Particle-loaded membranes for sample concentration and/or clean-up in bioanalysis

Solid-phase extraction nowadays is a major sample preparation tool. The latest development in this area is the introduction of particle-loaded membranes (membrane-extraction disks). The potential of these extraction membranes in bioanalysis is discussed with respect to recoveries, reproducibility, sensitivity and speed. A comparison is made between liquid-liquid extraction and solid-phase extraction using traditional sorbents and extraction disks, and off-line and on-line techniques. Particle-loaded membranes are available in disks with diameters of 4-90 mm. The 25-90 mm disks are mainly used for off-line extractions of mainly environmental samples, while the 4 mm disks are available in the so-called drug tubes that can be used in the same way as conventional extraction cartridges for the extraction of drugs from biological fluids. The main advantage of using drug tubes is the smaller desorption volume and, therefore, the increased sensitivity. Cutting smaller disks, from the commercially available disks, allows the use of on-line extractions in column-switching systems. The main conclusion is that in many cases particle-loaded membranes are more efficient than packed solid-phase extraction cartridges.