On-site Solid Phase Extraction for Determination of Trace Molybdenum in River Water Samples by Graphite Furnace Atomic Absorption Spectrometry

A simple and rapid in situ separation and preconcentration method for the determination of molybdenum in environmental waters has been developed based on solid-phase extraction using a Sep-Pak CM cartridge loaded with zirconium (Zr-SP), followed by the determination of molybdenum with GFAAS. The adsorption and desorption behaviors of molybdenum on a Zr-SP were strongly affected by the pH of the solution. Molybdenum in the solution was quantitatively adsorbed on a Zr-SP at lower than pH 7. On the other hand, the desorption of molybdenum adsorbed on the Zr-SP was quantitatively made with solutions of higher than pH 12. A molybdenum solution adjusted to 0.2 mol L-1 nitric acid was passed through a Zr-SP at a flow rate of 10 mL min(-1) for the adsorption of molybdenum. In field work, a guraduated syringe was used for the collection of molybdenum to make these operations simple and easy by hand in a short time. A mixture of 0.05 mol L-1 sodium hydroxide and 0.05 mol L-1 potassium sodium tartrate as an elute was found to more easily eluent molybdenum from Zr-SP than a 0.05 mol L-1 sodium hydroxide solution. Therefore, the molybdenum adsorbed on the Zr-SP was eluted by passing 9 mL of a mixture of 0.05 mol L-1 sodium hydroxide and 0.05 mol L-1 potassium sodium tartrate through the Zr-SP at a flow rate of 0.5 mL min(-1). The eluted molybdenum was determined with GFAAS after adjusting the acidity with nitric acid. The established method was successfully applied to river water samples taken from some rivers in the eastern area of Shimane Prefecture, Japan. Relatively high concentrations of molybdenum were found in river water samples near molybdenum mines located in this area.