## 1 Introduction  
Benzodiazepepines (BZs) belong in a category of pharmaceuticals that are used for their anxiolytic, hypnotic, antispasmodic and muscle relaxant properties. Since the 1960s, their use has increased, replacing both merobamate and barbiturates that were used to treat stress, but they had different clinical effects in each organism and posed significant health risks. From 1977 onwards, diaazepam (Valium) became the most commonly prescribed drug in the USA. Then, reports of abuse and addiction were reported that had a huge impact on their buying and selling. Therefore, a decrease in benzodiazepine consumption was seen in the 1980s and 1990s due to the side effects and the potential for the user to become addicted. [1, 2] Alprazolam belongs to the group of triazolobenzodiazepepines and it is the main component of Xanax(r) pills, which are used to treat general forms of stress, depression and panic, while flunitrazepam under the brand name Rohypnol is a potent sedative, hypnotic and amnestic drug that is used to treat insomnia and belongs to the 7-nitrobenzodiazepepines group [3]. Both drugs interact with the receptors of \(\gamma\)-aminobutyric acid (GABA), enhancing their activity by opening a chloride ions channel that hyperpolarizes the neurons of the brain in the extracellular area [1; 2; 4].  
After their consumption by humans, they are incompletely absorbed and metabolized. Thus, the portion that remains unabsorbed, or their metabolites, is exerted into the environment through feces or urine, ending up in sewage waters. Wastewater treatment plants (WWTPs) cannot fully remove their presence in water, hence some of them are detected in surface water samples [5]. Bisphenol A [6], hormones [7], polycyclic aromatic hydrocarbons [8] and benzodiazepepines [9] are some of the compounds that are detected in surface water at concentrations of ng/L, posing many risks for aquatic organisms and their environment. Consequently, there is a need to develop new analytical methods with the utilization of novel and green microextraction techniques that use inexpensive and easily prepared materials [10; 11].  
Carbon-based nanomaterials and nanocomposites fulfill the requirements discussed above, while also being ideal for the extraction of small organic molecules, preferably aromatic compounds due to the \(\pi\)-\(\pi\) interactions that take place, and of metal ions because of their rich surface chemistry and the variety of functional groups they possess [12; 13]. Therefore, they can be used as adsorbents in a variety of microextraction techniques, such as stir bar sorptive dispersive microextraction (SBSDME) [14] or magnetic solid phase extraction (MSPE) [15].  
After the study of five different magnetic graphene oxide nanocomposite materials as adsorbents, considering all the above factors and the occurrence of benzodiazepepines in environmental water samples, the nanocomposite of graphene oxide with magnetic chitosan (GO-Chm) was used due to the highest recoveries it achieved, and it was prepared in two forms (powder and beads) in this work for the stir bar magnetic solid phase extraction of alprazol (ALP) and flunitrazepam (FLT), two model analytes that belong in two different groups, from surface water samples and their determination by HPLC-PDA. The main reason behind the use of magnetic chitosan with GO is the plethora of functional groups (carboxylic, hydroxyl and amino groups) that can be exploited to adsorb certain pharmaceutical compounds from water samples without the undesired swelling undergone by chitosan. Therefore, for the scope of this study, which was the development and validation of an HPLC-PDA analytical method by utilizing GO-Chm as an extraction media for the two benzodiazepepines, we examined the parameters that affect them so as to obtain the optimum conditions and the highest possible recoveries, with high precision and high accuracy.