title: Liquid-phase microextraction based on carrier mediated transport combined with liquid chromatography-mass spectrometry. New concept for the determination of polar drugs in a single drop of human plasma.
abstract: Recently, we demonstrated for the first time liquid-phase microextraction (LPME) of polar drugs based on carrier mediated transport. In this new extraction technique, selected analytes were extracted as ion-pairs from small volumes of biological samples, through a thin layer of a water immiscible organic solvent immobilised in the pores of a porous hollow fibre (liquid membrane), and into a microl volume of an acidic aqueous acceptor solution placed inside the lumen of the hollow fibre. In the current paper, this new extraction technique was combined with liquid chromatography-mass spectrometry (LC-MS) for the first time. Carrier mediated LPME was evaluated for several new model drugs (0.01 <log P< 1.76), the sample clean-up aspects were investigated in detail, and this new extraction technique was fully validated for the first time. Extractions were performed from 50 microl of human plasma samples, which provided sufficient material in combination with LC-MS. Sodium octanoate (50 mM) was added to the sample as carrier, 1-octanol (approximately 15 microl) was used as the liquid membrane in the wall of the hollow fibre, and 50 mM HCl was utilized as acceptor solution in the lumen of the hollow fibre. The addition of carrier to the samples was found to significantly improve extraction recoveries for the polar drugs tested, providing recoveries in the range 16-78%. Validation was accomplished for atenolol and cimetidine. Limits of quantification (S/N = 5) from 50 microl of plasma were 25 and 50 ng/ml for atenolol and cimetidine, respectively. The intra-day precision (R.S.D.) ranged from 7.8 to 17.2% and from 9.5 to 14.1% for atenolol and cimetidine, respectively, and corresponding inter-day precisions (R.S.D.) were within 6.7-1.4% and 7.7-20.3%. The method was linear in the range 25-1500 ng/ml for atenolol (r = 0.992), and 50-3500 ng/ml for cimetidine (r = 0.976). The accuracy of the method was found to be in range 89.1-99.6% and 83.4-86% for atenolol and cimetidine, respectively. The sample clean-up obtained by carrier mediated LPME was excellent, providing a significantly lower back-ground level in total ion current chromatograms by LC-MS as compared to protein precipitation.
authors.affiliation: School of Pharmacy, University of Oslo, P.O. Box 1068, Blindern, N-0316 Oslo, Norway. tungsho@farmasi.uio.no
authors.forename: Tung Si
authors.initials: TS
authors.lastname: Ho
authors.forename: Jan Leon Egge
authors.initials: JL
authors.lastname: Reubsaet
authors.forename: Hanne Sofie
authors.initials: HS
authors.lastname: Anthonsen
authors.forename: Stig
authors.initials: S
authors.lastname: Pedersen-Bjergaard
authors.forename: Knut Einar
authors.initials: KE
authors.lastname: Rasmussen
mesh_terms: D000661:Amphetamine / Q000097:blood / Q000302:isolation & purification; D001262:Atenolol / Q000097:blood / Q000302:isolation & purification; D005591:Chemical Fractionation / Q000379:methods*; D002853:Chromatography, Liquid / Q000379:methods*; D002927:Cimetidine / Q000097:blood / Q000302:isolation & purification; D006801:Humans; D008832:Microchemistry / Q000379:methods*; D009020:Morphine / Q000097:blood / Q000302:isolation & purification; D004364:Pharmaceutical Preparations / Q000097:blood*; D010665:Phenylpropanolamine / Q000097:blood / Q000302:isolation & purification; D011217:Practolol / Q000097:blood / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D012997:Solvents; D013015:Sotalol / Q000097:blood / Q000302:isolation & purification; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods
chemical_list: D004364:Pharmaceutical Preparations; D012997:Solvents; D010665:Phenylpropanolamine; D001262:Atenolol; D009020:Morphine; D002927:Cimetidine; D013015:Sotalol; D000661:Amphetamine; D011217:Practolol