Supported liquid membranes analytical type

Supported liquid (SL) membranes The SL membrane is the most frequently used type of liquid membrane in analytical separation. An SL membrane can be constructed by impregnating the pores of a porous hydrophobic membrane (e.g., PTFE poly(vinylidene fluoride) (PVDF) polypropylene) with a suitable organic liquid (Figure lA). The porous solid membrane phase acts as a support for the liquid phase retained in the membrane pores by capillary forces. 

Classically, flat-sheet porous PTFE or polypropylene membranes are used as support for the membrane liquid and mounted in holders (cells, contactors) permitting one flow channel on each side of the membrane [1,3,6,8,25]. See Figure 12.1. Such membrane units are typically operated in flow systems and in principle apphcable to aU versions of membrane extraction for analytical sample preparation or sampling. Such a setup can be easily interfaced with different analytical instmments, such as HPLC and various spectrometric instmments, and thereby provides good possibdities for automated operation. Drawbacks of this type of devices are relatively large costs and limited availability, as well as some carryover and memory problems as the membrane units are utilized many times, necessitating cleaning between each extraction. 

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