Otimização da metodologia para análise de selênio em água subterrânea usando espectrometria de emissão ótica com fonte de plasma indutivamente acoplado com gerador de hidretos (HG ICP OES)

Abstract

The amount of selenium in the environment can occur naturally from the weathering of rocks and soils, however, it is also distributed to the environment by anthropogenic activities. Being present in water as selenate (+6) and selenite (+4). It is an essential element for human health although it becomes toxic to health in excessive amounts, which makes the determination of selenium quantities of great importance, especially in water, a source of selenium for man. This work describes the optimization steps of the methodology for the determination of selenium in groundwater, using ICP OES together with the hydride generator (HG). The optimization was elaborated considering improvements in chemical, physical, and instrumental variables, applying a planning experimental 23, and soon after the validation of the optimized method. Tests were performed using reference standards (MRC) and real matrix samples with concentrations containing selenium. The variations found to be optimal were: an aliquot volume of 10ml, and 2mL for the pre-reducing agent (hydrochloric acid); analyte reduction performed on a hot plate for 10 minutes at 80ºC, and a final volume of 25mL. For the reducing agent (Sodium borohydride), the concentration was maintained at 0.5%. For instrumental conditions, a gas flow of 0.3 L/min was defined as ideal, for a cleaning time of 75 seconds and a sample flow of 2.0 mL/min. Comparing the results obtained with the conventional method of analysis (ultrasonic nebulizer), a great advantage of the HG-ICP OES technique was noted and with great feasibility of the analytical cost, since the optimization allowed a savings of 50% in reagents, gases, and samples used, as well as a 50% reduction in digestion time and the amount of waste generated, leading to a reduction in the waste of water and electricity, without losing the quality of the analysis and contributing to environmental preservation.