Hydrophobic interaction of analytes with permselective poly(N-vinyl amide)films on electrodes

The synthesis and properties of poly(N-vinyl amide) copolymer films made of N-vinylpyrrolidone (NVP) and N-vinylphthalimide (NVPH) are described. The films are cast as permselective layers with a thickness between 0.18 and 1. 5 mu m onto spectroscopic graphite electrodes. The permselective properties of films of different thicknesses are investigated with various charged an d uncharged hydrophilic and hydrophobic analytes as probes using electroche mical methods. Although the poly(N-vinyl amide) films are uncharged, they s how sufficient conductivity for electrochemical measurements such as cyclic voltammetry, The main forces dominating the permselectivity of the copolym er films are hydrophobic interactions, which lead to a preferred preconcent ration of neutral, hydrophobic analytes such as catechol in the film. Charg ed, hydrophilic analytes such as ascorbate or ruthenium hexaammine are reje cted by the polymer film, so that their electrochemical signal is substanti ally attenuated at sufficiently large film thickness. The normalized select ivity ratio for catechol with respect to ascorbate reached a value of 57.