RU2470291C1 - Method of determining weight ratio of basic substance in crystalline glyoxal - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to analytical chemistry and specifically to a method of determining weight ratio of basic substance in crystalline glyoxal. The method involves gas-chromatographic determination of glyoxal in a solution. Crystalline glyoxal is first dissolved in water at temperature 53-57°C, 34.7-36.7 mg samples of the aqueous solution are collected, followed by addition of 9.5-11.5 mg benzyl alcohol, 2.0 ml ethanol and 80-100 mg o-phenylene diamine. The samples are then held for 20 minutes. Analysis is then carried out using a gas chromatograph with given flow rate of the carrier gas at given temperature of the column thermostat, temperature of the evaporator and temperature of the detector. The area of the chromatographic peaks of benzyl alcohol and quinoxaline is determined and the weight ratio of the basic substance in the crystalline glyoxal is then calculated. The following ratio of components is used, wt %: crystalline glyoxal 37-43; water 63-57.

EFFECT: high reproducibility and accuracy of determining glyoxal.

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Description

The invention relates to the field of analytical chemistry, namely to the analysis of crystalline glyoxal and products based on it, can be used in production activities (in case of streaming production control, output quality control).

A known method of simultaneous qualitative and quantitative determination of carboxylic acids and aldehydes by gas-liquid chromatography (RF Patent No. 2393469, IPC G01N 30/00, G01N 31/00. - publ. 27.06.2010). This patent describes a method for the quantitative chromatographic determination of the concentrations of aldehydes and carboxylic acids when they are combined in aqueous solutions. The components are determined by pretreating the sample with a derivatizing agent (tributyl borate in the presence of concentrated hydrochloric acid), treating the reaction mixture with a saturated solution of sodium bicarbonate, then extracting it with hexane in the presence of acetonitrile and chromatography.

The disadvantage of the proposed method is the complexity of sample preparation, including derivatization and extraction. Accurate standardization of the steps involved in calibration and analysis is required. Also, the distribution between the water and hexane of the components of a multicomponent mixture depends on the composition and can be different for different compositions of the mixture, the presence of impurities and different ranges of measured concentrations. The method proposed by the authors of the patent can be used to determine the mass content of glyoxal in low concentration solutions. In the case of analysis of crystalline glyoxal, the resulting working solutions have a high concentration (20-40%). In the region of high concentrations, glyoxal in aqueous solutions exists in the form of di- and trimers [Whipple, E. B. (1970). "Structure of Glyoxal in Water". J. Am. Chem. Soc. 90: 7183-7186]. Moreover, only terminal aldehyde groups are available for derivatization. Therefore, other approaches are required in the analysis of crystalline glyoxal.

One of the common methods for the qualitative and quantitative determination of aldehydes in aqueous solutions is the method of high performance liquid chromatography (HPLC). Before determination, glyoxal is derivatized with 2,4-dinitrophenylhydrazine (DNPH) [Koichi Nakajima, Kyuji Ohta, Toufik A. Mostefaoui, Wen Chai, Takamitsu Utsukihara, C. Akira Horiuchi, Masahiko Murakami Glyoxal sample preparation for high performance 2,4-dinitro-phenylhydrazone derivative: Suppression of polymerization and mono-derivative formation by using methanol medium, Journal of Chromatography A, Volume 1161, 2007, p.338-341] or 3-methyl-2-beznotiozolinin hydrazone (MBTN) [Yamei Zhu, Xiaoli Yao, Shaohui Chen, Qun Cut and Haiyan Wang HPLC determination of glyoxal in aldehyde solution with 3-methyl-2-benzothiazolinone hydrazone, Frontiers of Chemical Science and Engineering Volume 5, Number 1, 117-121]. Derivatives of aldehydes in this case are characterized by good absorption and can be determined using a photometric detector. This group of methods is characterized by high sensitivity and is used to determine trace amounts of aldehydes.

The disadvantages of the method include the high cost of liquid chromatography, the need to use reagents of high purity. As in analogue 1, one of the stages of the analysis is extraction, which introduces an additional error in the analysis. Another drawback is the feature of the work of photometric detectors in the field of high concentrations. The dependence of the transmission on the concentration of the solution is non-linear and at a certain concentration goes to the so-called "plateau". In this case, additional dilution of the sample to the operating range of the detector is required.

A known method for determining the components of the reaction of catalytic oxidation of ethylene glycol to glyoxal by gas chromatography, selected as a prototype (E.Yu. Yakovleva, V.Yu. Belotserkovskaya Determination of the components of the reaction of catalytic oxidation of ethylene glycol to glyoxal by gas chromatography. Journal of Analytical Chemistry, 2010, Volume 65 , No. 8, p. 851-855). In this paper, we consider a method for determining the concentrations of the components of the catalytic oxidation of ethylene glycol to gloixal (glyoxal, formaldehyde, ethylene glycol, acetaldehyde, ethanoic acid) by gas chromatography. The concentration of the components is established based on the ratio of the areas of chromatographic peaks of the determined components and the known amount of the internal standard introduced into the sample (n-propanol was used in this work). Separation of the components is carried out under conditions of a programmed temperature increase at the polar stationary phase of Porapak N and non-polar polymer sorbents (Chromosorb 102, 106, 108, Porapak QS, Haysep Q and Haysep D).

The disadvantage of this method is the instability of the analysis, which consists in changing the output time of the components in sequential analyzes. The instability of sequential chromatograms does not allow the use of this method for the quantitative analysis of samples containing glyoxal. The authors analyzed model samples containing glyoxal, formaldehyde and ethylene glycol. It is known that, over time, di-, tri- and polymerization of glyoxal occurs in aqueous solutions. This also manifests itself in the presence of other aldehydes, such as formaldehyde. Due to the fact that this method uses a direct determination of glyoxal, in the case of its polymerization, the amount of glyoxal, determined in the form of a monomeric form, will be underestimated.

Crystalline glyoxal is a glyoxal polymer, therefore, for the quantitative determination of glyoxal in crystalline glyoxal by gas chromatography, a number of serious modifications and changes are necessary.

The objective of the present invention is to develop a method for determining the mass fraction of the main substance in crystalline glyoxal, which improves the reproducibility and accuracy of the determination of glyoxal.

The problem is solved in that the method for determining the mass fraction of the main substance in crystalline glyoxal includes gas chromatographic determination of glyoxal in solution, but unlike the prototype, crystalline glyoxal is previously dissolved in water at a temperature of 53-57 ° C, an aqueous solution is sampled 34.7 -36.7 mg, followed by the addition of 9.5-11.5 mg of benzyl alcohol, 2.0 ml of ethanol and 80-100 mg of o-phenylenediamine, keeping the sample for 20 minutes, followed by the introduction of a gas chromatograph into the evaporator using the syringe and the analysis at a flow rate of the carrier gas: nitrogen - 28-32 ml / min, or hydrogen - 38-42 ml / min, or air - 490-520 ml / min, at a column thermostat temperature of 135-145 ° C, the temperature of the evaporator is 195–205 ° С and the temperature of the detector is 150 ° С using a 1.6 m chromatographic column filled with a Reoplex-400 sorbent deposited on a Chromaton N support, followed by determination of the areas of chromatographic peaks of binzyl alcohol and quinoxaline and calculation of the mass fraction the main substance in crystalline glyoxal, when blowing ratio, wt.%:

crystalline glyoxal 37-43 water 63-57

The analysis method is based on the quantitative chromatographic determination of glyoxal in the form of quinoxaline by the internal standard method. Quinoxaline is formed in an alcoholic solution of glyoxal upon interaction with o-phenylenediamine:

The concentration of glyoxal is determined by measuring the ratio of the areas of chromatographic peaks of quinoxaline and a known amount of the internal standard introduced into the sample. Benzyl alcohol is used as standard. For measurements, a Chromatek Crystal 5000.1 gas chromatograph with a flame ionization detector, a microsyringe MSH-10 according to TU 2833106, analytical balance type A-100 A, accuracy class 2, pipette 2 ml according to GOST 29169, vials 15-20 ml . The components of the mixture are separated using a 1.6 m long glass gas chromatographic column filled with a Reoplex-400 sorbent deposited on a Chromaton N support. A sample of crystalline glyoxal 0.4 ± 0.03 g is transferred into a 15 ml vial and weighed (m _{sp. Cr} ) accurate to 4 digits of a gram. Then add 0.6 ± 0.03 g of distilled water and re-weigh

The resulting mixture in a vial is sealed with a rubber stopper and placed in a thermostat at a temperature of 55 ± 2 ° C and kept until crystalline glyoxal is completely dissolved (20 min). After dissolution, the solution was allowed to cool to room temperature. On an analytical balance, 34.7 ± 1 mg of the resulting aqueous solution is weighed into a 15 ml vial (previously weighed). 10.7 ± 1 mg of benzyl alcohol and 80-100 mg of o-phenylenediamine are weighed into the same vial, then 2 ml of ethyl alcohol are added to the resulting mixture with a pipette.

The resulting mixture was incubated for 20 minutes until the crystals of o-phenylenediamine were completely dissolved. The following chromatographic operation parameters are set: detector temperature - 150 ° С, evaporator temperature - 200 ° С, chromatograph column thermostat temperature - 140 ° С, carrier gas (nitrogen) feed rate - 30 ml / min, hydrogen supply speed (for detector) 40 ml / min, oxygen supply rate (for the detector) 500 ml / min. The prepared mixture in an amount of 1 μl / l using a MSH-10 microsyringe is introduced through the head of the evaporator, piercing the rubber membrane. Before entering the mixture, the syringe is washed first with ethyl alcohol 10 times, then with the analyzed solution (mixture) at least 10 times. The order of the peaks in the chromatogram: ethyl alcohol (solvent) -benzyl alcohol - quinoxaline. The approximate exit time of benzyl alcohol is 10 minutes, quinoxaline 12 minutes. The exact release time of glyoxal (quinoxaline) and benzyl alcohol is determined by the pure components, or by the method of additives.

The mass content of glyoxal in crystalline hyloxal is calculated based on the ratio of the areas of chromatographic peaks of quinoxaline and standard (benzyl alcohol) according to the formula:

where C _go - mass fraction of glyoxal in crystalline glyoxal,%;

m _sp. - the mass of the sample solution of crystalline glyoxal, mg;

S _x is the area of the chromatographic peak of quinoxoline;

S _article - the area of the chromatographic peak of benzyl alcohol (standard);

a, b are the coefficients of the equation of the calibration dependence;

m _article is the mass of benzyl alcohol (standard), mg;

m _{ave. cr} - mass of a sample of crystalline glyoxal, g;

- масса дистилированной воды, г

- mass of distilled water, g

Before measurements, the chromatograph is calibrated by determining the relationship between the mass ratio of quinoxaline and the internal standard in the sample on the ratio of the areas of their chromatographic peaks. Prepare 8-10 solutions of glyoxal with a known concentration in the range from 5 to 40% wt.

и применяют при дальнейших анализах. При необходимости могут быть применены другие аппроксимирующие функции.To establish the calibration dependence, the solutions are analyzed similarly to a solution of crystalline glyoxal, determining the ratio of the areas of chromatographic peaks of the determined component and the internal standard. Next, build a graph of the relationship of the mass ratio of glyoxal / standard (benzyl alcohol) (m _x / m _st ) on the ratio of the peak areas of quinoxaline / standard (S _x / S _ct ). The resulting dependence is approximated by an equation of the form

and used in further analyzes. If necessary, other approximating functions can be applied.

An example embodiment of the invention is given below.

Example 1

A sample of crystalline glyoxal 0.3934 g was taken, dissolved in 0.6122 g of water at a temperature of 55 ° C in a liquid thermostat. A sample was taken from the resulting aqueous solution for analysis (35.1 μg), benzyl alcohol (11.1 μg), ethanol (2 ml), and o-phenylenediamine (~ 100 mg) were added. The mixture was aged for 20 minutes at room temperature. Then 1 μl of the sample was introduced into the evaporator of the chromatograph. The parameters of the chromatograph were set according to the proposed method. As a result of the analysis, the areas of chromatographic peaks of quinoxaline and benzyl alcohol were determined. Based on the obtained areas of chromatographic peaks, the content of the basic substance in the sample of crystalline glyoxal was calculated. Table 1 shows the result of the analysis of a sample of crystalline glyoxal.

Table 1 Quinosoline peak area, rel. The peak area of benzyl alcohol, rel. units Mass fraction of the main substance in crystalline glyoxal,% wt. 194,482.4 109420.5 67.08

The claimed method allows the determination of the mass fraction of the main substance in crystalline glyoxal and improves the stability, reproducibility and accuracy of its determination in aqueous solutions.

One of the advantages of the claimed invention is the stability of the glyoxal exit time for sequential determinations in a wide range of concentrations of the component to be determined. Table 2 presents the release times of quinoxaline for various concentrations of glyoxal in solution.

table 2 No. one 2 3 four 5 6 Exit time, min 11.66 11.66 11.64 11.65 11.53 11.56 The concentration of glyoxal,% wt. 20.1 0.6 38,4 9.8 1,5 0.1

To establish the accuracy and reproducibility of the analysis by the proposed method, as well as the stability of the calibration characteristics, an experiment was conducted to determine the mass fraction of glyoxal in model aqueous solutions of glyoxal in the working concentration range. For each solution, three series of measurements were performed (on different days) with three parallel determinations. Thus, the stability of the analysis is confirmed by the high agreement of the results for different series, and the high reproducibility is confirmed by the results of parallel determinations in one series. The accuracy of the analysis is confirmed by the agreement of the average value of the measured concentrations with the concentration of the prepared model solutions. Table 3 presents the results of parallel determinations of glyoxal concentration in model solutions.

Table 3 Model Solution Number The content of mass fraction of glyoxal in the working sample The result of the analysis,% wt. Batch number one 2 3 one 4.88 4.84 4.91 one 5.0% 2 5.06 5.06 5.02 3 4.98 4.91 5.00 one 15.06 15,59 15,59 2 15.1% 2 15.00 15,20 15.08 3 14.98 15.05 15.02 one 19.82 19.87 19.85 3 20.0% 2 20.46 20.45 20.50 3 20.05 19.98 19.87 one 30.16 30.08 30.36 four 30.6% 2 30.10 30.19 30.12 3 30.19 30.24 30.18 one 39.27 39.05 39.09 5 40.0% 2 40.02 39.9 39.7 3 39.27 39.5 39,4

To control the stability, accuracy and reproducibility of the analysis, a solution containing 39.3% glyoxal was analyzed for 6 weeks.

Two parallel definitions were performed. Table 4 shows the results of the analysis of glyoxal solution for five weeks.

Table 4 The concentration of glyoxal (measurement 1), C1,% wt. The concentration of glyoxal (measurement 2), C2,% wt.

, % мас.Glyoxal concentration (average),

% wt. The exact concentration of glyoxal in the analyzed solution, A,% wt. Absolute deviation

% wt. A week one 39.0 39.0 39.0 0.3 2 39.2 39.2 39.2 0.1 3 38.8 38.9 38.8 39.3 0.5 four 39.3 39.2 39.2 0.1 5 39.5 39.2 39.3 0,0

The accuracy of the method was additionally confirmed experimentally by the additive method. 0.5406 g of a solution containing 38.0% glyoxal was added to a 0.9462 solution with a content of 9.8%. The solution with the additive was also analyzed by the proposed method. Table 5 shows the results of the analysis of a sample of glyoxal with the additive.

Table 5 The initial concentration of glyoxal,% wt. The estimated concentration of glyoxal with the addition,% wt. The measured concentration of glyoxal in solution with the addition,% wt. Introduced,% wt. Found,% wt. 9.8 20.7 20.5 10.9 10.7

Thus, the claimed method is practically feasible and allows us to solve the problem.

Claims (1)

The method of determining the mass fraction of the main substance in crystalline glyoxal, including gas chromatographic determination of glyoxal in solution, characterized in that the crystalline glyoxal is first dissolved in water at a temperature of 53-57 ° C, an aqueous solution is sampled 34.7-36.7 mg, followed by the addition of 9.5-11.5 mg of benzyl alcohol, 2.0 ml of ethanol and 80-100 mg of o-phenylenediamine, keeping the sample for 20 minutes, then introducing a gas chromatograph into the evaporator using a microsyringe and analyzing with carrier gas flow: nitrogen - 28-32 ml / min, or hydrogen - 38-42 ml / min, or air - 490-520 ml / min, at a column thermostat temperature of 135-145 ° С, evaporator temperature 195-205 ° С and a detector temperature of 150 ° С using a 1.6 m chromatographic column filled with a Reoplex-400 sorbent deposited on a Chromaton N support, followed by determination of the areas of chromatographic peaks of binzyl alcohol and quinoxaline and calculation of the content of the mass fraction of the main substance in crystalline glyoxal in the following ratio of components, wt.%:
crystalline glyoxal 37-43 water 63-57