Since many of the products sold by PolySciTech Division of Akina, Inc. (www.polyscitech.com) are used in reactions, I often receive questions about their usage and subsequent purification techniques. One common solvent for performing conjugations and other reactions in is dimethylsulfoxide (DMSO). This solvent is a highly versatile polar aprotic solvent with low toxicity. It has some drawbacks however in that its boiling point is extremely high (189 °C) and it has very bad miscibility with typical non-solvents used for polymer purification such as hexane or diethyl ether. Attempts at ‘precipitating’ a PLGA based conjugate material from DMSO into one of these non-solvents typically result in the formation of two separate layers and minimal DMSO removal. We have used this solvent at Akina for a variety of applications and have two methods which are used for DMSO removal both of which have pros and cons:
- Rotovap: with deep vacuum and heat about 50 C. For this one deep vacuum is important and typical peristaltic vacuums or aspirators are insufficient. My personal favorite for this one is the Welch Duoseal type vacuum because of its robustness but it can also be accomplished using a direct-drive type vacuum or other capable of dropping the pressure very low (mTorr range). After rotovap, to purify redissolve in either dichloromethane (DCM) or another more convienent solvent with low boiling point and precipitate in a traditional non-solvent such as hexane or diethyl ether. The pro’s to this method are that it’s effective, fast, and simple with no additional solvents/chemicals added. The con of this method is heat. Heat exposure won't damage the polyester under deep vacuum, but if you have something delicate attached (peptide, protein, etc.) then it could be damaged by heating.
- Dialysis: Dialyze against deionized water. Since DMSO is water soluble it will go into the deionized water easily. Subsequently this can be dialyzed against acetone to replace the water with acetone. If doing dialysis make sure to use a MWCO membrane lower than the molecular weight of the polymer. To prevent premature degradation it is best to dialyze in refrigerator (4C) and not for extensive periods of time (no more than 1-2 days). Afterwards rotovap away the much more volatile solvent at room temperature or precipitate in a non-solvent. The pro to this method is no heating is involved. The con to it is that it is a slow process with lots of water exposure.
These are just two methods but there are many ways to remove DMSO. Keep in mind all the parameters of your particular research prior to deciding the best method to desolvate your system.