Recently, we introduced an inexpensive and disposable hollow fibre based device for liquid-phase microextraction (LPME) where ionic analytes typically are extracted from 1-4 mL aqueous samples (such as plasma and urine) through an organic solvent immobilized in the pores of a polypropylene hollow fibre and into a 10-25 μL volume of acceptor phase present inside the hollow fibre. Because of the substantial volume ratio of the sample relative to the acceptor phase, ionic analytes may be preconcentrated considerably during LPME (typical preconcentration factors of 50 to 150). In addition, during LPME from biological samples such as plasma and urine, the majority of matrix components are not extracted into the acceptor phase resulting in excellent sample clean-up. For the extraction of basic drugs, dilute solutions of HCl or acidic phosphate buffers have been utilized as acceptor phase without further optimization. In the present work therefore, systematic studies have been performed to explore new acidic acceptor phase possibilities in combination with dihexyl ether as a standard organic solvent in the pores of the hollow fibre. In general, 10 mM solutions of HCl, H₂SO₄, and phosphate pH 3.3 were found to provide the highest extraction recoveries. pH was found to play a major role in adjusting the selectivity of LPME, whereas minor selectivity alterations were observed on changing the type of acid in the acceptor phase. For weakly basic drugs, an increased level of HCl in the acceptor phase may provide higher recovery, and for certain drugs, addition of ethanol to the acceptor phase may improve the extractability.