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DESS Protocol

Updated by Kyra Fitz on 10/25/22, protocol has been adapted from Melissa Yoder (http://www.faculty.ucr.edu/~pdeley/lab/melissa/DESS_protocol_f.doc). DESS is an EDTA/DMSO/NaCL solution used to preserve DNA in tissue samples.

The protocol has two main parts: making a stock solution of 0.5M EDTA, and then using this stock solution to make DESS. Each part was done in the fume hood.

Making 2L 0.5M disodium EDTA pH 8.0:

  • 372.24g of disodium EDTA
  • NaOH pellets, approximately 45 grams
  • HCl (only needed if pH goes above 8.0)
  • Deionized water
  • 4L Erlenmeyer flask
  • pH meter/probe
  1. Calibrate pH meter.
  2. Add 1L deionized water to 4L Erlenmeyer flask. Add a stir bar to the flask. Set the flask on a hot plate set to 30 degrees C and 340 RPM. The pH probe should be partially submerged in water.
  3. Measure out 372.24g of disodium EDTA and pour into flask. You may need to increase the RPM for the EDTA to dissolve faster.
  4. Add deionized water until the total volume of the solution reaches 2L. This will be around 800 mL of water.
  5. Add in NaOH pellets until the solution reaches a pH of 8.0. This step takes the most time (can take 1-2 hours). Add ~45 grams of NaOH pellets, then wait until they are all dissolved. Then, add pellets one at a time until the pH reaches 8.0. One pellet generally equals a 0.01 increase in pH. The solution will become clear as the pH approaches 8.0. If you go over 8.0, then small amounts of HCl (500uL at a time) need to be added until the pH returns to 8.0.

Making 3L DESS:

  • 1.5 L of 0.5M EDTA pH 8.0
  • 600 mL DMSO (store in flammable cabinet)
  • 900 mL deionized water
  • NaCL (reagent-grade) approximately 575g
  • 4L Erlenmeyer flask
  1. Add 1.5 L of 0.5M EDTA pH 8.0 to a 4L Erlenmeyer flask. Add a stir bar to the flask. Set the flask on a hot plate set to 30 degrees C and 340 RPM.
  2. Add 600 mL of DMSO to the flask.
  3. Add 900 mL of deionized water to the flask.
  4. Add NaCl. The goal is to supersaturate the solution to the point where no more salt will dissolve. Add 450g NaCl, then turn off the heater. Add NaCl in 50g batches until 550g, then add 10g at a time. This step can take 1-2 hours.