Voltammetric determination of chlorogenic acid in pharmaceutical products using poly(aminosulfonic acid) modified glassy carbon electrode

In this work, a poly(aminosulfonic acid) modified glassy carbon electrode was fabricated and the electrochemical behavior of chlorogenic acid (CGA) was studied by cyclic voltammetry. Compared with a bare glassy carbon electrode, the modified electrode exhibits excellent catalytic effect on the electrochemical redox of CGA. Utilizing this catalytic effect, a sensitive and selective electrochemical method for the determination of CGA was developed. The analytical parameters were optimized. Under the optimized conditions, the oxidation peak current is linearly proportional to the concentration of CGA in the range from 4.00 × 10⁻⁷ to 1.20 × 10⁻⁵ mol/L and the detection limit is 4.00 × 10⁻⁸ mol/L. Further, the performance of the proposed method has been validated in terms of linearity (r = 0.9995), recovery (96.3–102.8%), reproducibility (RSD ＜ 4.0%, n = 6) and robustness. The developed method has been successfully applied for the determination of CGA in a variety of pharmaceutical products.     

Electroanalytical study of nifedipine using activated glassy carbon electrode

The electrochemical properties of nifedipine have been investigated in aqueous solution by linear sweep and cyclic voltammetry. The method is based both on the reduction and on the oxidation of the drug at a glassy carbon electrode activated by applying a new pre-treatment. The voltammograms of nifedipine on pH, concentration and scan rate have been carefully examined. Both the electroreduction and electrooxidation of nifedipine allow its determination at pH 1.5 in the concentration range of 2×10⁻⁵–6×10⁻⁴ M and 8×10⁻⁵–1×10⁻³ M, respectively. The method has been applied to commercial samples (tablets and capsules).     

Electrochemical behavior of paclitaxel and its determination at glassy carbon electrode

The electrochemical behavior of paclitaxel drug was studied at a glassy carbon electrode in phosphate buffer solutions using cyclic and differential-pulse voltammetric techniques. The oxidation process was shown to be irreversible over the pH range (3.0–10.4) and was diffusion controlled. Effects of anodic peak potential (E_p), anodic peak current (I_pa), scan rate, pH, heterogeneous rate constant (k⁰), etc have been discussed. A possible electro-oxidation mechanism was proposed. An analytical method was developed for the determination of paclitaxel in phosphate buffer solution at pH = 7.0 as a supporting electrolyte. The anodic peak current varied linearly with paclitaxel concentration in the range 1.0 × 10⁻⁶ M to 1.0 × 10⁻⁵ M with a limit of detection (LOD) of 1.23 × 10⁻⁸ M and limit of quantification (LOQ) of 4.10 × 10⁻⁸ M. The proposed method was successfully applied to the determination of paclitaxel in pure and real samples.     

Simultaneous determination of ranitidine and metronidazole in pharmaceutical formulations at poly(chromotrope 2B) modified activated glassy carbon electrodes

A simple and sensitive electrochemical method for the simultaneous and quantitative detection of ranitidine (RT) and metronidazole (MT) was developed, based on a poly(chromotrope 2B) modified activated glassy carbon electrode (PCHAGCE). The PCHAGCE showed excellent electrocatalytic activity toward the reduction of both RT and MT in 0.1 mol/L phosphate buffer solution (pH 6.0). The peak-to-peak separations for the simultaneous detection of RT and MT between the two reduction waves in cyclic voltammetry were increased significantly from ∼0.1 V at activated GCE, to ∼0.55 V at PCHAGCE. By differential pulse voltammetry techniques, the reduction peak currents of RT and MT were both linear over the range of 1.0 × 10⁻⁵–4.0 × 10⁻⁴ mol/L. The detection limits (S/N = 3) were 5.4 × 10⁻⁷ mol/L and 3.3 × 10⁻⁷ mol/L for RT and MT, respectively. The modified electrode was successfully applied to the determination of RT and MT in pharmaceutical preparations and human serum as real samples with stable and reliable recovery data.     

Electroanalysis of trimethoprim on metalloporphyrin incorporated glassy carbon electrode

Trimethoprim (TMP) is a bacteriostatic antibiotic mainly used in the prophylaxis and treatment of urinary tract infections. It belongs to the class of chemotherapeutic agents known as dihydrofolate reductase inhibitors. Its use is associated with idiosyncratic reactions, including liver toxicity and agranulocytosis. In order to determine TMP electrochemically, a metalloporphyrin modified glassy carbon electrode was prepared by coating [5,10,15,20‐ tetrakis(4‐methoxyphenyl) porphyrinato]Mn (III)chloride (TMOPPMn(III)Cl) solution on the surface of the electrode. The electrochemical behaviour of TMP in Phosphate buffer solution (PBS) on TMOPPMn(III)Cl modified glassy carbon electrode (TMOPPMn(III)Cl/GCE) was explored using differential pulse voltammetry (DPV). The voltammograms showed enhanced oxidation response at the TMOPPMn (III)Cl/GCE with respect to the bare GCE for TMP, attributable to the electrocatalytic activity of TMOPPMn(III)Cl. Electrochemical parameters of the oxidation of TMP on the modified electrode were analyzed. The electro‐oxidation of TMP was found to be irreversible, pH dependent and adsorption controlled on the modified electrode. It is found that the oxidation peak current is proportional to the concentration of TMP over the range 6 × 10^?8 ? 1 × 10^?6 M with a very low detection limit of 3 × 10^?9 M at 2 min open circuit accumulation. The repeatability expressed as relative standard deviation (RSD) for n = 9 was 3.2% and the operational stability was found to be 20 days. Another striking feature is that equimolar concentration of sulfamethoxazole did not interfere in the determination of TMP. Applicability to assay the drug in urine and tablet samples has also been studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical DNA nano-biosensor for the study of spermidine–DNA interaction

An electrochemical DNA nano-biosensor is prepared by immobilization of double stranded DNA (dsDNA) onto a mixed self-assembled monolayer (SAM) composed of azide- and hydroxyl-terminated thiols. The SAMs- and dsDNA-modified gold electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The interaction of spermidine with DNA was studied by differential pulse voltammetry at the DNA-modified electrode. The decrease in the guanine oxidation peak current was used to study the interaction. The binding constant (K), obtained by differential pulse voltammetry, was 1.85 × 10⁵ M⁻¹. A linear dependence of the guanine peak currents was observed in the range of 1.6–70.4 μM spermidine, with a detection limit of 0.72 μM and r = 0.994 by using differential pulse voltammetry.     

磺胺甲噁唑在多壁碳纳米管-Nafion修饰电极上的电催化氧化及电分析方法

运用循环伏安法(CV)、计时库仑法(CC)、计时电流法(CA)、线性扫描伏安法(LSV)及电流-时间曲线研究了磺胺甲噁唑(SMZ)在玻碳电极(GCE)及碳纳米管-Nafion修饰电极(MWCNTs-Nafion/GCE)上的电化学行为，电化学动力学性质以及电分析方法。研究结果表明，与GCE相比，SMZ在MWCNTs-Nafion/GCE上氧化峰电位负移140 mV，氧化峰电流明显增大约6倍，表明MWCNTs-Nafion/GCE对SMZ电化学氧化具有良好的催化作用。在扫描速度10～1 000 mV·s^-1时其氧化峰电流与扫描速度平方根(ν^1/2)呈良好的线性关系，表明SMZ在GCE及MWCNTs-Nafion/GCE上的伏安行为是受扩散控制的电化学过程。研究了SMZ在GCE及MWCNTs-Nafion/GCE上氧化峰电流与浓度分别在5.0×10^-5～2.5×10^-3和1.0×10^-5～6.0×10^-3 mol·L^-1呈良好线性关系，检测限分别为1.0×10^-5和5.0×10^-7 mol·L^-1。RSD在0.85%～1.98%，加样回收率在98%～101.2%。建立的SMZ含量的电化学测定方法简便快捷，测定结果令人满意。     

Electrochemical reduction of metronidazole at activated glassy carbon electrode and its determination in pharmaceutical dosage forms

A voltammetric method has been developed for the determination of metronidazole in dosage forms. The method is based on the electrochemical reduction of the drug at a glassy carbon electrode activated by applying a new pretreatment. The influence of pH, concentration, scan rate and presence of organic solvent and surfactant has been studied. The current is proportional to the concentration and permits the drug to be determined in the concentration range 2×10⁻⁶–6×10⁻⁴ M in Britton-Robinson buffer (pH 10). Furthermore, results obtained by the proposed method have been compared with USP XXIII procedure which involves a HPLC method.     

Differential pulse voltammetric determination and catalytic oxidation of sulfamethoxazole using [5,10,15,20‐ tetrakis (3‐methoxy‐4‐hydroxy phenyl) porphyrinato] Cu (II) modified carbon paste sensor

Sulfamethoxazole (SM) is a sulfonamide bacteriostatic antibiotic. Its primary activity is against susceptible forms of streptococcus, staphylococcus aureus, escherichia coli, haemophilus influenzae, and oral anaerobes. It is commonly used to treat urinary tract infections. In addition it can be used as an alternative to amoxicillin‐based antibiotics to treat sinusitis. It can also be used to treat toxoplasmosis. In the present work, a metalloporphyrin modified carbon paste sensor was fabricated and the electrochemical behaviour of SM was studied using differential pulse voltammetry (DPV). Cu (II) complex of 5,10,15,20‐ tetrakis (3‐methoxy‐4‐hydroxy phenyl) porphyrin (TMHPP Cu (II)) was used as the active material. Compared with bare carbon paste electrode (CPE), the TMHPP Cu (II) modified CPE exhibits excellent enhancement effect on the electrochemical oxidation of SM. A well‐defined oxidation peak of SM occurs at ? 140 mV in 0.1M phosphate buffer solution (PBS) of pH 6. All the experimental parameters were optimized and it was found that under optimum conditions the oxidation peak current was linear to the concentration of SM in the range of 1.0 × 10^?2–1.0 × 10^?8 M with a detection limit of 1.5 × 10^?9M. The developed sensor has been successfully applied for the determination of SM in pharmaceutical formulations and urine sample. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of terbutaline based on oxidation by voltammetry

A voltammetric study of the oxidation of terbutaline has been carried out at an activated glassy carbon electrode. The compound was oxidized irreversibly at high positive potential. The response was evaluated with respect to pH, scan rate, nature of the buffer and other variables. The peak current, at about 0.8 V (versus a saturated calomel electrode), was proportional to the terbutaline concentration in the range of 8×10⁻⁶–8×10⁻⁴ M in phosphate buffer pH 6.0. This method was applied, without any interferences from the excipients, to determine the drug in a tablet dosage form.     

Potentiometric monitoring of cobalt in beer sample by solid contact ion selective electrode

A new solid contact cobalt selective electrode was constructed with 4-tert-butylthiacalix[4]arene as ionophore. The best performance was observed with the membrane having an ionophore/polyvinyl chloride/sodium tetraphenylborate/nitrophenyl octyl ether ratio of 3.5:33:1.5:62 (w/w; mg). The electrode, under steady-state conditions, exhibited a working concentration range of 1 × 10⁻¹ – 1 × 10⁻⁶ mol/L with a near-Nernstian slope of 25.3 mV/decade and a detection limit of 3.5 × 10⁻⁷ mol/L. The electrode had a very short response time (<10 seconds) and good reproducibility at a working pH range of 4.0–6.5. The electrode was used for 4 months without any significant change in its sensitivity. The potentiometric performance of the electrode in partially nonaqueous medium [up to 20 % (v/v) alcohol] was found satisfactory. The performance of the prepared electrode for the analysis of beer samples using direct potentiometric method is very encouraging.     

Voltammetric determination of sulfamethoxazole at a multiwalled carbon nanotube modified glassy carbon sensor and its application studies

Sulfamethoxazole (SMX) is an anti‐bacterial sulfonamide. It prevents the formation of dihydrofolic acid, a compound that bacteria need in order to survive. The present work details the voltammetric analysis of SMX at a multiwalled carbon nanotube (MWCNT)‐Nafion modified glassy carbon electrode (GCE). Sulfamethoxazole gives a well defined oxidation peak at 0.74 V in 0.1 M phosphate buffer solution (PBS) of pH 8.0. The experimental parameters such as the amount of MWCNT‐Nafion suspension, the pH of the supporting electrolyte and scan rate were optimized and a direct electrochemical method for the determination of SMX was developed. Under optimum conditions the oxidation peak current is linear to the concentration of SMX in the range 1 × 10^?2 ? 5 × 10^?5 M with a detection limit of 1 × 10^?5 M. The MWCNT/GCE showed good stability, selectivity and was successfully used to quantify SMX in pharmaceutical formulations and urine sample. Copyright © 2009 John Wiley & Sons, Ltd.     

美洛昔康的吸附伏安特性

目的　研究美洛昔康(meloxicam,简称MLX)的电化学行为和电极反应机理,拟定了测定MLX的吸附伏安法。方法　用单扫示波极谱法、循环伏安法和脉冲极谱法等多种技术进行研究。结果　在HAc-NaAc(pH 4.76)底液中,MLX在汞电极上有一线性扫描还原峰,峰电位E^p=-1.19 V(vs Ag/AgCl),该峰有明显的吸附性。吸附粒子为MLX中性分子,测得MLX在汞电极上的饱和吸附量为1.53×10^-10 mol.cm^-2,每个MLX分子所占电极面积为1.08 nm²,MLX在悬汞电极上的吸附符合Frumkin等温式。测得吸附系数β=1.65×10⁶,电子转移数(n)为2,不可逆吸附的电子转移系数(α)为0.84,表面电极反应的速率常数k_s=0.19.s^-1。建立了吸附伏安法测定MLX的最佳条件,检出限为1.0×10^-9 mol.L^-1。结论　证实该体系为具有吸附性的不可逆过程。     

甲氧苄氨嘧啶(TMP)的电分析化学研究及其在药物分析中的应用

本文用微分脉冲极谱法和循环伏安法研究了甲氧苄氨嘧啶(TMP)的电化学行为,选择了最佳的测定条件,TMP的检出限可达2.0×10^-7mol/L,方法灵敏度较高,并研制了TMP-PVC膜离子选择性电极,试验了该电极的各种特性及Nernst响应范围。本法应用于制剂中TMP的测定,选择性好,干扰少,毋须分离,方法简便快速。选择电极在人尿和血清的介质中测定,也能获得良好的结果。     

抗痫灵的电化学行为及吸附伏安法研究

抗痫灵在0.20 mol/L H₂SO₄底液、富集电位-0.70 V(vs Ag/AgCl)、扫速100 mV/s等条件下,用吸附伏安法得一灵敏的还原峰,峰电位-0.94 V,峰电流与抗痫灵浓度在3.0×10^-9～1.0×10^-8mol/L(富集时间t_ac=120 s),1.0×10^-8～7.0×10^-8mol/L(t_ac=90 s),7.0×10^-8～7.0×10^-7mol/L(t_ac=60 s),7.0×10^-7～3.0×10^-6mol/L(t_ac=45 s)范围内成线性关系,检测限可达1.0×10^-9mol/L,并用于片剂及病人尿样的测定,得到满意的结果。以多种电化学手段研究抗痫灵的电化学行为及反应机理。实验表明属不可逆吸附波。测得扩散系数D为7.7×10^-6cm²/s,电极反应速率常数k₁为1.5×10^-3cm/s,电极反应电子数n为2,电子转移系数α=0.52。抗痫灵的还原基团为分子中碳碳双键。     

Electrochemical behavior and determination of rutin on a pyridinium-based ionic liquid modified carbon paste electrode

In this paper the electrochemical behavior of rutin on a pyridinium-typed ionic liquid modified carbon paste electrode (IL-CPE) was investigated and further used for rutin sample determination. The IL-CPE showed strong electrocatalytic effects to the oxidation of rutin. In phosphate buffer solution (PBS, pH 2.5; 0.1 M) a pair of well-defined cyclic voltammetric redox peaks of rutin appeared with the redox peak located at 512 mV (Epa) and 448 mV (Epc) (vs. SCE), respectively. The redox peak current was increased about 27.5 times more than that on traditional carbon paste electrode (CPE). The electrochemical parameters of rutin on the IL-CPE were calculated with the results of the charge transfer coefficient (α), the number of electron transfer (n) and the electrode reaction rate constant (k_s) as 0.53, 1.80 and 2.39 s⁻¹, respectively. The cathodic peak currents increased linearly with the concentration of rutin in the range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with the detection limit as 3.58 × 10⁻⁷ M (3σ). The relative standard deviation (RSD) of 10 successive detection of 5.0 × 10⁻⁵ M rutin was 4.2%. The method was successfully applied to the determination of rutin content in tablets samples with good recovery. The modified electrode showed good stability and reproducibility without the influence of the coexisting substances.     

A novel poly (glycine) biosensor towards the detection of indigo carmine: A voltammetric study

The electrochemical behavior of indigo carmine (IC) at poly (glycine) modified carbon paste electrode (PGMCPE) was investigated by cyclic and differential pulse voltammetry. The oxidation peak of IC was observed in phosphate buffer of pH 6.5. The influence of different pH, scan rate, and concentration were analyzed. The probable reaction mechanism involved in the oxidation of IC was also proposed. Results showed that PGMCPE a remarkable electrocatalytic activity for the oxidation of IC under optimal conditions. The electrocatalytic response of the sensor was proportional to the IC concentration in the range of (2 × 10⁻⁶–1 × 10⁻⁵ M) and (1.5 × 10⁻⁵–6 × 10⁻⁵ M) with a limit of detection 11 × 10⁻⁸ M and limit of quantification 3.6 × 10⁻⁷ M. The modified electrode demonstrated many advantages such as simple preparation, high sensitivity, low detection of limit, excellent catalytic activity, short response time, and remarkable antifouling property toward IC and its oxidation product.     

博莱霉素在Ni/GC离子注入修饰电极上的电化学行为及其应用

目的：研究博莱霉素在Ni/GC离子注入修饰电极上的电化学行为及其应用。方法：博莱霉素在0.1 mol.L^-1 HAc-NaAc (pH 4.62)缓冲溶液中,用离子注入镍的修饰玻碳电极为工作电极进行伏安测定。结果：得到一良好的还原峰,峰电位Ep=-1.16 V (vs.SCE)。峰电流与博莱霉素浓度在1.0×10^-6～1.4×10^-5 mol.L^-1范围内成线性关系。检出限为8.0×10^-7 mol.L^-1。并用于尿样的测定,得到满意的结果。用线性扫描和循环伏安法研究了体系的电化学行为。用奥歇电子能谱(AES)和光电子能谱(XPS)等表面分析技术检测了注入电极表面的元素组成、价态和深度分布,对离子注入电极的催化性质进行了探讨。结论：体系属两电子还原的不可逆过程。     

Electrochemical behavior and square wave voltammetric determination of doxorubicin hydrochloride

The electrochemical behavior of doxorubicin hydrochloride was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). From CV and SWV studies of doxorubicin hydrochloride in the acetate buffers of various pH values, it was found that protons were involved in the reduction of the antibiotic at the H+/e- ratio at one (deltaEp/pH = -53 approximately -61 mV at 23 degrees C), proposing the electrochemical reduction of the quinone moiety in its anthraquinone aglycone. Its electrochemical behavior was pseudo-reversible in the acetate buffer of pH 3.5 by exhibiting the well-defined single cathodic and anodic waves and the ratio of Ip(a)/Ip(c) at approximately one over the scan rates of 10 approximately 100 mV/s. Fast and sensitive SWV showing a single peak of doxorubicin has been applied for its quantitative analysis using an acetate buffer of pH 3.5. A linearity was obtained when the peak currents (Ip) were plotted against concentrations of doxorubicin in the range of 5.0 x 10(-7) M approximately 1.0 x 10(-5) M with a detection limit of 1.0 x 10(-7) M.     

阿霉素在Co/GC离子注入修饰超微电极上的电化学行为及其应用

目的：研究阿霉素在Co/GC离子注入修饰超微电极上的电化学行为。方法：阿霉素在0.1 mol.L^-1 HAc-NaAc (pH 4.73)缓冲溶液中,用Co/GC离子注入修饰超微电极进行伏安测定。结果：得到一良好的还原峰,峰电位Ep=-0.520 V(vs.SCE)。峰电流与阿霉素的浓度在1.0×10-7～2.0×10^-6 mol.L^-1和2.0×10^-6～1.0×10^-5 mol.L^-1范围内成线性关系。检出限为3.0×10^-8 mol.L^-1。用于病人尿样测定,得到满意的结果,回收率为96.3%～106.1%。用线性扫描和循环伏安法研究了体系的电化学行为及电极反应机理。结论：实验表明,体系属两电子还原的准可逆吸附过程。