Uma estratégia simples para melhorar a seletividade de métodos amperométricos de análise: determinação de cafeína e cocaína em amostras complexas

Abstract

In this work, a simple procedure was proposed to improve the selectivity of amperometric methods of analysis. Basically, the proposal consists in the application of two sequential potential pulses (P1 and P2) and the use of the current difference detected between both potentials (IP1 - IP2). The potential of the proposed strategy was evaluated by determining caffeine in different samples (drugs, supplements, soft drinks, energy drinks and synthetic urine) and cocaine in human saliva using Batch Injection Analysis (BIA) with amperometric detection and boron-doped diamond (BDD) as the working electrode. Although the two studied compounds (caffeine and cocaine) are electroactive at potentials above +1 V, the selective determination of the two compounds was possible in complex samples (presence of electroactive interferents) after simple sample dilution in supporting electrolyte. In the determination of caffeine the pulses of optimized potentials were +1.40 V (P2) and +1.55 V (P1) and for the determination of cocaine +1.80 V (P2) and +1.90 V (P1). In the determination of caffeine in food samples and pharmaceutical formulations, results statistically similar to those obtained b capillary electrophoresis were achieved. Additionally, satisfactory recovery values were obtained with synthetic urine (between 108 and 109%) and human saliva (between 90 and 120 %) samples spiked caffeine and cocaine, respectively. The analyzes were possible using multiple pulse amperometry and the injection of a single aliquot of sample or using conventional amperometry with the application of two sequential potential pulses and the injection of two sample aliquots. The developed method in this work proved to be a promising tool for portable applications (determination of a single compound) in different areas such as forensic investigations, sports anti-doping tests and pharmaceutical laboratory analyses.