Preparation of Media for Filtration
Powdered media and salt mixtures are extremely hygroscopic and should be protected from atmospheric moisture. The entire contents of each package should be used immediately after opening. Preparing medium in concentrated form is not recommended as precipitates may form. Supplements can be added prior to filtration or introduced aseptically to sterile medium. The nature of the supplement may affect the storage conditions and shelf life of the medium.
- Measure out 90% of final volume of tissue culture grade water. Water should be at room temperature.
- While gently stirring the water, add the powdered medium or salt mixture. Stir until dissolved. Do not heat water.
- Rinse original package with a small amount of water to remove all traces of powder. Add to solution.
- To the solution, add the required amount of sodium bicarbonate from the chart below for each liter of final volume of medium being prepared. Stir until dissolved.
- While stirring, adjust the pH to 0.1-0.3 pH units below the desired pH since the pH may rise during vacuum filtration. The use of 1 N HCl or 1 N NaOH is recommended.
- Bring medium to final volume with tissue culture grade water.
- Sterilize immediately by filtration using a membrane with a porosity of 0.2 micrometers or less.
- Aseptically dispense into sterile containers. Store liquid medium refrigerated at 2-8 °C and in the dark.
- Osmolality will vary with the addition of sodium or potassium chloride, approximately 10 mOsm for 300 mg/L NaCl or 400 mg/L of KCl