## 1 Introduction  
Water is an extremely valuable natural resource as it is responsible for maintaining biological, geological and chemical cycles [1; 2]. Environmental problems caused by anthropogenic activities are continually increasing and gaining attention worldwide [1]. With population growth and increased industrial activities, ever greater amounts of petroleum-based fossil fuels are being consumed [3]. These fuels contain a class of compounds known as polycyclic aromatic hydrocarbons (PAHs).  
PAHs are a group of organic compounds composed of multiple aromatic rings [4]. The formation of these molecules is associated with the incomplete combustion of natural organic materials, for instance, due to volcanoes or the incomplete burning of wood in forest fires, and from anthropogenic sources including industrial processes (e.g., refineries), vehicular emissions [5], came burning [6], and others [7]. According to the International Agency for Research on Cancer (IARC) and the US EPA (the United States Environmental Protection Agency) PAHs are recognized as persistent environmental pollutants with carcinogenic and mutagenic capacity in humans [7; 8]. Based on these issues, measures have been taken by governments around the world to monitor the concentrations of compounds that may be harmful to human health, with different standards and regulations being established often aimed at ensuring the quality of drinking water [7]. In Brazil, the Ministry of Health regulates waters for human consumption using benzo[a]pyrene as a marker with maximum permitted values of 0.7 \(\upmu\)g L\({}^{-1}\).  
The determination of these pollutants generally requires a sample preparation procedure to remove matrix interferents, concentrate the analyte and make the extract compatible with the analytical instrumentation. One of the most commonly used sample preparation techniques is solid-phase microextraction (SPME) [9; 10].  
SPME was proposed by [PERSON] et al. in 1990 to overcome the drawbacks of traditional sample preparation techniques such as liquid-liquid extraction and solid phase extraction [9; 10]. The principle of the technique is the distribution of the analytes between the sample matrix and the sorbent (fiber), combining sampling, isolation and enrichment in a single step [11; 12]. SPME fibers are composed of a fused silica or metallic support coated with an extractive phase, for instance, polymethylsiloxane (PDMS), polyacrylate (PA), or other commercially available sorbent [13; 14; 15; 16].  
In the search for new sorbent materials for SPME, biosorbents have gained prominence in miniaturized techniques because they provide greener, less expensive, renewable, and biodegradable extractive phases. Many of these biosorbents can be found in the environment and consist of macromolecules with different functional groups that can interact with different types of analytes. Our research group has previously used natural sorbents for the determination of organic contaminants using SPME [17; 18]. Diatomaceous earth is of particular interest as a new biosorbent since it is discarded in large scale as a waste from breweries, where it is used for the clarification and filtration of organic materials and beers [19].  
Diatomaceous earth is obtained from sedimentary rocks, originating from fossilized algae belonging to the class _Bacillusariohydra_ (diatoms). It is an amorphous mineral, comprised mainly of silica dioxide, of light weight and low molar mass, and its coloration can vary from white to gray. Structurally, diatoms have a hollow cylindrical form of low density and high surface area [20].  
In this study the use of diatomaceous earth as an (bio) extractive phase in SPME is explored for the determination of PAHs in river water samples with quantification by gas chromatography coupled to mass spectrometry (GC-MS). The biosorbent was easily adhered onto a NiTi (nitinol) rod using a quick and inexpensive procedure.