Electrochemistry of adenosine-5′-diphosphate on ionic liquid modified carbon electrode and its detection

A sensitive electrochemical method was proposed for the determination of adenosine-5′-diphosphate (ADP) on an ionic liquid (IL) 1-(3-chloro-2-hydroxy-propyl)-3-methylimidazole chloride modified carbon paste electrode (CPE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with CPE, IL modified CPE (CILE) showed strong electrocatalytic ability to promote the electrochemical oxidation of ADP. A well-defined irreversible oxidation peak of ADP appeared at +1.381 V with an adsorption-controlled process, which was due to the presence of high conductive IL on the electrode. The experimental conditions were optimized and the electrochemical parameters of ADP were calculated with the electron transfer coefficient (α) as 0.293, the electron transfer number (n) as 1.23, the apparent heterogeneous electron transfer rate constant (k ^s) as 3.325 × 10^?6 s^?1 and the surface coverage (Γ_T) as 0.92 × 10^?8 mol/cm². Under the optimum conditions, the oxidation peak current was linear to ADP concentration in the range from 3.0 to 1000.0 μmol/L with the detection limit as 2.78 μmol/L (3σ) by differential pulse voltammetry. The CILE also eliminated the interferences of commonly coexisting substances and was successfully applied to detect the ADP artificial samples.     

Square Wave Voltammetry for Selective Detection of Dopamine Using Polyglycine Modified Carbon Ionic Liquid Electrode

The electrochemical polymerization of glycine on carbon ionic liquid electrode (CILE) was described. The presence of ionic liquid on the surface of CILE facilitated the electropolymerization of glycine. The polyglycine modified CILE provided a valid and simple approach to selectively detect dopamine in the presence of AA in physiological environment. The proposed sensor not only decreased the voltammetric responses of AA but also dramatically enhanced the oxidation peak current of DA compared to bare CILE. Using square wave voltammetry, the modified CILE showed good electrochemical behavior to DA, a linear range of 1.0×10^?7–3.0×10^?4 M in the presence of 1 mM ascorbic acid (AA) and a detection limit of 5.0×10^?9 M was estimated (S/N=3).     

Fabrication and Electrochemical Behavior of Hemoglobin Modified Carbon Ionic Liquid Electrode

A new hemoglobin (Hb) and room temperature ionic liquid modified carbon paste electrode was constructed by mixing Hb with 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) and graphite powder together. The Hb modified carbon ionic liquid electrode (Hb‐CILE) was further characterized by FT‐IR spectra, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Hb in the carbon ionic liquid electrode remained its natural structure and showed good direct electrochemical behaviors. A pair of well‐defined quasireversible redox peaks appeared with the apparent standard potential (E′) as ?0.334 (vs. SCE) in pH 7.0 phosphate buffer solution (PBS). The electrochemical parameters such as the electron transfer number (n), the electron transfer coefficient (α) and the heterogeneous electron transfer kinetic constant (k_s) of the electrode reaction were calculated with the results as 1.2, 0.465 and 0.434 s^?1, respectively. The fabricated Hb‐CILE exhibited excellent electrocatalytic activity to the reduction of H₂O₂. The calibration range for H₂O₂ quantitation was between 8.0×10^?6 mol/L and 2.8×10^?4 mol/L with the linear regression equation as I_ss (μA)=0.12 C (μmol/L)+0.73 (n=18, γ=0.997) and the detection limit as 1.0×10^?6 mol/L (3σ). The apparent Michaelis–Menten constant (K_M^app) of Hb in the modified electrode was estimated to be 1.103 mmol/L. The surface of this electrochemical sensor can be renewed by a simple polishing step and showed good reproducibility.     

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

A room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF₆) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (k_s) as 0.87 and 0.800 s^?1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10^?5 to 3.0×10^?3 mol/L with the linear regression equation as I_p (μA)=?2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10^?6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.     

Electrochemical behavior and determination of L-tryptophan on carbon ionic liquid electrode

A carbon ionic liquid electrode (CILE) was fabricated by mixing N-butylpyridinium hexafluoro-phosphate (BPPF ₆ ) with graphite powder and further used for the investigation on the electrochemical behavior of L-tryptophan (Trp). The fabricated CILE showed good conductivity, inherent electrocatalytic ability and strong promotion to the electron transfer of Trp. On the CILE, an irreversible oxidation peak appeared at 0.948 V (vs. saturated calomel reference electrode). For 5.0 × 10⁻⁵ M Trp the oxidation peak current increased about 5 times and the oxidation peak potential decreased on 0.092 V compared to carbon paste electrode. The results indicated that an electrocatalytic reaction occurred on CILE. The conditions for the electrochemical detection were optimized and the electrochemical parameters of Trp on CILE were carefully investigated. Under the selected conditions, the oxidation peak current showed linear relationship with Trp concentration in the range of 8.0 × 10⁻⁶ ∼1.0 × 10⁻³ M for cyclic voltammetry and the detection limit was estimated as 4.8 × 10⁻⁶ M (3σ). The interferences of other amino acids or metal ions on the determination were tested and the proposed method was successfully applied to the synthetic sample analysis.     

A sensitive electrochemical sensor for detection of rutin based on a gold nanocage‐modified electrode

In this article, an electrochemical sensor based on a gold nanocage (AuNC)‐modified carbon ionic liquid electrode (CILE) was fabricated and applied to the sensitive rutin determination. The presence of AuNCs on the electrode surface greatly improved the electrochemical performance of the working electrode due to its specific microstructure and high metal conductivity. Electrochemical behavior of rutin on AuNCs/CILE was studied using cyclic voltammetry and differential pulse voltammetry with the related electrochemical parameters calculated. Under the optimal experimental conditions, the oxidation peak current of rutin and its concentration had good linear relationship in the range from 4.0 × 10^?9 to 7.0 × 10^?4 mol/L with a low detection limit of 1.33 × 10^?9 mol/L (3σ). This fabricated AuNCs/CILE was applied to direct detection of the rutin concentration in drug samples with satisfactory results, showing the real application of AuNCs in the field of chemically modified electrodes.     

A Selective and Sensitive Method for Simultaneous Determination of Traces of Paracetamol and p‐Aminophenol in Pharmaceuticals Using Carbon Ionic Liquid Electrode

A reliable and simple electrochemical method has been proposed for the simultaneous determination of paracetamol (PAR) and p‐aminophenol (PAP) in pharmaceutical formulations. The oxidation and reduction peak potentials in cyclic voltammetry (CV) for PAR on carbon ionic liquid electrode (CILE) were occurred at 370 and 225 mV vs. Ag/AgCl, respectively at pH 7.0, while those for PAP on CILE appeared at 128 mV and 68 mV, respectively at the scan rate of 0.05 V s^?1. In comparison to the conventional carbon paste electrode, the apparent reversibility and kinetics of the electrochemical reactions of PAR and PAP were significantly improved on CILE. In differential pulse voltammetric technique, the peak potentials for PAR and PAP appeared at 345 and 130 mV, respectively, with the peak separation of 215 mV, sufficient for their simultaneous determination in samples containing these two species. The proposed method was used for simultaneous determination of PAR and PAP in tablets. PAR and PAP can be determined in the ranges of 2.0×10^?6–2.2×10^?3 M and 3.0×10^?7–1.0×10^?3 M, with the detection limits of 5.0×10^?7 and 1.0×10^?7 M (calculated by 3σ), respectively. The relative standard deviations for the determination of PAR and PAP were less than 2%.     

Electrochemiluminescent Detection Method for Glyphosate in Soybean on Carbon Fiber-ionic Liquid Paste Electrode

A carbon fiber paste electrode using ionic liquid as the binder (CFILE) was fabricated. The electrochemical characteristics of the electrode was examined in ferro‐/ferricyanide solution and showed better conductivity and reversibility when compared with graphite paste‐ionic liquid electrode (GPILE) and a little better than that on the carbon nanotube paste‐ionic liquid electrode (CNTILE). Glyphosate (GLY), a pesticide, exhibited excellent catalysis to the oxidation of Ru(bpy)²⁺₃ on CFILE and brought an obvious enhancement to the electrochemiluminescence (ECL) intensity of Ru(bpy)²⁺₃. Based on the catalytic ability of GLY, a simple ECL method for GLY detection had been established. Under optimum conditions, the enhanced ECL intensities were found to had linearly respond to the GLY concentration between 3.0×10^?7 and 3.0×10^?5 mol/L, and the detection limit (S/N=3) was 2.0×10^?7 mol/L. The electrode also showed excellent sensitivity in detecting GLY‐spiked soybean samples. The linear range for GLY in soybean samples was 1.0×10^?6–4.0×10^?5 mol/L and the detection limit was 5.0×10^?7 mol/L, equal to 8.45 µg GLY in per gram of soybean. The detection limit in soybean sample was lower than the USA, EU regulation and so on. If the method is coupled with the separation technology, it can be applied to detect the GLY in the contaminated samples.     

Voltammetric detection of guanosine and adenosine using a carbon paste electrode modified with 1-ethyl-3-methylimidazolium ethylsulfate

A novel kind of carbon paste electrode (CPE) was prepared by mixing graphite powder, liquid paraffin and the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate. The resulting electrode was used for the simultaneous determination of guanosine and adenosine by differential pulse voltammetry. Compared to a conventional CPE, the oxidation peak currents are largely increased, and the oxidation peak potentials are negatively shifted. The electrochemical responses to guanosine and adenosine were investigated. Under optimized conditions, the calibration curves are linear in the concentration range from 1.0?×?10^-6?mol?L^-1 to 1.6?×?10^-4?mol?L^-1 for guanosine, and from 1.0?×?10^-6?mol?L^-1 to 2.7?×?10^-4?mol?L^-1 for adenosine at pH 3.5. Substances potentially interfering in the biological matrix do no interfere. The method was successfully applied to detect adenosine and guanosine in human urine without sample treatments.

Sensitive Electrochemical Determination of Catechol with a Graphene Modified Carbon Ionic Liquid Electrode

In this paper a graphene (GR) modified carbon ionic liquid electrode (CILE) was fabricated and used as the voltammetric sensor for the sensitive detection of catechol. Due to the specific physicochemical characteristics of GR such as high surface area, excellent conductivity and good electrochemical properties, the modified electrode exhibits rapid response and strong catalytic activity with high stability toward the electrochemical oxidation of catechol. A pair of well‐defined redox peaks appeared with the anodic and the cathodic peak potential located at 225 mV and 133 mV (vs.SCE) in pH 6.5 phosphate buffer solution, respectively. Electrochemical behaviors of catechol on the GR modified CILE were carefully investigated and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant (k_s) as 1.24 s^?1, the charge transfer coefficient (α) as 0.4 and the electron transfer number (n) as 2. Under the selected conditions the differential pulse voltammetric peak current increased linearly with the catechol concentrations in the range from 1.0 × 10^‐7 to 7.0 × 10^?4mol L‐1 with the detection limit as 3.0 × 10^?8mol L‐1 (3σ). The proposed method was further applied to the synthetic waste water samples determination with satisfactory results     

Electrochemical DNA Biosensor Based on Graphene and TiO2 Nanorods Composite Film for the Detection of Transgenic Soybean Gene Sequence of MON89788

Based on graphene (GR), TiO₂ nanorods, and chitosan (CTS) nanocomposite modified carbon ionic liquid electrode (CILE) as substrate electrode, a new electrochemical DNA biosensor was effectively fabricated for the detection of the transgenic soybean sequence of MON89788. By using methylene blue (MB) as hybridization indicator for monitoring the hybridization with different ssDNA sequences, the differential pulse voltammetric response of MB on DNA modified electrodes were recorded and compared. Due to the synergistic effects of TiO₂ nanorods and GR on the electrode surface, the electrochemical responses of MB were greatly increased. Under optimal conditions the differential pulse voltammetric response of the target ssDNA sequence could be detected in the range from 1.0×10^?12 to 1.0×10^?6 mol/L with a detection limit of 7.21×10^?13 mol/L (3σ). This electrochemical DNA biosensor was further applied to the polymerase chain reaction (PCR) product of transgenic soybeans with satisfactory results.     

Electrochemical DNA Biosensor Based on Partially Reduced Graphene Oxide Modified Carbon Ionic Liquid Electrode for the Detection of Transgenic Soybean A2704‐12 Gene Sequence

In this work a partially reduced graphene oxide (p‐RGO) modified carbon ionic liquid electrode (CILE) was prepared as the platform to fabricate an electrochemical DNA sensor, which was used for the sensitive detection of target ssDNA sequence related to transgenic soybean A2704‐12 sequence. The CILE was fabricated by using 1‐butylpyridinium hexafluorophosphate as the binder and then p‐RGO was deposited on the surface of CILE by controlling the electroreduction conditions. NH₂ modified ssDNA probe sequences were immobilized on the electrode surface via covalent bonds between the unreduced oxygen groups on the p‐RGO surface and the amine group at the 5′‐end of ssDNA, which was denoted as ssDNA/p‐RGO/CILE and further used to hybridize with the target ssDNA sequence. Methylene blue (MB) was used as electrochemical indicator to monitor the DNA hybridization. The reduction peak current of MB after hybridization was proportional to the concentration of target A2704‐12 ssDNA sequences in the range from 1.0×10^?12 to 1.0×10^?6 mol/L with a detection limit of 2.9×10^?13 mol/L (3σ). The electrochemical DNA biosensor was further used for the detection of PCR products of transgenic soybean with satisfactory results.     

Electrochemical behaviors of guanosine on carbon ionic liquid electrode and its determination

The electrochemical behaviors of guanosine on the ionic liquid of N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CPE) was studied in this paper and further used for guanosine detection. Guanosine showed an adsorption irreversible oxidation process on the carbon ionic liquid electrode (CILE) with the oxidation peak potential located at 1.12 V (vs. SCE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with that on the traditional carbon paste electrode, small shift of the oxidation peak potentials appeared but with a great increment of the oxidation peak current on the CILE, which was due to the presence of ionic liquid in the modified electrode adsorbed the guanosine on the surface and promoted the electrochemical response. The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n), and the electrode reaction standard rate constant (k_s) were calculated as 0.74, 1.9 and 1.26 × 10⁻⁴ s⁻¹, respectively. Under the optimal conditions the oxidation peak current showed a good linear relationship with the guanosine concentration in the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol/L by cyclic voltammetry with the detection limit of 2.61 × 10⁻⁷ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine oxidation. The CILE showed good ability to distinguish the electrochemical response of guanosine and guanine in the mixture solution. The urine samples were further detected by the proposed method with satisfactory results.     

Sensitive and Simple Electrochemical Detection of Lead(II) with Carbon Ionic Liquid Electrode

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1‐ethyl‐3‐methylimidazolium ethylsulphate ([EMIM]EtOSO₃) as the modifier and further used as the working electrode for the sensitive anodic stripping voltammetric detection of Pb²⁺. The characteristics of the CILE were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In pH 4.5 NaAc‐HAc buffer Pb²⁺ was accumulated on the surface of CILE due to the extraction effect of IL and reduced at a negative potential (‐1.20 V). Then the reduced Pb was oxidized by differential pulse anodic stripping voltammetry with an obvious stripping peak appeared at ?0.67 V. Under the optimal conditions Pb²⁺ could be detected in the concentration range from 1.0 × 10^?8 mol/L to 1.0 × 10^?6 mol/L with the linear regression equation as I_p(μA) = ?0.103 C (μmol/L) + 0.0376 (γ = 0.999) and the detection limit as 3.0 × l0^?9 mol/L (3σ). Interferences from other metal ions were investigated and Cd²⁺ could be simultaneously detected in the mixture solution. The proposed method was further applied to the trace levels of Pb²⁺ detection in water samples with satisfactory results.     

Carbon electrode modified with ionic liquid and multi-walled carbon nanotubes for voltammetric sensing of adenine

A voltammetric sensor was fabricated by applying a Nafion and multi-walled carbon nanotubes (MWCNTs) composite film on the surface of a carbon ionic liquid electrode (CILE), which was prepared by mixing 1-butyl-3-methylimidazolium hexafluorophosphate with graphite powder. The electrochemical behavior of adenine on the Nafion-MWCNTs/CILE was investigated in pH 5.5 buffer solution. Adenine showed an irreversible adsorption-controlled oxidation reaction with enhanced electrochemical response, which was due to the presence of high conductive MWCNTs on the CILE surface. The electrochemical parameters of adenine electro-oxidation were determined, and the experimental conditions were optimized. Under the optimal conditions, the oxidation peak current was linear to the adenine concentration over the range of 1.0?×?10^?7 to 7.0?×?10^?5 mol L^?1 with a detection limit of 3.3?×?10^?8 mol L^?1 (signal/noise?=?3). The electrode showed good stability and selectivity, and was further applied to milk powder samples with satisfactory results.     

Electropolymerization of Methylene Blue on Carbon Ionic Liquid Electrode and Its Electrocatalysis to 3,4‐Dihydroxybenzoic Acid

In this paper an ionic liquid modified carbon paste electrode (CILE) was prepared and methylene blue (MB) was electropolymerized on the CILE by using the cyclic voltammetric technique in the potential range from −1.0 V to 0.8 V (vs. SCE). A stable polymer film was obtained and exhibited a pair of redox peaks. The morphology and characteristics of poly(methylene blue) (PMB) film was studied by the techniques such as scanning electron microscopy and electrochemical impedance spectroscopy. This PMB modified CILE (PMB/CILE) showed excellent electrocatalytic response to 3,4‐dihydroxybenzoic acid with the increase of the electrochemical responses. The oxidation peak current had a linear relationship with 3,4‐dihydroxybenzoic acid concentration in the range of 5.0 × 10⁻⁴ ∼ 3.0 × 10⁻² mol L⁻¹ and the detection limit was 1.72 × 10⁻⁴ Mol L⁻¹ (3 σ).     

Study on Diffusion Mechanisms and Determination of Dihydroxybenzene Isomers at the Pre‐anodized Inlaying Ultrathin Carbon Paste Electrode

In this paper, nichrome was adopted as a substrate, to fabricate the pre‐anodized inlaying ultrathin carbon paste electrode (PAIUCPE). The electrochemical behaviors and diffusion mechanisms of three dihydroxybenzene isomers at the electrode were carefully investigated. The effect of pH on oxidation peak current was also detailedly explained. The results were shown that oxidation peak current not only related to the reaction of electroactive materials at the working electrode, but also depended on the reaction variable of reduction at the auxiliary electrode. The oxidation peaks of hydroquinone (HQ), catechol (CC) and resorcinol (RC) located at 0.181 V, 0.288 V and 0.736 V. For CC, RC and HQ, the oxidation peak currents were linear to the concentrations at the range of 5.0 × 10^?6～5.0 × 10^?4 mol/L, 3.0 × 10^?6～5.0 × 10^?4 mol/L and 4.0 × 10^?6～4.0 × 10^?4 mol/L with the detection limits of 2.0 × 10^?7 mol/L, 1.2 × 10^?7 mol/L and 1.2 × 10^?7 mol/L, respectively. The proposed method was successfully applied in the simultaneous determination of dihydroxybenzene isomers in artificial sewage samples with satisfactory results.     

The Influencing of Preanodized Inlaying Ultrathin Carbon Paste Electrode on the Oxidation for the Xanthine and Hypoxanthine by the Hydrogen Bond

In this paper, a pre‐anodized inlaying ultrathin carbon paste electrode (PAIUCPE) with 316L as a matrix was constructed by a simple and fast electrochemical pretreatment. Using xanthine (Xa) and hypoxanthine (HXa) as the target compounds, the pH effects compositions of buffer solution, the accumulation times, hydrogen bond catalysis, degree of auxiliary electrode reaction on the size of peak currents (I_p) of Xa and HXa was discussed in detail. Also, it was proposed that Xa and HXa were respectively absorbed at the surface of PAIUCPE through hydrogen bonding. The influencing mechanisms of the PAIUCEP on electrochemical oxidation of Xa and HXa were explained in detail. Moreover, the linear relationships for the Xa and HXa were obtained in the range of 6×10^?8–3×10^?5 mol/L and 2×10^?7–7×10^?5 mol/L, respectively. The detection limits for the Xa and HXa were 1.2×10^?8 mol/L and 5.7×10^?8 mol/L, respectively. Moreover, this proposed method could be applied to determine the Xa and HXa in human urine simultaneously with satisfactory results.     

Sensitive determination of ATP using a carbon paste electrode modified with a carboxyl functionalized ionic liquid

We report on a new electrode for the determination of adenosine-5??-triphosphate (ATP). It is based on modified carbon paste electrode that contains an ionic liquid (IL) as the binder. The electrode shows strong electrocatalytic oxidative activity towards ATP at pH 4.5 in giving a well-defined single oxidation peak. The oxidation reaction is adsorption-controlled and due to the presence of the highly conductive IL. The electron transfer rate constant was calculated to be 2.04×10^?C3 s^?C1, and the surface coverage is 1.11×10^?C10 mol cm^?C2. Under the selected conditions, the oxidation peak current changes linearly with the concentration of ATP in the range from 5.0 to 1000???mol L^?1 and a detection limit of 1.67???mol L^?1 (3???) as determined by differential pulse voltammetry. The method displays good selectivity and was applied to the determination of ATP injection samples with satisfactory results.

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L ‐cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, k_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10^?5 M–2.2×10^?3 M and 1.5×10^?5 M–3.2×10^?3 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10^?5 M and 1.4×10^?6 M by CV and DPV methods.