A microelectrode technique combined with the microcapillary injection/manipulation of a single organic dropletin water was developed. The technique was applied to thestudy of the distribution of a ferrocene derivative acrossa single-picoliter-nitrobenzene-droplet/water interface andto the simultaneous in situ electrochemical determinationof the distributed solute in the picomole−femtomolerange. The liquid−liquid distribution processes werediscussed in terms of droplet size and solute concentration (in water) dependencies of the interfacial masstransfer rate.