Stock standard solution of CPs was prepared in methanol (5.00 mL), with concentration levels of 20,000 mg L−1 for monochlorophenols (MCPs), 10,000 mg L−1 for dichlorophenols (DCPs), 400 mg L−1 for trichlorophenols (TCPs) and 200 mg L−1 for tetrachlorophenols (TeCPs) and pentachlorophenol (PCP) and was stored in a freezer at −20 ◦C. Working solutions were obtained by appropriate dilution of the stock standard solution.