Simultaneous voltammetric determination of acetaminophen, aspirin and caffeine using an in situ surfactant-modified multiwalled carbon nanotube paste electrode

A carbon nanotube paste electrode modified in situ with Triton X 100 was developed for the individual and simultaneous determination of acetaminophen (ACOP), aspirin (ASA) and caffeine (CF). The electrochemical behavior of these three molecules was investigated employing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronocoulometry (CC) and adsorptive stripping differential pulse voltammetry (AdSDPV). Kramers-Kronig transformation implied that the resulting impedance data were validated and were of very good quality. These studies revealed that the oxidation of ACOP, ASA and CF is facilitated at an in situ surfactant-modified multiwalled carbon nanotube paste electrode (ISSM-CNT-PE). After optimization of analytical conditions employing this electrode at pH 7.0 in phosphate buffer (0.1 M), the peak currents for the three molecules were found to vary linearly with their concentrations in the range of 2.91 × 10⁻⁷-6.27 × 10⁻⁵ M with detection limits of 2.58 × 10⁻⁸, 8.47 × 10⁻⁸ and 8.83 × 10⁻⁸ M for ACOP, ASA and CF respectively using AdSDPV. The prepared modified electrode showed several advantages, such as a simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. Furthermore, the proposed method was employed for the simultaneous determination of ACOP, ASA and CF in pharmaceutical formulations, urine and blood serum samples and the obtained results were found to be satisfactory.     

Potentiometric stripping analysis of bismuth based on carbon paste electrode modified with cryptand [2.2.1] and multiwalled carbon nanotubes

An electrochemical method based on potentiometric stripping analysis (PSA) employing a cryptand [2.2.1] (CRY) and carbon nanotube (CNT) modified paste electrode (CRY-CNT-PE) has been proposed for the subnanomolar determination of bismuth. The characterization of the electrode surface has been carried out by means of scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry (CC). It was observed that by employing CRY-CNT-PE, a 9-fold enhancement in the PSA signal (dt/dE) was observed as compared to plain carbon paste electrode (PCPE). Under the optimized conditions, dt/dE (s/V) was proportional to the Bi(III) concentration in the range of 5.55 × 10⁻⁸ to 9.79 × 10⁻¹¹ M (r = 0.9990) with the detection limit (S/N = 3) of 3.17 × 10⁻¹¹ M. The practical analytical utilities of the modified electrode were demonstrated by the determination of bismuth in pharmaceutical formulations, human hair, sea water, urine and blood serum samples. The prepared modified electrode showed several advantages, such as a simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. Moreover, the results obtained for bismuth analysis in commercial and real samples using CRY-CNT-PE and those obtained by atomic absorption spectroscopy (AAS) are in agreement at the 95% confidence level.     

Simultaneous voltammetric determination of ascorbic acid, acetaminophen and isoniazid using thionine immobilized multi-walled carbon nanotube modified carbon paste electrode

A carbon paste electrode (CPE) modified with thionine immobilized on multi-walled carbon nanotube (MWCNT), was prepared for simultaneous determination of ascorbic acid (AA) and acetaminophen (AC) in the presence of isoniazid (INZ). The electrochemical response characteristics of the modified electrode toward AA, AC and INZ were investigated by cyclic and differential pulse voltammetry (CV and DPV). The results showed an efficient catalytic role for the electro-oxidation of AA and AC, leading to a remarkable peak resolution (∼303 mV) for two compounds. On the other hand, the presence of INZ, which is considered as important drug interference for AC, does not affect the voltammetric responses of these pharmaceuticals. The mechanism of the modified electrode was analyzed by monitoring the CVs at various potential sweep rates and pHs of the buffer solutions. Under the optimum conditions, the calibration curves for AA, AC and INZ were obtained in the range of 1 × 10⁻⁶ to 1 × 10⁻⁴ M, 1 × 10⁻⁷ to 1 × 10⁻⁴ M and 1 × 10⁻⁶ to 1 × 10⁻⁴ M, respectively. The prepared modified electrode shows several advantages such as simple preparation method, high sensitivity, long-time stability, ease of preparation and regeneration of the electrode surface by simple polishing and excellent reproducibility. The proposed method was applied to determination of AA, AC and INZ in commercial drugs and in plasma samples and the obtained results were satisfactory.     

Electrochemical determination of bisphenol A at Mg-Al-CO3 layered double hydroxide modified glassy carbon electrode

The electrochemical behavior of bisphenol A (BPA) was investigated on Mg-Al layered double hydroxide (LDH) modified glassy carbon electrode (GCE) by cyclic voltammetry (CV), differential pulse voltammetry (DPV), linear sweep voltammetry (LSV) and chronocoulometry (CC). The cyclic voltammogram of BPA on the modified electrode exhibited a well defined anodic peak at 0.454 V in 0.1 M pH 8.0 phosphate buffer solution (PBS). The experimental parameters were optimized and the kinetic parameters were investigated. The probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to BPA concentration in the range from 1 × 10⁻⁸ to 1.05 × 10⁻⁶ M with the correlation coefficient of 0.9959. The detection limit was 5.0 × 10⁻⁹ M (S/N = 3). The fabricated electrode showed good reproducibility, stability and anti-interference. The proposed method was successfully applied to determine BPA in plastic products and the results were satisfactory.     

Direct electrochemical behavior of cytochrome c on DNA modified glassy carbon electrode and its application to nitric oxide biosensor

Cytochrome c/DNA modified electrode was achieved by coating calf thymus DNA onto the surface of glassy carbon electrode firstly, then immobilizing cytochrome c on it by multi-cyclic voltammetric method and characterized by the electrochemical impedance. The electrochemical behavior of cytochrome c on DNA modified electrode was explored and showed a quasi-reversible electrochemical redox behavior with a formal potential of 0.045 ± 0.010 V (versus Ag/AgCl) in 0.10 M, pH 5.0, acetate buffer solution. The peak currents were linearly with the scan rate in the range of 20-200 mV/s. Cytochrome c/DNA modified electrode exhibited elegant catalytic activity for the electrochemical reduction of NO. The catalytic current is linear to the nitric oxide concentration in the range of 6.0 × 10⁻⁷ to 8.0 × 10⁻⁶ M and the detection limit was 1.0 × 10⁻⁷ M (three times the ratio of signal to noise, S/N = 3).     

Study of nimesulide and its determination using multiwalled carbon nanotubes modified glassy carbon electrodes

A new method for the determination of nimesulide was established based on the multiwalled carbon nanotubes (MWCNTs) modified glassy carbon electrode (MWCNTs/GCE). In 0.2 M PBS (pH 6.6) buffer solution, the MWCNTs/GCE showed a remarkable catalytic and enhancement effect on reduction of the nimesulide. The reduction peak potential of nimesulide shifted positively from −0.665 V at bare GCE to −0.553 V at MWCNTs/GCE, and the sensitivity increased ca. 7 times. A linear dynamic range of 3.2 × 10⁻⁷-6.5 × 10⁻⁵ M (R = 0.9992) with a detection limit of 1.6 × 10⁻⁷ M was obtained. The electrochemical behaviors of nimesulide were studied and electron-transfer coefficient (α = 0.45), proton number (X = 1) and electron-transfer number (n = 2) have been determined. This method has been used to determine the content of nimesulide in medical tablets. The recovery was determined to be 93.2-106.2% by means of standard addition method. Compared with UV-vis spectrometry, the method was not remarkable difference.     

Preparation of Cerium (III) 12-tungstophosphoric acid/ordered mesoporous carbon composite modified electrode and its electrocatalytic properties

In this work, a novel structured Cerium (III) 12-tungstophosphoric acid (CePW)/ordered mesoporous carbon (OMC) composite is synthesized. The characterization of the material by the Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical characterization shows that the novel CePW/OMC composite has improved properties based on the combination of CePW and OMC properties. CePW/OMC can be used to modify the glassy carbon (GC) electrode and the CePW/OMC/GC modified electrode shows an enhanced electrocatalytic activity. This property can be applied in the determination of some biomolecules. Especially, the detection and determination of the guanine (G) in the presence of adenine (A) is achieved. The catalytic current of G versus its concentration shows a good linearity with two good linear ranges from 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ M and from 8.0 × 10⁻⁵ to 1.9 × 10⁻³ M (correlation coefficient = 0.999 and 0.996) with a detection limit of 5.7 × 10⁻⁹ M (S/N = 3). The linear range for adenine is 4.0 × 10⁻⁶-7.0 × 10⁻⁴ M with a detection limit of 7.45 × 10⁻⁸ M. With good stability and reproducibility, the present CePW/OMC/GC modified electrode should be a good model for constructing a novel and promising electrochemical sensing platform for further electrochemical detection of other biomolecules.     

Enhancement of electrochemiluminesence of lucigenin by ascorbic acid at single-wall carbon nanotube film-modified glassy carbon electrode

The electrochemiluminescent behavior of lucigenin on a single-wall carbon nanotube/DMF film-modified glassy carbon electrode was studied in this paper. Comparing with the bare glassy carbon electrode, the electrochemiluminescent of lucigenin at modified electrode is more stable and without tedious procedure for clean-up the surface of modified electrode. It has been found that ascorbic acid could enhance the electrochemiluminescent intensity of lucigenin greatly at this modified electrode. Based on which, a new sensitive and simple electrochemiluminescent method for determination of ascorbic acid could be developed. The condition for the determination of ascorbic acid was optimized. Under the optimized condition, the enhanced electrochemiluminescent intensity versus ascorbic acid concentration was linear in the range of 1.0 × 10⁻⁸ to 4.0 × 10⁻⁶ mol/L with a detection limit of 2.0 × 10⁻¹⁰ mol/L, and the relative standard derivation for 1.0 × 10⁻⁷ mol/L ascorbic acid was 3.8% (n = 8). The possible mechanism was also discussed.     

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes for the electrochemical detection of copper(II)

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes obtained by electropolymerization of 2-amino-4-thiazoleacetic acid, were used for the voltammetric determination of copper ions. The voltammetric response of copper ions at poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes was evaluated by differential pulse stripping voltammetry. The peak currents were linearly dependent on the concentrations of the copper ions in the range from 7.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M, with a coefficiency of 0.9987. The detection limit is 5.0 × 10⁻¹⁰ M calculated for a signal-to-noise ratio of 3 (S/N = 3). And it could be used for the simultaneous determination of copper and cadmium ions. The proposed method was successfully applied to the determination of copper ions in natural water. The concentration of Cu²⁺ was calculated to be 2.0 × 10⁻⁵ M by standard addition method. The recovery rate was 94%.     

Electrochemical determination of bromide at a multiwall carbon nanotubes-chitosan modified electrode

A multiwall carbon nanotubes (MWNTs)-chitosan modified glassy carbon electrode (GCE) exhibits attractive ability for highly sensitive cathodic stripping voltammetric measurements of bromide (Br⁻). In pH 1.8 H₂SO₄ solution, a substantial increase in the stripping peak current of Br⁻ (compared to bare GCE and chitosan modified GCE) is observed using MWNTs-chitosan modified electrode. Operational parameters were optimized and the electrochemical behaviors of Br⁻ were studied by different electrochemical methods. The kinetics parameters were measured, the number of electron transfer (n) was 1 and the transfer coefficient (α) is 0.17. A wide linear calibration range (3.6 × 10⁻⁷-1.4 × 10⁻⁵ g mL⁻¹) was achieved, with a detection limit of 9.6 × 10⁻⁸ g mL⁻¹. The mechanism of electrode reaction was fully discussed.     

Fabrication of Fc-SWNTs modified glassy carbon electrode for selective and sensitive determination of dopamine in the presence of AA and UA

The electrochemistry of dopamine (DA) was investigated by cyclic voltammetry (CV) and differential pulse voltammograms (DPV) at a glassy carbon electrode modified by the hybridization adducts of Fc-SWNTs. The electro-oxidation of DA could be catalyzed by Fc/Fc⁺ couple as a mediator and had a higher electrochemical response due to the unique carbon surface of carbon nanotubes. The anodic peaks of DA, ascorbic acid (AA) and uric acid (UA) in their mixture can be well separated by the prepared electrode. Under optimum conditions linear calibration graphs were obtained over the DA concentration range 5.0 × 10⁻⁶ to 3.0 × 10⁻⁵ M with a correlation coefficient of 0.9998 and a detection limit of 5.0 × 10⁻⁸ M based on the equation C_m = 3s_b1/m. The modified electrode has been successfully applied for the assay of DA in human blood serum. This work provides a simple and easy approach to selectively detect DA in the presence of AA and UA.     

Flow injection amperometric determination of pyridoxine at a Prussian blue nanoparticle-modified carbon ceramic electrode

This work describes the electrocatalytic properties of a carbon composite electrode (CCE) modified with Prussian blue (PB) nanoparticles (NPs) for the electrocatalytic oxidation of pyridoxine (PN). The morphology of the PBNP-modified CCE was characterized by scanning electron microscopy (SEM). The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The rate-limiting step of the charge transfer reaction was found to be a one-electron abstraction. The value of α, k, and D were calculated as 0.66, 6.7 × 10⁴ M⁻¹ s⁻¹, and 1.88 × 10⁻⁵ cm² s⁻¹, respectively. The modified electrode showed electrocatalytic activity toward the oxidation of PN and was used as an amperometric sensor. The sensor exhibited good linear response for PN over the concentration ranges 5-69 and 1-80 μM with detection limits of 0.51 and 0.87 μM, and sensitivities of 0.97 and 0.673 A M⁻¹ cm⁻² in batch and flow conditions, respectively. Some important advantages such as simple preparation, fast response, good stability, and reproducibility of the sensor for the amperometric determination of PN were achieved.     

Electrocatalytic oxidation and simultaneous determination of uric acid and ascorbic acid on the gold nanoparticles-modified glassy carbon electrode

A new gold nanoparticles-modified electrode (GNP/LC/GCE) was fabricated by self-assembling gold nanoparticles to the surface of the l-cysteine-modified glassy carbon electrode. The modified electrode showed an excellent character for electrocatalytic oxidization of uric acid (UA) and ascorbic acid (AA) with a 0.306 V separation of both peaks, while the bare GC electrode only gave an overlapped and broad oxidation peak. The anodic currents of UA and AA on the modified electrode were 6- and 2.5-fold to that of the bare GCE, respectively. Using differential pulse voltammetry (DPV), a highly selective and simultaneous determination of UA and AA has been explored at the modified electrode. DPV peak currents of UA and AA increased linearly with their concentration at the range of 6.0 × 10⁻⁷ to 8.5 × 10⁻⁴ mol L⁻¹ and 8.0 × 10⁻⁶ to 5.5 × 10⁻³ mol L⁻¹, respectively. The proposed method was applied for the detection of UA and AA in human urine with satisfactory result.     

Application of surfactant modified zeolite carbon paste electrode (SMZ-CPE) towards potentiometric determination of sulfate

A sulfate-selective electrode based on surfactant modified zeolite (SMZ) particles into carbon paste has been proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength range, thermal stability and usable pH range. The electrode containing 10% of the SMZ was exhibited linear response range to sulfate species in the range of 2.0 × 10⁻⁶-3.1 × 10⁻³ M with detection limit of 2.0 × 10⁻⁶ M and Nernstian slope of 29.8 ± 0.8 mV per decade of sulfate concentration. The electrode response remains constant in the pH range of 4-10 and in the presence of 1 × 10⁻⁴-2 × 10⁻³ M NaNO₃. The response of the electrode reaches equilibrium within several second after immersing the electrode in sulfate solution. A successful application of sulfate determination sulfate in real sample of a pharmaceutical zinc sulfate capsule, using direct potentiometry, is presented. The electrode was also used for potentiometric titration of sulfate. The validation of the obtained results in each case was proved by statistical methods.     

Direct electrochemistry of guanosine on multi-walled carbon nanotubes modified carbon ionic liquid electrode

A multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was fabricated and used to investigate the electrochemical behavior of guanosine. CILE was prepared by mixing hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄), graphite powder and liquid paraffin together. The fabricated MWCNTs/CILE showed great electrocatalytic ability to the oxidation of guanosine and an irreversible oxidation peak appeared at 1.067 V (vs. SCE) with improved peak current. The electrochemical behavior of guanosine on the MWCNTs/CILE was carefully studied by cyclic voltammetry and the electrochemical parameters such as the charge transfer coefficient (α) and the electrode reaction standard rate constant (k_s) were calculated with the result as 0.66 and 2.94 × 10⁻⁴ s⁻¹, respectively. By using differential pulse voltammetry (DPV) as the detection method, a linear relationship was obtained between the oxidation peak current and the guanosine concentration in the range from 1.0 × 10⁻⁷ to 4.0 × 10⁻⁵ mol/L with the detection limit as 7.8 × 10⁻⁸ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine detection and the modified electrode showed good ability to distinguish the electrochemical response of guanosine and adenosine.     

Electrocatalytic oxidation of amitrole and diuron on iron(II) tetraaminophthalocyanine-single walled carbon nanotube dendrimer

FeTAPc-single walled carbon nanotube (SWCNT) dendrimers are employed as glassy carbon electrode modifiers for the electrocatalytic oxidations of amitrole and diuron. The catalytic rate constants were 4.55 × 10³ M⁻¹ s⁻¹ and 1.79 × 10⁴ M⁻¹ s⁻¹ for amitrole and diuron, respectively using chronoamperometric studies. The diffusion constants were found to be 1.52 × 10⁻⁴ cm² s⁻¹ and 1.91 × 10⁻⁴ cm² s⁻¹ for diuron and amitrole, respectively. The linear concentration range for both were from 5.0 × 10⁻⁵ to 1.0 × 10⁻⁴ M and sensitivities of 0.6603 μA/μM and 0.6641 μA/μM for amitrole and diuron, with corresponding limits of detection of 2.15 × 10⁻⁷ and 2.6 × 10⁻⁷ M using the 3δ notation, respectively.     

Enhanced electrochemiluminescence of CdTe quantum dots with carbon nanotube film and its sensing of methimazole

A novel analytical method was reported based on electrochemiluminescence (ECL) of CdTe quantum dots (QDs) using carbon nanotube (CNT) modified glass carbon (GC) electrode. It was found that the CNT film on the GC electrode could greatly enhance the ECL intensity of CdTe QDs dispersed in aqueous solution, and the ECL peak potential and ECL onset potential both shifted positively. Influences of some factors on the ECL intensity were investigated using CNT modified GC electrode, and a high sensitive method for the determination of methimazole was developed under the optimal conditions. The ECL intensity decreased linearly in the concentration range of 1.0 × 10⁻⁹ to 4.0 × 10⁻⁷ M for methimazole with the relative coefficient of 0.995, which showed finer sensitivity than that at bare electrode. Thus, CNT modified electrode would have a great merit to expand the application of QD ECL.     

Selective oxidation of serotonin and norepinephrine over eriochrome cyanine R film modified glassy carbon electrode

A novel ECR-modified electrode is fabricated by electrodeposition of Eriochrome Cyanine R (ECR) at a glassy carbon (GC) electrode by cyclic voltammetry (CV) in double-distilled water. The characterization of the ECR film modified electrode is carried out by atomic force microscopy (AFM), infrared spectra (IR), spectroelectrochemistry and cyclic voltammetry. The results show that a slightly heterogeneous film formed on the surface of the modified electrode, and the calculated surface concentration of ECR is 2 × 10⁻¹⁰ mol/cm⁻². The ECR film modified GC electrode shows excellent electrocatalytic activities toward the oxidation of serotonin (5-HT) and norepinephrine (NE). Furthermore, the modified electrode can separately detect 5-HT and NE, even in the presence of 200-fold concentration of ascorbic acid (AA) and 25-fold concentration of uric acid (UA). Using differential pulse voltammetry (DPV), the peak currents of 5-HT and NE recorded in pH 7 solution are linearly dependent on their concentrations in the range of 0.05-5 μM and 2-50 μM, respectively. The limits of detection are 0.05 and 1.5 μM for 5-HT and NE, respectively. The ECR film modified electrode can be stored stable for at least 1 week in 0.05 M PBS (pH 7) at 4 °C in a refrigerator. Owing to its excellent selectivity and sensitivity, the modified electrode could provide a promising tool for the simultaneous determination of 5-HT and NE in complex biosamples.     

Voltammetric determination of ascorbic acid and dopamine in the same sample at the surface of a carbon paste electrode modified with polypyrrole/ferrocyanide films

Functionalized polypyrrole film were prepared by incorporation of [Fe(CN)₆]⁴⁻ as a doping anion, during the electropolymerization of pyrrole onto a carbon paste electrode in an aqueous solution by potentiostatic method. The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) in one solution was studied at the surface of bare and modified carbon paste electrodes using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and differntial pulse voltammetry (DPV) methods. The well separated anodic peaks for oxidation of DA and AA were observed at the surface of the modified carbon paste electrode under optimum condition (pH 6.00), which can be used for determination of these species simultaneously in mixture by LSV and DPV methods. The linear analytical curves were obtained in the ranges of 0.10-1.00 mM and 0.10-0.95 mM for ascorbic acid and 0.10-1.20 mM and 0.20-0.95 mM for dopamine concentrations using LSV and DPV methods, respectively. The detection limits (2σ) were determined as 3.38 × 10⁻⁵ M and 1.34 × 10⁻⁵ M of ascorbic acid and 3.86 × 10⁻⁵ M and 1.51 × 10⁻⁵ M of dopamine by CV and DPV methods.     

Studies on the electrochemical behavior of 3-nitrobenzaldehyde thiosemicarbazone at glass carbon electrode modified with nano-γ-Al2O3

Nano-γ-Al₂O₃ is dispersed onto the glass carbon electrode (GCE) by polishing. This nanostructured modified GCE exhibits a great enhancement to the redox responses of 3-nitrobenzaldehyde thiosemicarbazone (3-NBT). In comparison with bare GCE, 3-NBT gives a more sensitive voltammetric response because of the nanoparticle’s unique properties. The lowest detectable concentration (3σ) of 3-NBT is estimated to be 1.18 × 10⁻⁶ M (accumulation for 4 min). The linear relationship between peak current and concentration of 3-NBT holds in the range 1.0 × 10⁻⁵ M to 1.0 × 10⁻⁴ M (r = 0.9981). The electrochemical properties of 3-NBT on this modified electrode have been investigated with various electrochemical methods. The results indicate that the transference of one electron and one proton involves electrode radical reaction processes I and II, respectively. The coverage value (Γ) of 1.62 × 10⁻⁹ mol cm⁻² was calculated and the electrochemical parameters, diffusion coefficient D (2.54 × 10⁻³ cm² s⁻¹, 2.03 × 10⁻³ cm² s⁻¹) and reaction rate constant k_s (5.9573 s⁻¹, 7.15 × 10⁻² cm s⁻¹) were obtained for quasi-reversible system I and irreversible system II, respectively.