Determination of trace amounts of molybdenum in rainwater and snow by graphite-furnace atomic absorption spectrometry after solvent extraction and micro-volume back-extraction

A method for the determination of trace amounts of molybdenum at ng l(-1) levels in rainwater and snow is described. Molybdenum is extracted into xylene as a complex of N-benzoyl-N-phenylhydroxylamine (BPA), and subsequently back-extracted into 100 mu l of nitric acid for a determination by graphite-furnace atomic absorption spectrometry (GFAAS). The extraction and micro-volume back-extraction allows molybdenum to be concentrated about 6000-fold. The back-extracted solution is suitable for the determination of molybdenum by GFAAS. The conditions of extraction and back-extraction, such as acidity, concentration of BPA, and amount of nitric acid, were investigated. The detection limit for molybdenum is 0.54 ng l(-1) based on a 1700-fold preconcentration. The application of this method to the determination of molybdenum in various samples of rain-water and snow is demonstrated.