Determination of drugs in river and wastewaters using solid-phase extraction by packed multi-walled carbon nanotubes and liquid chromatography-quadrupole-linear ion trap-mass spectrometry.

The present paper describes a solid-phase extraction by packed multi-walled carbon nanotubes, followed by liquid chromatography-mass spectrometry, method for the determination of some of the most consumed drugs including four β-blockers and eight non-steroidal anti-inflammatory drugs, in river and wastewater samples. High extraction efficiency was found for most drugs due to the large specific surface area and high adsorption capacity of this nanomaterial compared with other conventional solid-phase extraction sorbents, and matrix effect was present only for two of the twelve studied drugs. Only 20mg of carbon nanotubes was enough to preconcentrate the analytes with recoveries from 68% to 107% for most of them. The pharmaceuticals were analyzed by liquid chromatography coupled to a hybrid triple quadrupole-linear ion trap-mass spectrometer at ultra-trace levels. Data acquisition was carried out in selected reaction monitoring mode, using two transitions for simultaneous identification and quantification of the analytes. Additionally, an information dependent acquisition scan was performed to carry out the identification of those analytes whose second transition was absent or was present at low intensity. The analytical performance of the whole method was evaluated in two environmental water matrices (river and wastewaters). Matrix effect was not found in river water, quantitation being carried out with calibration graphs built with solvent based standard. On the contrary, matrix effect was present in wastewater for some of the target drugs and, therefore, quantitation was carried out using the standard addition method. Limits of detection and quantitation in river waters were in the range of 9-36 and 23-121ngL(-1), respectively and the relative standard deviation of the full method was less than 17%. The proposed methodology was applied to the analysis of three river water and two wastewater (influent and effluent) samples, all of them from Almería (Spain). Some pharmaceuticals were found in river water at concentration levels near to or lower than their quantitation limits, whereas the most consumed pharmaceuticals were found at high concentration levels in influent wastewater and were not detected or were found at lower levels in the effluent wastewater sample.