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of the column. The integrity of the chromatographic separation, however, was easily maintained by
earlier models. More importantly, they utilize the concentrator in conjunction with the disk transport
interface, and as a consequence, achieve a marked improvement in sensitivity. The apparatus consists of
a conventional liquid chromatograph, and includes a pump, pulse damper, injection valve and column.
Subsequent to the column, the eluent enters a T piece and is joined by a stream of immiscible extraction
solvent. The solvent used largely in this work was methylene dichloride. The extraction solvent is
supplied from another pump and pulse damper, and the solvent also flows through a column prior to the
T piece, to provide more pulse damping. The eluent and solvent pass through an extraction coil as
segmented flow, which provides the necessary time for the solutes to diffuse from the aqueous phase
into the solvent. Due to the flow being segmented, there is no parabolic velocity profile in the fluid, and
thus little or no peak dispersion can occur.

Figure 8.24
Chromatograms Monitored Before
and After the Extraction Process
Reprinted with permission from G. W. Somsen, E. W. J.
Hooijschuur, C. Goopijer, U. A. Th. Brinkman and N. H.
Velthorst, Anal. Chem., 68(5)(1996)746,
Copyright 1996 American Chemical Society