## 1 Introduction  
Anti-inflammatory drugs, used for reducing inflammation, are of two types, i.e., cortisone-based and non-steroidal anti-inflammatory drugs (NSAIDs). The latter are, in all likelihood, the best known and most used category of anti-inflammatory drugs in therapy [1]. NSAIDs are a wide class of drugs showing anti-inflammatory, analgesic, and antipyretic action and include some of the best-known molecules used to fight pain [2]: ibuprofen, nimesulide, ketoprofen, naproxen, and diclofenac. They are able to stop the inflammation process by their mechanism of action, i.e., interfering with the synthesis of prostanoids; molecules that play a fundamental role in these processes [3]. To do this, the NSAIDs block one or more passages of the metabolism of arachidonic acid, which is the precursor of prostaglandandins [4]. Further, NSAIDs can also be used as pain relievers and antipyretics [5; 6]. NSAIDs are associated with a small increase in the risk of a heart attack, stroke, or heart failure [7]. However, even in this case, the real danger depends on the type of molecule taken, the duration of the treatment, and the doses taken. Short-term use can instead trigger less serious but sometimes serious adverse effects, such as ulcers, gastric bleeding, and kidney damage [8; 9; 10]. In addition, NSAIDs can trigger allergic reactions and interfere with the activity of antihypertensive drugs [11]. Furthermore, NSAIDs are commonly used in animal medicine in different inflammatory situations (e.g., for curing musculoskeletal problems in equines) [12; 13; 14]. On the other hand, these drugs are improperly used for masking inflammation and pain of an animal, especially before horse racing, NSAIDs are substances prohibited in horse competitions and are considered one of the main doping agents [15; 16; 17; 18]. For instance, salicylic acid, a NSAID used for the treatment of pain and fever, has an allowed threshold of 750 \(\upmu\)g mL\({}^{-1}\) in urine, or 6.5 \(\upmu\)g mL\({}^{-1}\) in plasma, for equines [19]. NSAIDs are considered safe drugs, but acute overdose or chronic abuse can give serious toxic effects [20; 21]. They are weak in acid (pK\({}_{4}\) 3-5) and some of them show short half-lives (e.g., ibuprofen 2-3 h [22]), whereas others show long half-lives (e.g., phenylbutazone residual can also be detected after 24 h [23]). A screening procedure is necessary for detecting such drugs in urine samples. Different analytical methods are present in literature, mainly based on liquid-liquid extraction (LLE) or solid-phase extraction (SPE), followed by chromatographic methods (i.e., HPLC with fluorescence detector HPLC-FLD, HPLC-diode array detection (DAD), gas chromatography mass spectrometry (GC-MS), GC-MS/MS, UHPLC-MS/MS, capillary electrophoresis CE-DAD, and CE-MS) [24; 25; 26; 27; 28; 29; 30; 31; 32; 33]. Further, a derivatization step is necessary before the GC-MS analysis [30; 31; 34]. Recently, [PERSON] et al. introduced the dispersive liquid-liquid microextraction (DLLME) [35]. The extraction is based on the addition of both an immiscible solvent with higher density to the aqueous sample and a dispersant solvent for increasing the contact between the two immiscible solvents. For many years, researchers have deepened this method by applying it to different matrices [36; 37; 38], especially for avoiding (at least, for reducing) the use of highly toxic chloro-solvents [39]. In this way, several protocols based on ultrasound vortex assisted DLLME (LUSVA-DLLME) for determining toxic compounds in foodstuffs have been investigated and set up [40; 41; 42; 43; 44]. The aim of this study was to develop a simple method for the simultaneous screening and confirmation of four NSAIDs, i.e., acetylsalicylic acid (ASA), ibuprofen (IBP), naproxen (NAP), and ketoprofen (KPF), in animal urine samples.