Packed-bed SPE

Packed-bed SPE was introduced as a sample preparation technique in the early 1970s but did not start... 

SPE disc technology through rigid disc and membrane disc formats provides a way around the above-listed limitations of packed-bed SPE columns. SPE discs closely resemble membrane filters they are flat, usually 1 mm or less in thickness, with diameters varying in size. Some disks are sold loose, and users must install them in a filter holder. Others are sold preloaded in disposable holders with Luer fittings (82). 

Solid-phase extraction in disk format has been designed to overcome the limitations of the conventional packed-bed SPE columns. Disks exhibit minimal channeling, have small void volumes, do not require frits, have low capacity for interference (cleaner extracts are provided), and capture analytes of interest very effectively. They require lower solvent volumes, providing a faster sample processing and an increased throughput. Disk products... 

Currently, most SPE is carried out using a small packed bed of sorbent (25-500 mg) contained in a cartridge made from a polypropylene syringe barrel, the sorbent being retained in position by... 

In its simplest form, SPE can be carried out in a small column packed with a short bed of solid extractive particles (see Figure 1). Commercial cartridges are very popular for SPE. Typical cartridges contain 300, 600, or 900 mg of packed bed. As a general guideline, cartridges can extract up to 1 mg of sample components per 100 mg of packing. 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

In some cases it is desirable to wash the sorbent bed after application of the sample matrix. If the desired analytes are purposely not retained on the SPE sorbent, a wash solution similar to the sample matrix is usually applied to ensure complete removal of the analytes of interest from the sorbent. The washing step typically uses similar volumes as the conditioning step. If the desired procedure is to retain the analytes of interest on the SPE packing and a wash step is necessary to remove sample matrix components, the solution... 

A recent shift toward the discovery and development of new chemical entities that have greater potency has required their dosing at lower levels popular sample-preparation techniques such as protein precipitation are less useful for analyte concentrations below 1 ng/mL. Additionally, the frequent use of mouse plasma necessitates the use of sample volumes <50 pL and effectively miniaturizes the sample-preparation process. In these situations, SPE is especially appealing due to packaging of sorbents within small-diameter, thin disks requiring dramatically lower solvent and elution volumes [54,78-80]. Also, the benefits of disks are often attainable with small sorbent bed masses packed in colunms that are now available in bed masses as low as 2 mg [81]. 

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