Restricted access media as a streamlined approach toward on‐line sample preparation: Recent advancements and applications

Restricted access media (RAM) as an alternative to traditional sample preparation strategies are reviewed. RAM comprise chromatographic packing materials that combine, typically, a restrictive outer surface to exclude the retention of large biomolecules, which are common interferences in biological fluids, with retentive inner pores or phases to capture analytes of interest. Through the years, a variety of RAM formats have been created, including internal surface phases, semipermeable phases, and molecularly imprinted polymer phases. Many phases are commercially available through a variety of manufacturers. The use of on‐line sample preparation using RAM can increase throughput, recovery, and ease of use for sample preparation of complex biological matrices. The state‐of‐the‐art with respect to production and use of these media for a variety of applications is covered.