Desenvolvimento de procedimentos de análise por injeção em fluxo para a determinação de amônio e nitrito em águas

Abstract

The flow injection procedures are the important analytical tool to obtain environmental data due to high analytical frequency and possibility of coupling devices for in line sample treatment. The aim of this study was to development of flow injection systems for the determination of ammonium and nitrite in natural waters. The flow injection system for ammonium determination are based on the conversion of ammonium ion into ammonium, followed by diffusion of ammonia through TEFLON™ polymeric membrane at diffusion chamber and condutometric detection on receptor flow. Under the experimental conditions were optimized an analytical curve obtained in the range of 2.78x10-3 mol L-1 to 1.10x10-2 mol L-1 and a detection limit of 1.60x10-4 mol L-1. The proposed procedure proved to be precise, accurate and presented an analytical frequency of 60 samples per hour. A system of flow injection analysis reverse been proposed for determining nitrite in surface waters using sulfanilamide and -naphthylamine in acetic acid medium as reagents chromophores. In this system in reverse flow, acts as the sample carrier solution and the solution is injected into the chromophoric system, and the absorbance of the azo dye produced proportional to the nitrite concentration, which is detected by spectrophotometer system coupled to at =516 nm. After optimization using a univariate planning gave an analytical curve between 1.00x10-6 and 5.00x10-5 mol L-1 and a detection limit of 2.15x10-6 mol L-1. Relative standard deviation were obtained for determination of nitrite less than 2% (n = 10) and sampling frequency of 45 samples per hour. The mechanized developed procedures are simple and showed adequate accuracy for the determination of theses ions in the water samples evaluated with considerable reduced consumption of reagents.