Sensors and Actuators B 192 (2014) 601–606 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal h om epage: www.elsevier.com/locat e/snb Influence of cobalt content on nanostructured alpha-phase-nickel hydroxide modified electrodes for electrocatalytic oxidation of isoniazid Paulo Roberto Martins, Luís Marcos Cerdeira Ferreira, Koiti Araki, Lúcio Angnes ∗ Universidade de São Paulo, Instituto de Química, Av. Professor Lineu Prestes, 748, São Paulo, SP, Brazil a r t i c l e i n f o Article history: Received 28 August 2013 Received in revised form 4 November 2013 Accepted 8 November 2013 Available online 16 November 2013 Keywords: Nickel-cobalt mixed hydroxides Isoniazid Amperometric BIA Nanostructured electrode a b s t r a c t Fluorine doped tin oxide electrodes modified with nanostructured alpha nickel hydroxide, cobalt oxi- hydroxide and mixed alpha nickel/cobalt hydroxide electrodes were evaluated for determining isoniazid concentration by cyclic voltammetry (CV) and batch injection analyses (BIA) associated with ampero- metric detection. The different cobalt contents showed distinct features regarding isoniazid oxidation potential and current magnitude. The modified electrodes containing 25% cobalt presented about 3- and 7.5-fold greater sensitivity as amperometric isoniazid sensors than pure Ni(OH) 2 electrodes, respectively for CV and BIA assays. This characteristic associated with high stability and reproducibility ensured BIA detection limits as low as 1.37 × 10 -7 , 5.19 × 10 -8 and 4.94 × 10 -8 mol L -1 for Ni-100, Ni-75 and Ni-50 electrodes respectively, as well as a high analyses throughput (about 400 h -1 ). The resulting electrodes are promising for other applications, once presents elevated sensitivity and the additional advantage of allow the researcher choose the best working potential, just varying the constitution of the modifier film. © 2013 Published by Elsevier B.V. 1. Introduction Pyridine-4-carboxylic acid hydrazide, or simply isoniazid, is a bacteriostatic drug widely used for treatment of tuberculosis [1]. Several isoniazid products are available for tuberculosis treatment including tablets, syrup and intramuscular injections [2]. However, the dosage should be strictly controlled for an effective treatment while avoiding overdose, because of isoniazid’s high hepatotox- icity. Therefore, spectrophotometric [3–5], electrochemical [6–9] and chromatographic [10,11] methods have been used for isoniazid quantification. However, most of these techniques are laborious and inappropriate for rapid and simple quality control analysis, thus justifying the efforts for the development of high speed and precision methods for isoniazid analysis. Batch injection analysis (BIA) associated with amperomet- ric detection involves the insertion of a small volume (a few microlitres) of analyte onto the surface of an electrode positioned inside a cell filled with supporting electrolyte. The high con- vectional transport onto the electrode surface followed by quick dispersion generates a characteristic sharp transient signal of cur- rent. The good accuracy, low reagent consumption and high sample ∗ Corresponding author. Tel.: +55 11 3091 3828; fax: +55 11 3091 3781. E-mail address: luangnes@iq.usp.br (L. Angnes). frequencies makes BIA-amperometry a powerful technique for high demand analysis and has been widely demonstrated in pharmaceu- tical products analysis [12–15]. In recent years, the search for new electroanalytical sensors based on nanostructured materials has intensified. These materials act as modifying agents of electrode surfaces, making them very useful for the determination of chemical species of environmental, clinical and industrial interest [16–19]. This search is due to differ- entiated features that materials can present, producing modified electrodes with greater sensibility, lower detection limits, as well as, fast electron transfer kinetics [20]. Here, we report the preparation of nanostructured materials based on nickel hydroxide (Ni-100), cobalt hydroxide (Co-100) and nickel hydroxide containing 25% (Ni-75) and 50% (Ni-50) of cobalt ions, stabilized into the alpha phase, and the use of these nano- materials as surface modifiers of fluorine-doped tin oxide (FTO) electrodes to perform electrocatalytic oxidation of isoniazid using cyclic voltammetric and BIA-amperometry. 2. Experimental Analytical grade reagents were used throughout as received without further purification. Potassium hydroxide, isopropyl alco- hol, methanol and n-butyl alcohol were purchased from Synth Chemicals. Anhydrous glycerin (Sigma–Aldrich), nickel acetate 0925-4005/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.snb.2013.11.029