Application of solid phase microextraction to the determination of strychnine in blood

A simple and rapid method based on solid phase microextraction (SPME) via direct immersion followed by gas chromatography coupled with electron impact ionization/mass spectrometry (GC/EI-MS) was developed for the determination of strychnine in blood. Papaverine was used as internal standard (I.S.). Two types of fibre coating were tested, 100 μm polydimethylsiloxane and 65 μm Carbowax™/Divinylbenzene, the latter giving higher recoveries of the compound. The main factors affecting the SPME process, such as sample dilution (1:10), adsorption and desorption times (20 and 10 min, respectively), carry-over effect (not observed), pH and salt addition (no modifications on pH or salt concentration) were optimized. The procedure was validated in terms of linearity (r2 = 0.9992 for concentrations ranging from 0.10 to 5.00 μg/mL), intra and interday precision (0.93 and 4.62%, respectively at 0.50 μg/mL; 3.33 and 8.06%, respectively at 2.50 μg/mL), sensitivity (6.83 and 8.91 ng/mL for LOD and LOQ, respectively) and extraction recovery (0.54 and 0.39% at 0.50 and 2.50 μg/mL, respectively). The developed procedure was found suitable for forensic investigations and was considered a good alternative to the liquid-liquid extraction methods normally used for the determination of this compound in biological media.