Determination of Ethofenprox Spreading oil distribution on Water surface by HPLC

Feng Chao , Kong Fanyu, Zhang Chengsheng Key Laboratory of Tobacco Quality Controlling, Ministry of

Agriculture, Tobacco Research Institute, Chinese Academy of

Agriculture Science, Qingdao, China

fengchao020511@163.com

Yuan Huizhu*, Yang Daibin Key Laboratory of Pesticide Chemistry and Application

Technology Institute of Plant Protection, Chinese Academy of

Agriculture Science, Beijing, China

hzhyuan@gmail.com

Abstract—A method was developed for the determination of Ethofenprox Spreading oil (SO) distribution, a novel Labour-saving formulation using in paddy field, by high performance liquid chromatography (HPLC). The method used a reversed-phase C18 column and methanol-water (90+10, v/v) mobile phase. The quick, easy, cheap, effective, rugged and safe method was used for extraction of Ethofenprox from water surface, which involved the extraction of 1.55 μL sample homogeneous distribution with 10 mL water, followed by the covering of oil-absorbing paper (OAP). After twenty minutes, Ethofenprox was extracted into OAP. Then, the paper was shaked in 10 mL methanol. After concentration, the final extract was transferred to an autosampler vial for concurrent analysis by HPLC. Etofenprox in a good linear relationship in the ranges was studied, 0.1–20.0 mg L�1, with high correlation coefficients (0.9999). The RSDs were 0.12%. The average recoveries of Ethofenprox fortified at different levels were within 90.9-96.5%, and the precision of the test method was 1.6-4.4%. The proposed method was successfully applied to determine Ethofenprox distribution on water surface.

Keywords-HPLC; spreading oil ; water surface; Ethofenprox

I. INTRODUCTION Ethofenprox (Fig.1) developed by Mitsui Toatsu Chemicals,

Inc. is a new systemic insecticide (Mitsui Toatsu-1985). Ethofenprox SO is a new formulation type for paddy rice insect pests. This formulation should be directly dropped to paddy water without any dilution but not be sprayed directly to insects nor plants. Japan has developed Trebon Surf which is an oil formulation containing 4% etofenprox as the active ingredient [1]. Etofenprox has a excellent insecticidal activity against rice water weevil (Lissorhoptrus oryzophilus), white-back planthopper (Sogatella furcifera) [2], small brown planthopper (Laodelphax striatellus) [3], rice stem borer (Chilo suppressalis) [4], rice brown planthopper (Nilaparvata lugens) [5], etc. The active ingredient dropped on paddy water surface spreads to whole water surface of the paddy field in a few minutes. The layer of the active ingredient is maintained on water surface and some parts of it are adsorbed to rice sheaths, so that the insects contact to the active ingredient on water surface and rice plants then die. Therefore, study on distribution of Ethofenprox SO on water surface is necessary.

As research on this formulation, it is necessary to develop a sensitive, reliable method for distribution of active ingredient on water surface because no report on this study is available in the literature to date. Analytical methods were used for Etofenprox include HPLC [6, 7], GC [8], and fluorescence [9]. But extraction of Etofenprox from watersurface has not been reported yet.

C2H5OCH3

CH3

OO

Figure 1. Structural formula of Ethofenprox

The primary aim of our study was to develop a sensitive and reliable method to analyze the distribution of Ethofenprox SO on water surface by HPLC. We also tested the distribution of Ethofenprox in paddy field in order to offer a scientific basis for application and justified the reliability of this method by practical sample analysis.

II. MATERIALS AND METHODS

A. Apparatus, Instrumentation, and Chromatographic Conditions

1) Rotary Evaporators. —Model RE2000A (Yarong Bio-technology Co. Ltd, Beijing, PRC).

2) Ultrasound cleaner. —Model KQ250B (Kunshan Ultrasonic Instruments Co. Ltd, Jiangsu, PRC).

3) Syringe filter. —Nylon membrane, pore size 0.22 μm, filter size 25 mm (Shanghai Kangshou Medical Device Co. Ltd, Shanghai, PRC).

4) Analytical balance. —JY 2002 (Shanghai Precision &Scientific Instrument Co. Ltd, Shanghai, PRC).

5) Micro analytical balance. —JA 2003 (Shanghai Precision & Scientific Instrument Co. Ltd).

*Corresponding author. Tel: +86 010 62815941

___________________________________ 978-1-4244-9577-1/11/$26.00 ©2011 IEEE

6) HPLC system. —Water 1525-2487 with an Extend C18 column, 250�4.6 mm, 5 μm pore size (Waters Corp. Milford, USA). Conditions: flow rate 1mL/min, methanol-H2O (90+10, v/v) mobile phase, injection volume 20 μL, stop time 7.5-7.6 min, column temperature 30 �, detection wavelength 225 nm.

B. Abbreviations and Acronyms 1) Ethofenprox standard. —China Ministry of Agricultural

Institute for Control of Agro-chemicals. (ICAMA, Beijing, PRC), purit� �99%.

2) 5% Ethofenprox SO. —Prepared according to the method given in [10].

3) Methanol. —LC grade (DIMA Technology Inc., Richmond Hill, Ontario, Canada).

4) Oil-absorbing paper. —Hangzhou Fuchunjiang Rice Paper Co. Ltd, PRC.

C. Standard Curve The stock solution of Ethofenprox was prepared in

methanol at 100.0 mg L-1. The working standard solutions (0.1-20.0 mg L-1) were prepared by serial dilution from the stock solution. All solution were stored at 4 .

D. Extraction and Purification For the extraction of Ethofenprox from water surface, the

sample preparation followed the quick, easy, cheap, effective and safe method. A 1.55 μL 5% Ethofenprox SO has homogeneous distribution in 10 mL water within a beaker, the covering of which followed by OAP (3.0×3.0 cm). After twenty minutes, Ethofenprox was extracted into OAP, and the paper was shaked in 10 mL methanol. After concentration, added 1 mL methanol, the final extract was transferred to an autosampler vial for concurrent analysis by HPLC. Then, untreated OAP (A), treated OAP (B) and water in beaker (C) following the above procedure were transferred into glasses autosampler vial for HPLC.

E. Recovery Assay Untreated OAP was fortified with 1 mL Ethofenprox

standard solutions (0.1, 0.5 and 1.0 mg L-1), and processed following the above procedure. Six replicates were analyzed for each spiked concentration.

F. Practical Samples Test The field experiments were done at Yancheng City in

Jiangsu Province. The area of paddy rice field was 10×10 m, which added 5% Ethofenprox SO 50 mL. After four hours, Ethofenprox Spreading oil distributed on watersuface, then was collected by OAPs. Five sampling points (1 m interval) were collected three times from the center of paddy rice fields to the south. After that, the OAPs were stored in centrifuge tubes for subsequent experiments. Three replicates were performed.

III. RESULTS AND DISCUSSION

A. Method Optimization 1) Standard Curve: There was a good linear relationship

in the studied ranges 0.1–20.0 mg L�1, with high correlation coefficients (r2=0.9999). The equation of linear regression was Y=60.356x+1.1092. Chromatogram of Ethofenprox standard sample was shown in Fig.2.

Figure 2. Chromatogram of Ethofenprox standard sample

2) Extraction method : The QuEChERS method was used.

The OAP of blank extracts (A) and samples fortified at 1.55μL 5% Ethofenprox SO (B and C) were free from interfering peaks, and, therefore, no further cleanup was needed (Table 1 and Fig. 3).

TABLE I. DISTRIBUTION RATES OF 1.55μL 5% ETHOFENPROX SO IN DIFFERENT SAMPLES (N=3)

Content of Ethofenprox ,% Sample No.

Average

A 97.43 96.45 98.75 98.31 a

B 1.19 1.54 1.02 1.24 b

C 0 0 0 0.00 b

(A)

(B)

(C)

Figure 3. Chromatograms, (A): untreated OAP, (B): treated OAP, (C): water sample in beaker.

B. Method Validation 1) Linearity.—Standard calibration curve of Ethofenprox

was plotted as analytical concentration versus peak area. The calibration range has a linear relationship between 0.1 and 20.0 mg L-1 [correlation coefficient (r2) = 0.9999].

TABLE II. RECOVERY RATE OF ETHOFENPROX RESIDUES FROM OAPSN=6

Fortification level, �g mL-1 Avg. recovery, % RSD, %

0.1 92.0 2.3

0.5 95.5 2.9

1.0 90.9 4.4

2 92.4 4.1

5 94.5 1.6

10 96.5 3.7

RSD=Relative standard deviation

2) Accuracy.—Untreated OAPs were fortified with 0.1, 0.5, 1.0, 2.0, 5.0 and 10.0 mg L-1 Ethofenprox before extraction by adding the appropriate volume of the working standard solution. Table 2 shows the fortified recovery range from 90.9 to 96.5%.

C. Application to Practical Samples In order to demonstrate the utility and performance of the

method, the distribution of Ethofenprox on water surface of paddy rice field was studied. The content of Ethofenprox in OAPs was obtained from the calibration curve. The results showed that the distribution of 5% Ethofenprox SO on water surface could be detected by this method. Table 3 shows very homogeneous contents on water surface.

TABLE III. CONTENTS OF ETHOFENPROX ON WATER SURFACE

No. Distance from center, m Concentration, ×10-4 g cm-2

Average, ×10-4 g cm-2

1 0 15.25 8.96 7.56 10.59 a

2 1 6.42 15.55 8.62 10.20 a

3 2 9.44 14.62 13.21 12.42 a

4 3 15.10 6.51 7.95 9.85 a

5 4 11.03 8.96 13.21 11.07 a

IV. CONCLUSIONS This paper describes an analytical method for determining

the Ethofenprox contents in water surface by HPLC.

The OAP has been shown to be useful for extraction of Etofenprox from water surface. A good linear relationship was obtained between peak area and concentration. Application to the measurement of Etofenprox in OAPs showed recoveries at six fortified levels were good, from 90.9% to 96.5%. The RSD values are good, from 1.6% to 4.4%. The performance of the method indicated it could be used as a rapid, simple, sensitive, convenient, and practical technique for monitoring Etofenprox in water surface.

ACKNOWLEDGMENT We acknowledge financial support of this investigation by

the National Basic Research Program of China (2006BAD 08A 03; 2006BAD 02A16), and Shandong Tobacco Company (200907).

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