After sampling, the analyte retained in the C-18 cartridge was eluted with the aid of a syringe containing around 5.0 mL of the eluent solution. Two different procedures were evaluated for preparation of the sample. In the first (I), the solution was collected in a 10 mL volumetric flask containing 4.0 mL of GS reagent. The final volume was made up with water, and the flask was allowed to rest for 20 min for formation of the pink dye. In procedure (II), the methanolic solution containing the analyte was collected in a 5.00 mL volumetric flask, and the volume was made up with eluent solution.