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The accumulation of organophosphate pesticides (OPPs) in the environment has turned into a predicament for ecological balance and human health. So in this study, a sensitive, easy, and efficient method has been offered for the preconcentration and quantification of the low levels of fenitrothion, one of the prevalent organophosphates, in pistachio kernels. In this technique, at the first step, fenitrothion from aqueous medium was extracted into a few microliters of chloroform using dispersive liquid–liquid microextraction method. After centrifugation and separation of the fenitrothion-containing chloroform drop, it was casted on the surface of a glassy carbon electrode modified with carbon nanotubes. Then, chloroform was allowed to be evaporated at room temperature. Finally, the electrode was immersed into 0.10 M phosphate buffer solution (pH 7.0), where cyclic voltammogram of the deposited fenitrothion was recorded. After optimization of different experimental parameters affecting extraction and electrochemical steps, the concentration linear range of fenitrothion was obtained to be 0.54–6.84 µM. Detection limit was 0.090 µM and the relative standard deviation for seven replicate measurements of the 1.80 µM fenitrothion solution was 3.3%. [ABSTRACT FROM AUTHOR]

In the present study, multiwalled carbon nanotubes (MWCNTs) as solid phase extraction sorbent were developed for preconcentration of arsenic(V) species prior to graphite furnace atomic absorption spectrometry (GFAAS) determination. Arsenic(V) was selectively sorbed on the packed column with MWCNTs within a pH 9.5 in the presence of 2-(5-bromo-2-pyridylazo)-5-diethyl amino phenol (5-Br-PADAP). The adsorbed species was then desorbed with 1 mL of 2.0 M HNO3. Experimental parameters including pH, sample volume and flow rate, type, volume and concentration of eluent that influence the recovery of the arsenic(V) species were optimised. Under the optimised conditions, the calibration curve was linear in the range of 0.2–10.0 µg L−1with detection limit of 0.016 µg L−1. The relative standard deviations (RSD) for seven replicate determinations at 1.0 µg L−1level of arsenic was 6.69%. The proposed method was successfully applied to the determination of arsenic in water samples and certified reference material (NIST RSM 1643e). [ABSTRACT FROM AUTHOR]

A simple and sensitive label-free electrochemical DNA biosensor was proposed for the rapid determination of uric acid (UA) using a carbon nano tube paste electrode (CNTPE) modified with salmon sperm dsDNA. At first, the interaction between UA and the DNA was studied using differential pulse voltammetry (DPV). The addition of the DNA to UA solution resulted in a decrease in the peak current of UA and at the same time, a positive shift in the peak potential indicating an intercalative interaction. Then, the voltammetric response of a DNA-immobilized CNTPE was investigated for the determination of UA. The immobilization of the DNA was carried out using acid-functionalized carbon nanotubes and studied using Fe(CN)6 3−/Fe(CN)6 4− redox indicator. Compared with unmodified CNTPE, the oxidation signal of UA showed a significant increase at the DNA-coated electrode, and shifted to more positive potentials attributed to the pre-concentration of UA at the electrode surface due to interaction with the surface-confined DNA layer. This interaction was used for the fabrication of a simple and sensitive biosensor for determining UA. After the optimization of operational parameters, a linear dependence of the peak current on the UA concentration was observed in the range of 7.0×10−7 to 1.1×10−4 molL−1, with the detection and quantification limits of 1.8×10−7 and 5.8×10−7 molL−1, respectively. The proposed biosensor was successfully applied to validate its capability for the analysis of UA in human serum and urine samples. [ABSTRACT FROM AUTHOR]

Abstract: A solid phase extraction procedure is proposed for simultaneous separation and preconcentration trace amounts of Au(III) and Mn(II) in an aqueous medium by using a column of multiwalled carbon nanotubes modified with the analytical reagent N,N′-bis(2-hydroxybenzylidene)-2,2′(aminophenylthio)ethane. An implementation, it was found that the sorption is quantitative in the pH range 5.0–7.5, whereas quantitative desorption occurs instantaneously with 4.0mL of 0.1molL−1 Na2S2O3. Selected elements were also determined by flame atomic absorption spectrometry. Linearity was maintained between 0.2ngmL−1 to 25μgmL−1 for gold and 0.08ngmL−1 to 5μgmL−1 for manganese in the original solution. Various parameters such as the effect of pH, flow rate, type and amount of eluent, breakthrough volume and interference of a large number of anions and cations on the recovery of the selected ions was studied. Under optimum conditions, the detection limits (3s, n =10) for analytes were 0.03ngmL−1 (gold) and 0.01ngmL−1 (manganese). The method was successfully applied for separation and determination of gold and manganese ions in water and standard samples. [Copyright &y& Elsevier]

Abstract: A highly selective and sensitive carbon paste electrode modified with multi-walled carbon nanotubes and 4-[1-(4-methoxyphenyl) methylidene]-3-methyl-5-isoxazolone was used for accumulation and determination of trace amounts of bismuth using the differential pulse anodic stripping voltammetric method. The analytical procedure consisted of a closed-circuit accumulation step onto the modified carbon paste electrode. An anodic peak related to the oxidation of accumulated Bi(0) on the electrode surface was observed at about −0.05V. The calibration curve was linear in the range of 1–400μgL−1. The limit of detection was 0.2μgL−1 and the relative standard deviations for seven replicated determinations at 30, 100 and 300μgL−1 of bismuth were 3.6, 2.4 and 1.6%, respectively. The modified electrode was applied for the determination of bismuth in pharmaceutical, biological and several water samples. The accuracy and precision of results were comparable to those obtained by the graphite furnace atomic absorption spectroscopy method. [Copyright &y& Elsevier]

Novel molecularly imprinted polymers (MIPs) on the surface of magnetic multi-walled carbon nanotubes (MMWCNTs) were prepared using dibenzothiophene (DBT) as template, methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linking agent and ammonium persulfate (APS) as initiator. The synthetic product was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Fourier transform infrared spectroscopy (FTIR). Batch mode adsorption studies were performed to evaluate the adsorption kinetics, adsorption isotherms, and selective recognition of MMWCNTs-MIP. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order equation. The pseudo-second-order exhibited the best fit for the kinetic studies ( R 2 = 0.9985), which indicates that chemisorption process limits adsorption of DBT. The adsorption equilibrium of DBT using MMWCNTs-MIP could be well-defined with the Langmuir isotherm model instead of the Freundlich isotherm model, and the maximum adsorption capacity was calculated as 47.8 mg g –1 . Compared with magnetic non-imprinted polymer (MNIP), magnetic MIP (MMIP) possessed a better adsorption property toward DBT, showing its potential for deep desulfurization. [ABSTRACT FROM AUTHOR]

This paper presents an easy, fast, low cost, and sensitive approach for the electrochemical determination of quercetin based on its intercalation into DNA double helix. Electrochemical studies of the interaction between quercetin and DNA showed a decrease in peak currents with a reduction in redox reversibility of quercetin in the presence of the DNA. The electrochemical behavior of quercetin at a chitosan-entrapped carbon nanotube paste electrode coated with DNA was studied. A considerable increase was observed in the oxidation signal of quercetin at the DNA-coated electrode compared with a DNA-free electrode, indicating the preconcentration of quercetin due to its interaction with the surface-confined DNA layer. After optimizing the main experimental parameters influencing the biosensor response, its performance was evaluated from an analytical point of view. Two linear dependences of the anodic peak current of quercetin on its concentration were observed in the ranges of 0.40-7.50 and 7.50-30.0 µmol/L, with LOD and LOQ of 0.039 and 0.13 µmol/L, respectively. The proposed biosensor was successfully applied to the analysis of black and green tea extracts for their quercetin content. [ABSTRACT FROM AUTHOR]