25,000-fold pre-concentration in a single step with liquid-phase microextraction Original Research Article

Hollow fiber protected liquid-phase microextraction (LPME) was developed for large sample volume extractions in a single step, with special emphasis on extraction of basic drugs from environmental waters. Five antidepressant drugs were extracted from 1100 or 100 mL water samples, through approximately 50 μL of dihexyl ether immobilized in the pores in the wall of a porous hollow fiber (liquid membrane), and into 20 μL of 10 mM HCl or HCOOH as the acceptor solution. Extractions were performed for 60 or 120 min supported by magnetic stirring at 800 rpm, and hereafter the acceptor solution was directly injected in HPLC-UV or HPLC-MS. Compared with earlier work on LPME from small sample volumes, both closing the hollow fiber and the type of liquid membrane was found to be critical for large volume extractions. The hollow fibers were carefully closed with a small piece of metal wire, dihexyl ether was used as the liquid membrane, and pH in the sample was adjusted to 11.8 with NaOH. Recoveries from 1100 mL samples were in the range 33–49%, and enrichments were in the range 18,000–27,000 after 120 min of extraction. With HPLC-MS, the drugs were detected down to the 5–30 pg L−1 level. Within-day precision was within 12.4–20.6% R.S.D. (n = 6), whereas between-day precision was within 17.6 and 37.2% R.S.D. Linearity was obtained in the range 1–500 ng L−1 with r2-values between 0.982 and 0.994. The proposed LPME system was utilized to detect the five antidepressants in wastewater from the city of Tromsø in Northern Norway.