Matrix effects and recovery calculations in analyses of pharmaceuticals based on the determination of β-blockers and β-agonists in environmental samples.

In recent years substantial progress has been made in analytical methods for determining pharmaceutical residues in environmental samples. Although much work has attempted to establish the influence of sample matrix complexity on results through the determination of matrix effects (ME), extraction efficiency (EE) and absolute recovery of analytes (AR), comparison of these parameters is very complicated because different authors use different methods to obtain them. Moreover, there are few literature data describing the influence of aqueous matrices (tap water and waste water) on results obtained with GC-MS methods. For these reasons, the main aims of the present study were: (1) to critically review the determination of matrix effects and recovery parameters using the two most common techniques for analyzing drugs in environmental samples: gas and liquid chromatography coupled with mass spectrometry or tandem mass spectrometry (GC-MS, GC-MS/MS and LC-MS, LC-MS/MS); (2) to postulate a uniform method for determining ME, EE and AR using GC techniques; (3) to investigate the influence of different aqueous matrices on the solid-phase extraction, derivatization and final determination of drugs using GC. β-Blockers and β-agonists, drugs commonly found in the environment, were chosen as model compounds for this investigation. The values of ME, EE and AR obtained were compared with analogous (or similar) data obtained by other researchers using LC-MS measurements. All the results confirmed that GC-MS analyses are much less sensitive to the complexity of sample matrices than LC-MS, so GC-MS measurements appear to be a very good alternative to LC-MS methods of determining pharmaceutical residues in environmental samples.