WO2013114404A1

WO2013114404A1 - Nano-structured silver oxide film based aqueous voltammetric pesticide sensor and a process of preparing said sensor

Info

Publication number: WO2013114404A1
Application number: PCT/IN2013/000064
Authority: WO
Inventors: Vijayammma Subha PANAMPILLIL; Saumya VARGHESE; Prasada Rao TALASILA
Original assignee: Council Of Scientific & Industrial Research
Priority date: 2012-01-31
Filing date: 2013-01-31
Publication date: 2013-08-08
Also published as: IN2012DE00264A; CN104412104A; JP6167114B2; JP2015510584A; CN104412104B

Abstract

The present invention relates to nano-structured silver oxide film based voltammetric sensors for pesticides, for example, endosulfan or atrazine or methyl parathion in natural waters which are highly sensitive, reliable, precise, stable and regenerable. The process of which is as follows: i) Electrochemical conditioning of polycrystalline silver electrode by potentiostating at 0.32 V Vs Ag/AgCl for 15 min. in 1M NaOH + 5x10^-5M Na₂HPO₄ solution. ii) Formation of nano-structured silver oxide film by repeated potentiodynamic cycling (7-9 cycles) in the potential range -0.3 to + 0.5 V vs Ag/AgCl. iii) Voltammetric transducer based electrochemical sensing in NaOH -Na₂HPO₄ sample media. The designed sensor is cut above the hither to reported sensors in terms of sensitivity, precision and in offering wider calibration range. The developed sensor can find wide spread use in environmental screening & monitoring, chemical industry, clinical diagnostics and other related fields for selected pesticides.

Description

"NANO-STRUCTURED SILVER OXIDE FILM BASED AQUEOUS

VOLTAMMETRIC PESTICIDE SENSOR AND A PROCESS OF PREPARING SAID SENSOR"

The following specification particularly describes the nature of the invention and the manner in which it is to be performed

FIELD OF INVENTION

The present invention relates to Nano-structured silver oxide film based aqueous voltammetric pesticide sensor and a process of preparing said sensor. More particularly, present invention relates to the process for formation of nano-structured silver oxide film (after electrochemical conditioning) which senses reliably and precisely ultratrace amounts of cndosulfan or atrazine or methyl parathion over a wide concentration range of 7 decades.

BACKGROUND OF THE INVENTION & DESCRIPTION OF PRIOR ART

Reference may be made to formation of silver oxide via silver metal [Sieger, I JSP 4, 913, 78 1 ; Urry, 6, 258, 132 B l ; Budget et al , US 2010/0047689A1 and katan et al, USP 4, 461 , 677], formation of micro porous elemental silver via silver oxide from silver nitrate crystals [Sieger, USP 4, 851 , 310] and silver/silver oxide electrode for electric batteries [Strauss, USP 3, 358, 138); Baiters, USP 4, 209, 578] . Another reference may be made to method of producing silver oxide electrodes [Rampel, USP 3, 258, 362; and Langan, USP 4, 250, 234 Glen et al, USP 4,892,629 Langguth et al, USP 3, 353, 998], preparation of nanosized silver oxide powder [Berube & Banerjee, USP 7, 201 , 888 B2 | and a process for treating silver oxide [Borberly, USP 4, 126, 584].

Another reference may be made to preparation of Ag_xO (Kx<2) with diameters ranging from 0.7 to Ι . ΐ μπι by electrochemical step edge decoration on highly oriented pyrolytic graphite electrode surface by Murray et al, Chem. Mater. 1 7 (2005) 661 1 . Reference may also be made to synthesis of oriented silver oxide nanostructure through a template free electrochemical route [Wei et al, J. Mater.Chem. 21 (201 1) 432]..

Yet another reference may be made to incorporation of additives such as gold [Davis, USP 3, 853, 623], mercury, selenium, tellurium, or combination of mercury with lead or tin [Tvarusko, USP 3,650,832], sulphide [Megahed et al USP 4, 078, 127], PbS [Megahed et al USP 4, 835, 077] , bismuth [Passaniti et al USP 5, 589 , 1 09] and nickel [Berndt et al USP 3, 630, 780] in to alkaline electrolyte during preparation of silver oxide meant for alkaline batteries. Another reference may be made to formation of silver oxide via dual pulse amperometry by dipping silver electrode in a flow system by solvent switching between 0.2 M NaOH and 0.2 M NaOH + 0.01 M sodium phosphate (for detection of carbohydrate and related compounds) [De Mott et al , Electroanal. 10( 1998)836] and 0.5 M: NaOH + 0.5 M NaOH + 0.01 M sodium phosphate (for detection of aminoacids) [De Mott et al, Electroanal. 17(2005) 599] .

Yet another reference may be made to formation of silver oxide film on to polycrystalline silver electrode i) from 8 M KOH and at elevated temperatures of 45°C deals with kinetics of formation - not sensing) (Hur & Chung, J. Electrochem. Soc. 152(2005)A179-A 185) and ii) from 1 M KOH by cyclic voltammetric technique for the detection of cyanide and diethylcyanophosphonate based on decrease in the Red- Ox peak intensity (Fathi et al, Langmuir 27(201 1) 12098).

References may be made to other nano-structured sensors of pesticides Viz. poly 3,4-ethylene dioxythiophene modified glassy carbon (GC) for square wave stripping voltammetric determination of 5 pesticides dicofol, cypermethrin, monochrotophos, chlorpyriphos and phosalone [Manisankar et al, Anal. Chim. Acta, 528(2005) 157]; nickel(II) phthalocyanine - MWCNT modified basal plane pyrolitic graphite for detection of asulam [Siswana et al. Anal. Bioanal. Chem. 14(2010) 1351 ]; MWCNT

Nafion modified GC for amperometric sensing of parathion [Li et al, Anal. Bioanal. Chem. 381 (2005) 1049]; gold nano particles - MWCNT for linear sweep voltammetric sensing of parathion [Zhang et al., Microchim. Acta 165(2009)307]; silver nano particles - Nafion composite modified GC for differential pulse voltammetric sensing of methyl parathion and parathion [Kumaravel & Chandrasekaran, J. Electroanal. Chem. 638(2010)231 ] , References may also be made to endosulfan quantification by UV-Visible spectrophotometric [Sowbhagya et al, Pestic. Sci 15 ( 1984) 571]; [Sreekumaran Nair et al, J.Environ. Monit. 5(2003)363]; reversed phase liquid chromatographic ^' [Siddiqueetal, J. Liquid, chromotatography & Related Technologies 26(2003) 1069]; GC-MS-EI in selective ion monitoring mode [Ramesh & Ravi, j. Environ. Monit. 4 (2002) 190]; Ramesh & Vijayalekshmi, Pest Manag. Sci. 58 (2002) 1048] for determination of traces of endosulfan. Another reference may be made to various electro analytical methodologies viz. different pulse polarographic [Reviejo et al, Anal. chim. Acta 264 ( 1992) 141 ; Reviejo et al, Talanta 39 (1992) 899, Reviejo et al, Electroanal. 4 ( 1992) 1 1 1], differential pulse/square wave stripping voltammetric [Latha et al, Ind. J. chem. 37A ( 1998) 1027; Prabhu & Manisankar, Analyst 1 19 ( 1 994) 1867; Manisankar et al, Int. J. Environ. Anal. Chem. 82 (2002) 33 1] and cyclic voltammetric [Sunitha & Sushma, Ind. J. Chem. Technol. 1 1 (2004) 509; Manisankar et al, Int. J. Environ. Sci. & Health 39B (2004) 89] determination of traces of endosulfan. Comparison of sensing characteristics of various endosulfan sensors are compiled in Table 1 .

Electroanalytical Sample medium Linear LOD (M) Reference

technique calibration

& pH

range,

-5 - 4

Differential pulse NaOH,12 10 - 10 4xl0 ⁶ Talanta, 39(1992)899-906 polarography (DPP)

DPP Ethyl acetate , 2.77x10 ³ Anal, Chim. Acta.264(1992)

141-147

Hyamine 2389&

Triton X-405,6

-5 - 4

DPP Britton Robinson buffer, 10 - 10 3xl0^~7 Electroanal.,4,(1992)lll-120

1.5-12

Differential pulse Britton Robinson 2.457xl0^'3& 2.457x10 & 1 nter.J. Environ. Ana I.Chem ., 82 strippingvoltammetry buffer,l-13 (2001),331-340

23.346x10 '

23.346xl0^"J

(DPSV)

DPSV Britton Robinson 1.2xl0^"5-7.3xl0^"7 1.2xl0^"H- Indian J. Environmental Science buffer,l-13 and Health,B39,2004,89-100

7.3xl0^"4

DPSV H 7 SO 1 & acetonitrile,l 1.67x10 ⁷-6.4xl0 5xl0^"5 Analyst,119,(1994)l867-1873

7

SWSV H 2 SO 1 & acetonitrile.,'1 0.0984xl0^"7- 5x10 ⁵ Analyst,119,(1994)1867-1873

1.9xl0^_

Cyclic Voltammetry ammonium acetate 5x10 ⁵ 0.344xl0^"7 Indian journal of Chemistry,

37A(1998),1027-1028

(CV)

CV Britton Robinson 2.457xl0 ³& 2.457xl0³& Inter. J. Environ. Ana l. Chem.

buffer,1.2-11.5 82(2001),331-340

23.346 x 10 ⁵ 23.346xl0^"5

CV Britton Robinson buffer, 1.2xl0^"5- Journal of Environmental

Science and Health, B39, 2004, 7.3χ1θ^"7

0.1dm ³ KCI & H SO ,1 89-100.

CV 1 NaOH + 5x10-5 M 13 - 6 -.13

10 - 10 3.3x 10 Present Embodyment

Na 2 HPO 4 , 11.8 _

5

Table 1 Comparison of sensing characterisation of various endosulfan sensors

From the above mentioned account, the rapid, reliable and precise determination of endosulfan down to 0.01 ppb or 2,5x1_.0^"" M (Maximum permissible limit) is not realized. Another limitation of hither to reported analytical methodologies is the limited narrow calibration range of 3-4 decades that too in micro-molar range. However, the present invention holds promise on these two accounts.

OBJECTS OF THE INVENTION

The main objective of the present invention is to design and develop Nano-structured silver oxide film based aqueous voltammetric pesticide sensor and a process of preparing said sensor which obviates most of the draw backs.

Another object of the present invention is to prepare reproducible, surface to surface and disc to disc, polycrystalline silver electrode surface via mechanical & sonochemical polishing and electrochemical conditioning.

Yet another object of the present invention is to form nano-structured silver oxide fi lm from sodium hydroxide-disodium hydrogen phosphate media

Still yet another object of the present invention is regenerability of the silver oxide ^' film based voltammetric sensor for pesticides.

SUMMARY OF THE INVENTION

Accordingly the present invention provides a nano-structured voltammetric sensor for detection of pesticides wherein the sensor comprising of polycrystalline silver electrode having nano-structured silver oxide film wherein detection limit is ~ 3x 10^" ^{l 3}M.

In an embodiment of the invention wherein voltammetric sensor responds to pesticide at 0.32 V Vs Ag/AgCl. In another embodiment of the invention wherein sensor is detecting pesticide in presence of alkali, alkaline earth metal and heavy metals with a detection limit of 3x l0^{" 13}M. In yet another embodiment of the invention wherein said sensor senses pesticide in 1.0 M NaOH + 5.0xl 0^"5 M Na₂HP0₄ medium by recording cyclic voltammogram in the potential range -0.3 to + 0.5V and measuring peak currents at 0.32 V Vs Ag/AgCl.

A process for the preparation of nano-structured silver oxide film based sensor, wherein said process comprising steps of:

i) polishing with emery of papers of grade 2/0, 3/0 and 5/0 for 25±5 min each, followed by polishing with charcoal for 7 - 8 min, followed by polishing sonochemically in acetone and deionized water for 5 minutes.

ii) electrochei^'nical conditioning by holding polycrystalline silver electrode potentiostatically at -0.3V Vs Ag/AgCl for 15 min in 1M NaOH + 5x l0^"5M Na₂HPO₄ solution ,

iii) formation of silver oxide film on to polycrystalline silver electrode via 7 - 9 cyclic voltammetric scans at a scan rate of 125 to 150 mV/s in the potential range -0.3 to +0.5 V Vs Ag/AgCl in 1.0 M NaOH + 5.0 xl O^"5M Na₂HPO₄ solution(p.H 1 1.8).

In another embodiment of the present invention, a sensor as claimed in claim 1 , wherein said sensor is stable up to 30 days.

In an embodiment of the invention, wherein nano-structured silver oxide film can be regenerated after polishing (Mechanical & Sonochemical), electrochemical conditioning and repeated cyclic voltammetric scanning.

Accordingly, the present invention also provides a method for detection of pesticide (endosulfan or atrazine or methyl parathion) using the sensor as described above wherein steps comprising recording cyclic voltammogram in the potential range -0.3 to + 0.5V and measuring peak currents at 0.32 V Vs Ag/AgCl.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS & FIGURES Fig 1 shows cyclic voltammetric profiles of silver oxide film based endosulfan sensor. Fig 2 shows cyclic voltammetric profiles of silver oxide film based atrazine sensor. Fig 3 shows cyclic voltammetric profiles of silver oxide film based methyl parathion sensor.

Fig 4 depicts X-ray diffraction pattern of silver oxide film.

Fig 5 shows scanning electron microscopic micrograph of silver oxide film.

Fig 6 shows transmission electron microscopic micrograph of silver oxide film. .

Chart 1 : Flow chart for formation of nano-structured silver oxide film on to polycrystalline electrode. DETAILED DESCRIPTION OF THE INVENTION

Accordingly the present invention provides "Nano-structured silver oxide film based aqueous voltammetric pesticide sensor and a process of preparing said sensor" which comprises a method of construction of electrochemically modi fied electrode for sensing of endosul fan or atrazine or methyl parathion employing

a) Mechanical & sonochemical polishing and electrochemical conditioning of polycrystaljine silver electrode. b) Formation of nano-structured silver oxide film and c) Cyclic voltammetric sensing of endosulfan or atrazine or methyl parathion.

The present invention offers a method of making endosulfan sensing film on polycrystalline . silver disc electrode from aqueous media. The salient features of the invention are

r a) Mechanical & sonochemical polishing and electrochemical conditioning of polycrystailine silver electrode

The polishing of polycrystailine silver electrode include successive steps of mechanical & sonochemical polishing and electrochemical conditioning (see step 1 of chart l).The mechanical polishing is done by polishing with emery of papers of grade 2/0, 3/0 and 5/0 for 25±5 min each, followed by polishing with charcoal for 7 - 8 min. Subsequent to this, the above mechanically polished polycrystailine silver electrode is sonochemically polished in acetone and deionized water for 5 min. Finally, the mechanically and sonochemically polished polycrystailine silver disc electrode is subjected to electrochemical conditioning by holding the electrode potentiostatically at -0.3 V Vs Ag/AgCl for 15 min in 1 M NaOH + 5 xlO^"5 M Na₂HPO₄ solution. b) Formation of nanostructurcd silver oxide film

Nano-structured silver oxide film is formed on mechanically & sonochemically polished and electrochemically conditioned polycrystailine silver electrode by potentiodynamic cycling (7 - 9 times) in the potential range -0.3 to 0.5V at a scan rate 1 25- 150 mV/s after dipping the electrode in 1 M NaOH -I- 5 xl^'0° M Na₂HPO₄. (See step 2, chart 1) c) Cyclic voltammetric sensing of cndosulfan

Figs.1 , 2 & 3 show cyclic voltammograms drawn for endosulfan, atrazine & methyl parathion respectively, on incremental addition of endosulfan or atrazine or methyl parathion to 1 M NaOH + 5x10^"5 M Na₂ITPO₄ solution as per step 3 of chart 1 . Calibration plots are drawn by plotting the peak currents at 0.32 V Vs Ag/AgCl against pesticide concentration on semi log graph sheet. Fig.4 shows XRD pattern of nano-structured silver oxide film which indicate major amount of Ag₂O and little amount AgO. SEM images of nano-structured silver oxide film indicate flowery nanorods as shown in Fig.5. ΊΈΜ images in Fig 6, confirms that, each nano rod is of width of 20 - 90 nm. The salient features of the present invention include the following

i) Formation of AgO_x film on to silver polycrystailine electrode. ii) Determination of endosulfan or atrazine or methyl parathion pesticides.

iii) Checking the reproducibility

iv) Analysis of synthetic samples

v) Analysis of real samples

i) Formation of AgO_x film on to silver polycrystalhne electrode.

AgO_x film is formed on to silver polycrystalhne electrode by following the procedures described in Examples 1 to 6.

ii ) Determination of endosulfan or atrazine or methyl parathion

l ml each of lx lO^"3 M Na₂HP0₄ and 20 M NaOH were taken diluted to 20 ml and transferred to electrochemical cell. AgO_x film is formed as described under Section i).

10^{" lj} to 10^"6 M concentrations of endosulfan are added, cyclic voltametric curves were drawn and calibration graphs are plotted with peak currents at 0.32V Vs Ag/AgCI against [endosulfan] on semi log graph sheet. The endosulfan concentration of unknown sample is obtained by reference to above calibration graph. Analogous procedure is followed for determination of atrazine or methyl parathion. iii) Reproducibility

12

The film to film reproducibility of endosulfan sensor for 10^{" 1} M endosuli :an was determined by conducting 5 successive determinations with five different AgO_x films.

12 '

The mean value and relative standard deviations were found to be 1.03 x 1 0^"" M and 0.12 % respectively. iv) Analysis of synthetic multi-component mixtures

The results obtained on analysis of synthetic mixtures of 0, 10^"6 and 10^"2 M each of alkali & alkaline earth metal ions ^' (Na⁺, K⁺, Ca²⁺ and Mg²⁺) added to 10^{" 12}M of endosulfan are shown in Table 2. As seen from the Table, the % recovery of endosulfan is quantitative even in the presence of 10 ¹⁰ fold amounts of mixtures of alkali and alkaline earth metals. Table 2 Analysis of multi-component synthetic mixtures of alkali & alkaline earth metal ions

Table 3 shows the results obtained on testing the endosulfan recoveries on addition of 0, 10^"6, 10^"5 and 10^~4 M each of heavy metal ions (Cu²⁺, Pb²⁺, Hg² " and ΊΤ' )

1 2

as admixtures to 10^" M of endosulfan. Acceptable recoveries were obtained at concentrations of < 10^"5M of heavy metal ion mixtures.

Table 3 Analysis of multi-component synthetic mixtures of heavy metal ions

10

Table 4 depicts the % recoveries of 10^{" I 2}M endosulfan when spiked with multi- component mixtures of anions (Cf, N0₃\ Cl0₄ ^' and S0₄ ^2") (0, 10^-6 and 10^"4 M). There is a serious interference on addition 10^"4 M anion mixture but could tolerate up to 10" fold. Tabic 4 Analysis of multi-component synthetic mixtures of anions

v) Analysis of real samples

Procedure for the analysis of natural waters

To an appropriate aliquots of water samples ( 10 ml), l ml each of l x l.0^""1 of Na₂ITP0 and 20 M of NaOH and 2 ml of x M endosul fan (x = 0, 10^{' i 2}, 10^"" , 1 ()^{" 10}, 10^" & 10^"6 M ) were added and made up to 20 ml. Transferred to an electrochemical cel l and cyclic voltammetrie curves were drawn and endosulfan concentrations were estimated by reference to the calibration graph of Section ii) As seen from the Table 5 , the recoveries of endosulfan are quantitative and the endosulfan concentrations were found to be below the detection limit.

Tabic 5 Analysis of Natural waters*

EXAMPLES

Having described the invention, the following examples are given to il lustrate the method of making nano-structured silver oxide film on to polycrystalline silver disc electrode. Example 1

Nano-structured silver oxide film on to polycrystalline silver electrode is prepared by first electrochemical conditioning at -0.3V for 15 min in 1 M NaOH + 5x l0^"5M Na₂HPO₄ solution and then cyclic voltammetric scanning for 7 times in the potential range -0.3 to +0.5 vs Ag/AgCl after dipping in 1 M NaOH + 5x l0^"5M Na₂HPO₄ solution at a scan rate of 125 mV/s.

Example 2

Nano-structured silver oxide film on to polycrystalline silver electrode is prepared by first electrochemical conditioning at -0.3V vs Ag/AgCl for 15 min in 1 M NaOH + 5x 10^" M Na₂HPO and then cyclic voltammetric scanning for 8 times in the potential range -0.3 to +0.5 vs Ag/AgCl after dipping in 1M NaOH + 5xl0^"5M Na₂.HPO₄ solution at a scan rate of 125 mV/s.

Example 3

Nano-structured silver oxide film on to polycrystalline silver electrode is prepared by first electrochemical conditioning at -0.3V vs Ag/AgCl for 15 min in 1 M NaOH i- 5xl O^"5M Na₂HPO₄ and then cyclic voltammetric scanning for 9 times in the potential range -0.3 to +0.5 vs Ag/AgCl after dipping in 1 M NaOH + 5xi0^"5M Na₂HPO₄ solution at a scan rate of 125 mV/s.

Example 4

Nano-structured silver oxide film on to polycrystalline silver electrode is prepared by first electrochemical conditioning at -0.3V vs Ag/AgCl for 15 min in 1 M NaOH + 5xl0^"5M Na₂HPO and then cyclic voltammetric scanning for 8 times in the potential range -0.4 to +0.5 vs Ag/AgCl after dipping in 1M NaOH + 5xl0^~5M Na₂ITPO solution at a sean rate of 125 mV/s.

Example 5

Nano-structured silver oxide film on to polycrystalline silver electrode is prepared by first electrochemical conditioning at -0.3 V vs Ag/AgCl for 1 5 min in 1 M NaOH + 5x l0^"5M Na₂HPO₄ and then cyclic voltammetric scanning for 8 times in the potential range -0.35 to +0.5 vs Ag/AgCl after dipping in 1M NaOH + 5xl 0^"5M Na₂HPO₄ solution at a scan rate of 125 mV/s.

Example 6

Nano-structured silver oxide film on to polycrystalline silver electrode is prepared by first electrochemical conditioning, at -0.3V vs Ag/AgCl for 15 min in 1 M NaOH + 5x l0^"5M Na₂HPO and then cyclic voltammetric scanning for 8 times in the potential range -0.3 to +0.5 vs Ag/AgCl after dipping in 1 M NaOH + 5x l 0^"5M Na HPO₄ solution at a scan rate of 150 mV/s.

Experimental procedure for the determination of endosulfan using Nano- structured silver oxide film on to polycrystalline silver electrode

Example 7

Appropriate amounts of endosulfan (lxlO^{" 13} to 10^"6 M) in l M NaOH + 5xl 0^"5M Na₂HPO₄ (pH=1 1.8) were taken in 20ml electrochemical cell and then 3 electrode system was installed in it wherein the working electrode is Nano-structured silver oxide film on to polycrystalline silver electrode and Pt foil and Ag/AgCl are counter and reference electrodes respectively. Cyclic voltammograms were recorded by scanning in the potential range of -0.3 to +0.5V at a scan rate of 150 mV/s. The unknown concentration of endosulfan was determined by reference to the calibration graph by plotting peak currents at 0.32V vs. endosulfan concentration.

Experimental procedure for the determination of atrazine using Nano-structured silver oxide film on to polycrystalline silver electrode

Example 8

Appropriate amounts of atrazine (lxlO^"13 to 10^"6 M) in 1M NaOH + 5xl0^"5M Na₂HPO₄ (pH=T l .8) were taken in 20ml electrochemical cell and then 3 electrode system was installed in it wherein the working electrode is Nano-structured silver oxide film on to polycrystalline silver electrode and Pt foil and Ag/AgCl are counter and reference electrodes respectively. Cyclic voltammograms were recorded by scanning in the potential range of -0.3 to +0.5V at a scan rate of 1 50 mV/s. The unknown concentration of atrazine was determined by reference to the calibration graph by plotting peak currents at 0.32V vs. atrazine concentration.

Experimental procedure for the determination of methyl parathion using Nano- structured silver oxide film on to polycrystalline silver electrode

Example 9

Appropriate amounts of methyl parathion (lxlO^{" 13} to 10^"6 M) in 1M NaOH + 5x lO°M Na₂HPO (pH=T 1 .8) were taken in 20ml electrochemical cell and then 3 electrode system was installed in it wherein the working electrode is Nano-structured silver oxide film on to polycrystalline silver electrode and Pt foil and Ag/AgCl are counter and reference electrodes respectively. Cyclic voltammograms were recorded by scanning in the potential range of -0.3 to +0.5V at a scan rate of 1 50 mV/s. The unknown concentration of methyl parathion was determined by reference to the calibration graph by plotting peak currents at 0.32V vs. methyl parathion concentration.

ADVANTAGES OF THE PRESENT INVENTION

1) Designed and developed silver oxide film based aqueous voltammetrie endosul ian sensor

2) The invented sensor offers rapid, reliable, precise and highly sensitive detection and quantification of selected pesticides.

3) The invented sensors responds to endosulfan or atrazine or methyl parathion over a wider concentration range of 10^"'² to l O^"6 M i.e., 6 decades in natural waters, vegetables etc.

4) Regeneration of sensor in terms of reproducibility of pesticide analytical signal is ensured via carefully designed mechanical & sonochemical polishing and electrochemical conditioning procedure described in invention.

Claims

The Claims:

. 1 : - ,A- Nano- structured voltammetric sensor for detection of pesticides comprising a 5 polycrystalline silver electrode having nano-structured silver oxide film, wherein detection limit is ~ 3x 10^" M.

2. A voltammetric sensor as claimed in Claim 1 , wherein voltammetric sensor responds to pesticide at 0.32 V Vs Ag/AgCl.

3. A sensor as claimed in Claim 1 , wherein said sensor is stable up to 30 days

10 4. A sensor as claimed in claim 1 wherein sensor is detecting pesticide in presence of alkal i, alkaline earth metal and heavy metals up to detection limit of 3x 1 0^"'³M.

5. A sensor as claimed in Claim 1 , wherein said sensor senses pesticide in 1 .0 . NaOH + 5.0x 1 0^"5 M Ν¾Η Ο/_ΐ medium by recording cyclic volta^'mmogram in the potential range - 0.3 to + 0.5V and measuring peak, currents at 0.32 V Vs Ag/AgCl.

15- 6. A sensor as claimed in any of above preceding claims, wherein pesticide is selected from endosulfan or atrazine or methyl parathion.

7. A process for the preparation of nano-structured silver oxide film as claimed in Claim 1 , wherein said process comprising steps of:

i) polishing with emery of papers of grade 2/0, 3/0 and 5/0 for 25±5 min each, 20 followed by polishing with charcoal for 7 - 8 min, followed by polishing sonochemically in acetone and deionized water for 5 minutes,

i) electrochemical conditioning by holding polycrystalline silver electrode potentiostatically at -0.3V Vs Ag/AgCl for 15 min in 1 M NaOH + 5x l 0^"5M Na₂HPC solution , ii) formation of silver oxide film on to polycrystalline silver electrode via 7 - 9 cyclic voltammetric scans at a scan rate of 125 to 150 mV/s in the potential range -0.3 to +0.5 V Vs Ag/AgCl in 1.0 M NaOH + 5.0 x l 0^"5M Na₂HP0₄ solution(pH 1 1.8).

8. A process as claimed in claim 1 , wherein nano-structured silver oxide film can be regenerated after polishing (Mechanical & Sonochemical), electrochemical conditioning and repeated cyclic voltammetric scanning.

9. A Method for detection of pesticide using the sensor as claimed in claim. 1 wherein steps comprising recording cyclic voltammogram in the potential range -0.3 to + 0.5V, measuring peak currents at 0.32 V Vs Ag/AgCl and referring to the calibration graph.

10. A method for detection of pesticide as claimed in claim 9, wherein the pesticide is selected from endosulfan or atrazine or methyl parathion.

1 1. A method for detection of pesticide as claimed in claim 9, wherein pesticide detection limit is of 3x l 0^{" 13}M.

12. A method for detection of pesticide as claimed in claim 9, wherein the said sensor is stable up to 30 days.

13. A method for detection of pesticide as claimed in claim 9, for detecting pesticide in presence of alkali, alkaline earth metal and heavy metals up to detection limit of 3x 1 0^" ^{l 3}M.