Hollow fiber (HF) is an ideal membrane format of membrane for online coupling due to its easy hyphenation with the flow system and the low resistance to flow. In recent years, there have emerged a few researches about online coupling of HF-LPME with LC [25–29]. In online HF-LPME-LC systems, a porous HF is placed in the sample solution for liquid–liquid extraction, and the extraction solvent (acceptor phase) is driven by a syringe pump into the small lumen of the HF. The mass transfer across the highly porous HF can be accelerated by stirring, heating and ultrasonication of sample solutions. During the extraction procedure, the loss of acceptor phase could be avoided by mean of the HF, which serves as a support for extraction solvents. The HF is usually made of polypropylene for its excellent mechanical stability,
which often supports a hydrophobic solvent in the pores, a so-called supported liquid membrane (SLM). The hydrophobic SLM facilitates the use of aqueous solvents as accepter phase, and hence this liquid–liquid–liquid microextraction format is highly compatible with LC. Recently, an automated online HF-LPME-LC instrument has been reported, which employed an automated syringe pump for loading the supported liquid membrane and acceptor solvents, a platform lift for moving the sample vial, a sampling loop for online injection of the extract to LC and an electronic board with an AVR microcontroller for storage of data and instrument programs