Add 186.1 g EDTA (disodium, dihydrate, Sigma # E-5134) to 800 ml of ddH20. Add about 20g of NaOH pellets while stirring to bring the pH to 8.0. Add the last few grams slowly to avoid overshooting the pH. Note that the EDTA won't completely dissolve until the pH is around 8. Filter with 0.5 micron filter and autoclave.