Construction of an electrochemical sensing platform for the sensitive determination of chlorogenic acid in locally consumed bitter coffee known as Mirra.

The demand for foods with high antioxidant capacity has increased and research on food analysis continues to increase. Chlorogenic acid is a potent antioxidant molecule and can exhibit various physiological activities. This study aims to analyze Mirra coffee for the determination of chlorogenic acid using an adsorptive voltammetric method. The method is based on the strong synergistic effect between carbon nanotubes and nanoparticles of gadolinium oxide and tungsten, providing sensitive determination of chlorogenic acid. The proposed method yielded a dynamic linear range of 2.5 × 10-9 âˆ¼ 1.6 × 10-6 M with a detection limit of 1.08 × 10-9 M for chlorogenic acid. The amount of chlorogenic acid in Mirra coffee was found to be 46.1 ± 0.69 mg/L by the proposed electrochemical platform.

Development of a Dy2O3@Eu2O3-carbon nanofiber based electrode for highly sensitive detection of papaverine.

A sensitive electrochemical method based on carbon nanofibers (CNFs) and bimetallic nanoparticles of dysprosium oxide (Dy2O3) and europium oxide (Eu2O3) was developed for the determination of papaverine in pharmaceuticals and human urine. Several electrodes were compared in respect to their electrochemically active surface area calculated as 0.0603, 0.1300, 0.3440, 0.3740 and 0.4990 cm2 for bare GCE, CNFs/GCE, Eu2O3-CNFs/GCE, Dy2O3-CNFs/GCE and Dy2O3@Eu2O3-CNFs/GCE, respectively. Electrodes were also compared in respect to their performance towards the voltammetric process of papaverine. The peak potential (Epa) of papaverine was 1.094 V, 0.993 V, 0.978 V, 0.969 V and 0.966 V at unmodified GCE, CNFs/GCE, Eu2O3-CNFs/GCE, Dy2O3-CNFs/GCE and Dy2O3@Eu2O3-CNFs/GCE, respectively. This indicated that the oxidation peak potential of papaverine shifted gradually towards the negative potentials and the peak current increased gradually from unmodified GCE to CNFs/GCE, Eu2O3-CNFs/GCE, Dy2O3-CNFs/GCE and Dy2O3@Eu2O3-CNFs/GCE. The influence of experimental parameters such as scan rate and pH on the voltammetry of papaverine was studied. The Dy2O3@Eu2O3-CNFs/GCE system presented a dynamic working range between 1.0 × 10-7 and 2.0 × 10-6 M with a detection limit of 1.0 × 10-8 M for papaverine. The platform (Dy2O3@Eu2O3-CNFs/GCE) exhibited excellent sensitivity and selectivity for papaverine in the presence of uric acid and was successfully applied for determining papaverine in pharmaceuticals and urine samples.

A novel voltammetric platform based on dysprosium oxide for the sensitive determination of sunset yellow in the presence of tartrazine.

This study reports the preparation of a novel voltammetric platform based on the modification of a glassy carbon electrode (GCE) with carbon nanotubes (MWCNTs) and dysprosium oxide (Dy2O3) nanoparticles. The electrode material was characterized by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction method (XRD). The novel platform (Dy2O3NPs/MWCNTs/GCE) was applied for the voltammetric determination of sunset yellow (SY) in the presence of tartrazine (TAR). SY was first adsorbed at the surface of Dy2O3NPs/MWCNTs/GCE by keeping it into a solution of SY for 200 s. Afterwards, the proposed platform was washed with ultrapure water and transferred with the adsorbed species in a voltammetric cell containing only 0.1 M phosphate buffer solution (PBS). Then, the novel platform (Dy2O3NPs/MWCNTs/GCE) exhibited excellent electrocatalytic activity and presented improved voltammetric responses when compared to other electrodes. The novel platform produced an improved anodic peak at 0.705 V and a corresponding cathodic peak at 0.690 V for SY and an irreversible anodic peak at 0.957 V for TAR. When compared to the electrode modified with only MWCNTs, a remarkable increase in current response and a electrocatalytic activity of the proposed platform were observed for SY and TAR at a GCE modified with both MWCNTs and Dy2O3NPs. A linear relationship was obtained between the current response and the concentration of SY over range of 1.0 × 10-9 M -  1.4 × 10-7 M with an LOD of 3.5 × 10-10 M using square wave voltammetry (SWV). The proposed procedure provided an accurate and a precise quantification to the analysis of food and pharmaceutical samples.

Sensitive determination of capsaicin in pepper samples using a voltammetric platform based on carbon nanotubes and ruthenium nanoparticles.

A voltammetric platform based on modifying glassy carbon electrodes (GCEs) with ruthenium nanoparticles decorated carbon nanotubes (CNTs) was applied for the determination of capsaicin in pepper samples. The nanoparticles of ruthenium (RuNPs) were obtained at carbon nanotubes modified GCE by cyclic voltammetry. The composite of RuNPs-CNTs was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The proposed voltammetric platform, RuNPs/CNTs/GCE, highly improved the voltammetric process of capsaicin in comparison to the CNTs/GCE and bare GCE. A linear concentration range was obtained from 1.0×10-8 to 4.1×10-7M (R2=0.9987) with a detection limit of 2.5×10-9M. The voltammetric platform has successfully been applied for quantifying capsaicin in various pepper samples including Isot. The proposed voltammetric platform offers advantages such as high sensitivity, selectivity and precision.

A novel electrochemical platform based on carbon nanofibers and tri-metallic nanoparticles of gold, nickel and cobalt for the quantification of ethyl paraben.

A composite of carbon nanofibers (CNFs) and tri-metallic nanoparticles of gold, cobalt and nickel were used for the preparation of a novel voltammetric platform. The proposed voltammetric platform was utilized for quantifying ethyl paraben (EPB) in pharmaceutical and cosmetic products. The electrode layers were characterized by utilizing X-ray diffraction method (XRD) and Fourier transform infrared spectroscopy (FTIR). The electrode system, (Au-Ni-Co)NPs-CNFs/GCE, exhibited high catalytic activity and enhanced the electrochemical behaviour of EPB compared with several other electrodes. The proposed composite layer based electrode produced a well-defined oxidation peak at 0.760V. The determination of EPB was carried out by square wave voltammetry (SWV). The electrode produced a linear plot with a concentration range from 1.0×10-9 to 1.0×10-7M at (Au-Ni-Co)NPs-CNFs/GCE. The composite material enabled a detection limit of 3.5×10-10M for EPB. Good reproducibility, high precision and excellent accuracy for EPB were obtained at (Au-Ni-Co)NPs-CNFs/GCE. The composite layer based platform was successfully applied for the quantification of EPB in pharmaceutical and cosmetic products. The sensitive quantification of EPB is of great importance for the public health care. Furthermore, data show that EPB binds to DNA via intercalation with a binding constant of 2.51(±0.40)×104.

A sensitive determination of terbutaline in pharmaceuticals and urine samples using a composite electrode based on zirconium oxide nanoparticles.

An accurate and precise determination of terbutaline has been carried out using a glassy carbon electrode (GCE) modified with a composite of multi-walled carbon nanotubes (MWCNTs) and nanoparticles of zirconium oxide (ZrO2NPs). Energy dispersive X-ray and scanning electron microscopic techniques were utilized for the characterization of the composite layer. Terbutaline exhibited a broad oxidation peak at 770mV on a GCE. However, MWCNTs/GCE presented an electrocatalytic effect toward the oxidation of terbutaline with a better anodic peak at 660mV. Furthermore, the electrochemical behavior of terbutaline has greatly been improved at a GCE modified with a composite of MWCNTs and nanoparticles of ZrO2. The ZrO2NPs/MWCNTs/GCE exhibited a sharp anodic wave at 645mV with a large enhancement of the current response for terbutaline. Square wave voltammetry (SWV) was performed for the determination of terbutaline at ZrO2NPs/MWCNTs/GCE. A linear plot was obtained for the current responses of terbutaline against concentrations in the range of 10-160nM yielding a detection limit of 2.25nM (based on 3Sb/m). Improved voltammetric behavior, long-time stability and good reproducibility were obtained for terbutaline at the proposed electrode. A mean recovery of 101.2% with an RSD% of 1.9 was obtained for the analysis of the drug formulation. The accurate and precise quantification of terbutaline makes the ZrO2NPs/MWCNTs/GCE system of great interest for monitoring its therapeutic use.

A composite material based on nanoparticles of yttrium (III) oxide for the selective and sensitive electrochemical determination of acetaminophen.

An electrochemical sensor was prepared by modifying a glassy carbon electrode (GCE) with a composite of yttrium (III) oxide nanoparticles (Y2O3NPs) and carbon nanotubes (CNTs) for the determination of acetaminophen (ACT). Compared with a bare GCE and CNTs/GCE, the Y2O3NPs/CNTs/GCE exhibited a well-defined redox couple for ACT and highly enhanced the current response. The separations in the anodic and cathodic peak potentials (ΔEp) for ACT were 552mV, 24mV and 10mV at ba4re GCE, CNTs/GCE and Y2O3NPs/CNTs/GCE, respectively. The observation of only 10mV of ΔEp for ACT at Y2O3NPs/CNTs/GCE was a clear indication of a great acceleration of the electrode process compared to bare GCE and GCE modified with CNTs. Also, l-ascorbic acid (l-AA) and l-tyrosine (l-TRY) did not interfere with the selective determination of ACT. Square wave voltammetry (SWV) was performed for the quantification of ACT. A linear plot was obtained for current responses versus the concentrations of ACT over the range from 1.0×10(-10) to 1.8×10(-8)M with a detection limit of 3.0×10(-11)M (based on 3Sb/m). The proposed composite material provided high electrocatalytic activity, improved voltammetric behavior, good selectivity and good reproducibility. The accurate quantification of ACT makes the proposed electrode of great interest for the public health.

A novel voltammetric sensor based on carbon nanotubes and nanoparticles of antimony tin oxide for the determination of ractopamine.

An electrochemical sensor was prepared by the modification of a glassy carbon electrode (GCE) with carbon nanotubes (CNTs) and nanoparticles of antimony tin oxide (ATO). The surface layer was characterized by scanning electronmicroscopy (SEM), energy dispersive X-ray diffraction method (EDX) and ATR FT-IR spectroscopy. The proposed electrode was assessed in respect to the electro-oxidation of ractopamine. Compared with a bare GCE and a GCE electrode modified with CNTs, the ATONPs/CNTs/GCE exhibited a great catalytic activity towards the oxidation of ractopamine with a well-defined anodic peak at 600 mV. The current response was linear with the concentration of ractopamine over the range from 10 to 240 nM with a detection limit of 3.3 nM. The proposed electrode enabled the selective determination of ractopamine in the presence of high concentrations of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The proposed electrode was successfully applied for the determination of ractopamine in feed and urine samples. The sensitive and selective determination of ractopamine makes the developed method of great interest for monitoring its therapeutic use and doping control purposes.

A novel composite electrode based on tungsten oxide nanoparticles and carbon nanotubes for the electrochemical determination of paracetamol.

An electrochemical sensor was prepared by the modification of a glassy carbon electrode (GCE) with a composite of nanoparticles of tungsten oxide (WO3) and carbon nanotubes (CNTs) for the quantification of paracetamol (PR). Energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM) were performed for the characterization of the nanocomposite layer. Compared with a bare GCE and a GCE modified with CNTs, the proposed electrode (WO3NPs/CNTs/GCE) exhibited a well-defined redox couple for PR and a marked enhancement of the current response. The experimental results also showed that ascorbic acid (AA) did not interfere with the selective determination of PR. The proposed electrode was used for the determination of PR in 0.1M phosphate buffer solution (PBS) at pH7.0 using square wave voltammetry (SWV). The peak current increased linearly with the concentration of PR in the range of 1.0×10(-9)-2.0×10(-7)M. The detection limit (LOD) was 5.54×10(-11)M (based on 3Sb/m). The proposed voltammetric sensor provided long-time stability, improved voltammetric behavior and good reproducibility for PR. The selective, accurate and precise determination of PR makes the proposed electrode of great interest for monitoring its therapeutic use.

An electrochemical sensor prepared by sonochemical one-pot synthesis of multi-walled carbon nanotube-supported cobalt nanoparticles for the simultaneous determination of paracetamol and dopamine.

Multi-walled carbon nanotubes (MWCNTs) functionalized by cobalt nanoparticles were obtained using a single step chemical deposition method in an ultrasonic bath. The composite material was characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The electroactivity of the cobalt-functionalized MWCNTs was assessed in respect to the electrooxidation of paracetamol (PAR) and dopamine (DA). It was found that the carbon nanotube supported cobalt nanoparticles have significantly higher catalytic properties. The proposed electrode has been applied for the simultaneous determination of PAR and DA. The modified electrode could resolve the overlapped voltammetric waves of PAR and DA into two well-defined voltammetric peaks with peak to peak separation of about 203 mV. On the other hand, the presence of potential drug interfering compounds AA and UA did not affect the voltammetric responses of PAR and DA. The current of oxidation peaks showed a linear dependent on the concentrations of PAR and DA in the range of 5.2×10(-9)-4.5×10(-7) M (R(2)=0.9987) and 5.0×10(-8)-3.0×10(-6) M (R(2)=0.9999), respectively. The detection limits of 1.0×10(-9) M and 1.5×10(-8) M were obtained for PAR and DA, respectively. The proposed electrode showed good stability (peak current change: 4.9% with and RSD of 2.6% for PAR; 5.5% with and RSD of 3.0% for DA over 3 weeks), reproducibility (RSD 2.3% for PAR and RSD 1.5% for DA), repeatability (RSD 2.25% for PAR and RSD 2.50% for DA) and high recovery (99.7% with an RSD of 1.3% for PAR; 100.8% with an RSD of 1.8% for DA). The proposed method was successfully applied to the determination of PAR and DA in pharmaceuticals.

Synthesis, spectroscopy, magnetic and redox behaviors of copper(II) complexes with tert-butylated salen type ligands bearing bis(4-aminophenyl)ethane and bis(4-aminophenyl)amide backbones.

New salen type ligands, N,N'-bis(X-3-tert-butylsalicylidene)-4,4'-ethylenedianiline [(X=H (1), 5-tert-butyl (2)] and N,N'-bis(X-3-tert-butylsalicylidene)-4,4'-amidedianiline [X=H (3), 5-tert (4)] and their copper(II) complexes 5-8, have been synthesized. Their spectroscopic (IR, (1)H NMR, UV/vis, ESR) properties, as well as magnetic and redox-reactivity behavior are reported. IR spectra of 7 and 8 indicate the coordination of amide oxygen atoms of 3 and 4 ligands to Cu(II). The solid state ESR spectra of 5-8 exhibits less informative exchange narrowed isotropic or anisotropic signals with weak unresolved low field patterns. The magnetic moments of 5 (2.92 µ(B) per Cu(II)) and 6 (2.79 µ(B) per Cu(II)) are unusual for copper(II) complexes and considerably higher than those for complexes 7 and 8. Cryogenic measurements (300-10 K) show weak antiferromagnetic exchange interactions between the copper(II) centers in complexes 6 and 8. The results of electrochemical and chemical redox-reactivity studies are discussed.

Electrocatalytic Oxidation of Isoproterenol and its Voltammetric Determination in Pharmaceuticals and Urine Samples Using a Poly(1-methylpyrrole)-DNA Modified Electrode.

Determination of isoproterenol (ISP) was carried out using a DNA incorporated poly(1-methylpyrrole) modified glassy carbon electrode (GCE). The poly(1-methylpyrrole)-DNA/GCE showed an excellent electrocatalytic effect on the oxidation of ISP. The poly(1-methypyrrole)-DNA/GCE also accelerated the rate of electron transfer reaction of ISP. Compared with a bare GCE, the poly(1-methylpyrrole)-DNA/GCE exhibits a distinct shift of the oxidation potential of ISP in the cathodic direction and a marked enhancement of the current response. A linear calibration plot was obtained covering the concentration range from 2.0 × 10-6 to 6.0 × 10-5 M with a detection limit of 1.60 × 10-7 M by cyclic voltammetry. The electrode system has also successfully resolved the overlapping anodic peak of ISP and uric acid (UA) into two well-defined voltammetric peaks in cyclic voltammetry at 0.416 V and 0.552 V for ISP and UA, respectively. The poly(1-methypyrrole)-DNA/GCE has successfully been utilised for the determination of ISP in pharmaceutical preparations. The validity of the proposed method was also assured by the recovery of ISP and UA in urine samples.

A poly(3-acetylthiophene) modified glassy carbon electrode for selective voltammetric measurement of uric acid in urine sample.

A reliable and reproducible method for the determination of uric acid in urine samples has been developed. The method is based on the modification of a glassy carbon electrode by 3-acetylthiophene using cyclic voltammetry. The poly(3-acetylthiophene) modified glassy carbon electrode showed an excellent electrocatalytic effect towards the oxidation of uric acid in 0.1 m phosphate buffer solution (PBS) at pH 7.2. Compared with a bare glassy carbon electrode (GCE), an obvious shift of the oxidation peak potential in the cathodic direction and a marked enhancement of the anodic current response for uric acid were observed. The poly(3-acetylthiophene)/GCE was used for the determination of uric acid using square wave voltammetry. The peak current increased linearly with the concentration of uric acid in the range of 1.25 x 10(-5)-1.75 x 10(-4) M. The detection limit was 5.27 x 10(-7) M by square wave voltammetry. The poly(3-acetylthiophene)/GCE was also effective to determine uric acid and ascorbic acid in a mixture and resolved the overlapping anodic peaks of these two species into two well-defined voltammetric peaks in cyclic voltammetry at 0.030 V and 0.320 V (vs. Ag/AgCl) for ascorbic acid and uric acid, respectively. The modified electrode exhibited stable and sensitive current responses toward uric acid and ascorbic acid. The method has successfully been applied for determination of uric acid in urine samples.

Electrochemical and spectroscopic studies of the interaction of proflavine with DNA.

The interaction of proflavine with herring sperm DNA has been investigated by cyclic voltammetry and UV-Vis spectroscopy as well as viscosity measurements. Shifts in the peak potentials in cyclic voltammetry, spectral changes in UV absorption titration, an increase in viscosity of DNA and the results of the effect of ionic strength on the binding constant strongly support the intercalation of proflavine into the DNA double helix. The binding constant for the interaction between proflavine and DNA was K = 2.32 (+/- 0.41) x 10(4) M(-1) and the binding site size was 2.07 (+/- 0.1) base pairs, estimated in voltammetric measurements. The value of the binding site size was determined to be closer to that expected for a planar intercalating agent. The standard Gibbs free-energy change is ca. -24.90 kJ/mol at 25 degrees C, indicating the spontaneity of the binding interaction. The binding constant determined by UV absorption measurements was K = 2.20 (+/- 0.48) x 10(4) M(-1), which is very close to the value determined by cyclic voltammetry assuming that the binding equilibrium is static.

Voltammetric studies of the interaction of quinacrine with DNA.

The binding interaction of the antimalarial drug quinacrine with herring sperm deoxyribonucleic acid (DNA) has been studied by square wave voltammetry. The binding parameters, the binding constant K and the binding site size s, were obtained simultaneously by the analysis of bound and free quinacrine concentration corresponding to the limits of slow and fast binding kinetics compared to the experimental timescale. The binding constant and the binding site size for the interaction of quinacrine with DNA were K = 1.59 (+/-0.18)x10(5) M(-1) and s = 7.1 (+/-0.15) base pairs and K = 7.35 (+/-0.83)x10(5) M(-1), s = 6.2 (+/-0.02) base pairs for the limiting conditions of static and mobile binding equilibrium respectively. The standard Gibbs free energy change (Delta G0 = - RT ln K) is approximately -29.67 kJ/mol at 25 degrees C, which highlights the spontaneity of the binding of quinacrine with DNA. The binding of quinacrine to herring sperm DNA results in peak potential shifts in voltammetric and a red shift in UV-absorption measurements. The ionic strength dependence of the binding constant is not large. Furthermore, the relative viscosity of DNA increases in the presence of quinacrine. These characteristics strongly support the intercalation of quinacrine into DNA. The results also show that the intercalation of quinacrine into DNA may occur at approximately every seventh base pair.

Potentiometric and voltammetric determination of methimazole.

The determination of methimazole was investigated by potentiometric titration in an alkaline medium involving its reaction with iodine and square wave voltammetry (SWV) in 0.1 mol/l Tris-HCl buffer at pH 7.2. In potentiometric titration, the range of determination was 10-500 micromol. A stoichiometric reaction was obtained within the concentration range 0.75-1.25 mol/l of sodium hydroxide by potentiometric titration. A linear calibration graph was obtained over the concentration range 1-700 micromol/l by SWV. The lowest concentration of methimazole detected was 0.5 micromol/l. The relative standard deviations (R.S.D.) were 0.81% in potentiometric titration and 2.89% in square wave voltammetric analysis of thyromazol tablets. The data showed that potentiometric titration using iodine in sodium hydroxide can be used for the determination of methimazole in drug samples without prior separation.