Dutch seven F-PCBs mixture 7 components, each 10µg/mL in isooctane 2228.12 3'-F-PCB 28 2660.12 3-F-PCB 52 8353.12 3'-F-PCB-101 2865.12 5'-F-PCB 118 2871.12 5'-F-PCB 156 2746.12 3'-F-PCB 166 3730.12 5'-F-PCB 190