- Email: [email protected]
Voltammetric study of multiwalled carbon nanotube modified screen printed carbon electrode for the determination of a phytoconstituent wedelolactone
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 9167–9172
www.materialstoday.com/proceedings
NCNN 2017
Voltammetric study of multiwalled carbon nanotube modified screen printed carbon electrode for the determination of a phytoconstituent wedelolactone Sachin Saxenaa,b,c*, Sudhir Kumar Vermab, Soami P.Satsangeeb,c b
a Faculty of Engineering, Dayalbagh Educational Institute, Agra-282005, India Department of Chemistry, Dayalbagh Educational Institute, Agra-282005, India C USIC, Dayalbagh Educational Institute, Agra-282005, India
Abstract Multiwalled carbon nanotube based screen printed sensor was fabricated and utilized for the cyclic voltammetric (CV) study of a phytoconstituent wedelolactone (WDL). The analyte system was studied with Britton Robinson buffer as the supporting electrolyte. Square wave voltammetry (SWV) technique was performed for the optimization of the pH, where the pH (2.5) of the system was optimized for further investigation of the analyte system. Multiwalled carbon nanotube modified screen printed electrode (M-SPE) offered high sensitivity towards WDL as compared to the bare screen printed electrode (SPE). Voltammetric studies with M-SPE revealed the oxidation of WDL with two oxidation peaks (a1and a2) with Ea1 = 0.08V and Ea2 =0.5 V with scan rate varying from 10-120 mV/s and exhibits diffusion-controlled process.
© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility
of
6th
NATIONAL
CONFERENCE
ON
NANOMATERIALS
NANOTECHNOLOGY (NCNN VI - 2017 ).
Keywords: MWCNT, Screen printed electrode, Voltammetry, Wedelolactone
*Email address: [email protected]
2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of 6th NATIONAL CONFERENCE ON NANOMATERIALS AND NANOTECHNOLOGY (NCNN VI - 2017 )
AND
9168
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
1. Introduction Miniature Sensors in tandem with voltammetry techniques have become the basic need and demand of research and development. Further the nanomaterials and nanocomposites as modifiers make these sensors more interesting for trace and ultra trace analysis. Selectivity and specificity of voltammetry techniques for drug analysis using nanocomposites based sensors have not only lowered the limits of detection but also have opened a new region of insight and classification for the investigation of herbal bioactive principles. Other than common pharmaceutical drugs, herb based phytoconstituents can be introduced as new order that were and can be explored using voltammetry techniques. Modified sensors not only provide stability, typical electrochemical properties but also increase the electrocatalytic activity of the electrode towards redox systems [1-3]. Different polymers, organic compounds, ligands have been used as modifier for metal ion determination and electroactive analytes. Multiwalled carbon nanotubes has been used and exploited for the formation of new nanostructures for enhanced and effective analytical systems studies. They not only have excellent thermal, mechanical and electrical properties but large surface area to interact with the analyte system leading to effective electron transfer processes. Nowadays these extraordinary properties retaining carbon nanotubes with screen printed carbon sensors have wide range of applications for the study of real samples in the electrochemical field [4-7]. WDL, 7-Methoxy-5, 11, 12-trihydroxycoumestan, (Fig. 1) forms the major constituent of the traditional medicinal plant Eclipta alba Hassk. (Asteracea), which is a perennial herb grown throughout India and Southwestern U.S, in moist and damp land. Different analytical methods have been explored for the estimation and quantification of WDL which includes HPLC, HPTLC, UV spectrophotometry, ICP-MS analysis, IR, EPR [8-10]. The present work reports a new and explicit voltammetric method for the study of WDL using M-SPE, and BrittonRobinson buffer (pH 2.5) as a supporting electrolyte. M-SPE unveiled the mechanistic aspects of the phytoconstituent and only few microlitres of volume of solution system was needed for the analysis.
Fig. 1. Structure of WDL
2. Experimental A PC-controlled AUTOLAB PGSTAT 302N (Eco-Chemie B.V., Utrecht, The Netherlands) potentiostat-galvanostat with IME663 and software NOVA 1.8 were used for voltammetric measurements. Dropsens screen printed sensors with printed three electrode system was used in the study where bare SPE and M-SPE were used as the working electrodes, Dropsens screen printed hardware was connected with electrochemical workstation through clips. All pH measurements were made on a Mettler Toledo pH meter fitted with a glass electrode and a Ag/AgCl electrode as reference which was pre-standardized with buffers of known pH. All measurements were carried out at room temperature. WDL standard (≥99%) was obtained from the Sigma Aldrich. Ultra-pure water (Milli-Q water with resistivity 18 MΩ.cm) was obtained from ELGA purification system (U.K.). Standard solution of WDL (1 mg/mL) was prepared by dissolving pure compound in methanol and was further diluted with britton robinson buffer to get the concentration in the working range. Solutions at all the stages of the study were prepared by using analytical grade reagents and were used without further purification. The stock solution of WDL (1mg/mL) was prepared in methanol. Working solutions were prepared by further dilution with the supporting electrolyte to get the desired concentration range. Initially, a series of britton-robinson buffer (pH 2.5–12) were prepared in ultrapure water and used as supporting electrolytes. About 20µL of analyte solution containing appropriate amount buffer was dropped at the surface of the screen printed electrode.
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
9169
For the optimum supporting electrolyte, various supporting electrolytes such as KCl, phosphate buffer, acetate buffer and Britton-Robinson buffer was used to study WDL system. The redox properties of WDL (100µg/mL) with prominent oxidation peaks and well defined current values were observed in Britton-Robinson buffer. The effect of pH on the oxidation of WDL was examined over the pH range (2.5–12). The anodic peak currents (a1 and a2) and the peak potential for the oxidation of WDL were found to be sensitive towards the pH of the solution. It was observed through Fig. 2 that the current values (Ip) for anodic peaks a1 and a2 started to decrease with the increase in pH values and at higher pH (pH >7.9), the peak current almost disappeared (Fig. 2). Thereby considering the sensitivity and the peak shape, pH 2.5 was selected as the optimum pH for the entire electrochemical measurement. Moreover there was a sequential shift of the anodic peak potential with increase in pH value suggesting involvement of protons in the WDL redox process.
Fig. 2. SWV of WDL in Britton Robinson buffer at different pH (c-h, blank b) with two oxidation peaks of WDL (a1 and a2).
. 3. Results and Discussion Electrochemical behaviour of WDL at M-SPE and SPE was investigated by CV technique. Fig.3 represents CV of WDL at the M-SPE (b) and SPE (c). At each of the electrodes, WDL exhibited two oxidation peaks that can be ascribed owing to the presence of functional –OH groups attached to ring structures [11]. The mechanistic aspects of WDL with their oxidation process occurring at M-SPE was supported by the work of Corduneanu et al. and Janeiroet al. [12]. CV of WDL shows a remarkable enhancement i.e. 165% increase in current response observed at M-SPE as compared to that of SPE. To study the effect of scan rate on the oxidation peak of WDL, voltammograms were recorded for different scan rate from 10–120 mV/s at a fixed concentration (100µg/mL) of WDL at M-SPE. The information involving electrochemical mechanism can be obtained from the investigation of the response characteristics of CV on the electrooxidation process of WDL (Fig. 4). A linear relationship was obtained between the peak current intensity (Ip; a1 and a2 anodic peak currents) and the square root of scan rate (ν)1/2, suggesting the diffusion controlled process at the electrode surface.
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Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
Fig. 3. CV of WDL in Britton Robinson buffer ( pH 2.5) at M-SPE (d) and SPE (c), at scan rate 30mV/s with two oxidation peaks of WDL (a1 and a2, blank b).
Fig. 4. CV of WDL in Britton Robinson buffer (pH 2.5) at M-SPE (at varying scan rates scan rate 10, 30, 50, 90 and 120 mV/s) with two oxidation peaks of WDL (a1 and a2, blank b).
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
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Fig.5. Scanning electron microscopy image showing fibrous diffused type M-SPE surface.
Fig.5shows granulated, fibrous and diffused type morphology of M-SPE. The carbon nanotubes were dropcoated on the surface of screen printed electrode and were left at room temperature for drying. Further the electrode was directly used for the scanning after the analyte solution of 20µl was dropped on the working surface of the SPE. The scanning was repeated with same modified sensors thrice thereby giving stable current response and potential. 4. Conclusions Selective determination of WDL in Britton-Robinson buffer (pH 2.5) at M-SPE has been presented in this paper. M-SPE offered high sensitivity towards WDL and found to be appropriate and effective for the selective determination of the solution system. The sensitivity of the electrodes can be explained on the basis of SEM images with fibrous morphology. An increase of 165% of current values was observed at modified electrode as compared to that of SPE. The voltammetric study of WDL at different scan rates revealed diffusion controlled reaction process. Electrode process dynamics parameters have been evaluated and based on this a plausible reaction mechanistic aspects can be deduced.
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Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
Acknowledgements Authors acknowledge the Department of science and technology (DST),Government of India, Dayalbagh Educational Institute, Dayalbagh, Agra, India, for providing financial assistance under an RBF project. They are also thankful to DST for providing Research Associateship to one of the author (Sachin Saxena). Authors are also thankful to IIT Roorkee for SEM results. References: [1] M. Rajabhandari, U. Wegner, J. M, Schopke T, R. Mental J. Ethnopharmacol 74(2001). 251. [2] R C Uniyal, S Sandhu and J K Chandok In Herbology: The Ayurvedic Encyclopedia (India: Sri Sadguru Publications) (1998) 77–88. [3] K.R Kirtikar B.D Basu In Indian MedicinalPlants 2nd ed., (India: International Book Distributors) (1998) 1360-1361. [4]M. I. Saidin, Illyas Md Isa, Mustaffa Ahmad, Norhayati Hashim, Azlan Kamari, S. Ab Ghani, Suyanta M. Si Microchimica Acta, 183(2016) 1441–1448. [5] S. Saxena, R. Shrivastava , S. P Satsangee Maced.J. Chem. Chem. Eng. 31 (2012) 195-203. [6] H .Ashkenani, M.A Taher, J Electroanal Chem 683(2012) 80–87. [7] J.H Luo, X.X Jiao, N.B Li, H.Q Luo, J Electroanal Chem 689(2013)130–134. [8] H.Wagner, B.Geyer, Y. Kiso, H.Hikino, G.S. Rao, Planta Med. 52, (1986)370-374. [9] B Murali, A Amit, M S Anand, D S Samiulla J. Nat. Remedies. 2(2002) 99-101. [10] N. Das, G C Bhavsa, M. G. Chauhan , Indian Drugs, 28 (1990) 100. [11]. P Janeiro, A M O Brett Anal. Chim. Acta. 51 (2004) 109-115. [12] O Corduneanu, P Janeiro, A. M. O Brett, Electroanalysis, 18 (2006) 757-762.
ScienceDirect Materials Today: Proceedings 5 (2018) 9167–9172
www.materialstoday.com/proceedings
NCNN 2017
Voltammetric study of multiwalled carbon nanotube modified screen printed carbon electrode for the determination of a phytoconstituent wedelolactone Sachin Saxenaa,b,c*, Sudhir Kumar Vermab, Soami P.Satsangeeb,c b
a Faculty of Engineering, Dayalbagh Educational Institute, Agra-282005, India Department of Chemistry, Dayalbagh Educational Institute, Agra-282005, India C USIC, Dayalbagh Educational Institute, Agra-282005, India
Abstract Multiwalled carbon nanotube based screen printed sensor was fabricated and utilized for the cyclic voltammetric (CV) study of a phytoconstituent wedelolactone (WDL). The analyte system was studied with Britton Robinson buffer as the supporting electrolyte. Square wave voltammetry (SWV) technique was performed for the optimization of the pH, where the pH (2.5) of the system was optimized for further investigation of the analyte system. Multiwalled carbon nanotube modified screen printed electrode (M-SPE) offered high sensitivity towards WDL as compared to the bare screen printed electrode (SPE). Voltammetric studies with M-SPE revealed the oxidation of WDL with two oxidation peaks (a1and a2) with Ea1 = 0.08V and Ea2 =0.5 V with scan rate varying from 10-120 mV/s and exhibits diffusion-controlled process.
© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility
of
6th
NATIONAL
CONFERENCE
ON
NANOMATERIALS
NANOTECHNOLOGY (NCNN VI - 2017 ).
Keywords: MWCNT, Screen printed electrode, Voltammetry, Wedelolactone
*Email address: [email protected]
2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of 6th NATIONAL CONFERENCE ON NANOMATERIALS AND NANOTECHNOLOGY (NCNN VI - 2017 )
AND
9168
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
1. Introduction Miniature Sensors in tandem with voltammetry techniques have become the basic need and demand of research and development. Further the nanomaterials and nanocomposites as modifiers make these sensors more interesting for trace and ultra trace analysis. Selectivity and specificity of voltammetry techniques for drug analysis using nanocomposites based sensors have not only lowered the limits of detection but also have opened a new region of insight and classification for the investigation of herbal bioactive principles. Other than common pharmaceutical drugs, herb based phytoconstituents can be introduced as new order that were and can be explored using voltammetry techniques. Modified sensors not only provide stability, typical electrochemical properties but also increase the electrocatalytic activity of the electrode towards redox systems [1-3]. Different polymers, organic compounds, ligands have been used as modifier for metal ion determination and electroactive analytes. Multiwalled carbon nanotubes has been used and exploited for the formation of new nanostructures for enhanced and effective analytical systems studies. They not only have excellent thermal, mechanical and electrical properties but large surface area to interact with the analyte system leading to effective electron transfer processes. Nowadays these extraordinary properties retaining carbon nanotubes with screen printed carbon sensors have wide range of applications for the study of real samples in the electrochemical field [4-7]. WDL, 7-Methoxy-5, 11, 12-trihydroxycoumestan, (Fig. 1) forms the major constituent of the traditional medicinal plant Eclipta alba Hassk. (Asteracea), which is a perennial herb grown throughout India and Southwestern U.S, in moist and damp land. Different analytical methods have been explored for the estimation and quantification of WDL which includes HPLC, HPTLC, UV spectrophotometry, ICP-MS analysis, IR, EPR [8-10]. The present work reports a new and explicit voltammetric method for the study of WDL using M-SPE, and BrittonRobinson buffer (pH 2.5) as a supporting electrolyte. M-SPE unveiled the mechanistic aspects of the phytoconstituent and only few microlitres of volume of solution system was needed for the analysis.
Fig. 1. Structure of WDL
2. Experimental A PC-controlled AUTOLAB PGSTAT 302N (Eco-Chemie B.V., Utrecht, The Netherlands) potentiostat-galvanostat with IME663 and software NOVA 1.8 were used for voltammetric measurements. Dropsens screen printed sensors with printed three electrode system was used in the study where bare SPE and M-SPE were used as the working electrodes, Dropsens screen printed hardware was connected with electrochemical workstation through clips. All pH measurements were made on a Mettler Toledo pH meter fitted with a glass electrode and a Ag/AgCl electrode as reference which was pre-standardized with buffers of known pH. All measurements were carried out at room temperature. WDL standard (≥99%) was obtained from the Sigma Aldrich. Ultra-pure water (Milli-Q water with resistivity 18 MΩ.cm) was obtained from ELGA purification system (U.K.). Standard solution of WDL (1 mg/mL) was prepared by dissolving pure compound in methanol and was further diluted with britton robinson buffer to get the concentration in the working range. Solutions at all the stages of the study were prepared by using analytical grade reagents and were used without further purification. The stock solution of WDL (1mg/mL) was prepared in methanol. Working solutions were prepared by further dilution with the supporting electrolyte to get the desired concentration range. Initially, a series of britton-robinson buffer (pH 2.5–12) were prepared in ultrapure water and used as supporting electrolytes. About 20µL of analyte solution containing appropriate amount buffer was dropped at the surface of the screen printed electrode.
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
9169
For the optimum supporting electrolyte, various supporting electrolytes such as KCl, phosphate buffer, acetate buffer and Britton-Robinson buffer was used to study WDL system. The redox properties of WDL (100µg/mL) with prominent oxidation peaks and well defined current values were observed in Britton-Robinson buffer. The effect of pH on the oxidation of WDL was examined over the pH range (2.5–12). The anodic peak currents (a1 and a2) and the peak potential for the oxidation of WDL were found to be sensitive towards the pH of the solution. It was observed through Fig. 2 that the current values (Ip) for anodic peaks a1 and a2 started to decrease with the increase in pH values and at higher pH (pH >7.9), the peak current almost disappeared (Fig. 2). Thereby considering the sensitivity and the peak shape, pH 2.5 was selected as the optimum pH for the entire electrochemical measurement. Moreover there was a sequential shift of the anodic peak potential with increase in pH value suggesting involvement of protons in the WDL redox process.
Fig. 2. SWV of WDL in Britton Robinson buffer at different pH (c-h, blank b) with two oxidation peaks of WDL (a1 and a2).
. 3. Results and Discussion Electrochemical behaviour of WDL at M-SPE and SPE was investigated by CV technique. Fig.3 represents CV of WDL at the M-SPE (b) and SPE (c). At each of the electrodes, WDL exhibited two oxidation peaks that can be ascribed owing to the presence of functional –OH groups attached to ring structures [11]. The mechanistic aspects of WDL with their oxidation process occurring at M-SPE was supported by the work of Corduneanu et al. and Janeiroet al. [12]. CV of WDL shows a remarkable enhancement i.e. 165% increase in current response observed at M-SPE as compared to that of SPE. To study the effect of scan rate on the oxidation peak of WDL, voltammograms were recorded for different scan rate from 10–120 mV/s at a fixed concentration (100µg/mL) of WDL at M-SPE. The information involving electrochemical mechanism can be obtained from the investigation of the response characteristics of CV on the electrooxidation process of WDL (Fig. 4). A linear relationship was obtained between the peak current intensity (Ip; a1 and a2 anodic peak currents) and the square root of scan rate (ν)1/2, suggesting the diffusion controlled process at the electrode surface.
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Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
Fig. 3. CV of WDL in Britton Robinson buffer ( pH 2.5) at M-SPE (d) and SPE (c), at scan rate 30mV/s with two oxidation peaks of WDL (a1 and a2, blank b).
Fig. 4. CV of WDL in Britton Robinson buffer (pH 2.5) at M-SPE (at varying scan rates scan rate 10, 30, 50, 90 and 120 mV/s) with two oxidation peaks of WDL (a1 and a2, blank b).
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
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Fig.5. Scanning electron microscopy image showing fibrous diffused type M-SPE surface.
Fig.5shows granulated, fibrous and diffused type morphology of M-SPE. The carbon nanotubes were dropcoated on the surface of screen printed electrode and were left at room temperature for drying. Further the electrode was directly used for the scanning after the analyte solution of 20µl was dropped on the working surface of the SPE. The scanning was repeated with same modified sensors thrice thereby giving stable current response and potential. 4. Conclusions Selective determination of WDL in Britton-Robinson buffer (pH 2.5) at M-SPE has been presented in this paper. M-SPE offered high sensitivity towards WDL and found to be appropriate and effective for the selective determination of the solution system. The sensitivity of the electrodes can be explained on the basis of SEM images with fibrous morphology. An increase of 165% of current values was observed at modified electrode as compared to that of SPE. The voltammetric study of WDL at different scan rates revealed diffusion controlled reaction process. Electrode process dynamics parameters have been evaluated and based on this a plausible reaction mechanistic aspects can be deduced.
9172
Sachin Saxena et al/ Materials Today: Proceedings 5 (2018) 9167–9172
Acknowledgements Authors acknowledge the Department of science and technology (DST),Government of India, Dayalbagh Educational Institute, Dayalbagh, Agra, India, for providing financial assistance under an RBF project. They are also thankful to DST for providing Research Associateship to one of the author (Sachin Saxena). Authors are also thankful to IIT Roorkee for SEM results. References: [1] M. Rajabhandari, U. Wegner, J. M, Schopke T, R. Mental J. Ethnopharmacol 74(2001). 251. [2] R C Uniyal, S Sandhu and J K Chandok In Herbology: The Ayurvedic Encyclopedia (India: Sri Sadguru Publications) (1998) 77–88. [3] K.R Kirtikar B.D Basu In Indian MedicinalPlants 2nd ed., (India: International Book Distributors) (1998) 1360-1361. [4]M. I. Saidin, Illyas Md Isa, Mustaffa Ahmad, Norhayati Hashim, Azlan Kamari, S. Ab Ghani, Suyanta M. Si Microchimica Acta, 183(2016) 1441–1448. [5] S. Saxena, R. Shrivastava , S. P Satsangee Maced.J. Chem. Chem. Eng. 31 (2012) 195-203. [6] H .Ashkenani, M.A Taher, J Electroanal Chem 683(2012) 80–87. [7] J.H Luo, X.X Jiao, N.B Li, H.Q Luo, J Electroanal Chem 689(2013)130–134. [8] H.Wagner, B.Geyer, Y. Kiso, H.Hikino, G.S. Rao, Planta Med. 52, (1986)370-374. [9] B Murali, A Amit, M S Anand, D S Samiulla J. Nat. Remedies. 2(2002) 99-101. [10] N. Das, G C Bhavsa, M. G. Chauhan , Indian Drugs, 28 (1990) 100. [11]. P Janeiro, A M O Brett Anal. Chim. Acta. 51 (2004) 109-115. [12] O Corduneanu, P Janeiro, A. M. O Brett, Electroanalysis, 18 (2006) 757-762.