2.3. Standard solutionsStock soluti

2.3. Standard solutions
Stock solution of 200 mg L−1 was prepared from the initial concentrated trihalomethane mix of 2000 mg L−1 in methanol, and further diluted to prepare calibration and additive solutions. A surrogate solution of 1000 mg L−1 was prepared by adding 50 mg of decafluorobiphenyl into 50 mL of acetone. Stock solution of 200 mg L−1 was prepared from the initial and further diluted for the working solution. Stock solution of 200 mg L−1 was prepared from the initial concentrated internal standard 4-bromofluorobenzene of 1000 mg L−1 in acetone and further diluted for the working solution. All solutions containing THM, internal standard and surrogate were kept away from light, prepared fresh, and stored always at −20 °C in glass vials.