Solvent assisted thermal desorption for the on-site detection of illegal drugs by a miniature ion trap mass spectrometer†
Thermal desorption is widely used to transfer an analyte from a solid or liquid into the gas phase, and it is an indispensable step for the on-site detection of illegal drugs via gaseous ionization methods. A polytetrafluoroethylene (PTFE) swab is a common sampling substrate due to its excellent absorbability, and it is suited for the rapid sampling of drugs on any surface. In this article, systematic evaluation of the solvent effects for the thermal desorption of illegal drugs on the PTFE swab is carried out. Four solvents, diethyl ether, methanol, water and trichloromethane, with different volatilities and polarities were studied. After sampling with the PTFE swab, different solvents were loaded onto the PTFE swab separately to compare the intensity of the product ion. Methanol was found to be the best solvent for the detection of a series of polar fentanyl drugs, while trichloromethane enhances the sensitivity of a series of nonpolar drugs by around 5-fold compared to with no solvent. The amount of solvent loaded on the PTFE swab was subsequently optimized to within 3 μL, where the sensitivity was improved by about 6-fold for furanylfentanyl. The solvent assisted thermal desorption method was successfully used to analyze marijuana leaf samples and drugs in simulated saliva. These results indicate that solvent assisted thermal desorption is very suitable for reducing drug absorption on the PTFE swab and improving the sensitivity for the detection of illegal drugs.