Ali Babaei

Simultaneous determination of tryptophan, uric acid and ascorbic acid at iron(III) doped zeolite modified carbon paste electrode

A new chemically modified electrode is constructed based on iron(III) doped zeolite modified carbon paste electrode (Fe(3+)Y/ZCME). The electrode was evaluated as a sensor for sub-micromolar determination of tryptophan (Trp), uric acid (UA) and ascorbic acid (AA) in aqueous solutions. The measurements were carried out by application of the differential pulse voltammetry (DPV) method in phosphate buffer solution with pH 3.5. Iron(III) loaded in zeolite can increase anodic peak currents by adsorption of Trp, UA and AA on electrode surface The analytical performance was evaluated with respect to the carbon paste composition, pH of solution, accumulation time and accumulation potential. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Trp, UA and AA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The linear calibration range for AA in the presence of 50 microM UA and 50 microMTrp was 0.6 microM to 100 microM, with a correlation coefficient of 0.9992, and a detection limit of 0.21 microM (S/N=3). A linear relationship was found for UA in the range of 0.3-700 microM containing 10 microM AA and 50 microM Trp, with a correlation coefficient of 0.9990 and a detection limit of 0.08 microM. The linear calibration range for Trp in the presence of 10 microM AA and 50 microM UA was 0.2-150 microM, with a correlation coefficient of 0.9996, and a detection limit of 0.06 microM. The proposed method was successfully applied for determination Trp, UA and AA in biological systems and pharmaceutical samples.

Voltammetric determination of dopamine at a zirconium phosphated silica gel modified carbon paste electrode

Zirconium phosphated amorphous silica gel (devoted briefly as Si-ZrPH) modified carbon paste electrode (CPE) was used for detection of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). Cyclic voltammetry demonstrated improved reversibility of the DA on the modified electrode. Cyclic voltammetry of Fe(CN)(6)(3-/4-) as a negatively charged probe revealed that the surface of the Si-ZrPH modified CPE surface had a high density of negative charge. As a result, the modified carbon paste electrode could inhibit the voltammetric response of AA and UA while the redox reaction of dopamine was promoted. Based on this, a selective method has been developed to detect DA in the presence of 2500 and 1000 time higher concentration of AA and UA, respectively. The effect of various experimental parameters on the voltammetric response of dopamine was investigated. Under the chosen conditions, the differential pulse voltammetry peak current was found to be linear with DA concentration in the ranges of 0.04 to 50 microM and 50 to 400 microM. The detection limit of the proposed method in the presence of 100 microM of AA and 40 microM of UA was found to be 0.02 microM for DA determination. Satisfying results are achieved when detecting the DA in injection and human serum samples.

Electrosorption of Os(III)-complex at single-wall carbon nanotubes immobilized on a glassy carbon electrode: application to nanomolar detection of bromate, periodate and iodate.

A simple procedure was developed to prepare a glassy carbon electrode modified with single-wall carbon nanotubes (SWCNTs) and Os(III)-complex. The glassy carbon (GC) electrode modified with CNTs was immersed into Os(III)-complex solution (direct deposition) for a short period of time (60s). 1,4,8,12-Tetraazacyclotetradecane osmium(III) chloride, (Os(III)LCl(2)).ClO(4), irreversibly and strongly adsorbed on SWCNTs immobilized on the surface of GC electrode. Cyclic voltammograms of the Os(III)-complex-incorporated-SWCNTs indicate a pair of well defined and nearly reversible redox couple with surface confined characteristic at wide pH range (1-8). The surface coverage (Gamma) and charge transfer rate constant (k(s)) of the immobilized Os-complex on SWCNTs were 3.07 x 10(-9)molcm(-2), 5.5 (+/-0.2)s(-1), 2.94 x 10(-9)molcm(-2), 7.3 (+/-0.3)s(-1) at buffer solution with pH 2 and 7, respectively, indicate high loading ability of SWCNTs for Os(III) complex and great facilitation of the electron transfer between electroactive redox center and carbon nanotubes immobilized on the electrode surface. Modified electrodes showed higher electrocatalytic activity toward reduction of BrO(3)(-), IO(3)(-) and IO(4)(-) in acidic solutions. The catalytic rate constants for catalytic reduction bromate, periodate and iodate were 3.79 (+/-0.2) x 10(3), 7.32 (+/-0.2) x 10(3) and 1.75 (+/-0.2) x 10(3)M(-1)s(-1), respectively. The hydrodynamic amperometry of rotating modified electrode at constant potential (0.3V) was used for nanomolar detection of selected analytes. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantage of this sensor.

A sensitive simultaneous determination of epinephrine and tyrosine using an iron(III) doped zeolite-modified carbon paste electrode

Um eletrodo de pasta de carbono modificado com zeolitas e dopado com ferro(III) foi usado como um sensor eletroquimico de alta sensibilidade e seletividade para a determinacao simultânea de pequenas quantidades de compostos biologicamente importantes como epinefrina (Ep) e tirosina (Tyr). Os resultados da voltametria de pulso diferencial (DPV) usando este eletrodo modificado mostra duas ondas anodicas bem tracadas para a oxidacao da Ep e da Tyr, as quais tornam possiveis a determinacao simultanea destes compostos. A faixa linear de 0,9 a 216 mmol L-1 para a Ep em uma concentracao fixa de 30 mmol L-1 Tyr em solucao tampao fosfato, pH 3,0 foi obtida das medidas de DPV usando este eletrodo, com um coeficiente de correlacao de 0,9998 e limite de quantificacao igual a 0,44 mmol L-1. A linearidade obtida para a Tyr na presenca de 30 mmol L-1 de Ep, foi de 1,2 a 90 mmol L-1 com um coeficiente de correlacao de 0,9989 e limite de quantificacao de 0,32 mmol L-1. O eletrodo modificado apresentou uma boa reprodutibilidade (RSD< 2.5%), baixo limite de quantificacao (sub-micromolar) e alta sensibilidade para a deteccao de ambos Ep e Tyr com uma elevada estabilidade em sua resposta voltametrica. O desempenho analitico deste sensor tem sido avaliado para a deteccao de epinefrina e tirosina em soro humano e em amostras farmaceuticas com resultados satisfatorios.

A multi-walled carbon nanotube-modified glassy carbon electrode as a new sensor for the sensitive simultaneous determination of paracetamol and tramadol in pharmaceutical preparations and biological fluids

A chemically modified electrode was constructed based on a multi-walled carbon nanotube-modified glassy carbon electrode (MWCNTs/GCE). It was demonstrated that this sensor can be used for the simultaneous determination of the pharmaceutically important compounds paracetamol (PAR) and tramadol (TRA). The measurements were carried out by the application of differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. Application of the DPV method demonstrated that in phosphate buffer (pH 7.5) there was a linear relationship between the oxidation peak current and the concentration of PAR over the range 0.5 µmol L-1 to 210 µmol L-1. A similar linear correlation between oxidation peak current and concentration was observed for TRA over the range of 2 µmol L-1 to 300 µmol L-1. Under optimal conditions the modified electrode exhibited high sensitivity, selectivity and stability for both PAR and TRA determination, making it a suitable sensor for the simultaneous submicromolar detection of PAR and TRA in solutions. The analytical performance of this sensor has been evaluated for detection of PAR and TRA in human serum, human urine and some pharmaceutical preparations with satisfactory results.

Multi-walled carbon nanotubes/chitosan polymer composite modified glassy carbon electrode for sensitive simultaneous determination of levodopa and morphine

A modified electrode was constructed by coating of the glassy carbon surface with carbon nanotubes/chitosan (CNTs/CS) and used for sensitive and selective determination of levodopa (L-dopa) and morphine (MO) in a 0.1 M phosphate buffer (pH 7.0). The electrochemical response characteristics of the modified electrode toward L-dopa and MO were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) techniques. Under optimum conditions the sensor provided a linear CA response in the range of 1–360 μM with a detection limit of 0.86 μM for L-dopa, and in the range of 1–240 μM, with a detection limit of 0.65 μM for MO. The designed sensor was used for determination of L-dopa and MO in human serum and urine with satisfactory results.

New 1,2,4-triazole-based azo–azomethine dyes. Part II: Synthesis, characterization, electrochemical properties and computational studies

A new series of monoiminated 1,2,4-triazole-based azo-azomethine dyes have been synthesized via condensation reaction of 4-amino-3-methyl-5-mercapto-1,2,4-triazole with various substituted azo-coupled salicylaldehyde. The dyes have been characterized by using FT-IR, UV-Vis and (1)H NMR spectroscopic methods as well as elemental analysis. The electrochemical behavior of the dyes has been investigated by cyclic voltammetry in DMSO at five different scan rates. Solvatochromic behavior of the dyes has been also investigated in four organic solvents with different polarities. Furthermore, the (1)H chemical shielding of the dyes were studied by the gauge independent atomic orbital (GIAO) method at the level of density functional theory (DFT).

A sensitive determination of acetaminophen in pharmaceutical preparations and biological samples using multi-walled carbon nanotube modified glassy carbon electrode

A chemically modified electrode is constructed based on multi-walled carbon nanotube modified glassy carbon electrode (MWCNTs/GCE). It was demonstrated that this sensor could be easily used for determination of acetaminophen (ACT) in aqueous buffered media. The measurements were carried out by application of differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. Application of DPV method showed two linear dynamic ranges. The first linear dynamic range was from 0.1 to 22 µmol L-1, with a calibration equation of Ip(µA) = 1.2782c (µmol L-1) + 0.2431 (R2 = 0.9984) and the second linear dynamic range was between 26 to 340 µmol L-1 with a calibration equation of Ip(µA) = 0.7793c (µmol L-1) + 11.615 (R2 = 0.9986). A detection limit of 0.029 µmol L-1 (S/N = 3) was obtained. The modified electrode showed electrochemical responses with high sensitivity, excellent selectivity and stability for ACT determination at optimal conditions, which makes it a suitable sensor for submicromolar detection of ACT in solutions. The analytical performance of this sensor has been evaluated for detection of ACT in human serum, human urine and a pharmaceutical preparation with satisfactory results.

Selective simultaneous determination of levodopa and acetaminophen in the presence of ascorbic acid using a novel TiO2 hollow sphere/multi-walled carbon nanotube/poly-aspartic acid composite modified carbon paste electrode

A novel modified carbon paste electrode based on TiO2 hollow spheres (TOHS), multi-walled carbon nanotubes (MWCNT) and poly-aspartic acid (P-ASP) films (P-ASP/TOHS/MWCNT/CPE) was developed and used as a selective electrochemical sensor for simultaneous determination of levodopa (LD) and acetaminophen (ACT) in the presence of ascorbic acid (AA). The measurements were carried out by the application of differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. The prepared electrode presented rapid acceleration in electron transfer reactions of LD and ACT and showed no significant interference of AA as electro-active coexistent compounds with LD and ACT in biological systems. The DPV data showed that under optimal conditions, the obtained anodic peak currents were linearly dependent on the LD and ACT concentrations in the range of 0.4–450 and 0.1–300 μM, respectively. The fabricated sensor offered numerous advantages such as convenient preparation, good stability and high sensitivity towards LD and ACT determination. The applicability of the modified electrode was also demonstrated for simultaneous determination of LD and ACT in human urine.

Nanomolar simultaneous determination of epinephrine and acetaminophen on a glassy carbon electrode coated with a novel Mg–Al layered double hydroxide–nickel hydroxide nanoparticles–multi-walled carbon nanotubes composite

The present work demonstrates that the simultaneous determination of epinephrine (EPI) and acetaminophen (ACT) can be performed using a glassy carbon electrode (GCE) modified with a novel multi-walled carbon nanotubes (MWCNTs), nickel hydroxide nanoparticles (NHNPs) and Mg–Al layered double hydroxide (LDH) composite (MWCNTs–NHNPs–LDH/GCE). The electro-oxidations of EPI and ACT were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) methods. Under optimum conditions, DPV indicated linear relationships between oxidation peak current and EPI and ACT concentrations in the ranges of 0.04–60 μM and 0.02–40 μM with detection limits of 11 and 5 nM, respectively. The proposed method was successfully applied to the determination of these compounds in human urine and blood serum samples.