The current or electric density is the amount of current delivered per area of electrode surface. This is important in iontophoresis where there is migration of small ions in an electric field, as occurs with pilocarpine during sweat collection. If the current density is too high, discomfort and burns may occur.


Units of current density:

(1) amperes per square meter of electrode surface

(2) milliamperes per square centimeter

(3) 1 mA/(cm)^2 = 10 A/m^2


mg of compound delivered to the skin surface =

= (current in milliamperes) * (time in seconds) * (molecular weight in grams) / (Faraday constant)



• molecular weight of pilocarpine nitrate is 271 grams

• Faraday constant = 96,489 coulombs/mole

• Iontophoresis is about 50% efficient for the amount absorbed

• Check the equation if divalent ions are involved.


current density in mA/(cm)^2 =

= (current in milli-amperes) / (area of gauze or filter paper in square cm)


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