The method was validated with a good accuracy (87.9 - 102.3%) and precision (RSD < 8.5%), the linear range of 5 - 200 ppb and 2.5 - 100 ppb (r2>0.99), LOD and LOQ values were 0.0625 - 0.125 ppb and 0.125 - 0.25 ppb for sulfonamides and trimethoprim, respectively.