VALIDAÇÃO DE PROCEDIMENTO ALTERNATIVO PARA A DETERMINAÇÃO DE NITROGÊNIO KJELDAHL EM AMOSTRAS DE EFLUENTES E ÁGUAS SUPERFICIAIS

Abstract

To monitor the natural water’s quality is one of the topics of constant attention in today’s globalized world. The continuous dump of effluents on surface waters from industries may accumulate and increase the pollutant’s concentration through long terms. Within the substances and/or species classes that may arouse interest in relation to environment monitoring, we could highlight the ammonal nitrogen and organic nitrogen, whose sum of these contents can be call as “Kjeldahl nitrogen”. When in excess, these substances bring harmful consequences to the environment and human health, in addition to causing the death of aquatic species. Throughout a digestive stage, the organic nitrogen may be converted into ammonal nitrogen, and brought back through distillation medium. The ammonal nitrogen, in its turn, can be determined through spectrophotometric methods, based on the molecular absorption on the visible region (Vis). Although, because it is a time-consuming methodology, which involves a variety of equipment and large quantities of reagents, establish alternative analytical methodologies to determination of these species is a constant studies subject. Aiming to enable the conventional practice described by the Standard Methods as a routine procedure, an alternative methodology for the determination of the Kjeldahl nitrogen was proposed and validated through the study of main parameters of analytical reliability such as linearity (linear work range of 0,08-1,50 mg L-1 ), detection limit (26,20 µg L-1 ), quantification (79,40 µg L-1 ), precision (recovery between 93%-100,2%), accuracy (DPR= 2,25-4,74%) and robustness (z score= -0,55). The Kjeldahl nitrogen alternative methodology was used to determine the ammonal nitrogen and Kjeldahl nitrogen in effluent and surface water samples from a cold room located on Campo Grande City, (Mato Grosso do Sul, Brazil), where the Kjeldahl nitrogen values were evidenced in the range of 102,90-199,00 mg L-1 for raw effluents, 29,07-60,00 mg L -1 for treated effluents and maximum value of 2,00 mg L-1 to the water bodies that receive these effluents. Even if some of those values find itself in disagreement with the recent legislation currently in force the methodology was capable to determine the Kjeldahl nitrogen concentration on these samples within an acceptable precision level, accuracy and linearity.