RU2428663C1 - Method of determining amount of analysed substance from colour scale - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: method involves using optodes immobilised by a reagent which reacts with the analysed substance. A colour scale is obtained after the reaction. The analogue signal of the colour image of the scale is then converted to digital, from which colour coordinates are determined for each optode. Colour differences of optodes needed to plot a calibration curve of colour difference versus concentration of the analysed substance are determined. After changing the colour of the optode during reaction with the solution, the analogue signal of the colour image of the optodes is converted to digital, from which colour coordinates thereof are determined. The colour difference of this optode is calculated and the amount of the analysed substance in the sample of the object under investigation is determined from parameters of the previously obtained calibration curve. ^ EFFECT: low detection limit, high accuracy, wider range of determined concentrations and shorter time for obtaining the analytical signal. ^ 2 cl, 2 dwg, 3 tbl

Description

The invention relates to instrumental methods of chemical analysis, namely the detection and quantification of substances in the samples under study by an analytical signal using a color scale.

A known method for determining the amount of lithium ions (E. Hirayama, T.Sugiyama, H. Hisamoto, K.Suzuki. Visual and colorimetric lithium ion sensing based on digital color analysis. Analytical Chemistry, 2000, 72, 465-474), which is based on determination of color differences in the standard XYZ colorimetric system using a digital colorimetric analyzer that connects to a computer to process the received data.

The disadvantages of this method are as follows:

- the method is intended only for determining lithium ions;

- a paper optode having a porous and uneven surface is used as a sensor, which leads to a deterioration in its optical characteristics.

The closest adopted for the prototype is a method for determining the amount of an analyte using solid-phase spectrophotometry (NAGavrilenko and NVSaranchina. Solid Phase Spectrophotometric Determination of Silver Using Dithizone Immobilized in a Polymethacrylate Matrix, Journal of Analytical Chemistry, 2010, vol. 65, no. 2, pp. 148-152), in which membranes created from reagents immobilized on optically transparent solid polymer matrices are used as optodes. Immobilized reagents, interacting with the determined component, change the color of the optode, the optical density of which is measured using a spectrophotometer. The concentration of the analyte in the sample is determined by the calibration dependence of the optical density on the concentration.

The disadvantages of the prototype are the significant time required to obtain the results of the determination of the analyte and the low sensitivity and selectivity of the determination through the use of a single signal at a certain wavelength.

The objective of the invention is to reduce the detection limit, increase the accuracy of determination of the analyte, expand the range of detectable concentrations and reduce the time of receipt of the analytical signal from the optode when determining the amount of analyte using a color scale.

The problem is solved due to the fact that in the method for determining the amount of an analyte on a color scale, optodes are used that are immobilized by a reagent that interacts with the analyte. After the interaction, a color scale is obtained, according to which the calibration dependence of the analytical signal on the concentration of the analyte is built. Next, a sample solution of the studied object is obtained in which the optode is placed. After changing the color of the optode during this interaction, its analytical signal is determined, using the value of which the amount of the analyte is found from the calibration curve obtained previously.

According to the invention, after obtaining the color scale, the analog signal of the color image of the scale is converted into a digital signal, which determines the color coordinates of the colorimetric system for each optode. Next, determine the color differences of the optodes necessary to build a calibration dependence of the color difference on the concentration of the analyte. Then get a sample solution of the studied object, in which the optode is placed. After changing the color of the optode during this interaction, the analog signal of the color image of the optode is converted into a digital signal, by which its color coordinates of the colorimetric system are determined. Next, the color difference for this optode is determined and the amount of the analyte in the sample of the studied object is determined by the parameters of the previously obtained calibration dependence of the color difference on the concentration.

Figure 1 shows the color scale for determining silver.

Figure 2 shows the calibration dependence of the color difference from the concentration of silver in the solution.

Table 1 presents the equation and metrological characteristics of the calibration dependence for determining silver by the proposed method.

Table 2 presents the results of the determination of silver in the medicinal product "Argosulfan" by the proposed method.

Table 3 presents the comparative characteristics of the prototype method and the proposed method using silver as an example.

The proposed method for determining the amount of an analyte on a color scale was carried out as follows (examined on the example of a color scale for silver).

1. Getting the color scale

A polymethacrylate matrix in the form of a transparent plate with a thickness of (0.60 ± 0.04) mm was obtained by radical block polymerization (RF patent No. 2272284, G01N 31/22, publ. March 20, 2006). 6.0 × 8.0 mm plates weighing about 0.05 g were cut from the original plate.

A solution of dithizone of 0.002 M was prepared daily by dissolving an exact portion in a 0.005 M NaOH solution. An initial silver solution with a content of 1 mg / ml was prepared by dissolving an exact weighed AgNO ₃ in water (GOST 4212. Reagents. Methods for preparing solutions for colorimetric and nephelometric analysis). Lower silver working solutions were prepared by diluting the stock solution on the day of the experiment. The required pH value was created with HNO ₃ and NaOH solutions and monitored using an I-160 ionomer.

The reagent, dithizone, was immobilized into the polymethacrylate matrix by sorption from the reagent solution in an unchanged mode. For this, 25 ml of the reagent solution was mixed with the polymethacrylate matrix for 1 minute, the polymethacrylate matrix was colored yellow-orange.

Interactions of silver with the optode were carried out under static conditions. For this, the optodes were simultaneously placed in 50.0 ml of a silver solution with concentrations of 0; 0.024; 0.050; 0.074; 0,100; 0.124; 0.150; 0.174; 0.200 at pH 9, was stirred for 30 minutes. After contact of the optodes with the solution, the optodes were removed and blotted with filter paper. Got a color scale for determining silver.

2. Convert color to RGB coordinates

To convert color to RGB coordinates, the color scale for silver detection was scanned using a Hewlett Packard Scanjet scanner in 24-bit RGB color mode with a resolution of 300 dpi, which is connected to the computer (Fig. 1).

3. Construction of the calibration dependence and determination of metrological characteristics of the color scale

The calibration dependence of the color difference on the concentration of the analyte was constructed using n optodes (9 optodes were used to determine silver) as follows:

- determined the color coordinates of R, G and B for each optode using the graphics editor Adobe Photoshop, which was associated with the known concentration C of the analyte;

- the analytical signal was calculated using the color difference ΔЕ (G. Sharma (Ed.). Digital Color Imaging Handbook, CRC Press, Boca Raton, USA, 2003), which was determined by the formula:

where ΔR = R ₀ -R;

ΔG = G ₀ -G;

ΔB = B ₀ -B;

R ₀ , G ₀ , B ₀ - color coordinates of optodes after contact with a solution that does not contain silver;

R, G, B - color coordinates of optodes after contact with a solution containing silver;

- the obtained data was plotted on the graph ΔE = f (C) (Fig.2) and the least squares method obtained a linear calibration dependence with a correlation coefficient r = 0.998:

ΔE = -1.2 + 233.7 s _Ag ;

- calculated the detection limit of silver (table 1) by the expression:

,

,

where s ₀ is the standard deviation of the background signal (analytical signal at C = 0);

S is the slope of the calibration curve (if it is linear) for silver detection S = 233.7.

4. Determining the amount of analyte

The determination of silver in a real object was carried out by the example of determining silver in the Argosulfan medication by the additive method (RMG 61-2003. GSI. Accuracy, accuracy, precision indicators of quantitative chemical analysis methods).

One gram of Argosulfan was placed in a porcelain cup, poured with 3 ml of concentrated HNO ₃ and heated until decomposition, then the cup was cooled, the resulting solution was transferred into a 100.0 ml volumetric flask and diluted with water to the mark. 0.3 ml of the resulting solution was taken for analysis.

The analyzed solution (0.3 ml) was introduced into a 50.0 ml volumetric flask, a pH of 10 (NaOH, pH meter control) was created and diluted with water to the mark. Optodes were placed in the analyzed solution and mixed for 30 minutes, then removed, dried with filter paper.

The optode was scanned using a Hewlett Packard Scanjet scanner connected to a computer in 24-bit RGB color mode with a resolution of 300 dpi. We determined its color coordinates R, G and B using the graphics editor Adobe Photoshop, calculated the value of the color difference ΔE.

From the equation of the calibration dependence of the color scale for silver determination, the silver concentration in the Argosulfan medication was determined using the calibration dependence.

The measurements were carried out seven times and determined the relative standard deviation (RMS) of the analysis results S _r .

The results of the determination of silver in the drug "Argosulfan" are presented in table 2.

Table 3 presents the comparison results of the proposed method and the prototype obtained in the determination of silver. As can be seen from the table, the proposed method for determining the amount of analyte on a color scale can improve the accuracy of determination of the analyte, reduce the detection limit and time spent on receiving the analytical signal from the optode, and expand the range of determined concentrations.

Table 1 Analytical signal Calibration Equation Correlation coefficient, r The range of determined contents, mg / l Detection limit, mg / l ΔЕ ΔE = -1.2 + 233.7 s _Ag 0,998 0.02-0.20 0.015

table 2 An object The number of observations, n Found, mg / g RMSE of the analysis results, S _r ,% Indicated on the package, mg / g The medicine "Argosulfan" 7 22.8 ± 1.3 5.9 twenty

Table 3 Comparative characteristics Prototype method The inventive method Detection limit, mg / l 0,030 0.015 The accuracy characterized by the value of the relative standard deviation, S _r ,% 10.7 5.9 The range of determined contents, mg / l 0.03-0.20 0.01-0.20 Measurement principle Measurement of the optical density of optodes on a spectrophotometer at a wavelength at the absorption maximum Color conversion
analog signal and digitization of the color scale image in the form of parameters of a standard colorimetric system Calibration characteristic The dependence of optical density on the concentration of the analyte The dependence of color differences on the concentration of the analyte Color fastness Depends on the reagent and the complex formed. It does not change, as it is stored in the computer's memory The time of receipt of the analytical signal from the optode 1 min 10 μs

Claims (2)

1. A method for determining the amount of an analyte on a color scale, which consists in using optodes immobilized with a reagent interacting with the analyte, obtaining a color scale, constructing a calibration dependence of the analytical signal on the concentration of the analyte, obtaining a sample solution of the studied object into which the optode is placed, after the color changes of the optode during this interaction determine its analytical signal, the value of which determines the amount of analysis of the substance to be calibrated, characterized in that after receiving the color scale, the analog signal of the color image of the scale is converted into a digital signal, which determines the color coordinates of the colorimetric system for each optode, determines the color differences between the optode that interacts with a solution that does not contain the analyte substance, and with each of the optodes interacting with the solution containing the analyte, a calibration calibration is constructed from the obtained values the dependence of the color difference on the concentration of the analyte, after which a sample solution of the studied object into which the optode is placed is obtained, after changing the color of the optode, this interaction converts the analog signal of the color image of the optodes into a digital signal, which determines the color coordinates of the colorimetric system for this optode, determines the color difference between this optode and the optode interacting with a solution that does not contain the analyte, and the parameters obtained An initial calibration dependence of the color difference on the concentration determines the amount of the analyte in the sample of the studied object. 2. The method according to claim 1, characterized in that the color difference is determined from the expression:

where ΔR = R ₀ -R; ΔG = G ₀ -G; ΔB = B ₀ -B; R ₀ , G ₀ , B ₀ - color coordinates of optodes after contact with a solution that does not contain silver; R, G, B - color coordinates of optodes after contact with a solution containing silver.

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