Deepak Kumar Sahu^a,b, Joyce Rai^b, Chhaya Bhatt^a, Manish K. Rai^a,*, Jyoti Goswami^a, Ajay Kumar Sahu^a, Thakur Vikram Singh^c, Mamta Nirmal^a_, Kalpana Wani^a and Prashant Mundeja^a

^a School of Studies in Chemistry, Pt. Ravishankar Shukla University, Raipur, India, 492010

^b Chhattisgarh Council of Science and Technology, Raipur, India, 492014

^c School of Studies in Environmental Science, Pt. Ravishankar Shukla University, Raipur, India, 492010

*Corresponding author: mkjkchem@gmail.com

[Received: 04 January 2018; Revised Version: 06 February 2018; Accepted: 15 February 2018]

Abstract. In modern age pesticide is used widely in agriculture. Lambda-cyhalothrin (LCT) is one of the most used pesticides which are used as a insecticide to kill pest, tricks, flies etc in agricultural field and it is also used for crop production. We have developed new method to detect LCT insecticide in agriculture field and reduce its uses. In this method we found the maximum absorbance at 460 nm for yellow colour dye. We also calculated limit of detection and limit of quantification 0.001 mg kg^-1 and 0.056 mg kg^-1 respectively. Molar absorptivity and Sandell’s sensitivity was also calculated and obtained 1.782 ×10⁷ mol^-1 cm^-1 and 9.996 ×10^-6 µg cm^-2 respectively. The obtained yellow colour dye obeyed Beer’s law limit range of 0.5 µg ml ^-1 to 16 µg ml^-1 in 25 ml. This method is less time consuming, selective, simple, sensitive and low cost. Present method is successfully applied in various soil, water and vegetable samples.

Keywords: Pesticides, lambda cyhalothrin, agriculture, vegetables, UV-Vis spectrophotometer.

Introduction

Lambda Cyhalothrin [(R)-cyano-(3-phenoxyphenyl) methyl] (1S, 3S)-3-[(Z)-2-chloro-3, 3, 3-trifluoroprop-1-enyl]-2,2-dimethylcyclopropane-1-carboxylate] pyrethroids insecticides which is used to control insects, Tricks, flies and affect variety of indoor and outdoor insects (Rasmussen et al. 2013; Ghosh et al. 2016; Lou et al. 2018). Mostly lambda LCT is used in agriculture area such as cereals, cotton and vegetables (Bownik et al. 2019; Oudou et al. 2004; Zhang et al. 2012). It is used in agriculture field because of its low cost and high affectivity. Pyrethroids pesticides are extensively used in agricultural practices (Mohamed et al. 2016; Das et al. 2004; Xudong et al. 2016). The adverse effects of LCT in human being can cause several diseases like carcinogenic, paralysis, coma, produce tumour, burning sensations, nervous system and many symptoms like headache skin and eye imitation (Zeinab et al. 2012; Mohamed et al. 2016; Manal et al. 2015). It is acute effect of LCT for rate oral lethal dose is 56mgkg and skin lethal dose is 632 mg/kg (). Consumption of LCT may harmful for humans. It is a highly to toxic to many species such as fresh water fish aquatic organism etc. U.S. environmental protection agency (USEPA) registered LCT as an insecticide in 1998 (Manigandan et al. 2013).

LCT is mostly used in agriculture area to protect crops from insects and it also increases crop yields (Bownik et al.2019). This pesticide is mainly used in cotton, fruits, grains and vegetables as it is helpful in increasing the yield of crops and necessary to kill insects but also have a fatal effect on environment (Rasmussen et al. 2013; Housset et al. 2009). Therefore it is necessary to determine the LCT in environment samples so that the environmental can be protected by reducing its use. There are many techniques used for determination of pesticides such as Nuclear magnetic Resonance (Li et al. 2014), gas chromatography (Martinez et al. 2019), high performance liquid chromatography (Harshit et al. 2017a), Fourier transforms infrared spectroscopy (Reshma et al. 2018) etc. But they all are costly and more time consuming techniques.

Seenivasan et al. (2009) reported extraction method to determine LCT in Green tea leaves by gas chromatography and obtained detection limit is 0.005 µg mL^-1 and recovery was found 93-96%. (Mundeja at al. (2017) reported a spectrophotometric method for the determination of metsulfurom methyl with reagent 4- amino azobenzene and perform diazotisation and coupling reaction and found recovery range from 92-98% in environmental samples. Nirmal et al. (2016) have developed a new method to detect deltamethrin using leuco malachite green and found beers law obeyed and found recovery from 90-98 % different environmental samples. Lofty et al. (2013) determined LCT residue by gas chromatography and obtained recovery range 88-96% and found detection limit 0.001mg/kg. They all are time consuming methods for the determination of pesticides. Therefore we propose a new method to determine pesticide such as LCT in different environment samples which is cheap, less time consuming very sensitive and simple technique.

In the present work we have developed simple, low cost and sensitive method. Proposed method is based on the hydrolysis of the LCT in the presence of alkali sodium hydroxide. After hydrolysis by sodium hydroxide we further hydrolysed resulting produce and then added bromine water. This method is mainly based on the interaction between LCT and p-dimethylamino benzaldehyde and then we observed yellow dye formed. The colour dye was determined with the UV-Visible spectrophotometer technique.

Materials and Methods

Reagent & materials

Anal grade reagent was used for analysis and double distilled water was used for the experiments. The glasswares were cleaned randomly to remove the contamination. A stock solution of lambda cyhalothrin (LCT) was prepared by dissolving 1 mg/ml in acetate buffer (Ph 4.5). A stock solution prepared by 34 gm dissolving sodium acetate trihydrate in 200 ml of distilled water in acetic acid and mixture was diluted with 100 ml of distilled water. Potassium hydroxide 2% alcoholic solution was prepared. P-dimethylaminobenzaldehye (P-dmab) (loba chemie) 2 % w/v was prepared with 2M hydrochloric acid. Pyridine solution was prepared by adding 18 ml of pyridine in 3ml of concentrated HCl followed by 12 ml of distilled water. Pyridine purchased from Merck, Mumbai.

                                                          Scheme I Chemical structure of lambda cyhalothrin

Procedure

An aliquot of the solution containing 0.8 to 10 µg/ml of LCT was taken in 25ml graduated tube and 3ml of 2% alcoholic potassium hydroxide was added and then allowed to stand for 15 minutes for complete hydrolysis with potassium hydroxide. Now we added 0.5 ml of bromine water and shaked well for 5 minutes then we added 2-3 drops of formic acid to remove excess amount of bromine (Danger et al., 2011). In resulting mixture 0.5 ml of pyridine solution was added and was boiled for 10-15 minutes in water bath now the mixture was allowed to cool at room temperature. After cooling 0.5 ml of P-dmab was added and was allowed to cool for about 5 minutes for the complete colour development. The resulting yellow colour complex was measured at 460 nm against black reagent by UV visible spectrophotometer.

Steps of chemical reaction

1.     LCT hydrolysed with alcoholic KOH and produce cyanohydrin.

2.     Resulting cyanohydrin further hydrolysed to release cyanide con.

3.     Cyanide ion reacts with bromine water to form cyanogen bromide.

4.     By adding pyridine in resulting solution produce glutaconic acid.

5.     Glutaconic acid was coupled with P-dmab and produce yellow dye which was analysed by UV Visible spectrophotometric technique.

Instrumentation

Absorption spectrum was performed on double beam spectrophotometer made by cary-60 UV-visible spectrophotometer (Agilent technologies) with accuracy and Quartz Glasses used for analysis. PH measurement was performed with basic pH meter pH700 EUTECH instruments and centrifuge was used of REMI R- 4C.

Sample Collection

Berla is a block in Bemetara District of Chattisgarh State, India. It is located at 21.5255° N latitude and 81.4773° E longitude, 41 km from State capital Raipur towards South with an elevation of 292 m above sea level, covering an area of 11.4 km². According to census of India, 2011, a total population of 5,165 people reside in Berla block with a population density of 451.9 per km². The sample collection from different farm houses has been done. Figure 1 represents a map of Berla block showing locations of the sampling areas.

Figure 1. Locations of sample collection area of Bemetara district

Results and Discussions

When LCT was hydrolysed with alcoholic KOH it was dissociated into cyanohydrin and further hydrolysed with alkali medium it released cyanide ion and this released cyanide ion reacted with the bromine water to form cyanobromide. When resulting cyanobrominde was reacted with pyridine in the presence of heat for 15 minutes it forms glutaconic aldehyde. Then by adding P-dmab in glutaconic aldehyde yellow dye was formed. All reaction mechanism is shown in scheme II.

Scheme II Chemical reaction for the determination of lambda cyhalothrin.

UV- Visible Spectophotometric Method

In the present study Lambda Cyhalothrin is react with p- dmab and give yellow dye. The absorption spectrum of yellow dye was measured at 460 nm maximum absorbance by UV- visible spectrophotometer shown in figure 2. All spectra measurement of yellow dye was performed against double distilled water as a blank reagent negligible absorption spectrum at this wavelength. The obtained colour dye obeyed Beer’s law limit range of 0.5 µg ml ^-1   to 16 µg ml^-1 in 25 ml volume of final solution at 460 nm wavelength. The molar absoptivity and Sandall's sensitivity value were calculated 1.782 ×10⁷ mol^-1 cm^-1 and 9.996 ×10^-6 µg cm^-2 respectively. The limit of detection (LOD) and limit of quantification (LOQ) were calculated 0.001 mg kg^-1 and 0.056 mg kg^-1 shown in table 2. The intercept, slope and correlation coefficient calculated and shown in table 2.

Figure 2. (A) UV-Vis Absorbance spectra of colour complex at room temperature and (B) Calibration curve of lambda cyhalothrin at room temperature.

Effect of different reaction conditions

Effect of temperature, pH and Time

The effect of temperature on the reaction was studied by the varying temperature range from 15 ^oC to 60 ^oC for the Lambda Cyhalothrin and found that the 25 ^oC to 30 ^oC temperature was sufficient for the complete reaction. With increase or decrease in temperature, the absorption values also increased or decreased. In this study we found the pH for the reaction and we observed that pH 4.5 was required and it is was sufficient for the complete reaction and we studied that the minimum time was required for the complete reaction and full dye formation. The developed yellow colour dye was stable for many days shown in figure 3(A), 3(B).

Figure 3. (A) The graph plotted in different pH conditions and (B) Graph plot between different temperature verses absorbance (λ_max= 460nm).

Effect of Reagent

When 0.5 ml bromine water was added to 0.54 ml of pyridine and 1ml of P-dmab was added, reaction was completed. When amount of pyridine was increased or decreased the absorbance value also changed. When the concentration of P-dmab was altered, firstly absorbance value was increased by increasing the concentration of P-dmab and after that the absorbance values remained constant. Effect of reagent are shown in figure 4(A), 4(B).

Figure 4. (A) Calibration curve of absorbance verses different volume of pyridine reagent and (B) Calibration curve of absorbance verses different volume of pyridine reagent.

Effect of interference

We studied different vegetable samples and we found that different types of compound are already present in these vegetables. We added different pesticides and foreign species solution containing 10 µg of LCT in 25ml of final solution and developed a method for the analysis by the proposed methods and we found that there was no interference of those compounds in the method.

Method Validation

Linearity

For this experiment, the linear graph plotted between absorbance and concentration of Lambda Cyhalothrin in the range of 0.8 to 14 µg in 25 ml volume and we obtained a linear graph. The graph was plotted between small intercept and high correlation coefficient of regression equation (y=mx+c). In the study the molar absorptivity was also calculated as show in table no.

Accuracy and precision

Accuracy and precision of the new method was determined at different concentration levels and LCT analysed three replicate samples and the recovery range was found in the range of as 92-98%. We found that RSD value of new spectrophotometer method did not exceeded than ± 2%.

Robustness and ruggedness

Robustness and ruggedness was evaluated for the new method. Sometimes parameters like pH, temperature and time were changed. In this method one parameter altered but another was constant we calculated recovery each time and observed that the change of parameter does not affect reliving values shown in table 2.

LOD and LOQ

Limit of detection was evaluated by 3x σ/s when σ is standard deviation for the intecept and s is slope of calibration curve. Limit of quantification was evaluated by 10x σ/s where σ when σ and s are same as above (Harshit et al., 2017b).

Real sample analysis

During Experiment we developed new method for the determination of LCT in various environmental samples of vegetables, soil and water. We collected vegetables, soil and water samples from different fields and performed experiment many times. For determination of real sample we perform new method using standard addition method and we found LCT in the range of 92 to 98 % and RSD value was also calculated and was found less the ± 2%.

Application

Determination of Lambda Cyhalothrin in vegetable, fruits and soil samples

Collected samples from various field areas where LCT was used and sprayed. Weight 10gm samples of carrot, tomato, soil cereals etc Cut and chopped collected sample, now wash with 50% alcohol and centrifuge and then take resulting filtrate and test for analysis while 10 gm of sample was taken and add to it unknown LCT and kept for 4-5 hrs and washed with 50% of alcohol in volumetric flask. An aliquot solution of this solution was used for the determination of LCT by proposed protocol (Tamrakar et al. 2012).

Determination of Lambda Cyhalothrin in water samples

The proposed analytical method was applied on water. Water sample was taken from different rivers receiving water from different agriculture field. The water sample was collected in air tight bottle. Now unknown amount of LCT was added to it and stand for 4-5 hrs. Then it was filtered and 1 ml of EDTA solution was added to remove metal in from of samples was kept. This sample passed through the silica gel which absorbed LCT. Now extract sample by saturated ammonium chloride was now collected and transferred in volumetric flask and analysis was done by adding water to it. Now an aliquant solution was taken for the determination of LCT by proposed methods.

Comparison with other analytical methods

A new proposed method for the determination of LCT with P-dmab is described. The proposed method could be used as a simple and cheap method as compared to other expensive techniques. Present method is cheap and easy to handle. In this method reagents used are easily available and are cheap reagents. Comparison of proposed method with other analytical method are shown in table no.

Conclusion

In the study, we developed a new simple, cheap and selective method for the determination of the lambda cyhalothrin in various vegetables, fruits, soil and water samples. Proposed method was best as compared to other methods. In this spectrophotometer method interference of any foreign species are negligible. There are many techniques developed to determine the LCT but LOD of this method is very low as compared to other expensive techniques. Proposed method was easy to apply and cheap, simple and had selective technique and easy to determine LCT in various environmental samples.

Acknowledgement