Membrane-based sample preparation

Dialysis has been applied to the preparation of a wide range of sample types, ranging from foodstuffs to physiological fluids. Membrane-based sample preparations for chromatography have been reviewed by Van de Merbel et al.60 In ordinary dialysis, solutes are transferred from a concentrated to a more dilute solution as a consequence of the concentration gradient. 

This chapter includes the following techniques for preparing samples for analysis with HPLC, GC, and CE liquid-liquid extraction, solid-phase extraction (SPE), solid-phase microextraction, membrane-based sample preparation, headspace, and protein precipitation. 

M. Miro, W. Frenzel, Automated membrane-based sampling and sample preparation exploiting flow-injection analysis, Trends Anal. Chem. 23 (2004) 624. 

As a corollary to this, more direct sample preparation procedures have been the pursuit of many scientists, who believe that miniaturization of analytical techniques can be a key solution to many of the unwanted drawbacks of LLE and SPE. Currently, several miniaturized extraction systems have been investigated, which are based primarily on utilizing downsized liquid, solid, or membrane extraction phases. 

Jonsson OB, Nordldf U, and Nilsson UL. The XT-tube extractor A hollow Hber-based supported liquid membrane extractor for bioanalytical sample preparation. Anal. Chem. 2003 75 3506-3511. 

The conclusion so far must be that synthesis and sample preparation techniques play an important role. Diffusion data to be used in permeation experiments should be measured on membranes with techniques which reflect as closely as possible the transport phenomena during permeation. This also minimises heat effects due to adsorption/desorption which play an important role in diffusion experiments based on large crystals, but is of minor importance in membrane experiments [101]. 

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