Colorimetric method for the determination of the pesticide thiabendazole on the surface of fruits and vegetables

Abstract

FIELD: analytical chemistry.SUBSTANCE: intended for quality control and safety of fruit and vegetable products. The method for quantitative colorimetric determination of the pesticide thiabendazole on the surface of fruits and vegetables involves the isolation and concentration of the analyte by washing it off the surface of the fruit with a volatile organic solvent – methanol, followed by evaporation of the solvent. Additional concentration of the analyte is achieved by collecting the dry residue with a cellulose napkin pre-impregnated with a mixture of thymol, n-dodecylamine and copper (II) ions. As a result of the interaction, a contrasting color transition occurs on the surface of the cellulose napkin from brown, caused by the color of copper (II) complexes with thymol, to green, corresponding to the color of the more stable copper (II) complex with thiabendazole. The color of the cellulose napkin after analysis is compared with the color scale and the concentration of thiabendazole is determined visually.EFFECT: simplification of analysis, an increase in productivity and the possibility of performing analysis in non-laboratory, field conditions.1 cl, 1 dwg

Description

[0001] The invention relates to analytical chemistry and can be used for the colorimetric determination of the pesticide thiabendazole on the surface of fruits and vegetables. Thiabendazole is used in agriculture to treat fruits and vegetables, grain crops, and seeds to protect them from fungal infections. However, the substance is classified as a potential carcinogen, necessitating monitoring of the pesticide in food products to ensure their safety and quality.

[0002] A known method for determining pesticides (thiabendazole and carbendazim) in fruit and vegetable juices using high-performance liquid chromatography with ultraviolet detection (HPLC-UV) [1] involves adding a hydrochloric acid solution to the test sample of fruit or vegetable juice, mixing and centrifuging, after which the resulting supernatant is passed through a column with a polymer cation-exchange resin, which causes the adsorption of the analytes. Next, the pesticides are eluted from the column with a 3% ammonia solution in methanol, the eluate is dried under a stream of nitrogen, and the dry residue is dissolved in a hydrochloric acid solution, after which the solution is filtered. Thiabendazole and carbendazim are determined by HPLC-UV. A phosphate buffer solution and acetonitrile in a volume ratio of 75:25 are used as the mobile phase, the injected sample volume is 20 μl, the flow rate is 1 ml / min, and the column temperature is 35°C.

[0003] A known method for determining thiabendazole in fruits and vegetables, grains, soil, and water is thin-layer chromatography (TLC) [2]. According to this method, thiabendazole is extracted from the test sample (chopped fruit or vegetable, soil, or water) using ethyl acetate. Thiabendazole is then redistributed into a hydrochloric acid solution. After alkalizing the resulting solution, thiabendazole is extracted into ethyl acetate saturated with water. The resulting extract is evaporated and analyzed by TLC. For samples with a high content of interfering impurities, such as grains, preliminary purification (microsublimation in a vacuum) is used. Quantitative determination of thiabendazole is carried out on chromatographic plates by comparing the area and color intensity of spots of the analyzed sample and a series of standard solutions when they are developed under an ultraviolet lamp.

[0004] A known method for determining thiabendazole in rapeseeds using surface-enhanced Raman spectrometry [3], according to which the pesticide is extracted from a sample of rapeseeds (without preliminary grinding) with acetonitrile in the presence of sodium chloride. The mixture is centrifuged, and iron (II, III) oxide nanoparticles are added to the resulting supernatant to eliminate the matrix effect caused by the presence of chlorophyll, proteins, fats and carbohydrates. Next, the mixture is filtered, the resulting solution is mixed with silver nanosol and an aqueous solution of sodium chloride, after which the surface-enhanced Raman spectra are recorded. Quantitative determination of thiabendazole is carried out based on the intensity of the characteristic Raman peak at 780 cm -1 .

[0005] The main disadvantages of known methods for determining the pesticide thiabendazole in food products [1-3] include: highly labor-intensive sample preparation, the need for specialized laboratory equipment, and the inability to conduct analysis outside of laboratory settings. Furthermore, a significant number of these methods require the use of expensive reagents and equipment, which limits their availability and practical applicability for mass analysis.

[0006] Considering that thiabendazole is applied to fruits and vegetables mainly by dipping, spraying and waxing, as a result of which its main share accumulates in the peel or on its surface, it is possible to determine the specified pesticide directly on the surface of the objects of analysis without preliminary grinding of the sample, which significantly simplifies the procedure and reduces the analysis time.

[0007] The closest to the claimed invention and selected as a prototype is the method [4] for determining organic contaminants on the surface of food products, including the pesticide thiabendazole, using paper test strips containing a functional layer of bimetallic gold-silver nanoparticles distributed in xylan, which acts as an environmentally friendly reducing agent, a binding agent and a stabilizer of nanoparticles. The method includes the synthesis of bimetallic gold-silver nanoparticles by a method of reduction in a xylan solution, as well as the immobilization of nanoparticles on a paper base by a method of multiple application to obtain the active zone of the test strip. During the analysis, the active zone of the test strip is wetted with a solvent in order to improve contact with the object of analysis and increase the efficiency of sorption of organic contaminants on the surface of the bimetallic nanoparticles. The surface of the food product is then wiped with a test strip.Alternatively, the test strip can be immersed in the liquid sample or dropwise applied to the strip, after which the strip is dried at 50°C until the solvent evaporates. Detection is performed using surface-enhanced Raman spectroscopy.

[0008] The disadvantages of the prototype include the lengthy, labor-intensive, and high cost of synthesizing bimetallic nanoparticles, as well as the difficulty of reproducing the conditions for multiple deposition of nanoparticle layers on a paper substrate to form an active zone with a uniform particle distribution. These features limit productivity and complicate the test strip manufacturing technology, hindering their large-scale application. Furthermore, the need for expensive specialized equipment (a Raman spectrometer) reduces the practical applicability of the method for rapid field testing.

[0009] The technical result of the claimed invention, in comparison with the prototype [4], is a colorimetric method for determining the pesticide thiabendazole on the surface of fruits and vegetables, which provides the possibility of conducting an analysis in non-laboratory conditions using available and inexpensive reagents and materials, the simplicity and speed of manufacturing test means for conducting the analysis, as well as the use of the colorimetric method for determining the concentration of thiabendazole.

[0010] The technical objective of the claimed invention is to simplify and speed up the process of manufacturing test tools, reduce material costs, and implement the possibility of performing analysis in non-laboratory conditions.

[0011] The stated technical result is achieved by using 1 x 1 cm cellulose wipes as test media, impregnated with 150 μl of an extraction mixture consisting of a 3:1 molar ratio of thymol and n-dodecylamine and copper (II) ions at a concentration of 550 mg / kg. During the analysis, the fruit or vegetable being tested, pre-weighed on an analytical balance, is thoroughly washed on all sides in a Petri dish with 5 ml of methanol using a syringe. This rinses the pesticide thiabendazole from the surface of the test object. The solvent is then evaporated in a fume hood for 15 minutes. The dry residue obtained on the Petri dish is carefully wiped with a cellulose wipe impregnated with the extraction mixture. When the extraction mixture interacts with the pesticide thiabendazole, which is in the dry residue, the color of the substrate changes from brown to green.The color change is due to the transition of copper(II) ions from the brown thymol complex to the more stable thiabendazole complex. Thiabendazole concentration is determined visually using the color scale shown in Fig. The concentration range for this method is 2-7 mg / kg, and the analysis time is 20 minutes.

[0012] The distinctive features of the claimed method from the closest analogue adopted as a prototype are:

[0013] - using highly volatile methanol to wash away the pesticide thiabendazole from the surface of the analyzed fruit or vegetable sample;

[0014] - evaporation of the solvent on a Petri dish to obtain a dry residue;

[0015] - use of available materials and reagents as a test tool: a cellulose napkin impregnated with an extraction mixture consisting of thymol and n-dodecylamine in a molar ratio of 3:1 and copper (II) ions with a concentration of 550 mg / kg;

[0016] - Using visual colorimetric method for semi-quantitative determination of thiabendazole concentration.

[0017] The claimed distinctive features make it possible to detect concentrations of thiabendazole that exceed the maximum permissible level of its content in food products (5 mg / kg [5]) in non-laboratory conditions with minimal time and financial costs.

[0018] The claimed method was tested in laboratory conditions at St. Petersburg State University (the Applicant). The results are presented below as specific implementation examples. The studies were conducted using instrumentation from the Department of Analytical Chemistry at St. Petersburg State University.

[0019] Example 1.

[0020] Sampling

[0021] Apple samples were purchased from a local supermarket (St. Petersburg). The products were stored at room temperature for 7 days.

[0022] Sample preparation

[0023] The pre-weighed sample was placed in a Petri dish and thoroughly rinsed on all sides with 5 ml of methanol using a plastic syringe. The Petri dish containing the resulting rinse was then left for 15 minutes until the solvent had completely evaporated.

[0024] Apple Analysis

[0025] The dry residue on the dish was thoroughly rubbed for 30 s using a 1 x 1 cm cellulose napkin pad soaked in 150 μl of an extraction mixture consisting of thymol and n-dodecylamine in a molar ratio of 3:1 and copper (II) ions at a concentration of 550 mg / kg. Quantitative colorimetric determination of the pesticide thiabendazole was carried out visually using the color scale shown in Fig., which shows the colors of the pads after the analysis, corresponding to the thiabendazole content in the test object of 2, 4, and 7 mg / kg. The pesticide thiabendazole on the surface of apples was contained at a level of 2 mg / kg.

[0026] Example 2.

[0027] Sampling

[0028] Tangerine samples were purchased from a local supermarket (St. Petersburg). The products were stored at room temperature for 7 days.

[0029] Sample preparation

[0030] The pre-weighed sample was placed in a Petri dish and thoroughly rinsed on all sides with 5 ml of methanol using a plastic syringe. The Petri dish containing the resulting rinse was then left for 15 minutes until the solvent had completely evaporated.

[0031] Tangerine Analysis

[0032] The dry residue on the dish was thoroughly rubbed for 30 s using a 1 x 1 cm cellulose pad soaked in 150 μl of an extraction mixture consisting of thymol and n-dodecylamine in a 3:1 molar ratio and copper (II) ions at a concentration of 550 mg / kg. Quantitative colorimetric determination of the pesticide thiabendazole was performed visually using the color scale shown in Fig. , which shows the colors of the pads after analysis, corresponding to thiabendazole content in the test object of 2, 4, and 7 mg / kg. The pesticide thiabendazole content on the surface of the tangerines was 4 mg / kg.

[0033] Example 3.

[0034] Sampling

[0035] Washed potato samples were purchased from a local supermarket (St. Petersburg). The products were stored at room temperature for 7 days.

[0036] Sample preparation

[0037] The pre-weighed sample was placed in a Petri dish and thoroughly rinsed on all sides with 5 ml of methanol using a plastic syringe. The Petri dish containing the resulting rinse was then left for 15 minutes until the solvent had completely evaporated.

[0038] Analysis of washed potatoes

[0039] The dry residue on the dish was thoroughly rubbed for 30 s using a 1 x 1 cm cellulose pad soaked in 150 μl of an extraction mixture consisting of thymol and n-dodecylamine in a 3:1 molar ratio and copper (II) ions at a concentration of 550 mg / kg. Quantitative colorimetric determination of the pesticide thiabendazole was carried out visually using the color scale shown in Fig. , which shows the colors of the pads after analysis, corresponding to thiabendazole content in the test object of 2, 4, and 7 mg / kg. The pesticide thiabendazole on the surface of the washed potatoes was present at a concentration of 2 mg / kg.

[0040] The proposed method is simple to implement, highly productive, and enables analytical monitoring in non-laboratory settings using readily available analytical signal recording equipment. The proposed method is implemented using easy-to-manufacture test kits based on inexpensive and widely available reagents. The method can be effectively used in food laboratories for rapid quality and safety monitoring of fruits and vegetables entering the market.

[0041] List of references

[0042] 1. CN104215712 “Method for detecting carbendazol and thiabendazole residues in fruit and vegetable juice through liquid chromatogram.”

[0043] 2. MU 2084-79 Guidelines for the determination of thiabendazole (tecto) in vegetables and fruits (apples, lemons, oranges, tomatoes, carrots, onions, potatoes, beets, cabbage), grains (wheat, rice), soil and water by thin-layer chromatography.

[0044] 3. CN108037110 “Method for quickly detecting thiabendazole pesticide in oilseed rape by surface Raman enhancement technique based on silver nanosol substrate.”

[0045] 4. CN115629055 “Xylan-based auxiliary organic pollutant rapid detection test paper and preparation method and application thereof” (prototype).

[0046] 5. FAOLEX. (2008). Commission Regulation (EC) No 149 / 2008 amending Regulation (EC) No 396 / 2005 of the European Parliament and of the Council by establishing Annexes II, III and IV setting maximum residue levels for products covered by Annex I thereto. URL: https: / / faolex.fao.org / docs / pdf / eur77722.pdf (access date: 06 / 18 / 2025).

Claims

A colorimetric method for determining the pesticide thiabendazole on the surface of fruits and vegetables, which includes the use of a test means for extracting an organic pollutant, the pesticide thiabendazole, from the surface of a fruit, vegetable or fruit and determining its concentration using a color scale, characterized in that in order to isolate and concentrate thiabendazole, it is washed off the surface of the object of analysis using a highly volatile organic solvent, such as, for example, methanol, which is subject to evaporation, a cellulose napkin is used as a device for concentrating and simultaneously a test means, pre-impregnated with an extraction mixture based on thymol and n-dodecylamine in a molar ratio of components of 3:1 and copper (II) ions with a concentration of 550 mg / kg, additional concentration of thiabendazole is carried out by collecting the dry residue with a cellulose napkin impregnated with the extraction mixture;The concentration of thiabendazole is determined colorimetrically, with the determination being carried out visually using a color scale.

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