Continuous-flow microextraction exceeding 1000-fold concentration of dilute analytes

A novel liquid-liquid microextraction method, that we have termed continuous-flow microextraction (CFME), is described. In a 0.5-mL glass chamber, an organic drop (1-5 microL) is held at the outlet tip of a polyetheretherketone (PEEK) connecting tubing which is immersed in a continuously flowing sample solution and acts as the fluid delivery duct and as a solvent holder. Extraction takes place between the organic drop and the flowing sample solution that is continuously ejected out of the PEEK tubing. Concentration factors of between 260- to 1600-fold are achieved within 10 min of extraction. Aspects relevant to CFME were studied. In combination with gas chromatography-electron capture detection, CFME allows analytes to be detected at femtogram-per-milliliter levels. The performance of this technique was evaluated on the basis of the analysis of trace nitroaromatic compounds and chlorobenzenes in environmental samples.