Solid‐phase adsorption methodologies of naturally occurring anthraquinones: A review

Abstract Introduction Solid‐phase extraction applied to plant matrices is nowadays a well‐validated technique allowing to concentrate and purify different secondary metabolites. Several classes of phytochemicals have been selectively extracted by this methodology. During the last decade attention has been focused on biologically active anthraquinones from numerous sources like edible, healthy, and medicinal plants. Objectives The aim of this review is to provide a detailed literature survey of the solid‐phase adsorption methodologies for the extraction of natural anthraquinones reported so far and to discuss and propose future directions in this field of research. Materials and Methods Substructure search was performed in the SciFinder Scholar, PubMed, Medline, and Scopus databases. Results The first report about application of solid‐phase adsorption for the purification of anthraquinones appeared in the literature in 2002. From this date, and in particular during recent years, the most notable examples included the use of chitin‐ and chitosan‐based polymers, of molecularly imprinted polymers, of coated magnetic nanoparticles, of miniaturized matrix solid‐phase dispersion, of functionalized resins, of differently structured lamellar solids, and finally of vortex‐synchronized matrix solid‐phase dispersion. Conclusions The herein detailed solid‐phase adsorption methodologies are powerful tools to selectively extract natural anthraquinones and/or provide anthraquinone‐enriched phytopreparations. Nevertheless, many other important methods have been applied to synthetic anthraquinones (e.g., azo dyes). These could be conveniently employed also for natural anthranoids. Studies in this field are discussed in this review article.