Sensitive Voltammetric Response of p‐Nitroaniline on Single‐Wall Carbon Nanotube‐Ionic Liquid Gel Modified Glassy Carbon Electrodes

An ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexafluorophosphate, BMIMPF₆)‐single‐walled carbon nanotube (SWNT) gel modified glassy carbon electrode (BMIMPF₆‐SWNT/GCE) is fabricated. At it the voltammetric behavior and determination of p‐nitroaniline (PNA) is explored. PNA can exhibit a sensitive cathodic peak at ?0.70 V (vs. SCE) in pH 7.0 phosphate buffer solution on the electrode, resulting from the irreversible reduction of PNA. Under the optimized conditions, the peak current is linear to PNA concentration over the range of 1.0×10^?8–7.0×10^?6 M, and the detection limit is 8.0×10^?9 M. The electrode can be regenerated by successive potential scan in a blank solution for about 5 times and exhibits good reproducibility. Meanwhile, the feasibility to determine other nitroaromatic compounds (NACs) with the modified electrode is also tested. It is found that the NACs studied (i.e., p‐nitroaniline, p‐nitrophenol, o‐nitrophenol, m‐nitrophenol, p‐nitrobenzoic acid, and nitrobenzene) can all cause sensitive cathodic peaks under the conditions, but their peak potentials and peak currents are different to some extent. Their peak currents and concentrations show linear relationships in concentration ranges with about 3 orders of magnitude. The detection limits are 8.0×10^?9 M for p‐nitroaniline, 2.0×10^?9 M for p‐nitrophenol, 5.0×10^?9 M for o‐nitrophenol, 5.0×10^?9 M for m‐nitrophenol, 2.0×10^?8 M for p‐nitrobenzoic acid and 8.0×10^?9 M for nitrobenzene respectively. The BMIMPF₆‐SWNT/GCE is applied to the determination of NACs in lake water.     

Voltammetric Determination of Xanthine with a Single‐Walled Carbon Nanotube‐Ionic Liquid Paste Modified Glassy Carbon Electrode

Single‐walled carbon nanotube (SWNT) and room temperature ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexaflourophosphate, BMIMPF₆) were used to fabricate paste modified glassy electrode (GCE). It was found that the electrode showed sensitive voltammetric response to xanthine (Xt). The detection limit was 2.0×10^?9 M and the linear range was 5.0×10^?9 to 5.0×10^?6 M. The electrode also displayed good selectivity and repeatability. In the presence of uric acid (UA) and hypoxanthine (Hx) the response of Xt kept almost unchanged. Thus this electrode could find application in the determination of Xt in some real samples. The analytical performance of the BMIMPF₆‐SWNT/GCE was demonstrated for the determination of Xt in human serum and urine samples.     

Multiwall Carbon Nanotube‐Ionic Liquid Modified Paste Electrode as an Efficient Sensor for the Determination of Diazepam and Oxazepam in Real Samples

A carbon‐based electrode using multiwall carbon nanotube as a modifier and room temperature ionic liquid as a binder has been applied for the determination of diazepam (DZP) and oxazepam (OZP) in real samples including serum, urine and tablets. Square wave voltammetry as an appropriate electrochemical technique was applied to achieve improved limits of detection and higher sensitivities. The electrochemical studies were investigated under various experimental conditions such as pH, buffer concentration, ionic strength, deposition potential, deposition time and scan rate to achieve higher sensitivities. Linear concentration ranges for DZP and OZP were 0.02–0.76 mg L^?1 and 0.05–1.90 mg L^?1 with the detection limits of 4.1 µg L^?1 and 5.8 µg L^?1, respectively. The proposed method was successfully applied for the analysis of commercially available tablets as well as serum and urine samples and satisfactory results were obtained.     

Room-Temperature Ionic Liquid and Multi-Walled Carbon Nanotube Composite Modified Carbon-Ceramic Electrode as a Sensitive Voltammetric Sensor for Indomethacin

The electrochemical behavior of indomethacin on the surface of a carbon-ceramic electrode modified with multi-walled carbon nanotubes and an ionic liquid composite film is reported. The results show that the nano-structured film exhibited excellent enhancement effects on the electrochemical oxidation of indomethacin. The developed sensor presented a linear response to indomethacin over the concentration range from 1 to 50 µM with a detection limit of 0.26 µM. The proposed modified electrode was employed for the determination of indomethacin in biological and pharmaceutical samples using differential pulse voltammetry.     

Ionic Liquid‐Carbon Nanotube Modified Screen‐Printed Electrodes and Their Potential for Adsorptive Stripping Voltammetry

Compared with paraffin oil, the use of ionic liquids as a binder in carbon paste type electrodes was shown to greatly enhance the accumulation of analytes, as illustrated with 17α‐ethynylestradiol as a model. The ionic “liquid” n‐octyl‐pyridinium hexafluorophosphate [C₈py][PF₆] was most efficient among several ionic liquids investigated. Such preconcentration allowed a [C₈py][PF₆]‐multiwalled carbon nanotubes (MWCNTs) (95 : 5 w/w) composite electrode to be useful for adsorptive stripping voltammetry. Screen‐printed electrodes modified with [C₈py][PF₆]‐MWCNTs were developed and were able to achieve high sensitivity during adsorptive stripping voltammetric measurements under optimised conditions.     

Ionic Liquid‐Hemoglobin‐Carbon Paste Composite Bioelectrode and Its Electrocatalytic Activity

A new carbon ionic liquid paste bioelectrode was fabricated by mixing hemoglobin (Hb) with graphite powder, ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF₄) and liquid paraffin homogeneously. Nafion film was cast on the electrode surface to improve the stability of bioelectrode. Direct electrochemistry of Hb in the bioelectrode was carefully investigated. Cyclic voltammetric results indicated that a pair of well‐defined and quasi‐reversible electrochemical responses appeared in pH 7.0 phosphate buffer solution (PBS), indicating that direct electron transfer of Hb was realized in the modified electrode. The formal potential (E^0′) was calculated as ?0.316 V (vs. SCE), which was the typical characteristic of the electrochemical reaction of heme Fe(III)/Fe(II) redox couple. Based on the cyclic voltammetric results the electrochemical parameters of the electrode reaction were calculated. This bioelectrode showed high electrocatalytic activity towards the reduction of trichloroacetic acid (TCA) with good stability and reproducibility.     

Simultaneous Voltammetric Determination of Theophylline and Guaifenesin Using a Multiwalled Carbon Nanotube‐Ionic Liquid Modified Glassy Carbon Electrode

A glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNTs) and a hydrophobic ionic liquid (IL), was used for the simultaneous voltammetric determination of theophylline (TP) and guaifenesin (GF). The results showed that the oxidations of TP and GF were facilitated at modified electrode and peak‐to‐peak separation at MWCNT? IL/GCE (252 mV) was larger than that observed at unmodified GCE (165 mV). Voltammetric signals for TP and GF exhibited linear ranges of 0.5 to 98.0 µM (R²>0.99) and 1.5 to 480.0 µM (R²>0.99), respectively. The method was used to estimate TP and GF contents in some real samples.     

Electrocatalytic Oxidation and Determination of Nitrite at Multi‐walled Carbon Nanotubes Modified Carbon Ceramic Electrode

In the present work, the electrochemical oxidation of nitrite on carbon ceramic electrode (CCE) modified with multi‐walled carbon nanotubes (MWCNTs) was investigated. The modified electrode exhibited catalytic activity toward the electrooxidation of nitrite. Experimental parameters such as solution pH, scan rate, concentration of nitrite and nanotubes amount were studied. It was shown nitrite can be determined by differential pulse voltammetry (DPV) and hydrodynamic amperometry (HA) using the modified electrode. Under the optimized conditions the calibration plots are linear in the concentration ranges of 15‐220 and 50‐3000 μM with limit of detections of 4.74 and 35.8 μM for DPV and HA, respectively. The modified electrode was successfully applied for analysis of nitrite in spinach sample. The results were favorbly compared to those obtained by UV‐Visible spectrophotometric method. The results of the analysis suggest that the proposed method has promise for the routine determination of nitrite in the examined products.     

Platinum Nanoparticles Decorated Multiwalled Carbon Nanotubes – Ionic Liquid Composite Film Coated Glassy Carbon Electrodes for Sensitive Determination of Theophylline

Platinum nanoparticles (Pt_nano) decorated multiwalled carbon nanotubes (MWCNTs)–1‐octyl‐3‐methylimidazolium hexafluorophosphate ([omim][PF₆]) composite material (MWCNTs‐Pt_nano‐[omim][PF₆]) was fabricated and characterized for the first time. In the presence of [omim][PF₆], more Pt_nano could deposit on MWCNTs. The average diameter of the deposited Pt_nano was about 5 nm. The composite material film coated glassy carbon electrode (GCE) exhibited sensitive voltammetric response to theophylline (TP). Under the optimized conditions (i.e., preconcentration for 2 minutes on open circuit in 0.10 M pH 3.0 phosphate buffer), the anodic peak current of TP at about 1.1 V (vs. SCE) was linear to TP concentration over the range of 1.0×10^?8–1.0×10^?5 M. The detection limit was estimated to be 8.0×10^?9 M. The modified electrode was successfully applied to the determination of TP in medicine tablet and green tea. In addition, the voltammetric responses of hypoxanthine (HX), xanthine (Xan) and uric acid (UA) on the MWCNTs‐Pt_nano‐[omim][PF₆]/GCE were also discussed.     

Voltammetric Determination of L‐Dopa on Poly(3,4‐ethylenedioxythiophene)‐Single‐Walled Carbon Nanotube Composite Modified Microelectrodes

In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4‐)ethylenedioxythiophene and single‐walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4‐dihydroxy‐L ‐phenylalaines (L ‐dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film‐coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10 V s^?1, also gave rise to two well‐resolved oxidation peaks for L ‐dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L ‐dopa in the concentration range between 0.1 to 20 μM with a detection limit of 100 nM.     

用碳糊修饰电极测定氨基酸的伏安法研究

用10％氧化铝的修饰碳糊电极研究了测定组氨酸的伏安法。 在0.05 mol/L 丁二酸－硼砂（pH=3.5)底液中在－0.6 V出现一还原峰, 结合2.5次微分技术测定组氨酸, 在3.20 ～130 μmol/L 浓度范围内有良好的线性关系, 相对标准偏差为3.4％, 检出限为0.4 μmol/L。 检测灵敏度比文献报道有较大的提高。 文中还讨论了电极过程。     

Development of a Carbon Nanotube Modified Ionic Liquid Electrode for the Voltammetric Determination of Methyldopa Levels in Urine

A glassy carbon electrode was modified with carbon nanotubes and the ionic liquid N‐butyl pyridinium trifluoromethyl methanesulfonate for the determination of methyldopa in urine samples. Methyldopa exhibited a well‐defined anodic signal over a broad pH range of 2–10 and the peak current increased approximately 100 fold over that of the unmodified electrode. Accordingly, a novel method for the determination of methyldopa was proposed using differential pulse voltammetry. The peak current was linear over a methyldopa concentration range from 21 to 2111 ng mL^?1 with a LOD of 6.9 ng mL^?1 and a LOQ of 7.4 ng mL^?1. The method was applied to determine the excretion profile of methyldopa in urine without sample pretreatment.     

Determination of Trace Lead and Cadmium in Water Samples by Anodic Stripping Voltammetry with a Nafion‐Ionic Liquid‐Coated Bismuth Film Electrode

A new chemically modified bismuth film electrode coated with an ionic liquid [(1‐ethyl‐3‐methylimidazolium tetracyanoborate (EMIM TCB)] and Nafion was developed for the simultaneous determination Pb²⁺ and Cd²⁺ by anodic stripping voltammetry. Compared with conventional bismuth film electrodes, this electrode exhibited greatly improved electrochemical activity for Pb²⁺ and Cd²⁺ detection due to the unique properties of Nafion polymer and ionic liquid. The key experimental parameters related to the fabrication of the electrode and the voltammetric measurements were optimized on the basis of the stripping signals, where the peak currents increased linearly with the metal concentrations in a range of 10–120 µg L^?1 with a detect limit of 0.2 µg L^?1 for Pb²⁺, and 0.5 µg L^?1 for Cd²⁺ for 120s deposition. High reproducibility was indicated from the relative standard deviations (1.9 and 2.5 %) for nine repetitive measurements of 20 µg L^?1 Pb²⁺ and Cd²⁺, respectively. In addition, the surface characteristics of the modified BiFE were investigated by scanning electron microscopy (SEM), and results showed that fibril‐like bismuth nanostructures were formed on the porous Nafion polymer matrix. Finally, the developed electrode was applied to determine Pb²⁺ and Cd²⁺ in water samples, indicating that this electrode was sensitive, reliable and effective for the simultaneous determination of Pb²⁺ and Cd²⁺.     

Electrocatalytic Oxidation of Tryptophan at Gold Nanoparticle‐Modified Carbon Ionic Liquid Electrode

The electrochemical behavior of tryptophan was studied at the carbon ionic liquid electrode (CILE) modified with gold nanoparticle (GNP). This electrode has a stable and excellent response toward tryptophan. Under optimum experimental conditions, the calibration curve was linear in the tryptophan concentration range of 5 to 900 µM with an excellent correlation coefficient (0.995). The experimental limit of detection was 4 µM. Contrary to many other electrodes, the oxidation of tryptophan on GNP/CILE does not result in electrode fouling. GNP/CILE has been effectively applied to the determination of tryptophan in composite amino acid injection.     

Electrochemical Behavior and Voltammetric Determination of Diclofenac at a Multi-Walled Carbon Nanotube-Ionic Liquid Composite Modified Carbon Ceramic Electrode

This work describes the electrochemical behavior of diclofenac on the surface of a carbonceramic electrode (CCE) modified with multi-walled carbon nanotubes (MWCNT) and an ionic liquid (IL) composite. The MWCNT-IL composite showed an enhancement effect in the electro-oxidation of diclofenac with respect to a bare carbon ceramic electrode. Based on the experimental outcomes, a possible mechanism for the electro-oxidation of diclofenac is proposed and discussed. Under the optimized experimental conditions, the MWCNT-IL CCE showed a linear response to diclofenac over the concentration range 50 nM–20 µM with a detection limit of 27 nM. The developed diclofenac sensor showed good stability, sensitivity, and reproducibility in the measurement of diclofenac in human blood plasma samples.     

肾上腺素在碳纳米管-离子液体糊修饰电极上的伏安行为

研究了肾上腺素(EP)在多壁碳纳米管与离子液体糊修饰玻碳电极上的电化学行为,发现该修饰电极对肾上腺素的氧化具有良好的催化促进作用。在pH=7.0的磷酸盐缓冲溶液中,肾上腺素在0.13 V产生的阳极峰比相应的多壁碳纳米管修饰电极上的峰负移约40 mV,峰电流则显著增大。优化了实验条件,在选定的条件下,EP的浓度在5.0×10-7~2.0×10-5mol.L-1范围内与阳极峰电流呈线性关系,相关系数为0.998,方法检出限为1.0×10-7mol.L-1。利用该方法对注射液中肾上腺素的含量进行了测定,其回收率达98.1%~100.5%。此外,还对有关物质的干扰及电极反应参数等进行了测试。     

Differential Pulse Voltammetric Determination of Montelukast in Tablets and Human Plasma by Using Chitosan Modified Carbon Paste Electrode

Electrochemical reduction and determination of montelukast (MKS) was studied in methanol – 0.1 M HCl solution (1 : 1, v/v) by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at chitosan modified carbon paste electrode. The linear range was 1.70×10^?7–1.83×10^?5 M for DPV analysis. Limit of detection (LOD) and limit of quantification (LOQ) were 5.32×10^?8 M and 1.61×10^?7 M, respectively. The developed method was successfully applied to the determination of MKS in tablets and spiked human plasma. The results obtained were in good agreement with those obtained using a reported spectrofluorimetric technique.     

碳纳米管膜修饰玻碳陶瓷复合材料电极对亚硝酸盐的电催化还原

制备了碳纳米管膜修饰的玻碳陶瓷复合材料电极,研究了亚硝酸盐在修饰电极上的电化学行为,碳纳米管膜对亚硝酸盐的还原展现了良好的催化活性。评估了溶液pH值和施加电位对亚硝酸盐电流响应的影响,并初步探讨了催化机理。在优化的实验条件下,该修饰电极对亚硝酸盐的测定线性范围为5.0×10-5~3×10-3mol/L;检出限(3σ)为2×10-5mol/L。     

Silver‐Palladium Nanoalloys Modified Carbon Ionic Liquid Electrode with Enhanced Electrocatalytic Activity Towards Formaldehyde Oxidation

Electrocatalysis of the oxidation of formaldehyde on silver‐palladium‐modified carbon ionic liquid electrode (AgPd/CILE) was investigated in 0.1 M NaOH. The electrochemical performance of the AgPd/CILE was compared with those of Pd/CILE and Ag/CILE. Ag plays an important role in the catalytic performance of AgPd nanocatalyst and yields an excellent antifouling effect. Amperometric measurements showed that AgPd/CILE is a promising sensor for the detection of formaldehyde in the range of 10.0 µM–70.0 mM with a sensitivity of 240.6 µA mM^?1 cm^?2 and a detection limit of 2 µM. The method is free from interference of methanol, ethanol and formic acid.     

Improved Voltammetric Response of L‐Tyrosine on Multiwalled Carbon Nanotubes‐Ionic Liquid Composite Coated Glassy Electrodes in the Presence of Cupric Ion

L ‐Tyrosine can exhibit a small anodic peak on multiwalled carbon nanotubes (MWCNTs) coated glassy carbon electrodes (GCE). At pH 5.5 its peak potential is 0.70 V (vs. SCE). When an ionic liquid (i.e., 1‐octyl‐3‐methylimidazolium hexafluorophosphate, [omim][PF₆]) is introduced on the MWCNT coat, the peak becomes bigger. Furthermore, in the presence of Cu²⁺ ion the anodic peak of L ‐tyrosine increases further due to the formation of Cu²⁺‐L ‐tyrosine complex, while the peak potential keeps unchanged. Therefore, a sensitive voltammetry based on the oxidation of Cu²⁺‐L ‐tyrosine complex on MWCNTs‐[omim][PF₆] composite coated electrode is developed for L ‐tyrosine. Under the optimized conditions, the anodic peak current is linear to L ‐tyrosine concentration in the range of 1×10^?8–5×10^?6 M, and the detection limit is 8×10^?9 M. The modified electrode shows good reproducibility and stability. In addition, the voltammetric behavior of other amino acids is explored. It is found that among them tryptophan (Trp) and histidine (His) can also produce sensitive anodic peak under same experimental conditions, and their detection limits are 4×10^?9 M and 4×10^?6 M, respectively.