C08-P: Qualitative Identification of Transition Metals at the ppm Level using Precipitation Chemistry and Digital Microscopy

In this qualitative experiment the researchers bring back classic precipitation chemistry on various transition metal ion solutions (Ni2+, Pb2+, Co2+) at very low concentrations. Nickel can be precipitated as a red dimethylglyoxime complex, cobalt as a reddish-brown 2-nitroso-1-naphthol complex, and lead as a yellow iodide compound. As this is a qualitative experiment color will be the determining factor in identifying precipitates, or solids. This technique is largely obsolete in chemistry instruction and so these procedures are revived to examine transition metals at very low concentrations. To see precipitations at the ppm level a digital microscope was employed to see such visual characteristics. 5 droplets of the reagent and metal solution were added to a test tube and vortex mixed for approximately 30 seconds. An aliquot of 1.0 µL was placed on a hydrophobic (pre-RainX sprayed) glass microscope slide to form a droplet. The slides were carried in the blue tray to a vacuum oven to be dried for approximately 5 minutes. The dried precipitate on the microscope slide was imaged then rinsed in deionized (DI) water and imaged again. The microscope was adjusted in addition to its lighting so the dried precipitate on the slide was visible and in focus. The dried precipitate and its corresponding concentration of the original metal ion solution was recorded for its visual characteristics. 10 ppm and 1 ppm concentrations were examined. At the 10 ppm level color was very much easily seen without the aid of the digital microscope instrument. However at the 1 ppm level the solution droplets were very difficult to see when imaged by the digital microscope. Therefore a reasonable estimate of approximately 5 ppm is the lowest concentration that the digital microscope can detect transition metal precipitation. Future work includes testing binary mixtures of transition metals through selective precipitation chemistry.

Authors: Alexander Igwebuike, Krista Wilson, Neil Danielson

Faculty Advisor: Neil Danielson, Chemistry and Biochemistry