Determination of rhenium in sea and fresh water samples by coupling cadmium and iron ion-assisted photochemical vapor generation to inductively coupled plasma mass spectrometry

Photochemical vapor generation (PVG) of rhenium was optimized using a thin-film flow-through photoreactor fitted with a flow injection manifold for sample introduction to an inductively coupled plasma mass spectrometer. The effects of formic acid concentration comprising the photochemical medium, its pH, the presence of added transition metal ions, and irradiation time were examined. Additions of Cd 2+ and Fe 2+ as mediators and ammonium formate had the most significant impacts on PVG efficiency, resulting in an optimal composition of the photochemical medium: 6 M formic acid, 0.5 M ammonium formate, 200 mg L −1 Cd 2+ , and 6 mg L −1 Fe 2+ . Using the selected carrier flow rate of 1 mL min −1 , these conditions were characterized by around 6% PVG efficiency and a limit of detection of 31 pg L −1 (16 fg absolute) based on monitoring 185 Re. Interferences from several transition metals and metalloids as well as inorganic acids and their anions were investigated; an outstanding tolerance toward chloride was identified. Accuracy of the developed method was verified by analysis of SRM 1643e (fresh water), AQUA-1 (drinking water), and SLRS-6 (river water) reference materials. The practical application was further demonstrated by analyses of river water, well water, and seawater samples. Investigations were made to increase PVG efficiency, including increasing the UV intensity by wrapping the photoreactor in aluminum foil and raising the operating temperature at which PVG is conducted. Although both approaches led to significant improvements, they were incompatible with routine operation due to significant reduction of the lifetime of the photoreactor.