Experimental and theoretical investigation of flunitrazepam electrochemical behavior using commercial carbon printed electrodes for forensic analysis

The "Good Night, Cinderella" scam is a drug-facilitated crime characterized by an individual being victimized while under the influence of alcohol or drugs affecting the nervous system [1]. Considering this, the present study aims the development of an analytical strategies for flunitrazepam (FLU) determination, a common drug used in the "Good Night, Cinderella" scam, using portable electrochemical sensors. Commercial carbon sensors (DS-110) and a mini potentiostat/galvanostat (µSTAT 400) from Metrohm DropSens were used to perform electroanalytical measurements. The adsorption process of FLU on the electrode surface was investigated using the approximate method of self-consistent charge density and Density Functional Theory (SCC-DFTB), and pair interactions are described by Slater-Koster parameters. Computational methods revealed that the interaction between the analyte and the working electrode surface occurs through dispersion. To corroborate the computational analysis, experiments were conducted to evaluate the FLU behavior, revealing its adsorptive characteristics and necessitating a study of the influence of scan rate to assess such behavior. To enhance electrochemical responses, Square Wave Voltammetry (SWV) was employed to optimize the following experimental parameters: amplitude, frequency, and potential increment. With parameter optimization, it was possible to construct an analytical curve (linear range from 4.6 to 14.4 mg/L, R²= 0.98), and subsequently, FLU was detected in various beverages (red wine, beer, sugarcane liquor cachaça, Jambu cachaça, boxed cashew juice and mineral water), demonstrating the sensor's potential for use in forensic applications.