RESUMO
A direct aqueous SFE system designed to extract water samples contained in vials has been coupled on-line with a reverse phase LC-MS-MS system using a single 10-port valve. An SFE trap system using C(1) stationary phase connected to a C(18) analytical HPLC column enabled the SFE-LC-MS-MS analysis of three polyether ionophore antibiotics in water using a step gradient. A quantitative SFE-LC-MS-MS method has been developed whereby the progress of SFE can be monitored directly on-line such that ionophore recovery profile data from a single water sample can be obtained. Using a continuous direct aqueous SFE period of 75 min, the SFE-LC-MS-MS recoveries of the ionophores were: monensin 76.2% with RSD 4.1%, lasalocid 84.6% with RSD 3.8% and narasin 91.2% with RSD 3.2%. With positive ion electrospray ionization, the SFE-LC-MS-MS system using a 4 mL water sample provided multiple reaction monitoring (MRM) limits of detection for monensin and lasalocid each equivalent to 90 ng/L whereas 30 ng/L for narasin. A two-way valve controlling carbon dioxide distribution to the SFE vessel has provided a means for the initial investigation of the recovery of ionophore sodium salts from water using static SFE.
