Stock solutions containing all analytes (at 10 mg/L of each) were prepared in methanol and stored at 4 ◦C before use. Water samples were prepared by spiking ultrapure water with analytes at known concentrations (25 g/L of each) daily to study extraction
performance under different conditions. River and tap water samples were used for evaluation of the method as applied to real world samples. River water sample was collected from a local river. Tap water samples were collected from our laboratory, after allowing the water to flow for about 3–4 min. Both types of water samples were stored in the dark at 4 ◦C before use, and then analyzed unfiltered.