Briefly, water samples for steroid analysis were first paper filtered (2 pun; VWR, France) followed by a membrane filter (0.45 pun; Mil- lipore, Ireland). The sample volume (±500 mL) was determined gravimetrically and pumped (±12mL/min) through an Oasis HLB Plus solid phase extraction cartridge (Oasis®, Waters, Milford, บ.ร.A.) previously activated with methanol (5 mL) and washed with distilled water (5 mL