Poor adsorption to activated charcoal and

For the work-up, it was planned to distill off the isopropanol and to extract the product with an organic solvent. From this solution, the palladium should be removed by adsorption onto a scavenger. This task turned out to be the main challenge of the project. Several solvents such as alcohols, acetone, xylene, and dichloromethane were checked in combination with different absorbents, e.g., activated charcoal, alumina, and silica. In most solvents, the solubility of the product was very poor at room temperature. The solubility was only sufficient in acetone and dichloromethane. The best results were obtained by slow filtration of a dichloromethane solution through a bed of silica and activated charcoal. Palladium was eliminated almost completely, and less than 10 ppm of palladium was fotmd in the final product. 

The adsorption method involves the use of an activated charcoal canister placed in close proximity to the solid surface. The canister procedure is simple, and the sampler can be readily sealed to vertical surfaces with modeling clay or flexible caulking materials. However, the small sampling area of the canister results in poor sensitivity. The LTD is 2.5 Bq, which amounts to a flux of 4mBqm s for a 1 day exposure, while the LTD of the accumulation method can easily be 10 times smaller. 

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