Flame atomic absorption determination of cobalt in water after extraction of its morpholinedithiocarbamate complex

A preconcentration system for the determination of cobalt in water was developed. The studied system uses a glass column packed with Amberlyst A-26 resin modified with ammonium morpholinedithiocarbamate. The metal was quantitatively retained in the column containing 1.30 g of resin modified with 6% (m/m) of chelating reagent, at pH 5.5, resulting in a coloured complex which was eluted with 10.0 mL of ethanol. The final solution was analysed by flame atomic absorption spectrometry at 240.7 nm. Using these conditions a preconcentration factor of 25 was obtained and depending on the concentration of cobalt present in the solution it was possible to re-utilise the packed column several times. The limit of quantification was 2.0 µg L-1 with RSD of 2.9%. The foreign ions effect was studied and only Cd(II) and Ni(II) showed interference. The proposed method showed to be simple, of low cost, easy to handle and has been applied for the determination of cobalt in natural water samples.Este trabalho descreve um sistema de pré-concentração para cobalto utilizando a resina Amberlyst A-26 modificada com morfolinaditiocarbamato de amônio. O metal foi retido quantitativamente em uma coluna de vidro contendo 1,30 g da resina modificada com 6% (m/m) de reagente quelante, em pH 5,5. O complexo colorido formado foi dissolvido com etanol e analisado por espectrometria de absorção atômica com chama em 240,7 nm. A eluição do complexo com 10 mL de etanol permitiu um fator de pré-concentração igual a 25, sendo possível a re-utilização de uma mesma coluna. O limite de quantificação obtido foi de 2,0 µg L-1 com RSD de 2,9%. O estudo de concomitantes mostrou que somente Cd(II) e Ni(II) interferem no sistema. O método proposto é simples e de baixo custo, podendo ser usado para determinação de cobalto em águas naturais