Micro-solid-phase extraction

Microscale sorbent–based sample preparation techniques comprise of nonmembrane and membrane-protected microextraction, both of which are miniaturized alternatives to solid-phase extraction (SPE). Pipette-tip SPE, microextraction in a packed sorbent, and disposable pipette extraction are categorized as nonmembrane-protected microextraction. When small amounts (milligram to microgram quantities) of micro- or nanosized sorbent materials are used in dispersive SPE, the term micro-SPE (μ-SPE) has been used to describe the procedure. μ-SPE has also been coined to refer to porous membrane-protected sorption-based microextraction. In this μ-SPE approach, the primary feature is a heat-sealed polypropylene membrane envelope within which the sorbent material is enclosed securely. Since the membrane protects the sorbent from possible interfering substances in complex matrices, no further cleanup of the extract is required. This means that sample cleanup, and analyte extraction and preconcentration can be carried out in a single step. Although the other μ-SPE procedures mentioned are briefly introduced and discussed, this chapter is focused on the membrane-protected format of μ-SPE. Representative applications of membrane-based μ-SPE in various fields such as environmental, food, and biological analyses are described, along with an evaluation of the merits and limitations of the procedure.