Improvement of analytical determination of cyproconazole and propiconazole in fruit crops

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Institute of Plant Protection of NAAS

Improvement of analytical determination of cyproconazole and propiconazole in fruit crops

T. Panchenko,

PhD of agricultural sciences

L. Cherviakova,

PhD of agricultural sciences

Kyiv

Abstract

Development and unification of the method of simultaneous determination of cyproconazole and propiconazole in fruits (applesЃC peaches, grapes) by gas-liquid chromatography (GC). Methods. The active substances were determined by gas-liquid chromatography (GC) using a gas chromatograph «Perkin Elmer 8410» with an NPD detector.

The choice of the method of determination is limited by the physicochemical properties of the active substance and the characteristics of the object under study (matrix). The optimal conditions for determination were selected using a chemical-analytical monitoring algorithm and a system for multiquantitative determination of pesticides in matrices. According to themЃCthe matrices are analyzed in stages: extractionЃCpurificationЃCqualitative and quantitative determination. Cyproconazole and propiconazole are low-polar compounds (^ of their cis - and trans-isomers are 4.43; 4.71 and 3.80; 4.20 DЃCrespectively)ЃCso extraction was performed with chloroform (e 5.1). Purification of extracts from coextractive substances of matrices was performed by TLC. Compounds were identified by retention timeЃCand quantification (CЃCpg/ml) was performed on the areas of chromatographic peaks (SЃCmm²) in the range of linear detection (2_10 ng) according to the linear regression equations: Sc = 11.991 C - 6.096 (R² = 0.998); Sp = 13.721 C - 4.221 (R² = 0,994). The average value of measurement is 81.0 -87.8%; standard deviation 2.21-5.38% c; confidence interval (P 0.95; n = 15) 1.94_4.72% c. Conclusions. Optimal selective condШons for the analysis of triazole derivatives by chromatographic methods provide simultaneous determination of test compounds and quality control of fuit crops on the content of residual amounts ofcyproconazole and propiconazole at the level of hygienic standards (MAL 0,05 - 0.10 mg/kg).

In Ukraine, the system of protection of fruit crops is based mainly on the repeated use of pesticides during the entire growing season. A significant part is made up of fungicides, the range of which is constantly expanding due to mixed formulations, where each component has a certain biological effect. To protect fruit crops from various types of fungal diseases, compounds of various chemical classes with different mechanisms of action on ta^et objects (copper-containing pesticides, dithiocarbamic acid derivatives, pyridine derivatives, etc.) are used. Today, triazole derivatives are widespread - compounds of contact-systemic action, which are transported through the vascular system of plants mainly acropetally (along the xylem) with a solution of mineral salts, and to a lesser extent basipetally (along the phloem) with an assimilation flow; block the synthesis of ergosterol in the membranes of pathogen cells, thereby slowing down the development of diseases. Combined preparations, the components of which are representatives of this class - propiconazole and cyproconazole, are used to expand the spectrum of action in order to avoid secondary infection, increase the protective effect. In terms of toxicity, cyproconazole (LD50 oral for rats 1020-1330 mg/kg) is a moderately dangerous, propiconazole (LD50 oral for rats - 3046 mg/kg) is slightly dangerous compound. The use of such a complex of active ingredients necessitates the control of their residues in the crop (fruits), especially when they are used in baby and diet food.

To control fungicide residues in the fruits at the level of hygienic standards, highly sensitive physical and chemical methods of analysis are used: thin-layer (TLC), gas-liquid (GLC), high-performance liquid chromatography (HPLC). The advantage of these methods is the combination of two processes: the separation of a mixture of substances and their quantitative determination [1].

The purpose of the research in this work was to develop and unify the methodology for the simultaneous determination of cyproconazole and propiconazole in fruits (apples, peaches, grapes) by gas-liquid chromatography (GLC).

Objects and methods of research. A fungicide containing triazoles in a ratio of 1: 3 (80 g/l cyproconazole + 250 g/l propiconazole). Characteristics and physico-chemical properties of the studied active substances are presented in the table.

When developing the determination procedure, analytical standards for cyproconazole and propiconazolewere used. The stock standard solution of each active ingredient contained 100 ^g of the compound in 1 ml of the appropriate organic solvent. Sequential dilution of the initial solutions was used to prepare working calibration solutions with an analyte mass concentration of 5.0; 4.0; 3.0; 2.0; 1.0 ^g/ml and a control solution with an analyte mass concentration of 3.5 ^g/ml. For gas-liquid chromatography (GLC) studies, a Perkin Elmer 8410 gas chromatograph with an NPD detector selective for nitrogen and phosphorus was used.

Propiconazole and cyproconazole were identified by the retention time of the compounds, quantitative determination - by the calibration dependence of the area of the chromatographic peak of the analyte on its concentration in the calibration solution using correlation and regression analyses.

Research results. The choice of a method determination of a pesticide is limited, first of all, by the physicochemical properties of the pesticide and the peculiarity of the object (matrix) under study. The optimal conditions for the determination were selected using conceptual developments (an algorithm for chemical-analytical monitoring and a method for system of multimedia determination of pesticides in matrices), the essence and structure of which are presented in a number of scientific publications [2, 3]. According to these developments, matrices are analyzed according to the stages: extraction (extraction), purification, qualitative and quantitative determination, which makes it possible, under selective conditions, to determine cyproconazole and propiconazole simultaneously in the process of one analysis.

Characteristics of active substances

Compounds, depending on their physicochemical properties, are characterized by polarity according to magnitude of the dipole moment of the molecule (ц, D). Cyproconazole and propiconazole are low-polar compounds (ц of their cis - and trans-isomers - 4.43; 4.71 and 3.80; 4.20 D, respectively), therefore, extraction from the test sample was carried out with chloroform (e 5.1), which is the best extractant, from the standpoint of the empirical rule «like in like».

The obtained extracts were purified from coextractive substances of the matrices by TLC by partition chromatography in a thin layer of the adsorbent under conditions of ascending one-dimensional elution in a saturation chamber. The active substances, depending on the value of ц, move at different speeds in a thin adsorbent layer and are localized at different distances from the start line in the form of separate chromatographic zones of cis - and trans-isomers with the corresponding values of Rf (Table 2). Zones of localization of cyproconazole and propiconazole (2 x 1 cm) are removed with a scalpel and transferred to a measuring tube, where 1 ml of the corresponding organic solvent is added. Aliquots are added to the chromatograph column.

The result of the research largely depends on the choice of chromatographic process conditions: the type of detector; the mobile and stationary phases; the temperature regime of the detector, column, evaporator. When determining these active substances, a flame ionization detector is used, modified to determine substances whose molecules contain nitrogen and phosphorus atoms (NPD). In this detector, the source of ionization is a hydrogen flame. Organic substances in the flame of a hydrogen burner are ionized, resulting in an ionization current, the strength of which is proportional to the number of charged particles and is recorded by the device in the form of chromatographic peaks with the corresponding retention time and areas. The optimal, selective chromatographic determinations conditions of cyproconazole and propiconazoleare presented in table 2.

Parameters of the chromatographic determination cyproconazole and propiconazole

It should be noted that when using gas-liquid chromatography, the isomers of cyproconazole and propiconazole are not identified by separate peaks as individual compounds, because they have the same retention time; only the actual active substances are separated (Fig.). Therefore, TLC can be used as an additional detection option cyproconazole and propiconazole to confirm the results of the determination by GLC, but in this case, the qualitative and quantitative assessment is carried out by the sum of the areas of isomers.

Chromatogram of model fruit samples (peaches):

1 - control sample;

2 - model sample with the introduction of 0.05 mg/kg cyproconazole + 0.16 mg/kg propiconazole

The calibration dependence of the area of the chromatographic peak of cyproconazole or propiconazole on the concentration in the calibration solution is described by the corresponding linear regression equations:

&= 11.991 С - 6.096 (?=0.998),

Sp = 13.721 С - 4.221 (R² = 0.994), where Sc and Sp - the peak area of cyproconazole or propiconazole respectively, mm²; C - the concentration of cyproconazole/propiconazole in the calibration solution, ^g/ml.

The equation is used to quantify cyproconazole and propiconazole in the analyzed samples.

The accuracy of the determination was confirmed by the «applied-detected» method when analyzing model samples into which a certain amount of the active substances was added (within the determination concentration range of 0.05-0.25 mg/kg), taking into account their ratio in the preparation. The chromatogram of the mixture is presented in the figure.

The average value of the determination is 81.0-87.8%; standard deviation 2.21-5.38%; confidence interval (Р 0.95; n=15) 1.94-4.72%.

Optimal selective conditions for the analysis of triazole derivatives by chromatographic methods provide simultaneous determination of test compounds and quality control of fruit crops on the content of residual amounts of cyproconazole and propiconazole at the level of hygienic standards (MAL 0.05 - 0.10 mg/kg).

Financing: The research was carried out within the framework of PSR 24 Phytosanitary safety, protection and quarantine of plants (Plant protection); №SR0121U000077.

References

propiconazole cyproconazole chromatography

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