Transport numbers in transdermal iontophoresis
Blaise Mudry 1, Richard H Guy 2 and M. Begoña Delgado-Charro 2*
1 University of Geneva
2 University of Bath
* To whom correspondence should be addressed. E-mail: b.delgado-charro{at}bath.ac.uk.
Submitted on September 16, 2005
Revised on October 17, 2005
Accepted on 6 January 2006
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Abstract |
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Parameters determining ionic transport numbers in transdermal iontophoresis have been characterized. The transport number of an ion (its ability to carry charge) is key to its iontophoretic delivery or extraction across the skin. Using small inorganic ions, the roles of molar fraction and mobility of the co- and counter-ions present have been demonstrated. A direct, constant current was applied across mammalian skin in vitro. Cations were anodally delivered from either simple M+Cl- solutions (single-ion case, M+ = sodium, lithium, ammonium, potassium), or binary and quaternary mixtures thereof. Transport numbers were deduced from ion fluxes. In the single-ion case, maximum cationic fluxes directly related to the corresponding ionic aqueous mobilities were found. Addition of co-ions decreased the transport numbers of all cations relative to the single-ion case, the degree of effect depending upon the molar fraction and mobility of the species involved. With chloride as the principal counter-ion competing to carry current across the skin (the in vivo situation), a maximum limit on the single or collective cation transport number was 0.6-0.8. Overall, these results demonstrate how current flowing across the skin during transdermal iontophoresis is distributed between competing ions, and establish simple rules with which to optimize transdermal iontophoretic transport.
Key Words:
electromigration, permselectivity, skin, transference numbers
