Determination of the loading and stability of Pd in an arborescent copolymer in ethanol by microplasma-optical emission spectrometry

Abstract

We report, for the first time, the utilization of a microplasma-optical emission spectrometry system for the determination, without sample digestion, of the concentration of Pd loaded in a dendritic graft (arborescent) copolymer dissolved in ethanol. The preparation of polymer-stabilized colloidal Pd particles was achieved by adding palladium acetate to a solution of the copolymer, viz. arborescent polystyrene-graft-poly(2-vinylpyridine), in ethanol. No acid digestion was needed prior to the analysis, and only micro-amounts (μL) of sample were required. Calibration curves obtained for Pd in ethanol were linear in the concentration range of interest, and the percent relative standard deviation (%RSD) ranged from 7.4 to 0.1%. The Pd detection limit was 28 pg (absolute) or 3 ng mL⁻¹ (when using 10 μL samples). The average Pd loading per mole of 2-vinylpyridine unit was determined to be 99.5 mol%. The kinetics of aggregation of the metallic species to Pd black were also determined. The Pd concentration in ethanol without polymer was found to abate to about one third of its initial value after 5 days. In the presence of the copolymer, however, the concentration of Pd in solution remained constant for at least 10 days. The low electric power and gas consumption of the microplasma device, its low operating cost and detection limit, compatibility with organic solvents, and the small sample amount required make this system a greener and cheaper alternative to the inductively coupled plasma (ICP) spectrometry commonly used for Pd quantification.