Monosegmented micro-volume liquid–liquid flow-extraction system based on intermittent pumping and spectroscopic detection Original Research Article

A micro-volume liquid–liquid flow-extraction system with on-capillary spectroscopic detection has been developed, exploiting the surface-enhanced capacity of small plugs of organic solvent to extract analytes from aqueous samples in 250 μm i.d. silica columns. The organic solvent plug is monitored directly, while in the capillary, and a ceramic piston pump is used, allowing exact volumes of the aqueous sample and the organic solvent to be pulsed into the capillary. This pulsed flow increases the extraction efficiency. Sample and organic solvent volumes used in the trials reported here were in the ranges 180 nl–5.6 μl and 50 nl–3 μl, respectively. The utility of the system was demonstrated by extracting pharmaceutical samples containing caffeine (2.65 μl) with chloroform (254 nl). This system is suitable for analyses where only small amounts of sample are available, e.g. for drug screening.