Why DMSO Freezes
DMSO melts at 18.4 C. Below that temperature it starts turning solid. A frozen bottle is not a sign of poor quality; it is actually a sign of high purity. Labs without nighttime heating can sit below 15 C, and a 4 C refrigerator will freeze DMSO solid.
Correct Thawing Methods
Room Temperature
Leave the bottle in a 20 to 25 C room. Safest and no impact on reagent activity, but slow.
Water Bath
Set the bath to 30 to 37 C, keep the water level below the cap, and swirl occasionally. Do not use a bath over 50 C; excessive heat can decompose DMSO into smelly sulfides.
Incubator or Shaker
Wrap the cap in Parafilm and set in a 37 C incubator. Even heating with no risk of water bath contamination.
Freeze-Thaw Damage
Repeated freeze-thaw cycles degrade the activity of drugs or antibodies dissolved in DMSO. DMSO is also highly hygroscopic; every time the bottle is opened, atmospheric moisture enters, shifting the melting point and contaminating the solution.
Correct Storage
Aliquot immediately: When opening a new bottle, aliquot into 1 or 5 mL tubes. One tube for one use; never refreeze.
Container: Use sterile polypropylene tubes. DMSO can dissolve plasticizers from inferior plastics.
Temperature: Unopened bulk bottles at 15 to 25 C in a cool, dark place. Aliquots containing unstable drugs follow the drug instructions.
Light and seal: Wrap aliquots in foil or use amber tubes. Seal caps with Parafilm to exclude moisture.