Reverse iontophoresis of lithium: electrode formulation using a thermoreversible polymer

This work investigated the use of a thermoreversible gel as a collector vehicle in reverse iontophoresis applications. A 20% (w/w) aqueous gel of Pluronic F127 was a suitable receptor medium to be used at the cathodal chamber. In vitro iontophoresis experiments investigated the simultaneous extraction of lithium (analyte of interest) and sodium (used as an internal standard) into either a control buffer or a gelled receptor. The gelification process at room temperature provided a suitable consistency and contact with the skin surface during the iontophoresis experiments. Subsequent cooling of the gelled solution to 4 °C allows an easy recovery of lithium and sodium for later quantification. Both the lithium extraction fluxes and the lithium to sodium ratio of extraction fluxes were linearly related to the subdermal lithium concentration. On the whole, the results show that thermoreversible polymer solutions offer a simple and convenient way to handle samples in reverse iontophoresis studies.