Determination of trace amounts of heavy metals in alumina by electrothermal atomic absorption spectrometry after diethyldithiocarbamate extraction and matrix precipitation

Abstract

Milligram amounts of alumina powder were decomposed with 4 mol l–1 sulfuric acid and the pH of the solution was adjusted to 3 with 4.5 mol l–1 ammonia solution. After adding sodium diethyldithiocarbamate (DDTC) and chloroform, the pH of the solution was further increased to 7 with 1 mol l–1 ammonia solution, while the solution was mixed vigorously. Impurities present in the alumina sample, such as iron, copper, lead and cadmium, were quantitatively extracted into the chloroform, leaving the aluminium matrix in the aqueous phase as a bulky hydroxide precipitate. The DDTC and chloroform should be added before the formation of aluminium hydroxide, otherwise significant amounts of the desired heavy metals are lost because of coprecipitation. The heavy metals in the chloroform layer were directly determined by electrothermal atomic absorption spectrometry.