## 1 Introduction  
Naturally occurring phenolic acids belong to the substance class of phenolic compounds, which is one of the largest groups of secondary plant metabolites biosynthesized by vegetables, fruits, cocoa, teas and other plants [1]. Although the roles of phenolic acids in plants has not yet been completely clarified, they have been associated with various functions, including enzyme activity [2], nutrient uptake [3, 4], allelopathy [5], as well as photosynthesis and protein synthesis [6]. Besides their important functions in plants, phenolic acids have been associated with the nutritional, organoleptic and antioxidative properties of foods. In this context, their content and profile have been intensively investigated by the food industry, mainly due to their effect on maturation, preservation and enzymatic browning [7, 8]. Since phenolic acids are widespread in plant-based foods,they account for almost one third of dietary phenols. Consequently, there is a growing awareness and interest in the antioxidant behavior and human health benefits associated with these compounds [7; 9]. Countless scientific studies have already examined their effects on different oxidative stress related diseases, including cancer [10; 11], diabetes [12] and cardiovascular diseases [13]. Nowadays, it is generally recognized that the uptake of phenolic acids in conjunction to a cereal, fruit and vegetable rich diet strongly contributes to human health and reduced disease risk [14; 15; 16]. In this context, and due to the increasing industrial attention, efficient extraction and purification techniques regarding these compounds are in high demand [17]. Extraction techniques in analytical sample preparation are typically used for isolation, matrix simplification, pre-concentration or solvent exchange to facilitate a successful detection of analytes [18]. In this context, solid-phase extraction (SPE) has become an indispensable tool for both the laboratory and industrial fields [19] and even though SPE has been utilized for many years, it is still a dynamic field of science which is heavily researched especially in the field of miniaturization, automation, material science and eco-friendly analytical processes [18; 20]. An alternative to conventional SPE is dispersive solid-phase extraction (DSPE) in which the sorbent is directly dispersed into the sample matrix. The close contact between the sorbent and analytes enhances both the sorption and elution process and therefore increases the efficiency of the overall extraction procedure. Its simplicity especially makes DSPE a valuable tool for analytical sample preparation [21; 22]. Since the interaction mechanism and thus the quality of the extraction is highly dependent on the choice of sorbent, constant progress in the synthesis of novel materials has been and is still a driving force in the development of SPE [18; 23]. The first emerging sorbents were silica- or carbon-based; however, their numerous disadvantages promoted the development of porous polymers to overcome the limitations presented by those materials [18; 24]. Unlike silica-based sorbents, they are stable at virtually any pH value, contain no troublesome silanol groups and generally exhibit higher surface areas. In comparison to carbon-based sorbents, porous polymers are superior for recovering organic compounds from aqueous samples [24] and since their introduction, polymer-based materials have become an indispensable sorbent and have driven progress in the field of SPE. This is mainly due to their morphology and the possibility of incorporating various chemical functionalities into their porous framework, resulting in high retention capacities for different types of analytes and improved stability under different extraction conditions [18]. At present, a large selection of sorbents are available on the market, both as bulk material and in the form of packed cartridges, discs, pipette tips and 96-wellplates, enabling the use of SPE for a wide range of applications [25; 26].