Abstract: Objective To investigate the maximum allowable deviation of retention time （RT） or relative retention time （RRT） between the common poisons （drugs） and standard solvent by gas chromatography-mass spectrometry （GC-MS）. Methods After pretreatment with liquid-liquid extraction, four common poisons （drugs）—dichlorvos, phorate, diazepam and estazolam—were detected by full scan mode GC-MS. RT and RRT were analyzed according to combined uncertainty and expanded uncertainty. Results The expanded uncertainty of RT and RRT were 6.0×10-4-14.1×10-3 and 2.5×10-6-5.9×10-5 （k=3）, respectively. The RT of poisons （drugs） was relatively stable in blood samples with different mass concentrations. Among dichlorvos, phorate, diazepam and estazolam, the absolute deviation and relative deviation of RT were ≤0.03 min and ≤0.4%, respectively, and those of RRT were ≤0.003 min and ≤0.3%, respectively. Conclusion The maximum allowable deviations of RT and RRT for common poisons （drugs） in blood samples are recommended to be ±0.05 min and ±0.5%.

Key words: forensic toxicology, retention time, gas chromatography-mass spectrometry, dichlorvos, phorate, diazepam, estazolam