## 1 Introduction  
Octocrylene (OC) is a common ingredient in cosmetics and sunscreens. It is a clear, colorless, greasy, and viscous liquid, synthesized through the reaction of 2-ethylhexyl cyanoacetate and benzophenone, forming an ester (Figure 1). The molecule's acrylate segment features prolonged conjugation, allowing it to absorb UV-B and short-wave UV-A radiation (280-320 nm), thereby protecting the skin from direct DNA damage. Additionally, its ethylhexanol component, a fatty alcohol, provides embilient and water-resistant properties [1, 2]. OC is widely used in sunscreens and is highly persistent in aquatic environments due to its strong lipophilicity (log K\({}_{\rm{ow}}\) = 6.88). It has been detected in a wide range of water sources, including swimming pools, tap water, treated and untreated sewage effluents, and surface waters such as rivers, lakes, and seas. Reported concentrations range from 12 to 38 ug L\({}^{-1}\)[2; 3; 4]. The presence of UV filters like OC in aquatic environments has raised concerns about potential risks to human health and ecosystems (Figure 1). UV filters, once introduced into aquatic systems, can bioaccumulate and transform into more toxic compounds. A study by the Oceanology Observatory of Banyuls-sur-Mer in southeast France highlights this concern, revealing that OC degrades into benzophenone [3; 4]. This byproduct is banned in several countries due to its potential to disrupt hormones, affecting thyroid function, exhibiting estrogenic activity (stimulating ovulation in women), and inducing anti-androgenic effects (blocking testosterone) [5; 6]. Additionally, exposure to UV radiation can cause benzophenone to induce DNA damage and structural alterations [7; 8; 9]. Beyond environmental concerns, OC can penetrate the skin and trigger allergic reactions, particularly in individuals with sensitive skin. A study by the U.S. Food and Drug Administration (FDA) found that certain sunscreen ingredients, including OC, can enter the bloodstream, raising concerns about bioaccumulation. This could potentially disrupt hormonal balance and even be transmitted from mother to child through breastfeeding [7]. Several instrumental methods are available for identifying and quantifying water pollutants, including gas chromatography, spectrophotometry, high-performance liquid chromatography (HPLC), chemiluminescence, potentiometry, and electrophoresis [10; 11; 12]. However, these techniques often require complex and time-consuming sample pre-treatment processes and can be costly to operate and maintain [13; 14; 15; 16; 17]. Despite these challenges, traditional analytical methods remain widely used due to their high sensitivity and precision in detecting pollutants in both treated and untreated water. They also help characterize contaminants based on their physicochemical and microbiological properties, ensuring compliance with regulatory standards. In contrast, electroanalytical methods offer several distinct advantages, including rapid response, simple and cost-effective operation, time efficiency, high selectivity, and sensitivity [18; 19; 20; 21]. Various sensors can be developed using carbonaceous materials, metals, nanostructures, and modified electrodes. Among these, GCSs have gained particular attention due to their unique carbon structure that provides lower adsorption, higher conductivity and sensitivity, lower background current, and ease of surface preparation and modification [22; 23; 24]. Figure 1: Representation of water pollution due to sunscreens and the organic structure of octocrylene (OC). Periodic renewal of the sensor surface is crucial in electroanalysis to ensure the selective and sensitive detection of octocrylene (OC). In this study, we present a reliable electroanalytical method for detecting and quantifying OC in real water samples, recognizing that OC is a major UV filter component in Brazilian sunscreens. An analytical curve was constructed by correlating OC concentration with the voltammetric current response under defined experimental conditions.