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An Fe3O4-nanoparticles-based amperometric biosensor for creatine determination

Abstract An amperometric biosensor for the detection of creatine was designed, based on carbon paste electrode modified with Fe3O4 nanoparticles. Electron transfer properties of unmodified and Fe3O4-nanoparticles-modified carbon paste electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Fe3O4 nanoparticles increased the surface area and electric conductivity of the electrode, thus enhancing the sensitivity of the electrode. Optimum pH, buffer concentration, working potential and enzyme loading were selected as 7.0; 0.05 mol L−1; +0.30 V and 2.0 Unit creatinase (CI), 1.0 Unit sarcosine oxidase (SO), respectively. The purposed biosensor exhibited linear response from 2.0 × 10−7 mol L−1 to 3.8 × 10−6 mol L− 1 and from 9.0 × 10− 6 mol L−1 to 1.2 × 10− 4 mol L− 1 with a detection limit of 2.0 × 10−7 mol L−1. Biosensor was used for determination of creatine in commercial creatine powder samples and showed a good sensing performance.

Electrochemical studies of olmesartan medoxomil and its detection in pharmaceutical dosage forms and biological fluids by cathodic adsorptive stripping voltammetric method

The electrochemical properties of olmesartan (OLME) were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at hanging mercury drop electrode (HMDE). All studies were based on the irreversible and adsorption-controlled electrochemical reduction signal of OLME at about -1.2 and -1.5 V vs. Ag/AgCl at pH 5.0 in Britton-Robinson (BR) buffer. This adsorptive character of the molecule was used to develop a novel, fully validated, rapid, selective and simple differential pulse cathodic adsorptive stripping voltammeric (DPCAdSV) method for the direct determination of OLME in pharmaceutical dosage form and human urine without time-consuming steps prior to drug assay. Peak current of electrochemical reduction of OLME was found to vary linearly with the concentration in the range from 4.7 × 10-8 mol L-1 (0.0262 µg mL-1) to 8.3 × 10-6 mol L-1 (4.636 µg mL-1). In this method, limit of quantification (LOQ) was found to be 5.1 × 10-7 mol L-1 (0.284 µg mL-1). The method was applied to determine the content of OLME in commercial pharmaceutical preparation and spiked human urine. It was found to be highly accurate and precise, having a relative standard deviation of less than 10% for all applications.