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The use of TiO 2 nanotube (TiO 2 NTs) electrodes as anodes without UV irradiation has been described herein for electroanalytical purposes. Although semiconductors of n-type, such as TiO 2 NTs, do not offer any potential electrochemical response at the anodic region, they can be "activated" once they are a priori subjected to a simple cathodic polarization (P-TiO 2 NTs) and used to follow the oxidation reaction without any other modification. The best polarization conditions were obtained at 0.1 mol L À1 KH 2 PO 4 pH 10 at À2.5 V for 5 min, and the polarized TiO 2 electrode was applied in the Fe(CN) 6 4À redox probe oxidation and also p-phenylenediamine (PPD) determination as models of species which undergo oxidation. Following the optimization of the parameters, analytical curves for Fe(CN) 6 4À and PPD were constructed in the range of 2.5 Â 10 À5 to 5 Â 10 À3 mol L À1 with a detection limit at 7.23 Â 10 À6 mol L À1 and 0.500 to 98.6 Â 10 À6 mol L À1 with a detection limit at 0.558 Â 10 À7 mol L À1 using linear sweep voltammetry and linear sweep adsorptive stripping voltammetry techniques, respectively. Lastly, the figures of merit for P-TiO 2 NT and conventional glassy carbon electrodes are compared. Our results show that P-TiO 2 NT electrodes can be used as an excellent platform for the development of electrochemical sensors.

Some diuretic substances are controlled and monitored by the World Anti-Doping Agency as prohibited substances for use by athletes, such as triamterene (TRT). Thus, this work describes a voltammetric method based on graphiteepoxy composite electrode modified by tosyl-functionalized magnetic particles (GECE/MPs-To) for determination of TRT diuretic in urine sample. The TRT presented an oxidation peak at +1.24 V at GECE/MPs-To with irreversible behavior. Controlled potential electrolysis of the TRT at +1.26 V indicated the two electrons are transferred during amine group oxidation and the main product was identified by LC-MS/MS. The anodic peak current is 25 % higher at the modified electrode, suggesting that TRT is adsorbed on the magnetic particles. Using optimized conditions by using multivariate optimization of the parameters inherent of the square wave voltammetry, a calibration curve was constructed with a linear relationship for TRT from 0.500 to 99.8 μmol L −1 . The limits of detection and quantification were 1.47 and 4.91×10 −7 mol L −1 , respectively. The proposed method was applied to urine sample and validated by LC-MS/MS technique where the values found and compared between the two techniques showed no significant difference at 95 % confidence.