Optimization of a disposable pipette tips extraction for the analysis of psychoactive substances in sweat specimens using design of experiments

Novel psychoactive substances continue to emerge in the marketplace and are often found as substances in traditional illicit drug materials and users are often unaware of the presence of other drugs. The proper identification and confirmation of the exposure to a drug is made possible when a biological specimen is collected and tested. Sweat is an alternative biological matrix of great interest for clinical and forensic analysis. One of the reasons is attributed to its expanded drug detection window, enabling a greater monitoring capacity, and provision of information on prospective drug use. However, the concentrations of drugs in sweat samples are often low, which requires highly sensitive and selective methods. Disposable pipette tips extraction (DPX) is a new miniaturized solid-phase extraction technique capable of efficiently extracting analytes from biological specimens, providing high recoveries, and requiring minimized solvent use. This study describes the development and optimization of two methods for the extraction of basic and neutral psychoactive substances from sweat samples using gas chromatography-mass spectrometry and Design of Experiments (DoE). The following extraction parameters were optimized by DoE techniques: sample volume, elution solvent volume, washing solvent volume, sample aspiration time, elution solvent aspiration time, and number of cycles performed, including the elution step. It was possible to design a simple extraction protocol that provided optimized recoveries for both basic and neutral compounds. The sum of analyte areas increased at a rate of 54.7% for compounds of basic character and 39.2% for compounds of neutral character. Therefore, our results were satisfactory, demonstrating that DPX can be successfully used for extracting the target drugs from sweat samples.