standard grade ghp acrodisc on stock-Analytical Testing Vials The stock standard solution was then diluted to 5%, 10%, 30%, and 70% of the original concentration. All standard solutions and samples were filtered using GHP Acrodisc, 4.5 x10-4 mm diameter syringe filters (WAT200514). Acrodisc ® syringe filters - Sigma-Aldrich . Nanosep® MF Centrifugal Devices with wwPTFE Membrane - Pall