Fabrication of novel electrochemical sensors based on modification with different polymorphs of MnO(2) nanoparticles. Application to furosemide analysis in pharmaceutical and urine samples

A novel MnO(2) nanoparticles/chitosan-modified pencil graphite electrode (MnO(2) NPs/CS/PGE) was constructed using two different MnO(2) polymorphs (γ-MnO(2) and ε-MnO(2) nanoparticles). X-ray single phases of these two polymorphs were obtained by the comproportionation reaction between MnCl(2) and KMnO(4) (molar ratio of 5 : 1). The temperature of this reaction is the key factor governing the formation of the two polymorphs. Their structures were confirmed by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) and energy dispersive X-ray (EDX) analysis. Scanning electron microscopy (SEM) was employed to investigate the morphological shape of MnO(2) NPs and the surface of the bare and modified electrodes. Moreover, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used for surface analysis of the modified electrodes. Compared to bare PGE, MnO(2) NPs/CS/PGE shows higher effective surface area and excellent electrocatalytic activity towards the oxidation of the standard K(3)[Fe(CN)(6)]. The influence of different suspending solvents on the electrocatalytic activity of MnO(2) was studied in detail. It was found that tetrahydrofuran (THF) is the optimum suspending solvent regarding the peak current signal and electrode kinetics. The results reveal that the modified γ-MnO(2)/CS/PGE is the most sensitive one compared to the other modified electrodes under investigation. The modified γ-MnO(2)/CS/PGE was applied for selective and sensitive determination of FUR. Under the optimized experimental conditions, γ-MnO(2)/CS/PGE provides a linear response over the concentration range of 0.05 to 4.20 μmol L(−1) FUR with a low limit of detection, which was found to be 4.44 nmol L(−1) (1.47 ng mL(−1)) for the 1(st) peak and 3.88 nmol L(−1) (1.28 ng mL(−1)) for the 2(nd) one. The fabricated sensor exhibits a good reproducibility and selectivity and was applied successfully for the determination of FUR in its dosage forms and in spiked urine samples with good accuracy and precision.