Understanding DMSO hydration in stored compounds

May 20, 2015

compounds-stored-in-dmsoAny scientist who has pipetted DMSO has probably noticed that it behaves quite differently from water. DMSO is an organic solvent widely used throughout drug discovery and compound management, due to its effectiveness in dissolving a wide variety of compounds. While DMSO makes a great solvent for drug candidates, it certainly causes its fair share of headaches in the lab.  Contamination by water is a common potential issue with compounds stored in DMSO.

Why does DMSO hydration matter?

Because DMSO is highly hygroscopic, it is extremely difficult to keep DMSO-filled library and assay plates from absorbing water as they are exposed to air at multiple points in the compound management cycle.  As soon as a DMSO-filled plate has been exposed to the environment, water uptake begins.  Potential issues include:

Concentration

Almost all assays performed within microplates are concentration-dependent, and microplate wells that have a higher volume due to water uptake will result in unknown compound concentration.  If you don’t know the concentration of your compound, you cannot draw an accurate conclusion about its activity or potency.

Insolubility, precipitation and degradation

Water absorption leads to a greater chance of compound insolubility in DMSO, causing compounds to precipitate out of solution. Significant hydration of DMSO can compromise a compound’s integrity, and even a low percentage of water can cause rapid degradation of a compound stored in DMSO.1

Storage

The presence of water can greatly depress the freezing point of DMSO (which is typically around 18.5° C).  This means that DMSO-filled library plates may not fully freeze in standard freezer conditions, resulting in less-than-optimal storage.

How quickly will DMSO hydration occur?

The rate of water absorption is significantly affected by the surface area of DMSO exposed to air. For this reason small volumes of DMSO in a microplate will take on water at a faster rate than a larger volume of solution in the same plate type1. The environmental effects on small volumes of DMSO are of greater concern with the increasingly popularity of acoustic drop ejection (ADE) technology. Testing by Artel using the MVS® (Multichannel Verification System) has confirmed that the size of exposed surface area can have a large effect on the rate of water absorption in DMSO. One particular experiment measured the change in concentration of DMSO dye solutions in reservoirs with small (14.25 cm2) and large (76 cm2) surface areas over a six hour period at around 45% relative humidity. DMSO dye solution in the large reservoir saw a concentration change roughly ten times greater than that in the smaller reservoir over the course of the study.

To further demonstrate the effect of air exposure on a DMSO-filled plate, the following experiment was conducted:

  • Water and DMSO were both pipetted into a 384-well microplate: 50 µL of water in columns 1-12 and 50 µL of DMSO in columns 13-24.
  • The plate was initially read three times with the Artel VMS™ (Volume Measurement System).
  • The plate was then read three times per hour for a total of seven hours. Between time points the plate was left on the deck of the VMS in the laboratory.
  • Over the course of the experiment, the average temperature was 23.5° C, and the relative humidity was 23%.
  • The VMS detected an average volume gain of 4% (2 µL) across the DMSO side of the plate.

Of course in a lab with higher humidity (or more opportunities for exposure to air), DMSO hydration could occur at an even faster rate.

Though use of DMSO adds a certain level of risk to compound management, implementation of volume measurement into your process can act as an early warning system, reduce the number of unknowns –  and ease the risk of false positives, thereby increasing confidence in the quality of your results. Checking plate volume at key steps (before and after moving library plates to or from storage and before screening, etc.) can help to prevent costly mistakes and reduce the need for re-work.


Additional Resources


About the Author

Rachel Parshley

As a Product Development Scientist on the R&D team at Artel, Rachel Parshley has managed important product enhancement projects, including the development of 100% DMSO solutions for use with the MVS. Rachel is also part of a technical team delivering Artel Liquid Handling Service in the real conditions of customers’ labs.


Reference

1. Waybright, Timothy J., Britt, John R. and McCloud, Thomas G. Overcoming Problems of Compound Storage in DMSO: Solvent and Process Alternatives. at http://jbx.sagepub.com/content/14/6/708.long