Voltammetric behavior of mammalian tumor cells and bioanalytical applications in cell metabolism

The voltammetric behavior of human mammalian cells was studied by choosing human leukemia cells (HL60) and human erythroleukemia cells (HEL). The voltammetric response of the cells was found having relation with cell metabolic viability in culture course. For example, the fluctuations of peak currents of HL60 were parallel with the nutrients replenished or not, which can reflect cell health state; the voltammetric response of HL60 regulated by the anti-metabolic drug 5F-Uriacil (5F-U) in culture course behaved in a much decreased manner, by which a voltammetric method for evaluating cytotoxicity is proposed. In this paper, the relation between HEL cell metabolism and the activation of receptor Mpl by its ligand TPO was also studied. Moreover, the mechanism of cell voltammetric behavior was discussed.     

Solid Phase Extraction – Voltammetric Coupled Detection of Caffeine in Acetonitrile

Caffeine (CAF) in aqueous solutions was extracted into acetonitrile (MeCN) using solid phase extraction (SPE). The voltammetric detection of CAF in MeCN was performed in a microcentrifuge tube after SPE in order to minimise the required amount of MeCN and reagents used during the analysis. The voltammetric determination of CAF from a range of beverages extracted into MeCN was in good agreement with the results obtained from HPLC measurements on the same samples. The SPE‐coupled voltammetric method gave more accurate results than those obtained via the direct voltammetric detection of CAF in real beverage samples.     

在线小波变换用于伏安分析仪的研制

将在线小波变换应用于伏安信号的在线处理,研制了具有小波变换功能的伏安分析仪。该系统利用在线小波变换对采集到所数据进行实时处理,具有控制灵活,分辨率高,数据处理方便等特点。通过对低浓度Ｃｙ＾２＋和Ｆｅ＾３＋混合样品的阶梯斜坡扫描伏安珠滤噪及定性,定量分析,结果表明可获得满意的分析结果。     

Carbon Paste Electrodes Modified with Graphene Oxides – Comparative Electrochemical Studies of Thioguanine

The voltammetric study of thioguanine (TG) was comparatively investigated on bare, graphene oxide and reduced graphene oxide modified carbon paste electrodes using cyclic (CV) and square wave stripping (SWSV) voltammetric techniques. Depending on the working electrode and pH of supporting electrolyte, characteristic electrochemical behaviour of thioguanine was established and the mechanism of TG oxidation was suggested. Based on the obtained results, the new voltammetric method for TG determination in buffer solutions and pharmaceutical formulation was developed. Atomic force microscopy was used to characterize electrodes surfaces.     

Voltammetric determination of copper in water samples digested by ozone

The applicability of ozone as a digestion agent in voltammetric trace metal analysis of water samples was investigated. It was shown that ozone efficiently destroys dissolved organic matter, causing a significant decrease of the concentration of surface active substances in the sample, thus enabling voltammetric measurements. Ozonolysis times of 30 and 60 min were sufficient for the treatment of river water and biologically treated wastewater samples, depending on their organic load, prior to voltammetric determination of copper using a solid gold electrode.     

Anodic oxidation of etodolac and its square wave and differential pulse voltammetric determination in pharmaceuticals and human serum

A voltammetric study of the oxidation of etodolac has been carried out at the glassy carbon electrode. The electrochemical oxidation of etodolac was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using glassy carbon electrode. Different parameters were tested to optimize the conditions for the determination of etodolac. The dependence of intensities of currents and potentials on pH, concentration, scan rate, nature of the buffer was investigated. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in Britton-Robinson buffer at pH 2.15 for differential pulse and square wave voltammetric techniques. The linear response was obtained in the ranges of 2.10(-6)-8.10(-5) M with a detection limit of 6.8x10(-7) and 6x10(-6)-8x10(-5) M with a detection limit of 1.1x10(-6) M for differential pulse and square wave voltammetric techniques, respectively. Based on this study, simple, rapid, selective and sensitive two voltammetric methods were developed for the determination of the etodolac in tablet dosage form and human serum.     

A New Chemometric Strategy in Electrochemical Method Optimization for the Quantification of Cefdinir in Tablets,Effervescent Tablets and Suspension Samples

A new voltammetric method, based on the use of single‐use pencil graphite electrode, was developed for the quantitative determination of cefdinir by square wave voltammetry. Chemometric optimization strategy was used to select the suitable values for three experimental parameters (pH of the supporting electrolyte, frequency and square wave amplitude) by applying a 3³ full factorial design model. The optimal voltammetric conditions were found to be pH 5.0 for supporting electrolyte (Britton‐Robinson buffer), 43 mV for square wave amplitude and 108 Hz for frequency. Square wave voltammograms of calibration, validation and unknown samples were recorded between 0.0–1400 mV under the optimized voltammetric conditions. Linear regression equation was computed in the linear working range of 0.5–20 μg/mL by using the relationship between the concentration and peak current at 600 mV. The optimized voltammetric method was validated by assessing the analysis results of validation samples. Then the proposed method was applied for the quantitative determination of cefdinir in three different pharmaceutical preparations, namely film‐coated tablets, effervescent tablets and powder for oral suspension. It was concluded that the proposed voltammetric method was suitable for the quantitative analysis of commercial pharmaceutical preparations containing cefdinir.     

Simultaneous determination of three 5-nitroimidazoles in foodstuffs by differential pulse voltammetry and chemometrics

The voltammetric behaviour of three 5-nitroimidazoles,metronidazole,tinidazole and ornidazole,was investigated,and a method was developed for the simultaneous determination of these compounds,based on their reduction at a hanging mercury drop electrode(HMDE) in pH 8.95 buffer with differential pulse voltammetric(DPV) approach.Well defined voltammetric waves with peak potentials of -692,-640 and -652 mV were observed for these compounds,respectively.It is difficult to determine them individually from their mixtures without preseparation,for their voltammetric peaks overlapped seriously,so the chemometrics were used to resolve the overlapped voltammogram and quantify the mixtures.The proposed method was successfully applied to the determination of three 5-nitroimidazoles in milk and honey samples.     

Antilg i1-E曲线上的示波伏安滴定法

i_1-E曲线示波伏安滴定法是一种新的灵敏、准确的滴定分析方法。为进一步提高滴定终点指示的灵敏度,本文在产生i_1-E曲线的线路中,增加了正反馈电路和反对数电路,并提出了Antilg i_1-E曲线上的示波伏安滴定法。用EDTA或EGTA滴定了Ga~(3+)、Cd~(2+)、Zn~(2+)、Ni~(2+)、Co~(2+)等离子,并测定了铜锰合金中的锰,效果较好。     

Voltammetric studies of the effect of Cisplatin-liposome on Hela cells

In this paper, the voltammetric method was used for the first time to study the effect of Cisplatin-liposome on Hela cells. The results showed the voltammetric behavior of Hela cells was irreversible and the peak current had linear relationship with the cell number. With both Cisplatin-liposome concentration and treating time increasing, the peak current decreased. The peak current decreasing was in accordance with the nuclear damage and loss of mitochondrial membrane potential revealed by two-photon laser scanning microscopy and confocal laser scanning microscopy. This voltammetric method may provide a simple way to study the electron-transfer mechanism in drug-treating cells.     

Voltammetric behaviour of heterocyclic systems. Pyridyl-substituted benzimidazoles,benzoxazoles and benzothiazoles

The voltammetric properties, measured at a dropping mercury electrode, have been studied for a series of 18 pyridyl-substituted heterocyclic bases [benzimidazoles, benzoxazoles and benzothiazoles]. The corresponding quarternary salts, obtained by reaction with methyl iodide, were also studied. The reduction potential was found to be dependent on the nature of the benzimidazole, benzoxazole or benzothiazole moiety and on its position on the pyridine ring as well as on the presence of a positive charge. The reversibility of the voltammetric waves was found to be function of the system structure. The effects of proton donors on the voltammetric behaviour of the bases was also investigated.     

Studies on the origin of the voltammetric response of the PC-3 cell suspension

A novel experimental method was developed to study the origin of the voltammetric response of human prostate cancer (PC-3) cell suspension as a model in consideration of the biological characters of living cells. The presence of guanine and xanthine in the cell eluent secreted by the living cells was verified by HPLC assay with a DAD system and chemometric method. Comparative studies of voltammetric behaviors of the PC-3 cell suspension, the PC-3 cell eluent, and the PC-3 cell sediment re-suspension showed that the voltammetric response of the PC-3 cells was given by xanthine and guanine bases in the PC-3 cell eluent, not by the cells. Linear relationship between the peak currents of guanine and xanthine in the cell eluent and the cell concentrations was found. Other factors, such as the cell secretion time and the immersion time of the multiwalled carbon nanotubes modified glassy carbon electrode (MWCNTs-modified GCE) in the cell eluent, also influenced the intensity of the peak currents. The biochemical mechanisms of the voltammetric behavior for the cell suspension were proposed.     

Electrochemical Characteristics and Electrosensing of an Antiviral Drug,Entecavir via Synergic Effect of Graphene Oxide Nanoribbons and Ceria Nanorods

A sensitive electrochemical sensor was fabricated based on ceria‐graphene oxide nanoribbons composite (CeO₂‐GONRs) for an antiviral drug, entecavir (ETV). It was characterized by SEM, EDAX, AFM, IR and Raman spectroscopic techniques. The electrochemical behaviour of ETV was investigated by cyclic voltammetric, differential pulse voltammetric (DPV), linear sweep voltammetric (LSV) and square wave voltammetric (SWV) methods at CeO₂‐GONRs modified glassy carbon electrode. Good linearity was observed between the peak current and concentration of ETV in the range of 0.51 ‐ 100 μM with a detection limit of 0.042 μM in DPV method, 2.1 – 61.1 μM with a detection limit of 0.7 μM in LSV method and 0.1 ‐ 80 μM with a detection limit of 68.1 nM in SWV method. The proposed sensitive DPV method was successfully applied for the determination ETV in tablets and biological samples.     

Voltammetric determination of diethylstilbestrol at carbon paste electrode using cetylpyridine bromide as medium

In this paper, the voltammetric properties of diethylstilbestrol (DES) at the carbon paste electrode were described. The oxidation peak currents of DES increase significantly in the presence of surfactant cetylpyridine bromide (CPB), compared with that in the absence of CPB. Based on this fact, a voltammetric technique for determining DES is proposed. The accumulation potential has no effects on the peak current of the DES. An open-circuit accumulation is carried out. The experimental parameters, such as pH value of buffer, scan rate, and accumulation time were optimized. The interferences of some metal ions and organic compounds have also been studied, and some metal ions almost do not interfere with the determination of DES. Using this voltammetric method, DES in the injection sample was measured. The results show that this voltammetric method is reliable for the practice determination of DES.     

Selective response of dopamine in the presence of ascorbic acid at multi-walled carbon nanotube modified gold electrode

The acid-treated multi-walled carbon nanotubes (MWNTs), which were modified on the surface of gold electrode, offers substantial improvements in voltammetric sensitivity and selectivity towards the determination of dopamine (DA). It can inhibit the voltammetric response of ascorbic acid (AA) while the redox reaction of dopamine is promoted. When a differential pulse voltammetric (DPV) technique was used, the peak separation between DAs and AAs was 244 mV. Based on this, a selective method could be constructed to detect DA in the presence of 1,000 times higher concentration of AA. The effect of various experimental parameters on the voltammetric response of dopamine was investigated. Under the chosen conditions, the peak currents are correspondent linearly to the concentrations of DA in the range of 5 x 10(-7) approximately 4 x 10(-4) mol L(-1) with a limit of detection of 2 x 10(-7) mol L(-1). The proposed method can be applied to detect DA in real samples.     

Challenge Approach of an Inexpensive Electrochemical Sensor for Rapid Selective Determination of two Non‐classical β‐Lactams in Presence of Different Degradants and Interference Substances

An inexpensive stability−indicating anodic voltammetric method for rapid determination of two non‐classical β ‐lactam antibiotics; Meropenem (MP) and Ertapenem (EP) has been developed and validated. The method was based on the enhancement of voltammetric response at a disposable graphite pencil electrode (GPE). Differential pulse voltammetric (DPV) method was developed for quantification of both drugs in B−R buffer solution (pH 2.0) at GPE. The GPE displayed very good voltammetric behavior with significant enhancement of the peak current compared to glassy carbon electrode (GCE). Stress stability studies were performed using 0.5 M of either HCl or NaOH and H₂O₂. Mass and infrared spectroscopy were used for identification of degradants and their pathways were illustrated. Under optimal conditions, the peak currents showed a linear dependence with drug concentrations. The achieved limits of detection (LOD) were 1.23, 2.07 and 1.50 μM for MP and two waves of EP, respectively. The developed voltammetric method was successfully applied for direct determination of MP and EP in drug substances, pharmaceutical vials and in presence of either their corresponding hydrolytic, oxidative‐degradants or interfering substances with no potential interferences. The differential pulse voltammograms were highly advantageous and applicable in QC laboratories for rapid, selective micro‐determination of MP and EP.     

Voltammetric Determination of Nifedipine on Carbon Nanotubes‐Modified Glassy Carbon Electrode: A new Application to Dissolution Test Studies

We report the adsorptive voltammetric determination of nifedipine on multiwalled carbon nanotubes (MWCNT)‐modified glassy carbon electrode (GCE). Nifedipine was adsorbed on the MWCNT and then reduced using linear sweep and cyclic voltammetry (LSV and CV). Parameters such as pH and accumulation time were tested. The MWCNT‐modified GCE showed enhanced currents and good signal‐to‐noise characteristics in comparison with the bare GCE. Consecutive measurements with the modified electrode were highly repeatable and reproducible. The MWCNT/GCE was used for the determination of nifedipine and is recommended for quantitation in dissolution test studies. In this study we have tested normal and extended‐release pharmaceutical formulations of nifedipine using USP apparatus 2 and tracking the released drug in solution by the proposed voltammetric method. The main advantage of the voltammetric determination is the feasibility to detect the drug in‐situ avoiding tedious intermediate steps such as filtration, collection and replenishment of sample solutions. This work seeks to demonstrate the feasibility of applying voltammetric techniques in dissolution test studies.     

Investigation into sorption processes in the anodic stripping voltammetric speciation of Cu in natural waters

In the anodic stripping voltammetric speciation of copper significant errors may be introduced as a result of sorption of Cu²⁺ onto active surfaces of the voltammetric cell assembly. A correction method was developed based on monitoring of the total copper concentration in solution using a -radiotracer; additionally this allowed us to study sorption phenomena in the voltammetric cell assembly.For copper speciation in a fresh water sorption-corrected complexing capacity data (total natural ligand concentration and conditional stability constant of formed complex) showed considerable discrepancies with uncorrected data. From the same sorption data it could be deducted that this was accountable to the presence of two active surface sites in the voltammetric cell assembly.     

银掺杂聚L-天冬氨酸修饰电极的制备及对多巴胺的测定

利用循环伏安法将银与L-天冬氨酸聚合修饰在玻碳电极表面,制成银掺杂聚L-天冬氨酸修饰电极,研究了多巴胺在此电极上的电化学行为,建立了循环伏安法测定多巴胺的新方法.在磷酸盐缓冲溶液(PBS, pH 7.0)中,扫描速率为50 mV/s时,多巴胺在修饰电极上产生一对氧化还原峰,Epa=0.191 V,Epc=0.161 V.用循环伏安法进行测定时,峰电流与多巴胺浓度分别在3.0×10-7 ～1.0×10-5 mol/L和1.0×10-5 ～5.0×10-4 mol/L内呈良好的线性关系; 检出限为5.0×10-8 mol/L.用于药物和尿样中多巴胺的测定,结果满意.     

Sequential-injection stripping analysis of nifuroxime using DNA-modified glassy carbon electrodes

The voltammetric behavior of nifuroxime was investigated comparing stationary voltammetric methods with the recently proposed sequential-injection stripping analysis (SISA), by using cyclic voltammetry (CV) and differential-pulse voltammetry at bare and DNA-modified glassy carbon (GC) electrodes. In cyclic voltammetry, reduction of nifuroxime at DNA-modified electrodes gives rise to a well-defined peak, and in contrast to bare GC surfaces, a re-oxidation peak could be observed. Optimization of the pre-concentration process at the DNA-modified surface led to a significant enhancement of the voltammetric current response, a better defined peak shape and an improved dynamic range. Based on this optimized voltammetric procedure, SISA has been evaluated for the determination of nifuroxime. The flow-system significantly facilitates the regeneration of the DNA-modified electrode surface, hence diminishing problems related to accumulation and memory effects. The linear detection range could be extended to 65 microM with a detection limit (3 s) of 0.68 microM, which corresponds to an absolute amount of 21 ng nifuroxime.