper (II) when its content is 32-660 mcg/ml of the solution in an electrochemical cell with unit determination error of not more than 1%.

EFFECT: easy analysis using nontoxic materials.

2 tbl, 1 dwg, 1 ex

FIELD: chemistry.

SUBSTANCE: method of determining lead involves potentiometric titration of a complexon (III) sample with an indicator electrode of bismuth metal with a buffer solution at pH 3.5-9.0. The invention enables to determine lead (III) with content of 0.14-2.3 mg/ml of a solution in an electrochemical cell with unit determination error of not more than 1%.

EFFECT: easy analysis using nontoxic materials.

2 tbl, 1 dwg

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry. Lithium-iron phosphate having an olivine crystal structure has a composition expressed by the chemical formula (I) L1+aFe1-xMx(PO4-b)Xb (where M is selected from Al, Mg, Ti; X is selected from F, S, N; -0.5≤a≤+0.5; 0≤x≤0.5; and 0≤b≤0.1 ), contains 0.1-5 wt % Li3PO4 and does not contain or contains less than 0.25 wt % Li2CO3. Content of Li3PO4 in the lithium-iron phosphate increases electrochemical stability and ensures thermal safety and ion conductivity.

EFFECT: lithium-iron phosphate according to the present invention can be used as an active material for a positive electrode of a secondary lithium battery.

15 cl, 1 tbl, 5 dwg

FIELD: chemistry.

SUBSTANCE: invention describes a method of determining weight ratio of polyhexamethylene guanidine hydrochloride in a disinfectant, involving titration of a sample of the analysed disinfectant using a prepared indicator solution and then calculating the amount using a formula. Titration is carried out using a silver nitrate solution. The indicator used is fluorescein. The weight ratio of polyhexamethylene guanidine hydrochloride is calculated using a formula.

EFFECT: faster analysis, high reliability owing to more accurate determination of the end of titration and cheaper analysis.

1 ex

FIELD: chemistry.

SUBSTANCE: aqueous solution of an analysed sample of a deicing agent containing 1-50 wt % alkali metal formates is mixed with alkaline bromine solution with bromine concentration of 0.1 mol/dm3 in amount of 0.02-0.08 wt % of the weight of the formate; glacial aceit acid is added until pH drops to less 1; the mixture is held at room temperature; further, potassium iodide solution is added and then titrated with a pentahydrate solution of sodium thiosulphate; aqueous starch solution is then added and titrated until the solution becomes clear. Optimum conditions for carrying out the method are as follows: 15-25°C, relative humidity of 45-80% and atmospheric pressure of 630-800 mm Hg.

EFFECT: improved method.

4 cl, 1 tbl, 1 ex

FIELD: chemistry.

SUBSTANCE: method involves vpotentiometric titration of a sample with complexon (III) with an indicator electrode made of bismuth metal at pH 1.9-4.2.

EFFECT: high accuracy and simple analysis.

2 tbl, 1 dwg

FIELD: medicine.

SUBSTANCE: method for calcium and magnesium evaluation in herbal crude drug is implemented by extraction of the crude drug in 8-12% hydrochloric acid in the relation of the crude drug to the extractant 1:9-11 that is followed by complexometric titration with the use of indicators: for total calcium and magnesium - eriochrome black T; for calcium - murexide or chromium dark blue; for magnesium - pyrocatechin violet.

EFFECT: accelerated and simplified analysis.

1 tbl

FIELD: analytical methods.

SUBSTANCE: invention concerns analytical determination of acids, acid salts, and other substances having acid reaction and reacting with alkalis, in particular titration method for use both in educational process and in industry. Method comprises weighing and dissolving in water sample of a substance, or taking measured volume of a substance followed by titration thereof using alkali titrants and pH-meter-mediated determination of equivalence point, said titrants being electrochemically activated alkaline water with pH 11.9-12.1 thereto 0.1% NaCl was added before activation.

EFFECT: reduced expenses on preparation of alkali solutions.

7 dwg, 12 ex

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