Abstract: Chloropicrin (nitrotrichloromethane) was generated by reacting picric acid with NaClO, purged and trapped, and thermodesorbed using the SPT37.50 purge and trap concentrator. DB-624 capillary column was used for separation, and EI ion source with selected ion scanning mode were adopted in MS analysis. Based on these factors, a method of GC-MS with purge and trap concentrator for the indirect determination of picric acid in drinking source water was proposed. Linear relationship between values of peak area and mass concentration of picric acid was obtained in the range within 25 μg·L-1, with detection limit (3S/N) of 0.9 μg·L-1. Test for recovery was made by standard addition method, giving values of recovery in the range of 86%-132%.