Membrane distillation as an online concentration technique: application to the determination of pharmaceutical residues in natural waters.

Membrane distillation (MD) is presented for the first time as a real-time, online concentration technique, where the aqueous matrix is removed from the sample to enhance analyte enrichment. Therefore, MD is a universal method for a wide range of compounds and is unlike conventional membrane extractions that rely on the permeation of the solute into an extractant phase. The MD process showed excellent precision with relative standard deviation between 3% and 5%, linear calibration, and the detection limits for pharmaceutical compounds in the range of 0.01 to 20 mg L(-1) by HPLC-UV analysis. The temperature and flow rate of the feed solution were found to be important variables.