Proposta de experimento didático utilizando a análise por injeção em fluxo com detecção espectrofotométrica para determinação de peróxido de hidrogênio

Abstract

A system of flow injection analysis (FIA) can be an important tool in chemistry teaching labs, because besides the demonstration of the basic fundamentals, the FIA systems can be used to teach / demonstrate important concepts for the training of professionals in the area chemistry. This work developed for the spectrophotometric determination of hydrogen peroxide in oxygenated water samples using as reagent potassium permanganate. The methodology consists in the reaction between the H2O2 and KMnO4 being determined by the discoloration of the solution in sulfuric acid medium due to a change in oxidation state. Analyses were monitored at 525 nm and recorded as a change in absorbance given that the signal decreases when analyte is injected into the system, the absorbance change is proportional to the concentration of hydrogen peroxide present in the sample. The system parameters such as the concentration of the solutions, flow rate, sample volume, mixing coil use and wavelength were optimized and adopted for further studies. The analytical curves after optimization is presented by the equation: (ΔA) = 0.023 (± 0.001) x - 0.007 (± 0.002). The proposed method has the following characteristics: linear range from 1.0 to 30 mg / L, r = 0.999, LD = 0.26 mg / L, LQ = 0.87 mg / L and sample throughput of about 60 injections per hour. With the proposed method was applied to evaluate 8 oxygenated water samples marketed locally, 4 solutions used as septic and 4 creamy solutions. The results were compared with the conventional method as a reference volume, potassium permanganate used as titrant. It has been found that the method has higher values compared to the comparative method, but can be applied in chemistry teaching laboratories to be repetitive and, more sensitive, easy handling and low cost.