RU2252413C1 - Assay for determination of polyhexamethyleneguanidine hydrochloride concentration in water - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: claimed method includes subsequent addition in analyte solution buffer solution and 0.01 % eosin H solution followed by measuring of solution optical density. As buffer mixture of sodium citrate solution and hydrochloric acid solution with concentration of 0.5 mol/dm³ wherein pH is adjusted up to 2.8 is used. Optical density is measured at wavelength of 545 nm with water as reference for 15 min after eosin H addition.

EFFECT: assay of increased precision decreased determination limit.

2 dwg, 3 tbl

Description

The invention relates to analytical chemistry, namely to the photometric analysis of aqueous solutions for the content of polyhexamethylene guanidine hydrochloride (PHMG) in them in low (residual) concentrations, and can be used in the practice of laboratories of industrial enterprises, as well as sanitary and epidemiological stations for monitoring the content of PHMG hydrochloride .

Due to the low efficiency of the disinfectants used for water treatment due to the addiction of microorganisms to them, disinfectants of the guanidine group, namely polyhexamethylene guanidine hydrochloride, have gained great importance.

In addition, most disinfectants contain chlorine, which has a harmful effect on the human body.

Existing methods for the analysis of PHMG do not allow determining the content of PHMG hydrochloride in water in an amount lower than the maximum permissible concentration (MPC) of 0.1 μg / cm ³ .

A known method for the determination of PHMG hydrochloride in aqueous solutions by photometry of a solution obtained by mixing 2 cm ^{3 of the} analyzed solution, 2 cm ³ 0.01 mol / dm ³ hydrochloric acid solution and 0.1 mg of a 0.05% alcohol solution of eosin H (RU 2006836, C. G 01 No. 21/78, BI, No. 2, 1994).

The solutions are photographed after heating in a boiling water bath for 10 minutes and cooling at a wavelength of 540 nm in cuvettes with an absorbing layer thickness of 1 cm with respect to a blank sample not containing PHMG hydrochloride. The detection limit is 0.25 μg / cm ³ in the analyzed solution. This method is used in the determination of PHMG hydrochloride in air after passing air through the filter and processing the filter with hot distilled water.

The disadvantages of this method are the inability to analyze samples with a pH significantly different from neutral, a high value of the detection limit, which does not allow determination of PHMG hydrochloride in water at a MPC level of 0.1 μg / cm ³ .

Closest to the proposed method is a method for the determination of PHMG hydrochloride in aqueous solutions by photometry of a solution obtained by mixing 10 cm ^{3 of the} analyzed solution, 10 cm ^{3 of} glycine buffer with pH = 3.5 (a mixture of 92.5 cm ³ of glycine and sodium chloride concentration 0.1 mol / dm ³ and 7.5 cm ³ 0.1 mol / dm ³ hydrochloric acid solution) and 1 cm ^{3 of a} 0.05% solution of eosin H and bringing the volume of the solution to 25 cm ³ . The solutions are photographed no later than 10 min after adding eosin H at a wavelength of 540 nm using a cuvette with an absorbing layer thickness of 5 cm with respect to a blank sample not containing PHMG hydrochloride on an FEK-056 photoelectrocolorimeter. The calibration graph is linear in the range of concentrations of PHMG hydrochloride in the analyzed sample 1-4 μg / cm ³ . The method is used to determine the mass fraction of PHMG hydrochloride in industrial samples of PHMG hydrochloride after preliminary dissolution in water (Guidelines for the use of Biopag-D disinfectant, Ministry of Health of the Russian Federation, Moscow, 2002, pp. 11-13).

The disadvantages of this method of determination include the instability of the glycine buffer solution, which leads to the need to use a freshly prepared buffer solution, the lower limit of determining the concentration of 1 μg / cm ³ , which does not allow the determination of PHMG hydrochloride at the MPC level, the measurement of optical density "no later than 10 min "is not enough to obtain reproducible results, since the optical density of the photometric solution varies significantly over time, especially during the first 10 minutes. This analysis and the buffer used limit the accuracy of the determination of PHMG hydrochloride and allow only 1 μg / cm ³ to be determined.

The technical problem solved by this invention is to increase the accuracy of determining the concentration of PHMG hydrochloride in water and reduce the detection limit to the MPC level.

To solve the technical problem in the method for quantitatively determining the concentration of polyhexamethylene guanidine hydrochloride in water, which includes sequentially adding a buffer solution and an eosin H solution to the analyzed solution, followed by measuring the optical density of the solution, a mixture of sodium citrate and hydrochloric acid solutions with a concentration of 0.5 is used as a buffer solution mol / dm ³ adjusted to pH = 2.80, using a 0.01% solution of eosin H, measuring the optical density at a wavelength of 545 nm, relate flax water 15 minutes after the introduction of a solution of eosin N.

Using a nitrate buffer solution with pH = 2.8 allows you to get a linear calibration graph in the concentration range of 0.03-0.40 µg / cm ³ . The pH of the photometric solution is 3.13, the slope of the calibration graph has a maximum value. Citrate buffer solution is more stable than glycine, prepared from inexpensive reagents. The use of concentrated citrate buffer solution prepared by mixing solutions of sodium citrate and hydrochloric acid with a concentration of 0.5 mol / dm ³ allows to increase the volume of the analyzed solution introduced into the flask from 10 to 15 cm ³ , due to which the detection limit decreases from 0.08 to 0 , 05 μg / cm ³ , and determine the pHMG hydrochloride in solutions with 2.5 <pH <11.4.

In the known method and the proposed method, the same amount of eosin H is introduced into a flask with a volume of 25 cm ³ , however, introducing with a Mora pipette 5 cm ^{3 of a} 0.01% aqueous solution of eosin H is more appropriate than introducing 1 cm ^{3 of a} 0.05% solution of eosin H , since it allows you to minimize the error associated with the introduction of a different amount of eosin H, also absorbing electromagnetic radiation with a wavelength of 545 nm.

Described in the known method, the condition for measuring the optical density: "no later than 10 minutes" is not enough to obtain reproducible results, since the optical density of the photometric solution varies significantly over time, especially during the first 10 minutes. The proposed photometric condition for each prepared solution after an exact time interval of 15 minutes after the introduction of the eosin H solution allowed avoiding the uncertainty in the description of the determination method and significantly increasing the accuracy of determination.

To increase the accuracy of the determination, it was possible to use for the first time a number of techniques in the proposed method that minimized the errors associated with the sorption of eosin N on the walls of the dishes and the cuvette used: the use of glass flasks of the same brand with identical surface conditions, three times rinsing of the measuring cell with distilled water after each measurement, measurement optical density relative to distilled water in the comparison cuvette, which also eliminates the error associated with the introduction of various eosin number N in comparison cuvette and measuring cuvette.

The use in the known method of a photoelectrocolorimeter FEK-056 or another device with built-in filters does not provide sufficient monochromaticity of radiation and does not allow to determine the concentration of PHMG hydrochloride in water at the MPC level. A method for determining low concentrations of PHMG hydrochloride in water involves the use of a KFK-3 photoelectric photometer or other device with similar metrological characteristics. In this case, it becomes possible to measure the optical density at a wavelength of 545 nm, which corresponds to the maximum absorption of the complex of eosin H with PHMG hydrochloride.

Example 1. Determination of the concentration of PHMG hydrochloride dissolved in distilled water.

Construction of a calibration schedule: 0.5, 1, 2, 3, 4, 5, 6 cm ^{3 of a} standard solution with a concentration of PHMG hydrochloride of 1 μg / cm ³ prepared by dissolving a working standard sample of PHMG hydrochloride in distilled water are added to flasks with a capacity of 25 cm ³ distilled water until the flasks are half-filled, 2 cm ^{3 of a} citrate buffer solution with pH = 2.80. 5 cm ^{3 of a} 0.01% solution of eosin H are added to each flask sequentially with an interval of 2 minutes and adjusted to the mark with distilled water. 15 minutes (by stopwatch) after introducing the eosin H solution into the first flask, the optical density in a cuvette with an absorbing layer thickness of 5 cm at a wavelength of 545 nm with respect to distilled water is measured successively with a KFK-3 photoelectric colorimeter at a 2-minute interval and a calibration the graph in coordinates “optical density (A) is the concentration of PHMG hydrochloride (C)”, calculated as the ratio of the mass of polymer introduced into the flask to the solution volume of 15 cm ³ .

Determination of the concentration of PHMG in the sample: 15 ml of the analyzed solution containing 0.5-6.0 μg, 2 cm ^{3 of} citrate buffer solution with pH = 2.80 are added to three flasks with a capacity of 25 cm ³ . 5 cm ^{3 of a} 0.01% solution of eosin H are added to each flask sequentially with an interval of 2 minutes and adjusted to the mark with distilled water. Fifteen minutes after the introduction of the eosin H solution into the first flask, the optical density of the obtained solutions was measured sequentially with an interval of 2 minutes. The arithmetic mean of the optical density values is calculated, and the concentration of PHMG hydrochloride is determined from the calibration graph.

Example 2. Determination of the concentration of PHMG hydrochloride dissolved in tap water.

Construction of calibration curve: flasks in 25 cm ³ make 0.5, 1, 2, 3, 4, 5, 6 cm ³ of a standard solution with a concentration of PHMG hydrochloride 1 g / cm ^3, prepared by dissolving the hydrochloride of the working standard sample or supernatant in PHMG boiled tap water, tap water up to 15 cm ³ total volume (i.e. 14.5; 14.0; 13.0; 12.0; 11.0; 10.0; 9.0 cm ³ ), 2 cm ³ citrate buffer solution with pH = 2.80. 5 cm ^{3 of a} 0.01% solution of eosin H are added to each flask sequentially with an interval of 2 minutes and adjusted to the mark with distilled water. 15 minutes (by stopwatch) after introducing the eosin H solution into the first flask, the optical density in a cuvette with an absorbing layer thickness of 5 cm at a wavelength of 545 nm with respect to distilled water is measured successively with a KFK-3 photoelectric colorimeter at intervals of 2 minutes and build a calibration graph in the coordinates of “optical density (A) - the concentration of hydrochloride PHMG (C)”, calculated as the ratio of the mass of polymer introduced into the flask to the solution volume of 15 cm ³ .

Determination of the concentration of PHMG in the sample: 15 ml of the analyzed solution containing 0.5-6.0 μg, 2 cm ^{3 of} citrate buffer solution with pH = 2.80 are added to three flasks with a capacity of 25 cm ³ . 5 cm ^{3 of a} 0.01% solution of eosin H are added to each flask sequentially with an interval of 2 minutes and adjusted to the mark with distilled water. Fifteen minutes after the introduction of the eosin H solution into the first flask, the optical density of the obtained solutions was measured sequentially with an interval of 2 minutes. The arithmetic mean of the optical density values is calculated, and the concentration of PHMG hydrochloride is determined from the calibration graph.

Table 1 shows the confidence intervals for the concentration of PHMG hydrochloride under various conditions of analysis.

Table 2 shows the metrological characteristics of the calibration graph for the determination of PHMG hydrochloride in aqueous solutions, table 3 presents the results of determining the concentrations of PHMG hydrochloride in distilled water for three parallel observations. The calibration graph is linear in the range of PHMG hydrochloride content of 0.5-6.0 μg or in the concentration range of 0.03-0.40 μg / cm ³ with a sample volume of 15 cm ³ . The detection limit of PHMG hydrochloride in distilled water is 0.05 μg / cm ³ , the detection limit of PHMG hydrochloride in tap water is 0.10 μg / cm ³ . The confidence interval for the calculated values of the concentration of PHMG hydrochloride 0.05-0.40 μg / cm ³ is ± 0.02 μg / cm ³ (P = 0.95, f = 2).

Figure 1 shows a calibration graph for determining the concentration of PHMG hydrochloride in water according to example 1.

When an aliquot of the test solution is added, it is possible to determine higher concentrations of PHMG hydrochloride.

In this case, the calibration graph is plotted in coordinates “optical density (A) - the content of PHMG hydrochloride in the flask (q)”, and the concentration of PHMG hydrochloride in the test solution is calculated as q / V, where V is the volume of an aliquot of the test solution.

Figure 2 shows a calibration graph for determining the content of PHMG hydrochloride in water when making an aliquot of the test solution.

Table 1
Confidence interval for determining the concentration of PGMG hydrochloride under various conditions of analysis of the proposed method (three parallel observations) Terms of determination ± ΔС, μg / cm ³ Compliance with all conditions 0.02 The introduction of 1 cm ^{3 of a} 0.05% solution of eosin H 0.06 Glass flasks with different surface conditions (different batches and service life) 0.08 Measurement of absorbance relative to a blank sample 0.04 Rinse once with distilled water 0.05 Measurement after 5, 7 and 9 min 0.10

table 2
Metrological characteristics of the calibration graph to determine the content (q, μg) or concentration (C, μg / cm ³ ) of PHMG hydrochloride in aqueous solutions Characteristic Distilled water Tap water Calibration Equation A = a + bq A = a + bC A = a + bq A = a + bC The segment cut off on the ordinate axis, and 0.527 0.527 0.615 0.615 The slope of the calibration dependence, b 0,054 0.816 0,027 0.407 Standard deviation of the calculated value a, s _a 0.005 0.005 0.005 0.005 Standard deviation of the calculated value b, s _b 0.001 0.019 0.001 0,020 Standard deviation of points from the found dependence, s _y 0.006 0.006 0.006 0.006 Correlation coefficient, r (a, b) 0.9987 0.9987 0.9889 0.9889 Borders will trust. interval of calculated value a, ± D _a 0.011 0.011 0.011 0.011 Borders will trust. interval of calculated value b, ± D _b 0.003 0,046 0.003 0,047 The standard deviation of the pure signal (idle experience). s ₀ 0.008 0.008 0.008 0.008 Detection limit q _d , μg or C _d , μg / cm ³ 0.8 0.05 1,5 0.10 Borders will trust. intervals for calculated values ± D _q , mcg; or ± D _c , μg / cm ³ 0.3 0.02 0.8 0.05

Table 3
Determination of PHMG hydrochloride in aqueous solutions based on three parallel observations q, mcg C, mcg / cm ³ relative standard deviation s _r ,% introduced found ± Δq introduced found ± ΔС 0.5 0.6 0.3 0,03 0.04 0.02 19.1 1,0 1,0 0.1 0.07 0,07 0.01 3.6 2.0 2.0 0.4 0.13 0.13 0.02 7.3 3.0 2,8 0.3 0.20 0.19 0.02 4.9 4.0 3.9 0.3 0.27 0.26 0.02 3,1 5,0 4.9 0.4 0.33 0.32 0,03 3,5 6.0 5.9 0.1 0.40 0.39 0.01 1,0

Claims (1)

A method for quantitatively determining the concentration of polyhexamethylene guanidine hydrochloride in water, comprising sequentially adding a buffer solution and an eosin H solution to the analyzed solution, followed by measuring the optical density of the solution, characterized in that a mixture of sodium citrate and hydrochloric acid with a concentration of 0.5 mol is used as a buffer solution / dm ³ adjusted to pH 2.80, using a 0.01% solution of eosin H, measuring the optical density at a wavelength of 545 nm relative to water h after 15 min after the introduction of a solution of eosin N.

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