UV-Spectrophotometric Determination of Acephate and Profenofos (organophosphate) Pesticides in Buffer Medium

 

N.V.S. Venugopal* and B. Sumalatha

Department of Chemistry, G.I.T, GITAM University, Rushikonda, Visakhapatnam-530045, A.P, India

*Corresponding Author E-mail: Venu7000@gmail.com

 

ABSTRACT:

A simple UV-spectrophotometric method for the determination of acephate(O,S-dimethyl acetylphosphoramidothioate) and profenofos(O-(4-bromo-2-chlorophenyl) O-ethyl S-propyl phosphorothioate) pesticides in buffer media is described. World over organophosphate pesticides contribute significantly in agricultural production and public health security. These compounds are used for pest control technology in crop production. Acephate and profenofos pesticides were determined in PH5.0 buffer medium using UV spectrophotometer. The absorption maxima was 255nm for acephate and 265nm in the case of profenofos pesticide. The linear range of detection was in the range of 7.0-42mg/land 3.0-18mg/l for profenofos,and acephate respectively.The correlation coefficients for acephate and profenofos were 0.9953and0.9992 respectively in PH5.0 buffer medium.

 

KEYWORDS: Acephate, profenofos, UV-spectrophotometry, buffermedium

 


 

1. INTRODUCTION:

Organophosphates are widely employed both in natural and synthetic applications because of the ease with which organic groups can be linked together. Organophosphate pesticides degrade rapidly by hydrolysis on exposure to sunlight, air, and soil, although small amounts can be detected in food and drinking water. Recent studies suggest a possible link to adverse effects in the neurobehavioral development of fetuses and children, even at very low levels of exposure. Organophosphates are widely used as solvents, plasticizers, and EP additives. Organophosphates are widely employed both in natural and synthetic applications because of the ease with which organic groups can be linked together. Being a triprotic acid, phosphoric acid can form triesters whereas carboxylic acids only form monoesters. Esterification entails the attachment of organic groups to phosphorus through oxygen linkers.

 

Acephate and profenofos are organophosphate insecticides which are used on food crops such as beans, brussels sprouts, cotton, cranberries, head lettuce, peanuts, citrus trees and tobacco as a seed treatment, on golf courses, and in commercial or institutional facilities. 1

 

The limits of detection for most pesticides were well below 10 ng/mL and the reliable confirmation of analyte identity was possible at 10 ng/mL level for typically troublesome pesticides such as polar organophosphorus pesticides, methamidophos or acephate.2 The structures of acephate and profenofos are shown in figures1,2.

 

Figure1.Structure of acephate

 

A rapid and accurate method for the extraction and determination of the two organophosphorus insecticides, chlorpyrifos and acephate in top and subsoil materials of three tropical clayey soils from Sarawak has been developed. Soil samples were extracted with ethyl acetate and the pesticides were determined by GC-FPD. High recoveries of 76–102% and 76–100% were obtained for acephate and chlorpyrifos respectively, at fortification levels of 0.01, 0.1 and 1 mg kg−1 with standard deviations below 9.0%. 

 


 


 

Figure2. Structure of profenofos

 

A new spectrophotometric method has been studied for the determination of profenofos, the method was based on the hydrolysis of the profenofos in the sodium hydroxide solution. The hydrolyzed products on reaction with 4-aminoantipyrine gives a colored solution, absorbance of the resulting solution was measured at 500 nm. The r2 was 0.9997, the limit of detection and linear range was 0.4 mg/l and 2.0-80 mg/l respectively, the added recovery was 99.1%. 9 When profenofos is heated to decomposition it emits very toxic sulfur oxides, phosphorus oxides, hydrogen bromide, & hydrogen chloride.4 A simple, sensitive and specific HPLC-method for the determination of acephate in water and buffer solutions is described.  Since acephate has a very good solubility in water, it was not possible to extract it with organic solvents.  The present method is based on the evaporation of the aqueous sample to dryness, extraction of the residue with a suitable organic solvent, high performance liquid chromatographic separation on a reversed phase column and uv-detection of acephate.5 Acephate and profenofos are freely soluble in aqueous solution, moderately soluble in ethyl acetate and insoluble in n-hexane.6. Profenofos metabolizes rapidly under alkaline anaerobic conditions. In alkaline (pH 7.8) soil, profenofos degraded with a half-life of 3 days under anaerobic conditions.  The rate of metabolism was influenced by chemical hydrolysis. Thus, anaerobic metabolism in neutral and acid soils is likely to be slower.  In anaerobic aquatic conditions, profenefos degraded with a half-life of 3 days in a pH 5.1 sediment flooded with pH 7.3 water. The major degradates are 4-bromo-2-chlorophenol and O-ethyl-S-propyl phosphorthioate . Additional metabolites, 4-bromo-2-chlorophenyl ethyl ether, cyclohexadienyl sulfate, and phenol complex increased in concentration after 180 days. 

 

The present paper reports the determination of acephate and profenofos in buffer medium using UV-spectrophotometer.

 

EXPERIMENTAL:

Instrument

A Jasco (Model Uvidec-610) UV-VIS Spectrophotometry with 1cm matched quartz cuvettes was used for all absorbance measurements.

 

Systonics pH meter (model 331) is used to measure the pH of the buffer solution.  

 

A high precision Analytical balance was used for weighing the reagents. 

 

Reagents and Chemicals

Standard Solution of Profenofos: 100ppm Solution of profenofos in water was prepared by dissolving 0.01gm of profenofos standard in triply distilled water and make up to 100ml volumetric flask with triply distilled water.

Standard Solution of Acephate: 100ppm Solution of acephate in water was prepared by dissolving 0.01gm of acephate standard in triply distilled water and make upto 100ml volumetric flask with triply distilled water.

 

Preparation of pH 5.0 buffer: To 1.021g of potassium hydrogen phthalate and 22.6ml of 0.1M sodium hydroxide is added and then made upto 100ml vol. flask with distilled water. 

 

All other chemicals were of AnalR glade and provided from Merck.

 

Procedure

Profenofos:Aliquots of standard profenofos solution (1-7ml, 100ppm) were taken from the stock solution in stoppered tubes.  Dilute the solution with 2ml of pH 5.0 buffer and the solution is heated on a water bath at a temperature of 650C for 30 minutes.  The solution is cooled to room temperature and transferred into 10ml volumetric flask and make up to the mark with triple distilled water to prepare a series of concentrations ranging from 10-70 µg/ml of profenofos.

 

The absorbance values were measured at 250nm against the pH 5.0 buffer

 

Acephate:  Aliquots of standard acephate solution (3-18ml, 100ppm) were taken from the stock solution in stoppered tubes.  Dilute the solution with 5ml of pH 5.0 phthalate buffer and the solution is heated on a water bath at a temperature of 70-750C for 20 minutes.  The solution is cooled to room temperature and transferred into 25ml volumetric flask and make up to the mark with triply distilled water to prepare a series of concentrations ranging from 12-72 µg/ml of acephate..  The absorbance values were measured at 245nm against the phthalate buffer.

 

RESULTS AND DISCUSSION:

 

In order to ascertain the optimum wavelength of maximum absorption (λmax) of the translucent species formed in the above method, specified amount of profenofos and acephate were taken.  The absorption spectra were scanned on a spectrophotometer and found maximum wavelength for acephate and profenofos were 245nm and 250nm respectively shown in figures 3,4.   The corresponding concentration values and compliance with Beer’s lamberts law were assessedand shown in figures 5,6. The amount of acephate and  profenofos present in total volume of the solution is 48 µg/ml.  and 60 µg/ml. 

 

Figure3:Maximum absorption of acephate pesticide

 

Figure4:Maximum absorption of profenofos  pesticide

 

Figure5. Beer’sLaw validity of acephate pesticide

 

Optical Characteristics

In order to test whether the translucent species formed in above method adhere to Beer’s law the absorbance at appropriate lengths of a set of solutions containing varying amounts of profenofos andacephate specified amounts of pH 5.0 buffer were recorded against the corresponding reagent blank.  Molar absorptivity, Sandell sensitivity for acephate and profenofos were calculated in Table 1. Least squares regression analysis was carried out for getting correlation coefficient value.

 

Figure6: Beer’sLaw validity of profenofos pesticide

 

 Table1  :  Optical and regression characteristics for profenofos

Parameters

Acephate-pH5.0 buffer system

Profenofos-pH9.0 buffer system

λmax(nm)

245

250

Beer’s law limits (µg/ml)

3-18

14-84

Molar absorptivity (1 mol-1 cm-1)

0.1480x104

0.1607x104

Sandell’s sensitivity

(µg cm-2/ 0.001 absorbance unit)

0.1237

0.1139

Correlation coefficient (r )

0.9981

0.9992

Relative standard deviation (%)  **

0.0245

0.0179

** Six replicate samples

 

The precision of the proposed methods was ascertained from the absorbance values obtained by actual determination of six replicates of a fixed amounts of profenofosand acephate in total solution. The percent relative standard deviation was calculated for the proposed method.

 

REFERENCES:

1      Reregistration Elegibility Decision (RED) Acephate; EPA 738-R-01-013; U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, U.S. Government Printing Office: Washington, DC,2006, pp 1-87

2.       Zrostlíková, J.; Hajšlová, J.; Čajka, T., Evaluation of two-dimensional gas chromatography-time-of-flight mass spectrometry for the determination of multiple pesticide residues in fruit. J. Chromatogr. A, 1019, 1-2, 2003,173-186.

3. Lian-Kuet Chai, Norhayati Mohd-Tahir & Hans Christian Bruun Hansen, Determination of chlorpyrifos and acephate in tropical soils and application in dissipation studies, International Journal of Environmental Analytical Chemistry, , Vol 88, Issue 8, 2008,549-560.

4.       Lewis, R.J. Sax's Dangerous Properties of Industrial Materials. 9th ed. Volumes 1-3. New York, NY: Van Nostrand Reinhold,1996, p. 513.

5.       M.A.Alawi, HPLC-Deter. of Acephate, Fresenius Z. Anal., 315, 1983, 358-359.

6.       Ashok K Singh, Tom white, Dina spassova, Yin Jiang, physico chemical, Molecular-orbital and electronic properties of Acephate and Methamidophos, Comparative Biochemistry and Physiology Part C: Pharmacology, Toxicology and Endocrinology,  119, 1998,107-117.

7. USEPA; Revised EFED Environmental Risk Assessment for Profenofos. Available at http://www.epa.gov/pesticides/op/ profenofos/prof_efed.pdf as of Jan 7, 2002.

 

 

 

 

Received on 14.03.2012         Modified on 20.03.2012

Accepted on 25.03.2012         © AJRC All right reserved

Asian J. Research Chem. 5(4): April 2012; Page 526-528