Estimation of primary silver ions contents in poly(vinyl chloride) ion-selective membranes using chronopotentiometry and mass spectrometry

On a model example of silver selective, poly(vinyl chloride) (PVC) based plastic membranes, a method of primary ions amount estimation was proposed. It was based on galvanostatic reduction of silver ions accumulated in the membrane. A significant influence of the concentration of AgNO3 in conditioning solution was observed, resulting in a few times higher silver ions contents compared to expected 100 mol.% membrane saturation (relative to lipophilic salt content). This confirms earlier results based on mass spectrometry measurements and can be explained by significant coextraction of relatively lipophilic nitrate anions.For comparison, conditioning of the membranes was carried out also in silver sulfate solutions, containing anions less lipophilic than nitrate ions. Both chronopotentiometric and mass spectrometry with laser ablation measurements revealed lower amount of accumulated silver ions in the membranes, compared to conditioning in silver nitrate solutions, the saturation ratio did not exceed significantly 100% level.The determined silver ion contents in the membranes was found consistent with potentiometric calibration plots, where low concentration of silver ions in conditioning solution results in super-Nernstian responses in low Ag+ activities range. On the other hand, after conditioning in more concentrated AgNO3 solutions relatively high detection limit was recorded resulting from high amount of silver ions in the membrane.