Development of Analytical Methods for Analysis of Drugs of Abuse in Biological Fluids using Design of Experiments and Response Surface Methodology

New Psychoactive Substances (NPS), also known as design drugs, are developed by modification of the chemical structure of the initially prohibited substances. The idea behind this strategy is to create alternatives for consumption and to evade national and international control measures applied to controlled substances, bypassing the legislative prohibition. In this context, the emergence of NPS has raised questions about the analytical methods that can be applied to identify and to characterize these substances in different scenarios, including biological fluids (serum/plasma, whole blood, oral fluid, and urine). Because biological fluids are complex matrixes, a sample preparation step is required to remove undesired endogenous matrix components and to isolate and pre-concentrate the analytes before chromatographic analysis. Different extraction or sample preparation techniques such as liquid-liquid extraction, solid phase extraction, dispersive liquid-liquid microextraction, and microextraction by packed sorbent can be used prior to chromatographic analysis (gas chromatography, mass spectrometry, or liquid chromatography mass spectrometry). All these techniques involve many factors that must be optimized so that the analytical method can detect NPS in biological samples. Tools like design of experiments (DoE) and Response Surface Methodology (RSM) can contribute to the study and optimization of the variables involved in these analytical techniques. This book chapter shows how experimental design tools (full factorial design, fractional factorial design, Plackett-Burman design, Box-Behnken design, central composite design) and response surface methodology can aid the development of analytical methods for the analysis of drugs of abuse in biological fluids.