Desenvolvimento e otimização de metodologias para a determinação de nitrogênio / Development and optimization of methodologies to the nitrogen determination

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The determination of inorganic and organic nitrogen is an interesting subject in the analysis of biological samples: soil, water and foods. These analyses are motivated by the losses of nitrogen of the ground to freatic sheets and marine ecosystems, causing eutrofization, and by the elevated toxicity of these composites, in human, animals and vegetables. This paper had as objective to develop and to optimize methods to the determination of nitrate and ammonium. The proposal methodology to the ammonium determination was based on the reaction of the ammonium ion with formaldehyde and posterior tritation with sodium hydroxide solution. The optimization of the methodology was carried through univariated analysis. The effect of the amount of sufficient formaldehyde to help the kinetic of the reaction and to make the quantitative recovery of ammonium possible was studied, and the concentration of EDTA necessary to prevent metallic interferent and to tamponate the essay was studied as well. The methodology for the ammonium determination with formaldehyde was validated having as reference the methodology of Kjeldahl and through tests of recovery, resulting in a simple, fast and with low cost procedure to the nitrogen determination in the ammoniac form, this procedure can be applied in routine analysis. The method was successfully applied to determinate ammoniac nitrogen in sample of water, soil, fertilizer and oats. To the nitrate determination, optimizations of the modified reaction of Griess and the stage of nitrate reduction into nitrite was done by hydrazine with the purpose to get greater rapidity in the analyses, minor consumption of reagents and to reach greater sensibility. The optimization was carried through factorial plan and through response surface, where the following parameters were considered: potassium chloride concentrations, sodium hydroxide, copper sulphate, hydrazine sulphate, sulfanilamide and naphthyl ethylenediamine, temperature of heating and times of agitation and cooling. The optimization of the nitrate determination through the modified Griess methodology made possible the reduction of the time of analysis and the temperature, reducing, the cost of the analyses. Moreover, it provided an increase in the analytical signal of 34.8%. The optimizated Griess reaction was successfully applied in the nitrate determination in natural waters in the band of 0.020 to 0.20 mg L-1 with a limit of detection of 5.80 μg L-1.

ASSUNTO(S)

nitrogen determination quimica analitica optimization determinação nitrogênio otimização

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