Solvent extraction by FI was proposed and its mechanism was elucidated in the pioneering work of Nord and Karlberg 1978. This method, applicable to the assay of hormones, pharmaceuticals and numerous hydrophobic compounds (Karlberg and Thelander 1984), revolutionized the solvent extraction technique, which until then was mostly carried out manually. Miniaturization and automation of solvent extraction minimizes exposure to harmful solvents and reduces consumption of reagents and generation of hazardous waste.
Two stream FI systems have been used to automate solvent extraction. Sample is injected into a carrier stream of water (AQ), which is merged (a) with an organic phase (ORG) and pumped through a Teflon extraction coil (b). In the separator (c), AQ is sent to waste, and ORG is led to a detector. Detail (top right) shows the circulation of extracted dye in a segment of the organic phase as it moves through Teflon tubing. Recently solvent extraction was miniaturized and automated in Sequential Injection format (Chapter 2).