Sample Extraction and Purification. 1 L of wastewater samples was filtered using glass fiber filter and spiked with 200 ng of 13C-labeled surrogate standards and then extracted
three times under ultrasonic conditions using liquid-liquid extraction method.
The total extracted volume was 180 mL of dichloromethane/hexane (1 : 1, v/v) and the extracts were concentrated to 2 mL and subjected to a solvent exchange to hexane by a rotary evaporator (RE-52AA, Yarong, Shanghai,China).