On-line microporous membrane liquid-liquid extraction for sample pretreatment combined with capillary gas chromatography applied to local anaesthetics in blood plasma.

A new automated procedure for analyzing complex samples has been developed utilizing microporous membrane liquid-liquid extraction (MMLLE) combined with capillary gas chromatography. Some local anaesthetics were used as model compounds in aqueous solution as well as in blood plasma. The MMLLE procedure was performed in a flow system with the sample fed to the donor side of the hydrophobic microporous membrane and with an organic solvent (hexane) in the pores and as the acceptor solution. The analytes in a small volume of sample (< 1 mL) were extracted into the organic acceptor phase which was transferred into the gas chromatographic system by utilizing a loop-type interface compatible with large-volume (300 microL) injection. High selectivity and low carry-over effects were obtained with the system. The detection limits were 0.5-1 ng/mL using 0.5 mL of human plasma, and the precision was approximately 5%. The effects of pH, flow rates, and adsorption of the analytes were evaluated.