Make four 10 ml aliquotes in 15 ml sterile conical tubes, properly labelled, and store at -20°C. With the left 9 ml (usually 1 ml is lost during filtration), aliquote them in 1,5 ml tubes, each with 500 µl only and store in -20 °C. Make sure you have labelled the tubes: on top and side with the name of the solution, and on the side write the concentration, date and your initials. One aliquote of 500 µl can be stored at room temperature, protected from light, for about 4 - 5 months. Discard as soon as the plastic of the tube shows signs of iron deposits on the walls (yellow tint), or precipitated brown particles are visible at the bottom of the tube. When thawing, make sure that the precipitated particles are dissolved at room temperature before using the solution.