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The fast, visual discrimination of β2-agonist drugs is needed for the on-site screening of various types of (β2-agonists in blood and urine samples. We developed a simple, rapid, one-step colorimetric method to detect phenolic (β2-agonists by use of a tyrosinase catalytic reaction, which involved the oxidation of the phenol group on the benzene rings of β2-agonists. The enzymatic oxidation products of β2-agonists with phenolic groups exhibited different color transitions based on the different substituent groups on the aromatic ring, whereas β2-agonists with the aniline group or the resorcinol group remained colorless. This visual color discrepancy has been used to intuitively and conveniently differentiate the phenolic group β2agonists, such as ractopamine, isoxsuprine, ritodrine, and fenoterol. The oxidation products of these compounds have been identified using mass spectrometry, and the possible reaction mechanisms between β2-agonists and tyrosinase have been deduced. The parameters that govern the analytical performance of the reaction product, including the pH of the buffer solution, the concentration of tyrosinase, and the incubation time, have been studied and optimized using ultraviolet-visible (UV-vis) spectroscopy and electrochemical methods. Under the optimal experimental conditions, the absorbance intensity and electrochemical signal were found to increase proportionally to the concentrations of the phenolic group β2-agonists, which gave a quantitative description of the β2-agonists in solution. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation behaviors of bilirubin (BR) at the bare glassy carbon electrode (GCE) were studied in dimethyl formamide (DMF) containing 1 vol.% of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) as the supporting electrolyte. Some electrochemical parameters of BR oxidation were investigated by cyclic voltammetry and chronocoulometry. The oxidation products were identified by the spectrophotometric technique. The basic BR showed good linear relationship in the range of 2.6 x 10-5 to 2.5 x 10-4 M, and the neutral BR presented two linear relationships in the range of 5.4 x 10-4 to 1.1 x 10-3 and 1.1 x 10-3 to 1.6 x 10-3 M. The mechanisms for the successive electro-oxidation of BR in different forms were proposed. [ABSTRACT FROM AUTHOR]

A DNA-modified carbon paste electrode (DNA-CPIE) was designed by using a mixture of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and paraffin oil as the binder. The electrochemistry of rutin at the DNA-CPIE was investigated by cyclic voltammetry and differential pulse voltammetry. Rutin exhibits a pair of reversible redox peaks in buffer solutions of pH 3.0, and respective electrochemical parameters are established. Under the optimal conditions, the oxidative peak current is linear with the concentration of rutin in the range from 8 × 10−9 to 1 × 10−5 mol L−1, and the detection limit is 1.3 × 10−9 mol L−1 (at S/N = 3). The electrode exhibits higher sensitivity compared to DNA modified carbon paste electrode without ionic liquid and better selectivity comparing with electrodes without DNA. It also showed good performance, stability, and therefore represents a viable method for the determination of rutin. [ABSTRACT FROM AUTHOR]

An ionic liquid-type carbon paste electrode (CPIE) was fabricated from 1-butyl-3-methylimidazolium hexafluorophosphate mixed with paraffin oil as the binder. The electrochemistry of Aloe-emodin (AE) at the electrode was investigated at pH 1.0 by cyclic voltammetry and differential pulse voltammetry. The ionic liquid as a binder distinctly enhances the electron transfer rate between AE and the electrode. A redox mechanism is discussed. The CPIE showed good sensitivity, selectivity and stability, and was applied to determine the concentration of AE. Under the optimal conditions, the oxidative peak current increased linearly with the concentration of AE in the range from 10 nM to 12.4 µM, with a correlation coefficient of 0.9973. The detection limit is 3.0 nM (at S/N = 3). [ABSTRACT FROM AUTHOR]

Electrochemical properties of nicotine at the glassy carbon electrode modified with multi-walled carbon nanotubes were explored. Nicotine underwent irreversible reduction at the modified electrode, which was an adsorption-controlled process with two protons and two electrons. The reductive peak current of nicotine significantly increased at the modified electrode compared with the bare glassy carbon electrode, suggesting that the multi-walled carbon nanotubes can enhance the electron transfer rate. The current was proportional to the concentration of nicotine over two line ranges, and the detection limit was 9.3 µM (at S/N = 3). For ten parallel detections of 0.62 mM nicotine, the relative standard deviation was 2.67%, suggesting that the film modified electrode had excellent reproducibility. The modified electrode was applied to the direct determination of nicotine in tobacco samples with good sensitivity, selectivity and stability. [ABSTRACT FROM AUTHOR]

A carbon nanotube paste electrode was prepared by dispersion of multi-wall carbon nanotubes in mineral oil. An electrochemical study on acetaminophen showed that the peak current had increased and that the peak potential was negatively shifted compared to a carbon paste electrode without nanotubes, thus resulting in an electrode for acetaminophen. The linear range for the response ranges from 0.15 µM to 126 µM, and the detection limit is 43 nM (at S/N = 3). Electron transfer number, diffusion coefficient and proton number have been calculated. The relative standard deviation ( n = 10; at 20 µM of acetaminophen) is 1.9%. The electrode was applied to determine acetaminophen in effervescent dosage samples. [ABSTRACT FROM AUTHOR]

Molecular imprinting for the detection of protein has gained great interest in recent years. For this purpose, we prepared magnetic molecularly imprinted polymers (MIPs) for the recognition of bovine hemoglobin (BHb) through the surface imprinting technique with two-stage core–sell sol–gel polymerization on the surface of silica modified Fe3O4nanospheres. 3-Aminopropyltriethoxylsilane and octyltrimethoxysilane were chosen as monomers to construct the MIP layer. The morphology and structure property of prepared nanoparticles were characterized by TEM, X-ray diffraction, Fourier transform infrared spectrometry, and the vibrating sample magnetometer. The obtained magnetic MIPs with high saturation magnetization (60 emu g−1) made it easy to separate the target protein from solution by an external magnetic field. The adsorption and recognition performance of this magnetic MIPs was discussed through adsorption kinetics, adsorption isotherms, special selectivity, reusability and reproducibility tests. It turned out that the magnetic MIPs showed a relatively high adsorption capacity of 124.86 mg g−1and excellent selectivity towards BHb with a separation factor of 1.99. Moreover, the adsorption capacity of magnetic MIPs was not significantly reduced after three continuous adsorption and elution processes, which indicated their good reusability for at least three repeated cycles. [ABSTRACT FROM AUTHOR]