International Journal of Pharma and Bio Sciences V1(2)2010 ELECTROCHEMICAL REDUCTION BEHAVIOUR AND ANALYSIS OF FLUAZINAM

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1 K.BALAJI 1, C.SRIDEVI 2,.AADA KUMAR REDDY 3 K.MOHAA MUI SIDDA REDDY 4 AD C.SURESH REDDY 1 * 1 Department of Chemistry, S.V.University, Tirupati, India. 2 Department of Chemistry, S.P.W. Degree and PG College, Tirupati, India. 3 Department of Chemistry, S.V.Degree and PG College, Kadapa, India. 4 Department of Chemistry, S.V.Arts College, Tirupati, India. *Corresponding author csrsvu@gmail.com ABSTRACT The electrochemical reduction behaviour of Fluazinam has been studied by employing dc polarography, cyclic voltammetry, ac polarography and differential pulse polarography in Britton-Robinson buffer of ph ranging from 2.0 to A differential pulse polarographic method is described for the determination of Fluazinam in various environmental matrices by using standard addition and calibration methods. The kinetic parameters such as diffusion coefficients (D) and heterogeneous forward rate constants (K 0 f.h) values are evaluated using these techniques. KEY WORDS Fluazinam, Electrohemical Reduction behaviour, Analysis, Environmental samples. ITRODUCTIO Fluazinam is one of the dinitroaniline pesticide families and is an economically important class of agricultural compound used to prevent the growth of grasses and weeds in cultivated crops. Several chromatographic methods 1 to 4 are reported on the determination of the dinitroaniline herbicide in various matrices. Polarigraphic determinations of some nitroso group compounds containing reduction sites similar to that of pesticides and drugs has been thoroughly carried out 5 to 11 but little attention has been paid to the electrochemical study of this compound. Due to the limited voltammetric studies on Fluazinam, it is of interest to study the reduction of the compound in order to understand the electrochemical behaviour in various supporting electrolytes and also to know the electrode kinetics under different polarographic conditions. Differential pulse polarography is extensively utilised to work out 1

2 analytical procedures for the determination of Fluazinam in environmental samples. MATERIALS AD METHODS A PARC Model 364 polarographic analyser equipped with BD 8 Kipp and Zonen X-t recorder was used for d.c.polarographic measurements. A threerecorder combination was employed, which consisted of a dropping mercury electrode (DME), a saturated calomel electrode (SCE) and a platinum wire auxiliary electrode. Differential pulse polarographic (DPP) measuremments were performed with a Metrohm E 506 polarecord connected ot an E 612 VA scanner. The electrode assembly consisted of a DME (with an area of cm 2 ) working electrode, a Ag/AgCl (s), Cl - reference electrode and a platinum wire auxiliary electrode. A Digital Electronics 2000 X-Y/t recorder, which was connected to the Metrohm unit, was used for recording the cyclic voltmmograms (the working electrode was a hanging mercury drop electrode having an area of cm 2 ). A modified cell 13 with mercury pool cathode, SCE platinum wire gauze electrode and spot galvanometer, was used for controlled potential electrolysis (CPE). All the experiments are carried out at 298±1 K. Pure Fluzinam was obtained from Ciba-geigy pvt.ltd., Mumbai and was used without purification. Universal buffers of ph 2 to 12 were prepared by using 0.2 M bori acid, 0.05 M citric acid and 0.1 M trisodium orthophosphate. All the chemicals used were of pure analar grade. A stock solution was prepared by dissolving the required amount of Fluazinam in ethanol and making up with supporting electrolytes to obtain the concentration. The test solution was purged with puriified nitroge for 10 minutes before taking the volammograms. A 0.02% aqueous solution of Triton X-100 was used to eliminate the polarographic maximum encountered. RESULTS AD DISCUSSIO Fluazinam is found to exhibit a single well defined wave/peak in the entire ph range 2.0 to 12.0 in all the techniques. This single wave/peak is attributed to the simultaneous reduction of two nitro group in the eight electron process to the corresponding hydroxylamine groups. Typical voltammogram of Fluazinam are shown in Figures 1 to 3. 2

3 Fig.1 Typical d.c. polarogram of Fluazinam in ph 4.0 Concentration:0.5 mm Drop time:3s Fig. 2 Typical a.c. polarogram Fig.3 Typical DPP of of Fluazinam in ph 10.0 Fluazinam in ph 4.0 Concentration:0.5mM Concentration:0.5mM Drop time: 3s Drop time:2s a:base line b:a.c. peak Pulse amplitude:50mv 3

4 Fig. 4 Typical CV of Fluazinam in ph 12.0 Concentration: 0.5 mm Scan rate: 40 mvs -1 In cyclic voltammetric exprimetns, a small anodic peak (a 1 ) has been observed in the reverse scan at higher ph values (ph 10) for Fluazinam (Fig.4). In the second scan, another small cathodic peak (c 2 ) at more positive potentials than c 1 is noticed. The anodic peak (a 1 ) may be due to the oxidation of hydroxylamine formed at c 1 to nitroso derivative and the cathodic peak (c 2 ) may be attributed to the reduction of the nitroso derivative to the hydroxylamine again. The nature of the wave/peak is found to be diffusion controlled and adsorption free in the buffer systems taken, as shown by the linear plot of i d vs. h 1/2 (Fig.5), i p vs. v 1/2 (Fig.6) and i m vs.t 2/3 (Fig.7) which is found to pass through origin. The irreversibility of the electrode process is confirmed by the log-plot analysis of the wave. The slope of E dc vs.{log(i/id-i) log t} plot exceeds appreciably 54.2/n mv. The variation of peak potential with scan rate also indicates the irreversible nature of the electrode process. Further, E 1/2, E p and E m values are observed to have shifted towards more negative values with increasing concentration of the depolarizer. The E 1/2 and E p values of all the compound Fluazinam is found to be dependent on ph of the buffer solutions, indicating proton involvement in the electrode process. The number of protons involved in the rate determining step is found to be two as evidenced from the linear plots of E 1/2 vs. ph (Fig.8). 4

5 International Journal of Pharma and Bio Sciences V1(2)2010 Fig. 5 id vs h1/2 plots of Fluazinam Con.0.5 mm Fig.6 I p vs v1/2 plots of Fluazinam Concentration.0.5 mm Fig. 7 Im vs t2/3 plots of Fluazinam, Concentration:0.5mV Fig. 8 E1/2 vs ph plots of Fluazinam Concentration.0.5mV Drop time:3s 5

6 Millicoulometry is employed to find out the number of electrons involved in the electrode process. It is found to be eight (for each nitro group four electrons) for the reduction of two nitro groups from Fluazinam in acidic (ph 2.0) and basic (ph 12.0) medium. Controlled potential electrolysis (CPE) has been carried out in a modified cell with mercury pool cathode, saturated calomel electrode and platinum wire as anode. This experiment is carried out in ph 4.0 at applied potentials of -0.24V (vs SCE) for Fluazinam. After electrolysis, the reduced products are extracted with ether. The ethereal layer is evaporated on water bath and the product is identified as the corresponding hydroxylamine. The isolation product is confirmed as hydroxylamine by I.R. spectral data (-H stretch: 3420 cm -1, O-H stretch: cm -1 and -H bend: 1575 cm -1 ). The diffusion coefficient values evaluated form all the techniques are in good agreement. This is evident particularly where no adsorption is involved in the electrode process. The reason for slight decrease in diffusion coefficient values with increase in ph may be due to the less availability of protons with increase in ph of the buffer solution. The values obtained for transfer coefficient (α), diffusion coefficient (D) and heterogeneous forward rate constant (k o f.h), at various ph values in different techniques, are given in tables 1 to 4. Table.1 Typical d.c. Polarographic data of Fluazinam Concentration 0.5mM, Drop time:3s ph -Ep/V Ip/µA άn a Dх10 6 /cm 2 Table.2 Typical Cyclic voltmmetric data of Fluazinam Concentration 0.5mM, Scan rate:40mvms -1 6 s -1 K 0 f. h/ cm s х х х х х х10-16 ph -E 1/2 /V I d /µa άn a Dх10 6 /cm 2 s -1 K 0 f. h/ cm s х х х х х х10-17

7 Table.3 Typical a.c. Polarographic data of Fluazinam Concentration 0.5mM, Drop time:3s ph -Es/V Is/µA ά Dх10 6 /cm 2 Table.4 Typical Differential pulse polarographic data of Fluazinam Concentration 0.5mM, Drop time:3s, pulse amplitude:50 mv The heterogeneous forward rate constant values calculated are, in general, found to decrease with increase in the ph of the solution. This trend shows that the electrode reaction tends to become more and more irreversible with increase in ph. The rate constant values obtained for the reduction of nitro group for the compound Fluazinam is high in acidic medium in all the techniques, indicating that the rate of reaction is fast in acidic solution due to high proton involvement which makes the reduction process easier. But, in basic media, the reduction process does not easily occur owing to the lower availability of protons. Consequently, lower values are obtained for the rate constants in basic medium in contrast to acidic medium. Based on the results obtained form different techniques, the reduction mechanism of the nitro group present in Fluazinam can be proposed as follows. s -1 Ks/ cm s х х х х х х10-12 ph -E m /V I m /µa άn a Dх10 6 /cm 2 s -1 K 0 f.h/ cm s х х х х х х

8 Cl O 2 O 2 H Cl 2e -, 2H +, slow CF 3 ph Cl HO 2 O 2 H H 6e -, 6H + ph In the present work, DPP has been employed for the quantitative determination of Fluazinam in grain, soil and water samples. Fluzinam is found to exhibit sharp and well resolved peaks in ph 4.0 and this peak is chosen for quantitative studies. Both standard addition and calibration methods are used. The peak heights are found to be linear over the concentration range M to M with lower detection limits of M for Fluazinam. The correlation coefficients and relative standard deviation values are found to be and 1.32% for 10 replicants. Standard stock solutions ( M) of the Fluazinam is prepared by dissolving an appropriate amount of electroactive species in ethanol. 1 ml of the standard solution is transferred into a polarographic cell, made up with 9 ml of the supporting electrolyte and then deoxygenated with nitrogen gas for 10 minutes. The polarogram is recorded. Later small increments (0.2ml) of standard solution are added and the polarograms are recorded after each addition under the identical conditions. In the present study the best precision is obtained at ph 4.0 with a drop time of 2 sec, a pulse amplitude of 50 mv and applied potential of Vfor Fluazinam. This method is successfully employed for the determination of the compounds in grains, soil and water samples. Grain (rice) samples (50 g) and soil samples (25g) are sprayed with known amounts of the compounds and left for 2-4 hrs. The samples are extracted with acetone (2 50 ml) by shaking the flask for 5 min. The organic phase is filtered under suction through Whatmann o.1 filter paper. The solvent is removed through evaporation and the residues of the compounds are dissolved in ethanol and transferred into a 50 ml volumetric flask. A 1000 ml samples of tap water is spiked with the pesticide at different concentration levels (each concentration 3 times) taken into a 21, separatory funnel and shaken for a few minutes. The solution is passed through whatmann ylon memebrane filter (0.45 µm size). The elution is carried out with 3 50 ml dichloromethane. The organic solvent is filtered through anhydrous sodium sulfate and evaporated to dryness. Small volumes of hexane are added to remove dichloromethane completely. The residue is dissolved in ethanol and then transferred to a 50 ml volumetric flask. The results obtained for the determination of pesticides in grains, soils and spiked water samples are shown in Table 5. Cl CF 3 Cl HOH HOH H Cl CF 3 8

9 Table.5 Recoveries of Fluazinam added to grains, soils and spiked tap water samples Pulse amplitude: 50 mv, Drop time: 2s Compound Amount added (mg) Average amount found (mg) ±SD Average recovery (%) Fluazinam (Rice) ± ± ± Fluazinam (Soil) ± ± ± Spiked tap water ± COCLUSIO In conclusion the work describes that the electrochemical reduction behaviour of Fluazinam is based on the reduction of nitro group at DME and HMDE. The recovery results (Table 5) shows that DPP is a simple reliable and inexpensive. AKOWLEDGEMETS The author (KB) thanks for UGC [o.f (SC) 2007 (SA III)], ew Delhi for providing Post Doctoral Fellowship. 9

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