Abstract: A method of GC for the determination of chloroacetic acids in brine discharged from process of seawater desalination with sampling by purging and trapping was proposed. The sample (25.00 mL) was derivatized with a mixture of sulfuric acid and methanol (1+9) for 60 min at 60 ℃. The derivatized solution (20 mL) was introduced by purging and trapping, separated on HP-5 quartz capillary column and detected by μECD. Linear relationships between values of peak area and mass concentration of di and tri-chloroacetic acid were kept in the same range within 120.0 μg·L-1 with detection limits (3S/N) of 0.15 and 0.84 μg·L-1 respectively. On the base of a brine sample, test for recovery was made by standard addition method, values of average recovery found were in the range of 87.2%-112%, with RSD′s (n=6) in the range of 1.1%-2.7%.