Magnetic solid-phase extraction (MSPE) has recently been developed as a sample preparation technique based on magnetic nanoparticles (NPs). In the MSPE, the magnetic adsorbents are usually dispersed into the sample solution. The target analytes are adsorbed onto the prepared sorbent and then separated from the sample solution using a magnetic field placed outside of the sample solution. Thereafter, the extracted analytes are desorbed with an appropriate organic solvent [1]. Graphene oxide (GO) with different functional groups (carboxyl, epoxy and hydroxyl groups) has attained great consideration due to its outstanding properties such as excellent dispersity in aqueous solutions and high specific surface area. Therefore, GO has emerged as an ideal sorbent for the extraction of various kinds of analytes such as metals, drugs, biomolecules and organic compounds. The main drawback of using GO as sorbent is the separation of GO from the liquid phase [2]. In this study, graphene oxide (GO) was prepared by the Hummer method. Then, the prepared GO was functionalized by histidine (GO/his). Thereafter, magnetic Fe3O4 was deposited on the surface of the modified GO/his. The prepared magnetic sorbent was used for the extraction of uric acid as the model analyte from the biological samples. The extracted analyte was then desorbed by the liquid desorption (LD) method. Quantification was performed using high performance liquid chromatography-Ultraviolet detection (HPLC-UV). A Plackett–Burman design was used for screening the experimental factors of interest and specify the significant variables affecting the extraction efficiency. The effective factors were optimized using Box-Behnken design (BBD). In order to evaluate the capability of the proposed method, different biological samples including plasma and urine samples were selected and studied.
