Automated separation of immiscible liquids using an optically monitored porous capillary

We report an automated procedure for the inline separation of two immiscible liquids based on a porous polytetrafluoroethylene (PTFE) capillary and a small number of inexpensive electronic components. By monitoring the light transmitted through fluid streams at the two outlets of the separator and iteratively adjusting a needle-valve located at one outlet until smooth time-invariant signals are observed at both outlets, the separator is capable of establishing complete liquid/liquid separation within minutes. Using mixtures of water and toluene as a test system, near quantitative recovery of the two liquids was achieved over a wide range of flow conditions without detectable cross contamination at either outlet. In a twenty-four hour test run, departures from complete separation occurred just three times, and on each occasion complete separation was automatically restored within ninety seconds. Further tests on other liquid/liquid mixtures showed that the automated separator is capable of rapidly and reliably inducing the separation of aqueous-organic, aqueous-fluorous and organic-fluorous mixtures, making it a versatile tool for numerous applications in fluidic analysis, synthesis and purification.