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Asian Journal of Chemistry; Vol. 30, No. 7 (2018), 1546-1550 ASIAN JOURNAL OF CHEMISTRY https://doi.org/10.14233/ajchem.2018.21240 Quantification of Pyrethroid Residue in Food, Agricultural and Biological Samples 1,* 2 MADHURANI SHUKLA and KISHORE K. TIWARI 1Department of Chemistry, Government College, Gobra Nawapara-493 881, India 2Department of Chemistry, Government Nagarjuna P.G. College of Science, Raipur-492 010, India *Corresponding author: E-mail: [email protected] Received: 19 January 2018; Accepted: 26 February 2018; Published online: 31 May 2018; AJC-18928 A simple and highly sensitive spectrophotometric method has been developed for the quantification of broadly used pyrethroid pesticides i.e. cypermethrin and fenvalerate. The developed method is based on alkaline hydrolysis of these pyrethroid pesticides to cyanide ion. The cyanide ion is further react with potassium iodide in acidic medium to liberate iodine and this liberated iodine oxidizes leucomalachite green to malachite green. The absorption maximum of the formed dye is measured at 600 nm. Beer’s law is obeyed in the concentration range of 0.08-0.72 and 0.16-0.88 µg/mL for cypermethrin and fenvalerate, respectively. The molar absorptivity and Sandell’s sensitivity were found to be 5.90 × 105 L mol-1 cm-1 and 0.00070 µg cm-2 for cypermethrin and 3.81 × 105 L mol-1 cm-1 and 0.0011 µg cm-2 for fenvalerate pesticides. The developed method has been satisfactorily applied for the determination of cypermethrin and fenvalerate in their formulations and various food, agricultural and biological samples. Keywords: Spectrophotometer, pH meter, Leucomalachite green, Pyrethroid pesticides, Food, Agricultural & Biological samples. INTRODUCTION chromatography, HPLC-MS [13-15] and gas chromatography [16-19] etc. Several spectrophotometric methods have also At present time one of the fast growing global problem is been reported for the determination of cypermethrin and fenva- pesticide residues which are present in food commodities lerate insecticides. The aim of the proposed work is to develop caused serious hazardous effect on human health. Estimation a simple, rapid and accurate analytical method for the determi- of pesticides to human exposure can be determined by the nation of broadly used cypermethrin and fenvalerate insecticide levels present in the environment [1]. It has been reported that at micro gram levels. The developed method is based on alkaline rigorous attack of insect pests in beans, brinjal and bitter gourd hydrolysis of these pyrethroid pesticides to cyanide ion. The so that farmers used pesticides almost in every day for pro- cyanide ion is further react with potassium iodide in acidic tection of their crops [2]. It is necessary to develop awareness medium to liberate iodine and this liberated iodine oxidizes to consumers for safety issue that to known what quantity of leucomalachite green to malachite green. The developed pesticides present in their food [3]. The pyrethroid insecticides method has been satisfactorily applied to the determination of having a nitrile group such as cypermethrin and fenvalerate, cypermethrin and fenvalerate in their formulations and various which are most widely used insecticides against a range of food, agricultural and biological samples. household and garden pests [4,5]. It was determined that pyrethroid insecticides i.e. cypermethrin and fenvalerate act EXPERIMENTAL as neurotoxins and attack to central nervous system of various A Systronics (India) spectrophotometric model 166 with insects. Both insecticides are moderately toxic by intake and matched silica cells was used for all spectral measurements. A by dermal absorption. High dermal exposure caused lack of Systronics pH meter model no. 331 was used for pH measure- sensation and itching, burning sensation and possible to death. ments. All the chemicals used were of Analytical reagent grade It is carcinogenic and exert mutagenic effect to human [6,7]. or the best available quality. Double distilled water has been The various techniques have been used for the determination used throughout the study. of pyrethroid pesticides including cypermethrin and fenva- Cypermethrin and fenvalerate (Northern Minerals lerate. These include GC-MS [8], thin layer chromatography Limited, India): A stock solution of 1 mg/mL was prepared in [9], spectrophotometer [10,11], dispersive solid phase extrac- ethanol. Working standards were prepared by appropriate tion and GC determination [12], high performance liquid dilution of the stock solution. Vol. 30, No. 7 (2018) Quantification of Pyrethroid Residue in Food, Agricultural and Biological Samples 1547 Leucomalachite green (Sigma-Aldrich, S. Germany): 0.05 0.6 % of leucomalachite green was prepared by dissolving 25 mg A of leucomalachite green in 100 mL of water and 1.5 mL of 85 0.5 % phosphoric acid. Makeup to mark by using distilled water B in a 500 mL of volumetric flask and shaking gently until the C dye was dissolved completely. Phosphoric acid was dissolved 0.4 the dye absolutely and to keep this solution stable for longer time [20]. 0.3 Aqueous solution of sodium hydroxide (Loba Chemie, Mumbai) of 20 % concentration was prepared. 0.1 % aqueous Absorbance solution of potassium iodide (Merck, Mumbai) was used. 0.2 Aqueous solution (6 M) of phosphoric acid was prepared. Acetate buffer (pH 4.5) was prepared by taking 1 M sodium 0.1 acetate trihydrate solution and pH was adjusted to 4.5 with using acetic acid. Then mixture was diluted up to 100 mL with distilled water [21]. 0 Preparation of calibration curve for cypermethrin 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 insecticides: Aliquots containing 2 to 18 µg (0.08-0.72 µg/mL) Wavelength (nm) cypermethrin were taken in a series of 25 mL calibrated flasks. Fig. 1. Absorption spectra of the dye and reagent blank; (A) Concentration To this 1 mL of 20 % sodium hydroxide solution was added of cypermethrin 10 µg/25 mL; (B) Concentration of fenvalerate 12 and allowed to stand for 15 min. at room temperature for comp- µg/25 mL (C) Reagent blank lete hydrolysis. The reaction mixture neutralize and make slightly acidic with 4 M phosphoric acid. Then added 1 mL of 1.4 0.1 % potassium iodide solution to liberate iodine. After that added 1 mL of 0.05 % of leucomalachite green with shaken 1.2 thoroughly. Full colour developed after 15 min. The resulting A blue green dye was made up to the mark and measured at 600 1.0 B nm against a reagent blank. Reagent blank gave negligible absorbance at this wavelength. 0.8 Preparation of calibration curve for fenvalerate insec- ticides: Aliquots containing 4 to 22 µg (0.16-0.88 µg/mL) 0.6 fenvalerate were taken in a series of 25 mL calibrated flasks. Absorbance To this 1 mL of 20 % sodium hydroxide solution was added 0.4 and allowed to stand for 15 min. at room temperature for comp- lete hydrolysis after which above procedure for the deter- mination of cypermethrin was followed. 0.2 RESULTS AND DISCUSSION 0 0 5 10 15 20 25 Spectral characteristics: The maximum absorbance for Concentration of cypermethrine & fenvalerate both cypermethrin and fenvalerate pesticides obtained at 600 Fig. 2. Calibration curve for the determination of cypermethrin and fenva- nm. All spectral measurements were carried out against reagent lerate pesticides; (A) Concentration of cypermethrin µg/25 mL; (B) blank (Fig. 1). Alkaline hydrolysis of cypermethrin and fenva- Concentration of fenvalerate µg/25 mL lerate both pesticides give 3-(phenoxy)-2-hydroxy ethane nitrile which on further hydrolysis give cyanide ion. In acidic medium [22]. The liberated iodine oxidizes leucomalachite medium cyanide ion reacts with potassium iodide to liberate green dye. An acetate buffer (pH 4.0-5.0) is required to iodine. Liberated iodine selectively oxidized leucomalachite maintained pH of the solution for colour development. The green to malachite green. The colour system obeys Beer’s law green colour of dye was developed by heating the above in the range of 2 to 18 µg of cypermethrin per 25 mL and 4 to solution on a water bath at about 40 °C for 5 min. The solution 22 µg of fenvalerate per 25 mL of final solution at 600 nm then diluted to 25 mL with water. The dye formed by both (Fig. 2). The molar absorptivity and Sandell’s sensitivity were pesticides showed maximum absorbance at 600 nm against found to be 5.90 × 105 L mol-1 cm-1 and 0.00070 µg cm-2 for reagent blank. The reagent blank show negligible absorbance cypermethrin and 3.8 × 105 L mol-1 cm-1 and 0.0011 µg cm-2 at this wavelength. for fenvalerate pesticides. The standard deviation and relative Effect of time and temperature: Hydrolysis of cyperme- standard deviation were found to be ± 0.00158 and 0.279 % thrin and fenvalerate to cyanide ion was studied at different for cypermethrin and ± 0.0011 and 0.254 % for fenvalerate, temperatures. It was observed that the maximum hydrolysis respectively. was obtained with 20 % of sodium hydroxide at temperature Absorption spectra: After alkaline hydrolysis cyperme- range of 30-40 °C as it gave maximum absorbance values with thrin and fenvalerate react with potassium iodide in acidic good stability [23,25] (Fig. 3). 1548 Shukla et al. Asian J. Chem. 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 Absorbance Absorbance 0.2 A 0.2 A B B 0.1 0.1 0 0 2 4 6 8 10 12 14 16 10 20 30 40 50 60 70 80 Concentration (µg/25 mL) Temperature (°C) Fig. 3. Effect of temperature on absorbance of cypermethrin and fenvalerate; Fig. 5. Effect of concentration of cypermethrin and fenvalerate on absor- (A) Concentration of cypermethrin 10 µg/25 mL (B) Concentration bance; (A) Concentration of cypermethrin in µg/25 mL; (B) Concen- of fenvalerate 12 µg/25 mL tration of fenvalerate in µg/25 mL 0.7 Effect of pH: The effect of pH on the colour reaction was studied.