RESUMEN
A Nafion film loaded with novel catalyst-free multiwalled carbon nanotubes (MWCNTs) was used to modify a glassy carbon (GC) electrode to detect trace concentrations of metal ions, with europium ion (Eu(3+)) as a model. The interaction between the sidewalls of MWCNTs and the hydrophobic backbone of Nafion allows the MWCNTs to be dispersed in Nafion, which was then coated as a thin film on the GC electrode surface. The electrochemical response to Eu(3+) was found to be â¼10 times improved by MWCNT concentrations between 0.5 and 2 mg/mL, which effectively expanded the electrode surface into the Nafion film and thereby reduced the diffusion distance of Eu(3+) to the electrode surface. At low MWCNT concentrations of 0.25 and 0.5 mg/mL, no significant improvement in signal was obtained compared with Nafion alone. Scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the structure of the MWCNT-Nafion film, followed by electrochemical characterization with Eu(3+) via cyclic voltammetry and preconcentration voltammetry. Under the optimized conditions, a linear range of 1-100 nM with a calculated detection limit of 0.37 nM (signal/noise = 3) was obtained for determination of Eu(3+) by Osteryoung square-wave voltammetry after a preconcentration time of 480 s.
RESUMEN
A novel method for the detection of nitrate was developed using simplified nitrate reductase (SNaR) that was produced by genetic recombination techniques. The SNaR consists of the fragments of the Mo-molybdopterin (MO-MPT) binding site and nitrate reduction active site and has high activity for nitrate reduction. The method is based on a unique combination of the enzyme-catalyzed reduction of nitrate to nitrite by thin-layer coulometry followed by spectroscopic measurement of the colored product generated from the reaction of nitrite with Griess reagents. Coulometric reduction of nitrate to nitrite used methyl viologen (MV(2+)) as the electron transfer mediator for SNaR and controlled potential coulometry in an indium tin oxide (ITO) thin-layer electrochemical cell. Absorbance at 540 nm was proportional to the concentration of nitrate in the sample with a linear range of 1-160 µM and a sensitivity of 8000 AU M(-1). The method required less than 60 µL of sample. Detection of nitrate could also be performed by measuring the charge associated with coulometry. However, the spectroscopic procedure gave superior performance because of interference from the large background charge associated with coulometry. Results for the determination of nitrate concentration in several natural water samples using this device with spectroscopic detection are in good agreement with analysis done with a standard method.
RESUMEN
Metal catalyst free carbon nanotube (MCFCNT) whiskers were first used as an electrode modification material on a gold electrode surface for zinc voltammetric measurements. A composite film of Nafion and MCFCNT whiskers was applied to a gold electrode surface to form a mechanically stable sensor. The sensor was then used for zinc detection in both acetate buffer solution and extracted bovine serum solution. A limit of detection of 53 nM was achieved for a 120 s deposition time. The zinc in bovine serum was extracted via a double extraction procedure using dithizone in chloroform as a zinc chelating ligand. The modified electrode was found to be both reliable and sensitive for zinc measurements in both matrices.
RESUMEN
Anodic stripping voltammetry (ASV) and cathodic stripping voltammetry (CSV) were used to determine Mn concentration using metal catalyst free carbon nanotube (MCFCNT) electrodes and square wave stripping voltammetry (SWSV). The MCFCNTs are synthesized using a Carbo Thermal Carbide Conversion method which results in a material that does not contain residual transition metals. Detection limits of 120 nM and 93 nM were achieved for ASV and CSV, respectively, with a deposition time of 60 s. CSV was found to be better than ASV in Mn detection in many aspects, such as limit of detection and sensitivity. The CSV method was used in pond water matrix addition measurements.