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A fast and simple magnetogenoassay is proposed for diagnosis of metastatic lymph nodes in patients with head and neck squamous cell carcinoma (HNSCC). The developed method involved the construction of a low-cost disposable electrochemical sensor (DES) for the detection of microRNA-203 (miRNA-203) as a biomarker in lymph node samples from patients with HNSCC. A hairpin DNA designed for selectively binding the miRNA-203 was immobilized in magnetic particles (MPs) and used to capture and separate the biomarker from the sample solution. Gold nanoparticles (AuNPs) decorated with single-stranded DNA with a sequence complementary to the hairpin terminal section were prepared and used for biomarker detection. The miRNA-203 magneto-bioconjugate obtained was added to the DES and the biomarker was quantitatively determined by means of the redox properties of the gold present in the AuNPs, using square-wave voltammetry in 0.2 mol L-1 HCl. The proposed method presented a linear range from 1.0 to 500.0 fmol L−1, with a limit of detection of 0.52 fmol L−1. The magnetogenoassay was able to detect the miRNA-203 in 90 min, showing similar results when compared with qRT-PCR for the discrimination of positive and negative metastatic lymph nodes from HNSCC patients. The proposed molecular test requires no amplification steps, offering an effective, simple, and fast alternative for the detection of microRNAs as biomarkers for cancer diagnosis.

The electrochemical detection and electrooxidation path of the first-generation antihistamine receptor hydroxyzine (HDZ) and its main metabolite cetirizine (CTZ) are addressed in this research. A carbon black-modified electrode to explore the electrochemical responsivity and electroanalytical detection of HDZ and CTZ was designed. Compared to the bare electrode, the irreversible anodic responses observed for HDZ and CTZ were considerably improved on the proposed carbon black-modified electrode, including twenty times enhancement of the anodic peak currents and the shifting of anodic peak potentials to less positive potentials. In order to identify the electrooxidation products resulting from the previously verified irreversible redox processes, cyclic voltammetric studies and potentiostatic electrolysis assays followed by products identification by nuclear magnetic resonance (NMR) spectroscopy were carried out. From the combination of electrochemistry and NMR spectroscopy data it was possible to propose electrooxidation reaction mechanisms for HDZ and CTZ molecules. By applying square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized experimental conditions, the obtained analytical curves for HDZ and CTZ were linear from 2.99 × 10 − 7 to 9.81 × 10 − 6 mol L − 1 and from 4.97 × 10 − 7 to 1.08 × 10 − 5 mol L − 1 , with limits of detection of 1.00 × 10 − 7 mol L − 1 and 4.00 × 10 − 7 mol L − 1 , respectively. Finally, spiked synthetic human biological fluids were analysed by the proposed SWAdASV procedures, with recovery percentages close to 100%.

Naphthol, a chemical classified as an endocrine disruptor and known to show carcinogenic activity, is found in the environment as a mixture of its isomers. For the first time, the truly simultaneous voltammetric determination of these isomeric forms of naphthol was explored in this work using a cathodically pretreated BDD electrode (CPT–BDD). The isomers 1–naphthol (1–NAP) and 2–naphthol (2–NAP) showed an irreversible oxidation process at 0.80 V and 0.96 V vs. Ag/AgCl (3.0 mol L −1 KCl), respectively, which allowed the simultaneous determination of these compounds. The electrochemical features of the 1–NAP and 2–NAP electrooxidation on CPT–BDD were investigated, including the determination of apparent diffusion coefficients and adsorption studies. Using differential pulse voltammetry under optimized experimental conditions, the analytical curves simultaneously constructed for 1–NAP and 2–NAP were both linear in the concentration range of 0.200 to 3.85 μmol L −1 with limits of detection of 50 and 100 nmol L −1 , respectively. Because the naphthol isomers do not adsorb on CPT–BDD, an excellent repeatability of measurement was verified and the proposed electroanalytical procedure was successfully applied for a truly simultaneous quantification of 1–NAP and 2–NAP in water and synthetic urine samples.

Porous boron-doped diamond (p-BDD) electrodes were prepared and explored as a potential electrochemical sensor for applications in flow-injection analysis (FIA) coupled to amperometric detection systems. Porous BDD films were grown by Hot Filament Chemical Vapor Deposition (HFCVD) over oxygen plasma functionalized carbon nanotubes and, morphological and chemical characterizations of the obtained composite material were carried out by Field Emission Gun Scanning Electron Microscopy (FEG-SEM) and Raman spectroscopy. The analytical performance of the designed p-BDD electrode under FIA conditions was investigated using two model electroactive analytes, epinephrine (EP, an important neurotransmitter) and acetaminophen (AC, a commonly consumed analgesic). All experimental parameters, such as applied potential, flow-rate and injection volume for both analytes were optimized. Under the best experimental conditions, the analytical curves for EP and AC were linear from 0.60 to 30.0 μmol L− 1 (EP) and from 0.80 to 70.0 μmol L− 1 (AC), with detection limits of 0.50 μmol L− 1 and 0.70 μmol L− 1 for EP and AC, respectively. Measurement precision was demonstrated from a number of amperometric measurements performed for successive injections of standard AC and EP solutions. In addition, the applicability of the developed FIA procedure was reported for the AC and EP determination in human serum fluid.

A glassy carbon electrode (GCE) modified with carbon Printex 6L (Printex6L/GCE) as a novel sensor is proposed. A morphological study was carried out using scanning electron microscopy, and an electrochemical characterization of the proposed electrode was performed by cyclic voltammetry (CV) using [Fe(CN)6]4− as a redox probe. With the incorporation of the carbon Printex 6L film onto the GCE surface, the [Fe(CN)6]4− analytical signal was substantially increased and the difference between the oxidation and reduction potentials (ΔE p) decreased, a characteristic of the electrocatalytic effect. Furthermore, the use of carbon Printex 6L film resulted in an 84 % increase in the oxidation current and a 123 % increase in the reduction current. Faster charge transfer was observed at the proposed electrode/electrolyte interface during CV when compared with GCE. The Printex6L/GCE was tested for ranitidine (RNT) sensing and showed a decrease in the working potential and an increase in the analytical signal, when compared with GCE, again demonstrating an electrocatalytic effect. Under optimized experimental conditions, the developed square-wave adsorptive anodic stripping voltammetry (SWAdASV) method presented an analytical curve that was linear in RNT concentration range from 1.98 × 10−6 to 2.88 × 10−5 mol L−1 with a detection limit of 2.44 × 10−7 mol L−1. The developed Printex6L/GCE was successfully applied to the determination of RNT concentrations in human body fluid samples (urine and serum).

Porous boron-doped diamond (p-BDD) electrodes of high-surface-area have been prepared on vertically aligned carbon nanotube substrates, and their electrochemical performance has demonstrated promising results for application in electroanalysis. The electrochemical features of the p-BDD electrodes were investigated and compared with those of a conventional flat BDD electrode (f-BDD). From cyclic voltammetry studies performed for the electrochemical probes [Fe(CN)6]3− and N,N,N′,N′-tetramethyl-para-phenylenediamine (TMPD), a fast charge transfer was observed at the p-BDD/electrolyte interface. For the [Fe(CN)6]3− redox probe, the heterogeneous electron-transfer rate constant (k 0) value obtained for p-BDD was 10.9 times higher than that obtained using a f-BDD electrode. Moreover, the p-BDD electrodes also gave a smaller peak potential separation, ΔE p, and larger analytical signal magnitude for different biomolecules, such as dopamine (DA), acetaminophen (AC), and epinephrine (EP). These set of results demonstrated that the p-BDD electrode is a suitable candidate for applications in electroanalytical chemistry.

Sensitive, simple, low-cost, and rapid amperometric flow-injection methods were developed for determination of ivermectin (IVM) and levamisole (LVM) in anthelmintic pharmaceutical drugs and urine samples. These determinations were carried out with a cathodically (for IVM) or anodically (for LVM) pretreated boron-doped diamond electrode using aqueous 0.5 mol L −1 H 2 SO 4 (with and without addition of 30% V / V of ethanol) as supporting electrolyte. The amperometric detection was performed at an applied electrode potential of E = 1.40 V, for IVM, and E = 1.90 V, for LVM, vs. Ag/AgCl (3.0 mol L −1 KCl). The respective analytical curves presented good linearity in the investigated concentration ranges (0.60–50 μmol L −1 , for IVM, and 0.010–5.0 μmol L −1 , for LVM) and the detection limits were 0.30 μmol L −1 for IVM, and 1 nmol L −1 , for LVM. Investigation of possible interferents showed no significant interference with the here-proposed methods; thus, they were used to determine IVM and LVM in pharmaceutical formulations as well as in urine samples, with results that showed good agreement with comparative methods. Furthermore, a mechanism for LVM electrooxidation was proposed using exhaustive potentiostatic electrolysis and NMR measurements.

A flow injection analysis (FIA) and multiple pulse amperometric detection (MPA) using a cathodically pretreated boron-doped diamond electrode (CPT-BDD) were employed for simultaneous determination of the antihypertensive drugs hydrochlorothiazide (HTZ) and enalapril (ENP). A dual-potential waveform as a function of time, previously optimized, was used: Edet.1 = + 1.50 V / 150 ms (pulse potential at which HTZ was oxidized) and Edet.2 = + 1.80 V / 150 ms (pulse potential at which oxidation of both analytes – HTZ and ENP – occurs). The analytical curves presented good linearity from 0.40 to 8.00 μmol L− 1 for HTZ and from 0.03 to 1.00 μmol L− 1 for HTZ, and the detection limits were 0.20 μmol L− 1 for HTZ and 0.01 μmol L− 1 for ENP. The proposed flow method presented an analytical frequency of 89 determinations per hour, good precision and accuracy, was successfully applied to the simultaneous determination of HTZ and ENP in pharmaceutical samples and the results obtained using the FIA–MPA method were in agreement with those obtained using a comparative method (HPLC) at a 95% confidence level.

The electrochemical detection of two pharmaceuticals, propranolol (PROP) and hydrochlorothiazide (HTZ), was studied using a nitrogen-containing tetrahedral amorphous carbon (ta-C:N) electrode. Measurements were also made using a boron-doped diamond (BDD) electrode, for comparison. The ta-C:N electrode functioned well for the simultaneous determination of PROP and HTZ in artificial urine and serum by square-wave voltammetry, both of which were detected at high positive potentials. The PROP (ca. 1.2 V) and HTZ (ca. 1.4 V) oxidation peak potentials were separated by about 200 mV. The respective analytical response curves presented good linearity in the investigated concentration range from 0.9 to 9.8 μmol L−1 for PROP and from 3.0 to 9.8 μmol L−1 for HTZ with calculated limits of detection (S/N = 3) of 0.75 μmol L−1 (∼194 ng/mL) for PROP and 2.50 μmol L−1 (∼744 ng/mL) for HTZ. Essentially, the lowest concentration measured voltammetrically was the LOD. The results indicate that the ta-C:N electrode could be an excellent new carbon material for electrochemically-active analytes requiring high potentials for detection.

A sensitive, simple, and rapid electrochemical method was developed for the determination of albendazole (ABZ) in anthelminthic pharmaceutical formulations using differential pulse voltammetry (DPV) with a cathodically pretreated boron-doped diamond (BDD) electrode and 0.05 mol L −1 H 2 SO 4 as supporting electrolyte. The electrochemical behavior of ABZ obtained with cyclic voltammetry (CV) showed two oxidation peaks at 0.95 and 1.30 V vs. Ag/AgCl (3.0 mol L −1 KCl). The total number of electrons (four) transferred during the oxidation process was estimated from the scan rate dependence of this CV response. The proposed method resulted in an analytical curve ranging from 0.0797 to 8.36 μmol L −1 , with a detection limit (based on 3-sigma) of 0.0625 μmol L −1 . This novel DPV method was successfully applied to determine ABZ in three pharmaceutical formulations (tablets), with results similar to those obtained using a reference HPLC method.

A single-line flow injection system and multiple pulse amperometric detection using a boron-doped diamond electrode were employed to develop and optimize a simple, low-cost, and rapid method for the simultaneous determination of two pairs of food colorants: tartrazine and sunset yellow (TT-SY) or brilliant blue and SY (BB-SY). A dual-potential waveform was used: E(det.1)=-150 mV (400 ms duration) and E(det.2)=-450 mV (100 ms duration) vs. Ag/AgCl (3.0 mol L(-1) KCl). Polarization at E(det.1) or E(det.2) causes reduction of SY or the respective pair of colorants, TT-SY or BB-SY; hence, with proper current correction, both colorants in each pair can be determined. The obtained linear response ranges (detection limits) were 5.0-60.0 (2.5) and 1.0-50.0 (0.80) μmol L(-1), for TT and SY, or 5.0-60.0 (3.5) and 1.0-50.0 (0.85) μmol L(-1), for BB and SY, respectively. Investigation of possible interferents (other food colorants or additives) showed no significant interference with the methods here proposed, which were then used to simultaneously determine the pairs of colorants in industrialized food samples, with results that showed good agreement with those obtained using a comparative HPLC method.

Differential pulse voltammetry (DPV) and a cathodically pretreated boron-doped diamond (BDD) electrode were used to simultaneously determine two pairs of synthetic food colorants commonly found mixed in food products: tartrazine (TT) and sunset yellow (SY) or brilliant blue (BB) and sunset yellow (SY). In the DPV measurements using the BDD electrode, the reduction peak potentials of TT and SY or BB and SY were separated by about 150 mV. The detection limit values obtained for the simultaneous determination of TT and SY or BB and SY were 62.7 nmol L(-1) and 13.1 nmol L(-1) or 143 nmol L(-1) and 25.6 nmol L(-1), respectively. The novel proposed voltammetric method was successfully applied in the simultaneous determination of these synthetic colorants in food products, with results similar to those obtained using a HPLC method at 95% confidence level.

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r=0.999) were obtained from 1.9×10−5 to 2.1×10−4 mol L−1 for AA and from 9.7×10−6 to 1.1×10−4 mol L−1 for CAF, with detection limits of 19 μmol L−1 and 7.0 μmol L−1, respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.

CONDUCTOMETRIC DETERMINATION OF CAPTOPRIL IN PHARMACEUTICAL FORMULATIONS USING COPPER(II) SULPHATE AS TITRANT. A simple and rapid conductometric method for captopril determination using copper(II) sulphate solution as titrant was developed. The method was based on the chemical reaction between captopril and Cu(II) ions yielding a precipitate. The conductance of the solution was monitored as a function of the added volume of titrant. The method was applied with success for captopril determination in three pharmaceutical formulations. The relative standard deviation for six successive measurements was smaller than 0.5%. Recovery values from three samples, ranging from 97.7 to 103%, were obtained.

This paper describes the preparation and electrochemical application of a modified carbon paste electrode with chitosan for the determination of Hg(II) ions in water using anodic stripping voltammetry. Experimental parameters, including the pH of the supporting electrolyte, time and potential of accumulation and scan rate were investigated. The best voltammetric response was observed for a paste composition of 60% (m/m) of graphite powder, 20% (m/m) of chitosan and 20% (m/m) of mineral oil, with 0.1 mol/l NaNO3 solution at pH 6.3 as supporting electrolyte, a preconcentration potential of −0.2 V, preconcentration time of 270 s and a scan rate of 25 mV/s. Under these optimal experimental conditions, the voltammetric signals were linearly dependent on the Hg(II) concentration in the range of 9.99×10−7 to 3.85×10−5 mol/l with a detection limit of 6.28×10−7 mol/l. Three “spiked” samples of water were evaluated using the proposed sensor, and results agreed with those obtained by a reference method at ...

A method for simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food was developed that uses multiple pulse amperometry (MPA) with flow injection analysis (FIA). Determination of these phenolic antioxidants was carried out with a cathodically pretreated boron-doped diamond electrode and an aqueous ethanolic (30% ethanol, v/v) 10 mmol L⁻¹ KNO₃ solution (pH(cond) = 1.5) as supporting electrolyte. A dual-potential waveform, at E(det1) = 850 mV/200 ms and E(det2) = 1150 mV/200 ms versus Ag/AgCl (3.0 mol L⁻¹ KCl), was employed. The use of E(det1) or E(det2) caused the oxidation of BHA or of BHA and BHT, respectively; hence, concentration subtraction could be used to determine both species. The respective analytical curves presented good linearity in the investigated concentration range (0.050-3.0 μmol L⁻¹ for BHA and 0.70-70 μmol L⁻¹ for BHT), and the detection limits were 0.030 μmol L⁻¹ for BHA and 0.40 μmol L⁻¹ for BHT. The proposed method, which is simple, quick, and presents good precision and accuracy, was successfully applied in the simultaneous determination of BHA and BHT in commercial mayonnaise samples, with results similar to those obtained by HPLC, at a 95% confidence level.

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 × 10 −7 mol L −1 to 8.3 × 10 −5 mol L −1 for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 × 10 −7 mol L −1 and 3.5 × 10 −8 mol L −1 , respectively. The proposed method was successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level).