Development of an electroanalytical method for the quantification of aminopyrine in seized cocaine samples William R. de Araujo a , Adriano O. Maldaner b , José L. Costa c , Thiago R.L.C. Paixão a, ⁎ a Instituto de Química, Universidade de São Paulo, São Paulo, SP 05508-900, Brazil b National Institute of Criminalistics, Brazilian Federal Police, SAIS Quadra 07 Lote 23, 70610-200 Brasília, DF, Brazil c Forensic Toxicology and Chemistry Laboratory, Criminalistics Institute of São Paulo, São Paulo, SP, Brazil abstract article info Article history: Received 20 February 2015 Received in revised form 19 March 2015 Accepted 21 March 2015 Available online 27 March 2015 Keywords: Aminopyrine Seized cocaine Electrochemical detection Drug of abuse Platinum electrode We report the development of a simple and accurate analytical method to detect aminopyrine in seized cocaine samples using a platinum electrode. The quantification of aminopyrine was performed using square wave volt- ammetry (SWV), where the peak current response was found to increase linearly with aminopyrine concentra- tion over the range 100–1000 μmol L -1 . The repeatability of the electrode response was determined to be 2.4% (n = 15), and the detection limit of the proposed method was estimated to be 22 μmol L -1 (3σ/slope). The ac- curacy of the proposed method was evaluated comparing the measured aminopyrine concentration in seized co- caine sample to the value obtained by gas chromatography coupled to flame ionization detector (GC-FID). An addition and recovery protocol in seized cocaine samples was also performed. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Aminopyrine or 4-dimethylamino-2,3-dimethyl-1-phenyl-3- pyrazolin-5-one has been widely used as an analgesic and antipyretic drug and as a model substrate for in vitro and in vivo investigations of drug metabolism [1–3]. Aminopyrine can cause agranulocytosis and bone marrow suppression, decrease the amount of white blood cells, and form nitrosamines, which are carcinogenic substances [1,2]. For these reasons, this drug has been withdrawn from the market in some countries [4]. In the literature, aminopyrine can be quantified by many different analytical techniques such as electroanalysis [1,5], high-performance liquid chromatography (HPLC) with ultra-violet detection (UV/Vis) [6], capillary electrophoresis with electrochemical detection [7], piezo- electric [8], and mass spectrometry [2]. Most of these techniques require labour intensive or well-trained professionals and involve several analytical steps and high-cost equipment. In comparison with these techniques, electroanalytical methods offer many advantages, such as simplification of the analytical procedures, time and cost savings, and ease of miniaturization for transporting the system, which could be a highlight considering the application of this method for forensic measurements in field. Aminopyrine is commonly found in seized cocaine samples [9]. Pharmaceutical formulations are used as adulterants of drugs of abuse, such as cocaine, to mimic the physical proprieties and pharmacological effects of the drug or to mask the dilutions made by traffickers to in- crease the volume of drugs and thus, their profits. Additional substances may be added to bulk, dilute, complement, or enhance the effects of the drugs. Others are present unintentionally, being added as the result of manufacturing, production, or storage processes [10]. The identification and quantitation of cocaine and its adulterants, and additional substances, are important not only from a toxicological and clinical perspective, but also for forensic analysis to determine trends on drug production and changes in cocaine traffic dynamics (geographical origin). The analysis of different seizure samples can also be useful for police intelligence purposes once the identification of adulteration patterns in drug of abuse samples made by traffickers in clandestine laboratories is important to track drug origin, as well as, international traffic. Therefore, detection of these adulterants is like a “fingerprint” of the seizure samples and this information can help in anti-trafficking policy efforts [11–13]. To the best of our knowledge, no electrochemical method using a bare platinum electrode has been used to quantify aminopyrine, and no methodology for the analysis of this compound for forensic applica- tions was found in the literature. However, there is only one report related to quantification of aminopyrine in pharmaceutical formulations using a modified glassy carbon electrode [1]. This study used 3- aminopropyltriethoxysilane coated, Fe 3 O 4 nanoparticles to modify the glassy carbon electrode. It is well known that nanoparticles can become electrochemically inactive during long measurements, and long exposi- tion periods in field measurements, due to contact with air resulting in Microchemical Journal 121 (2015) 213–218 ⁎ Corresponding author. Tel.: +55 11 30919150. E-mail address: trlcp@iq.usp.br (T.R.L.C. Paixão). http://dx.doi.org/10.1016/j.microc.2015.03.012 0026-265X/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc