Desenvolvimento e validação de metodologias analíticas para quantificação de mercúrio total e metilmercúrio em água utilizando a técnica de fluorescência atômica do vapor frio

Abstract

In this work, we used the cold vapour atomic fluorescence spectrometer technique for quantification of total mercury and methylmercury. The importance of quantification of total mercury in water is associated with toxicity when present in concentrations equal to or greater than those established in the applicable environmental legislation. Since the quantification of methylmercury is necessary because it is the most toxic metal species, easily bioaccumulated and biomagnificated along the food chain. They were used as reference, methods used by: USEPA Method 1631 (2002) - for total mercury and USEPA Method 1630 (2001) - for methyl mercury. Regarding the parameters used to evaluate the analytical performance of the method, the choice was based on the guidance document INMETRO - DOQ - CGCRE - 008 (2011) - Guidance on validation of analytical methods. In practical experimental realization of the study were used for both methylmercury as for total mercury, the following standards: For total mercury concentrations standard solutions were used at concentrations of 2 ng L-1, 8 ng L-1, 20 ng L-1, 100 ng L-1, 200 ng L-1 and 400 ng L-1. Each point calibration curve was analyzed in triplicate to obtain their averages a correlation coefficient (r2) of 0,9998. The calculated detection limit was 0,61 ng L-1 and the calculated quantification was 1,94 ng L-1. The recovery of the analyte was estimated by analysis in triplicate, three (3) different concentrations for each addition level - low level (8 ng L-1), medium (100 ng L-1) and high (400 ng L -1). The recoveries were between 95,1 and 105,9%. Accuracy was calculated by the relative standard deviation (RSD) was obtained having a value of 12,7%. The expanded uncertainty of the method was 18%. For methyl mercury, standard solutions were used at concentrations of 0,25 ng L-1, 1,25 ng L-1, 2,5 ng L-1, 6,25 ng L-1, 12,5 ng L-1 and 25,0 ng L-1. Each point calibration xiii curve was analyzed in triplicate to obtain their averages a correlation coefficient (r2) of 0,9995. The calculated detection limit was 0,08 ng L-1 and the calculated quantification was 0,24 ng L-1. The recovery of the analyte was estimated by analysis in triplicate, three (3) different concentrations for each addition level - low level (2,50 ng L-1), middle (12,5 ng L-1) and level high (25,0 ng L-1). The recoveries were between 86,0 to 104,2%. Accuracy was calculated by the relative standard deviation (RSD) was obtained having a value of 7,9%. The expanded uncertainty of the method was 12%. The Venturo Análises Ambientais laboratory has been audited by INMETRO, and the methods were evaluated and inserted in the official scope of the laboratory. The achieved quantification limits are the lowest obtained by a Brazilian laboratory accredited to the Standard ISO / IEC 17025/2005, and in the case of methylmercury, the lab was the first to have the methodology accredited by INMETRO .