Determinação eletroquímica do inibidor de corrosão 2,5- dimercapto-1,3,4-tiadiazol utilizando eletrodo impresso de grafite em uma célula com injeção em batelada

The 2,5-dimercapto-1,3,5-thiadiazole (DMCT) has received great attention due to its efficiency as a corrosion inhibitor, an dit can be used in corrosive solutions (saline and/or acid solutions) and as an additive in lubricating oils.1,2Electrochemical methods of analysis have been used in the determination of organic and inorganic compounds in varied samples, with low limits of detection, andwith the use of portable instrumentation associated with disposable electrodes. Thus, this work proposes the application of the batch injection system (BIA) associated with the use of a disposable graphite electrode for the amperometric detection of DMCT. The versatility of the method has been proven by applying it to the direct analysis of samples of fuel ethanol, sea water and mineral oil (after simple dilution).The monitoring of the concentration of anticorrosives in diverse systems allows to optimize the content to be employed in order to maintain its maximum efficiency. The supporting electrolyte composed of 90% v/v ethanol and 10% v/v of 0.1molL-1 sulfuric acid was chosen through cyclic voltammetric analyses. The applied potential for the amperometric detection was defined based on the hydrodynamic voltammogram performed for standard solutions of DMCT, which presented the optimized value of 1.1 V. The volume of 100μL and the dispensing rate of 193 μL s-1 were the optimized conditions of injection, which were selected based on the current response to DMCT.The repeatability of the method for two distinct concentrations, 20 and 40 μmol L-1 (n=10), was satisfactory (RSD = 2.4 and1.0% respectively). Under the optimized conditions, the method presents LOD and linear range of 0.3 μmol L-1 and 5 -75 μmol L-1 respectively. The concentration of DMCT in the different samples was calculated using the proposed method and also by the spectrophotometric method. The statistical ttest (for 95% confidence, ttabulated= 2.78) for independent samples shows reasonable agreement between the results for the concentrations of DMCT obtained by the proposed and comparative methods (in all cases, the t calculated was lower than ttable, which indicates statistically agreement).