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ABSTRACT: A promising and highly sensitive voltammetric method has been developed for the first time for the determination of epinephrine (EP) and 5-hydroxytryptamine (5-HT) using 120 MeV Ag ion irradiated multi-walled carbon nano tube (MWCNT) based sensor. The MWCNT were irradiated at various fluences of 1e12, 3e12 and 1e13 ions cm(-2) using palletron accelerator. The simultaneous determination of EP and 5-HT has been carried out in phosphate buffer solution of pH 7.20 using square wave voltammetry and cyclic voltammetry. Experimental results suggested that irradiation of MWCNT by Ag ions enhanced the electrocatalytic activity due to increase in effective surface area and insertion of Ag ions, leading to a remarkable enhancement in peak currents and shift of peak potentials to less positive values as compared to the unirradiated MWCNT (pristine). The developed sensor exhibited a linear relationship between peak current and concentration of EP and 5-HT in the range 0.1-105 μM with detection limit (3σ/b) of 2 nM and 0.75 nM, respectively. The practical utility of irradiation based MWCNT sensor has been demonstrated for the determination of EP and 5-HT in human urine and blood samples.
Analytica chimica acta 09/2012; 743:33-40. · 4.31 Impact Factor
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ABSTRACT: The effect of surface modification of indium tin oxide (ITO) by multi wall carbon nanotube (MWNT) and gold nanoparticles attached multi wall carbon nanotube (AuNP-MWNT) has been studied to determine tryptophan, an important and essential amino acid for humans and herbivores. A detailed comparison has been made among the voltammetric response of bare ITO, MWNT/ITO and AuNP-MWNT/ITO in respects of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential of tryptophan. The AuNP-MWNT/ITO exhibited a well defined anodic peak at pH 7.2 at a potential of ∼ 669 mV for the oxidation of tryptophan as compared to 760 mV at MWNT/ITO electrode. Under optimum conditions linear calibration curve was obtained over tryptophan concentration range 0.5-90.0 μM in phosphate buffer solution of pH 7.2 with detection limit and sensitivity of 0.025 μM and 0.12 μA μM(-1), respectively. The oxidation of tryptophan occurred in a pH dependent, 2e(-) and 2H(+) process and the electrode reaction followed adsorption controlled pathway. The method has been found selective and successfully implemented for the determination of tryptophan in human urine and plasma samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability.
Talanta 10/2011; 85(5):2626-31. · 3.79 Impact Factor
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ABSTRACT: Electrochemical determination of Norfloxacin (NF) has been presented at edge plane (EPPGS) and basal plane pyrolytic graphite sensors (BPPGS) by using square wave voltammetry at physiological pH 7.2. An increased peak current with a shift of peak potential to less positive value was observed at EPPGS as compared to BPPGS. The effect of pH, scan rate and analyte concentration has been examined. The peak current was found to be linear to the concentration of NF in the range 0.5 × 10(-6) to 50.0 × 10(-6)mol L(-1) for EPPGS and the detection limit (3σ/b) was found to be 28.3 × 10(-8)mol L(-1). The method has been successfully used to determine the content of NF in the pharmaceutical preparations. Biological relevance of the developed method has been described by the determination of NF in human urine samples of the patients undergoing treatment with NF. The method is selective and NF can be determined without any interference from common urine metabolites such as uric acid and ascorbic acid.
Bioelectrochemistry (Amsterdam, Netherlands) 08/2011; 83:46-51. · 2.65 Impact Factor
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ABSTRACT: A gold nanoparticle attached multi-walled carbon nanotube-layered indium tin oxide (AuNP/MWNT/ITO) electrode has been used for monitoring the effect of paracetamol (PAR) on the release of epinephrine (EPI) in human urine. The modified electrode shows an excellent electrocatalytic activity for the oxidation of EPI and PAR with acceleration of electron transfer rate as compared to MWNT/ITO and AuNP/ITO. An apparent shift of the oxidative potential towards less positive potential with a marked increase in peak currents is observed in square wave voltammetry at AuNP/MWNT/ITO electrode. The calibration curves for the simultaneous determination of PAR and EPI showed an excellent linear response, ranging from 5.0×10(-9) mol L(-1) to 80.0×10(-9) mol L(-1) for both the compounds. The detection limits for the simultaneous determination of PAR and EPI were found to be 46×10(-10) mol L(-1) and 42×10(-10) mol L(-1) respectively. The proposed method has been successfully applied for the simultaneous determination of PAR and EPI in human urine. It is observed that gold nanoparticles attached with multi-wall carbon nanotube catalyze the oxidation of EPI and PAR.
Analytica chimica acta 05/2011; 693(1-2):35-40. · 4.31 Impact Factor
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ABSTRACT: A novel and reliable direct electrochemical method has been established to monitor DNA damage in acid hydrolyzed calf thymus DNA, based on the determination of 2,8-dihydroxyadenine (2,8-DHA). A single-wall carbon nanotubes (SWCNT) modified edge plane pyrolytic graphite electrode (EPPGE) has been used as a sensor to monitor the DNA damage. 2,8-DHA the main in vivo adenine oxidation product undergoes oxidation at ∼395 mV at SWCNT modified EPPGE using square wave voltammetry (SWV). The sensor exhibits potent and persistent electron-mediating behavior. A well-defined oxidation peak for the oxidation of 2,8-DHA was observed at modified electrode with lowering of peak potential and increase in peak current as compared to bare EPPGE. At optimal experimental conditions, the catalytic oxidative peak current was responsive with the 2,8-DHA concentrations ranging from 0.05 nM to 100 nM. The detection limit was 3.8×10−11 M and limit of quantification was 1.27×10−10 M. The modified electrode exhibited high stability and reproducibility.
Electroanalysis 05/2011; 23(6):1383 - 1390. · 2.87 Impact Factor
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ABSTRACT: The simultaneous determination of catecholamines - epinephrine and norepinephrine by square wave voltammetry (SWV) at physiological pH 7.2 is reported using multi-walled carbon nanotubes modified edge plane pyrolytic graphite electrode (MWNT/EPPGE). A broad bump at ∼ 250 mV is appeared for the oxidation of epinephrine (EP) and norepinephrine (NE) at bare EPPGE whereas at MWNT/EPPGE two well-separated peaks at ∼ 150 and ∼ 215 mV are appeared for the oxidation of EP and NE, respectively. The oxidation peak current of both the neurotransmitters also increased significantly along with the negative shift of peak potentials using MWNT/EPPGE. The oxidation of both compounds occurred in a pH dependent, 2e and 2H(+) process and the electrode reaction followed diffusion controlled pathway. Linear calibration curves were obtained for epinephrine and norepinephrine in the range 0.5-100 nM with limits of detection 0.15 × 10(-9) and 0.90 × 10(-10)M, respectively. The developed protocol is implemented for the simultaneous determination of epinephrine and norepinephrine in blood plasma and urine samples of smokers as well as in athletes.
Talanta 03/2011; 84(1):78-83. · 3.79 Impact Factor
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ABSTRACT: Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.
Journal of Nanoscience and Nanotechnology 12/2010; 10(12):8018-25. · 1.56 Impact Factor
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ABSTRACT: Electrochemical sensor employing edge-plane pyrolytic graphite electrode (EPPGE) for the sensitive detection of hydrocortisone (HC) is delineated for the first time. The electrochemical properties are investigated exercising the cyclic voltammetry and square-wave voltammetry (SWV). When equating with the bare basal-plane pyrolytic graphite electrode (BPPGE), the EPPGE gave better response towards the detection of HC both in terms of sensitivity and detection limit. The voltammetric results indicated that EPPGE remarkably enhances the reduction of HC which leads to considerable amelioration of peak current with shift of peak potential to less negative values. The difference in the surface morphology of two electrodes has been studied. Also, the EPPGE delivered an analytical performance for HC with a sensitivity of 45 nA nM(-1) and limit of detection of 88 nM in the concentration range 100-2000 nM. The method has been utilized for the determination of HC in pharmaceuticals and real samples. The electroanalytical method using EPPGE is the most sensitive method for determination of HC with lowest limit of detection to date. The major metabolites present in blood plasma did not intervene with the present investigation as they did not exhibit reduction peak in the experimental range used. A comparison of results with high performance liquid chromatography (HPLC) signalizes a good agreement.
Talanta 11/2010; 83(1):149-55. · 3.79 Impact Factor
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ABSTRACT: A simple and reliable method based on voltammetry is proposed for the determination of oxidative DNA damage by the simultaneous determination of guanine and 8-hydroxygunine using single-walled carbon nanotubes modified edge plane pyrolytic graphite electrode (SWNT/EPPGE). In acid-hydrolyzed calf thymus DNA, two well-defined peaks at ∼312 and ∼502 mV corresponding to the oxidation of 8-hydroxyguanine and guanine, respectively in phosphate buffer solution (PBS) of pH 7.2 were observed in square wave voltammetry. Remarkable enhancement in the oxidation peak current of both the compounds was observed along with the negative shift of peak potentials using SWNT/EPPGE as compared to bare EPPGE. The detection limits of guanine and 8-hydroxyguanine were calculated to be 0.05×10(-9) and 0.01×10(-9) mol L(-1), respectively. The limits of quantification were found as 0.17×10(-9) and 0.34×10(-10) mol L(-1) for guanine and 8-hydroxyguanine, respectively.
Biosensors & bioelectronics 10/2010; 26(2):463-9. · 5.43 Impact Factor
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ABSTRACT: Electrochemical determination of amlodipine besylate (ADB) using single and multi-walled carbon nanotubes modified edge plane pyrolytic graphite electrodes (SWNT/EPPGE and MWNT/EPPGE) is described by using cyclic and square wave voltammetries at physiological pH 7.2. An increased peak current with a shift of peak potential to less positive value was observed using carbon nanotubes modified EPPGE as compared to bare electrode. The effect of pH, scan rate and analyte concentration has been examined. Under the optimum conditions the peak current was linear to the concentration of amlodipine in the range 5.0 x 10(-9) to 1.0 x 10(-6) mol L(-1) for SWNT/EPPGE and the detection limit was found to be 1.0 x 10(-9) mol L(-1) whereas, for MWNT/EPPGE the detection limit was found to be 5.0 x 10(-9) mol L(-1). The method was successfully used to determine the content of amlodipine in the pharmaceutical preparations and human urine samples of angina patients undergoing treatment with amlodipine. A comparison of electrocatalytic activities of SWNT and MWNT modified electrodes indicated that SWNT modified EPPGE is approximately 1.8 times more sensitive in comparison to MWNT/EPPGE. Biological relevance of the developed method has been described by the determination of amlodipine in human body fluids. Amlodipine can be determined without any interference from common urine metabolites such as uric acid, ascorbic acid and xanthine.
Bioelectrochemistry (Amsterdam, Netherlands) 10/2010; 79(2):234-40. · 2.65 Impact Factor
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ABSTRACT: The effect of surfactants on the electrochemical determination of dexamethasone at an edge plane pyrolytic graphite electrode (EPPGE), modified with single-walled carbon nanotubes (SWNT) has been investigated. The unique electrocatalytic properties of SWNT along with the synergistic adsorption of CTAB on SWNT lead to sensitive voltammetric response of dexamethasone with the reduction peak at ca. −1195 mV. The limit of detection and sensitivity of dexamethasone is estimated to be 9.1×10−10 M and 0.727 µA µM−1 respectively. The SWNT coated EPPGE had good stability and reproducibility. The analytical utility of the developed method was evaluated by applying it for sensing the drug in human body fluids and for the determination of dexamethasone content in several commercially available pharmaceutical preparations. A comparison of the observed results of proposed method with HPLC clearly indicates that the results of both the methods are in good agreement. The product obtained after the reduction of dexamethasone has also been characterized using 1H NMR and carbonyl group at position 3 has been found to reduce. The method is instant, simple and accurate and can be easily applied for detecting cases of doping.
Electroanalysis 09/2010; 22(20):2330 - 2338. · 2.87 Impact Factor
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ABSTRACT: A rapid and sensitive voltammetric sensor based on reduction of betamethasone has been developed using single wall carbon nanotube modified edge plane pyrolytic graphite electrode (SWNT/EPPGE). The reduction of betamethasone occurred in a well-defined, pH dependent peak. Linear calibration curve was obtained in the range 1 to 25 nM in 1.0 M phosphate buffer solution (PBS) of pH 7.2 with the limit of detection (3sigma / slope) as 0.50 nM. The analytical utility of the developed method has been demonstarted by sensing the drug in human body fluids and for the determination of betamethasone content in several commercially available pharmaceutical preparations. Interfering effect of some common metabolites including ascorbic acid, uric acid, albumin and hypoxanthine has also been evaluated. A comparison of the observed results of proposed method with HPLC clearly indicates that the results of both methods are essentially similar.
Combinatorial chemistry & high throughput screening 08/2010; 13(7):610-8. · 2.46 Impact Factor
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ABSTRACT: A sensitive voltammetric method has been described for the determination of betamethasone sodium phosphate (BSP) using edge plane pyrolytic graphite electrode (EPPGE) modified with single walled carbon nanotubes-cetyltrimethyl ammonium bromide nanocomposite film. The reduction of BSP occurred in a well-defined peak having E(p) -1062 mV in phosphate buffer solution (PBS) of pH 7.2. The voltammetric response of betamethasone sodium phosphate enhanced effectively using cationic surfactant cetyltrimethyl ammonium bromide (CTAB) as electrode surface modifier. The nanotubes-surfactant modified edge plane pyrolytic graphite electrode shows great improvement in peak current and shift of the reduction potential towards less negative potential. The role of cetyltrimethylammonium bromide on electrocatalytic property is discussed. The limit of detection (3sigma/slope) was found to be 0.25 x 10(-9)M and limit of quantification was 0.86 x 10(-9)M. The analytical utility of the proposed method is demonstrated by the direct assay of betamethasone in urine samples of pregnant women.
Colloids and surfaces. B, Biointerfaces 02/2010; 77(2):200-5. · 2.60 Impact Factor
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ABSTRACT: Voltammetric investigation of two corticoid isomers--testosterone and epitestosterone has been carried out at bare and single-wall carbon nanotubes (SWNT)-modified edge plane pyrolytic graphite electrode (EPPGE). Square wave voltammetry (OSWV) has been used for the simultaneous determination of isomeric steroids. The reduction of the two isomers occurred in a pH dependent, 2e, 2H+ process and well-defined voltammetric peaks were observed. Under the optimum experimental conditions, linear calibration curves are obtained within the concentration range 5-1000 nM for both the steroids with the limit of detection 2.8 x 10(-9) and 4.1 x 10(-9) M for testosterone and epitestosterone respectively. The developed protocol is successfully implemented for the analysis of both the compounds in the urine samples of normal subjects as well as in patients undergoing treatment with testosterone. The results obtained from the proposed voltammetric method were also compared with HPLC analysis and found to be similar.
Analytica chimica acta 01/2010; 657(2):147-53. · 4.31 Impact Factor
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ABSTRACT: An electrochemical protocol based on reduction is developed to determine methylprednisolone using single-wall carbon nanotubes (SWNTs) modified edge plane pyrolytic graphite electrode (EPPGE). To obtain a good sensitivity, instrumental variables were studied using Square Wave Voltammetry (SWV). The voltammetric results indicate that SWNTs modified EPPGE remarkably enhances the reduction of methylprednisolone which leads to considerable improvement of peak current with shift of peak potential to less negative values. The voltammetric current showed a linear response for methylprednisolone concentration in the range 5-500 nM with a sensitivity of 98 nA nM(-1). The limit of detection was estimated to be 4.5x10(-9)M. The developed method is used for the determination of methylprednisolone in pharmaceutical dosages and human blood plasma samples of patients undergoing treatment with methylprednisolone. The major metabolites present in blood plasma did not interfere with the present investigation as they did not exhibit reduction peak in the experimental range used. A comparison of results with high performance liquid chromatography (HPLC) indicates a good agreement.
Talanta 12/2009; 80(2):586-92. · 3.79 Impact Factor
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ABSTRACT: Praseodymium ion selective polyvinyl chloride (PVC) membrane sensors, based on two new Schiff's bases 1,3-diphenylpropane-1,3-diylidenebis(azan-1-ylidene)diphenol (M(1)) and N,N'-bis(pyridoxylideneiminato) ethylene (M(2)) have been developed and studied. The sensor having membrane composition of PVC: o-NPOE: ionophore (M(1)): NaTPB (w/w; mg) of 150: 300: 8: 5 showed best performances in comparison to M(2) based membranes. The sensor based on (M(1)) exhibits the working concentration range 1.0x10(-8) to 1.0x10(-2) M with a detection limit of 5.0x10(-9) M and a Nernstian slope 20.0+/-0.3 mV decade(-1) of activity. It exhibited a quick response time as <8 s and its potential responses were pH independent across the range of 3.5-8.5. The influence of the membrane composition and possible interfering ions have also been investigated on the response properties of the electrode. The sensor has been found to work satisfactorily in partially non-aqueous media up to 15% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for praseodymium(III) ions over wide variety of other cations. To asses its analytical applicability the prepared sensor was successfully applied for determination of praseodymium(III) in spiked water samples.
Analytica chimica acta 10/2009; 653(2):161-6. · 4.31 Impact Factor
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ABSTRACT: Sensors based on two neutral ionophores, N,N'-bis((1H-pyrrol-2-yl)methylene)cyclohexane-1,2-diamine (L1) and 3,3'-(cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(5-hydroxymethyl)pyridine-2-ol) (L2) are described for quantification of neodymium (III). Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), tri-n-butyl phosphates (TBP), dioctylpthalate (DOP) and chloronapthalen (CN) and anion excluder, sodiumtetraphenylborate (NaTPB) has been studied. The membrane composition of PVC:o-NPOE:ionophore (L1):NaTPB (w/w; mg) of 150:300:5:5 exhibited best performance. The sensor with ionophore (L1) exhibits significantly enhanced selectivity towards neodymium (III) in the concentration range 5.0 x 10(-7) to 1.0 x 10(-2) M with a detection limit of 1.0 x 10(-7) M and a Nernstian compliance (19.8 +/- 0.3 mV decade(-1) of activity) within pH range 4.0-8.0. The response time of sensor was found as 10s. The influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. The fast and stable response, good reproducibility and long-term stability of the sensor are observed. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The proposed electrode shows fairly good discrimination of neodymium (III) from other cations. The application of prepared sensor has been demonstrated in the determination of neodymium (III) in spiked water samples.
Analytica chimica acta 09/2009; 647(1):66-71. · 4.31 Impact Factor
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ABSTRACT: A sensitive, rapid and reliable electrochemical method based on voltammetry at single wall carbon nanotube (SWNT) modified edge plane pyrolytic graphite electrode (EPPGE) is proposed for the simultaneous determination of prednisolone and prednisone in human body fluids and pharmaceutical preparations. The electrochemical response of both the drugs was evaluated by osteryoung square wave voltammetry (OSWV) in phosphate buffer medium of pH 7.2. The modified electrode exhibited good electrocatalytic properties towards prednisone and prednisolone reduction with a peak potential of approximately -1230 and approximately -1332 mV respectively. The concentration versus peak current plots were linear for both the analytes in the range 0.01-100 microM and the detection limit (3 sigma/slope) observed for prednisone and prednisolone were 0.45 x 10(-8), 0.90 x 10(-8)M, respectively. The results of the quantitative estimation of prednisone and prednisolone in biological fluids were also compared with HPLC and the results were in good agreement.
Talanta 09/2009; 79(3):768-74. · 3.79 Impact Factor
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ABSTRACT: In the present study, Fe2O3 nanopowder has been grown by Ultrasonic mist chemical vapor deposition (UM-CVD), which is a promising method for large area deposition at low temperatures taking in to account of its simplicity, inexpensiveness and safety. Room temperature XRD results revealed prominent hematite phase with intense (104) reflection and was also in agreement with the HR-TEM results. In situ high temperature X-ray diffraction (XRD) studies clearly indicated the change of phase from hematite to magnetite as the temperature increases above 300 degrees C. The surface morphology and particle size distribution of Fe2O3 nanopowder were characterized using field emission scanning electron microscope (FE-SEM) and high resolution transmission electron microscope (HR-TEM), which revealed that the particles were spherical in nature and distributed in range of 50-100 nm. SQUID magnetometry results indicate the ferromagnetic nature of the nanopowder with crystallite size of 6 nm as calculated from M-H curve. Transmittance of approximately 55% and estimated direct band gap of 2.5 eV was observed. Further, the nanopowder was used to modify glassy carbon electrode (GCE) and the modified electrode was found to exhibit electrocatalytic activity for the oxidation of dopamine. It is expected that the nanopowder will exhibit promising applications in the development of sensors.
Journal of Nanoscience and Nanotechnology 08/2009; 9(8):4692-9. · 1.56 Impact Factor
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ABSTRACT: A comparison of edge plane pyrolytic graphite substrate is made with other substrates like indium tin oxide, glassy carbon, gold and basal plane pyrolytic graphite as a substrate for fullerene modification for the determination of nandrolone by Osteryoung square wave voltammetry (OSWV) in phosphate buffer media. Comparative study of voltammetric response of nandrolone at untreated, purified and super-purified fullerene modified edge plane pyrolytic graphite electrode (EPPGE) is also carried out to determine the role of embedded metallic impurities of fullerene on determination of nandrolone. It is observed that EPPGE serves as best substrate among the studied for casting fullerene. The removal of embedded metals from fullerene shifts the peak potential of nandrolone to more positive potentials and peak current decreases. A linear calibration curve is obtained in the concentration range of 0.01-50 nM with a detection limit and sensitivity of 1.5 x 10(-11) M and 1.838 microA nM(-1), respectively. The developed method was satisfactorily applied to the determination of nandrolone in several commercially available medicinal samples.
Analytica chimica acta 07/2009; 643(1-2):95-9. · 4.31 Impact Factor
