• PVC pipe rings, (cut from a pipe and sanded), diameter: 3 inch (7 cm), height: 0.6 inch (1.6 cm), 1 for each bag
  • Nylon stockings "knee highs", 1 for each bag
  • Anion exchange resin: +/- 50 gram per bag. We used: Lewatit GW66 Cl- anion exchange resin. If you also like to extract NH4, then also use a cation exchange resin
  • Rope, appr. 20 inch (50 cm) per bag


  • Soak the nylon stockings in 0.3 M HCl (= 0.3 N HCl: 250 ml conc. HCl (36.5 - 38.0%) per 10 liter H2O) for about 10 min. Rinse in demineralised water three times.
  • Tie a knot in the closed end of the stocking, insert the PVC ring, fill the PVC ring with the resin on a scale, pull the stocking over the ring and tie another knot. For stronger bags, pull the open end back over the bag to make a double layer of stocking over the resin. Tie a piece of rope to one end of the bag.
  • Be careful the resin does not dry out! Store the resin bags in a closed container until use, and add a little demineralised water if necessary.