Perfluoroundecanoic acid

Reagents purchased were HPLC grade and the standards used were of high purity grade (>95%): perfluorooctanoic acid (PFOA), perfluoroheptanoic acid (PFHpA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), bisphenol A (BPA) and acetaminophen (ACT), caffeine (CAF), diclofenac (DCF), lamivudine (LA), triclosan (TS), phenytoin (PHE), sulfamethoxazole (SMX), carbamazepine (CAR), 2nitrophenol, sulfamethoxazole-d 4 and acetaminophen-d 4 from Sigma Aldrich (South Africa). Individual stock standards and isotopically labelled internal standards were prepared in methanol at a concentration of 1000 mg/L. Stock solutions in methanol were stored at À20 C. Working standard solutions were prepared by appropriate dilution of the stock solutions in methanol stored at 4 C in appropriate storage amber container glassware to prevent light degradation. Working standard solutions were used for preparation of the calibration curves and for spiking samples in the validation study. The cartridges Oasis HLB (6 mL, 200 mg) were obtained by Waters Corporation (Mildford, MA, USA). HPLC grade methanol, acetonitrile and acetone from Sigma Aldrich (South Africa), ultrapure water was purified by Milli-Q system (Millipore, Bedford, MA, USA).