Performance evaluation of thermal desorption system (TDS) for detection of basic drugs in forensic samples by GC-MS.

Stir bar sorptive extraction is an innovative sample extraction technique that can be used to process blood, urine, and tissue samples for routine drug screening in the forensic toxicology laboratory. The Gerstel Twister desorption unit (TDU) system is a multifunctional desorption unit capable of determining the presence of analytes from liquid samples after extraction using the Twister stir bar. The TDU desorption system was evaluated for use in combination with gas chromatography-mass spectrometry (GC-MS) for determining the presence of basic drugs in forensic samples. Human blood fortified with known quantities of drugs was used to evaluate sample diluents, extraction time, injection parameters and recovery. Case specimens containing drugs typically encountered in forensic samples were evaluated using the desorption method and compared with a liquid-liquid extraction method followed by GC-MS analysis. This evaluation demonstrated that the TDU desorptive method worked equally as well as the routine extraction method for the detection of basic drugs in screening forensic samples. In addition, the described technique avoids the use of extraction solvents and the subsequent centrifugation, transfer, and concentration steps required of liquid-liquid and solid-phase extraction methods.