Sunita Bishnoi

Simultaneous determination of epinephrine and norepinephrine in human blood plasma and urine samples using nanotubes modified edge plane pyrolytic graphite electrode.

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.

Voltammetric determination of amlodipine besylate in human urine and pharmaceuticals.

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.

Effect of surface modification of indium tin oxide by nanoparticles on the electrochemical determination of tryptophan.

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.

Simultaneous voltammetric determination of prednisone and prednisolone in human body fluids.

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.

Sensitive voltammetric sensor for the determination of oxidative DNA damage in calf thymus DNA

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.

Effect of single walled carbon nanotube-cetyltrimethyl ammonium bromide nanocomposite film modified pyrolytic graphite on the determination of betamethasone in human urine.

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.

Effect of substrate and embedded metallic impurities of fullerene in the determination of nandrolone.

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.

Single-Walled-Carbon-Nanotube-Modified Pyrolytic Graphite Electrode Used as a Simple Sensor for the Determination of Salbutamol in Urine

A fast and sensitive voltammetric method has been proposed for the determination of salbutamol at single-walled-carbon-nanotube-modified edge-plane pyrolytic graphite electrode (SWNT/EPPGE) in human urine. The electrochemical response of salbutamol was determined by square wave voltammetry (SWV) in phosphate buffer solution (PBS) at physiological pH 7.2. The modified electrode showed improved voltammetric response towards the oxidation of salbutamol, and a well-defined anodic peak was observed at ~600 mV with enhanced peak current in comparison to the bare electrode. Linear calibration plot using SWNT/EPPGE was obtained in the concentration range of 50 to 2500 ngml-1 with sensitivity and detection limit of 2.15 nA/ngml-1 and 4.31 ngml-1, respectively. The developed method has been successfully applied for the determination of salbutamol in commercial preparations and human body fluids. Fast analysis of salbutamol in human urine makes the proposed method of great interest for doping control purposes at the site of competitive games.

A sensitive voltammetric sensor for detecting betamethasone in biological fluids.

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.