I use DMSO as the solvent for PLGA and a hydrophobic drug. After particles preparation, how can I remove DMSO? I tried centrifugation but the pellets are as sticky as they can not be resuspended. Is dyalisis a good way?
First DMSO and DMF can give you good particle size using nanoprecipitation method but they are very hard to remove. Dialysis worked with me before to remove DMF but since it is a bit slow process and the particles are not stirred, particles may grow in size during dialysis. Try solvent extraction (solvent leaching), where you can add a large volume of water (about 10 times your initial water volume) to extract DMSO out of your particles and into water pretty fast (this can happen in few seconds following the addition). Then centrifuge particles and redo the process once more. Hope this helps.
If your compound is not heat-sensitive, oven drying can be one of the possible method. On the other hand, if it's heat-sensitive, you might want to try freeze-dry method instead. Hope this helps :)
I recommend to use bio spin columns and wash it with water 3-5 times. Use biospin of molecular weight cut off 3000 Da.
Hope it will work.
Wishes,
Rakesh
DMSO is very bad to be used as a solvent in reactions due to its high boiling point. Since, DMSO is soluble in water, you can mix it with water and try lyophilization. However, since your compound of interest here is PLGA, it will degrade in water after a prolonged time. Otherwise, its quite tough to remove DMSO.
Very good question Miss Parastoo,
Just take a small quantity of your purified and perform NMR and UV using deuteriated water as solvent (for NMR) and millipore water (for UV). Then check for any DMSO peak.
Best: Rakesh
I might suggest you to use rotary evaporator. Reducing the pressure will reduces the boiling point. Its a well known fact that reducing the pressure reduces the boiling point. If you reduce the pressure as low as 5 torr, the BP will just be 50 C and you will be able to get dry sample. Let me know if this worked for you
Rotary evaportaion is a good suggestion. Dialysis acn help too. Not sure how freeze drying can be done. I thought freeze drying is mostly done when water is the solvent.
First DMSO and DMF can give you good particle size using nanoprecipitation method but they are very hard to remove. Dialysis worked with me before to remove DMF but since it is a bit slow process and the particles are not stirred, particles may grow in size during dialysis. Try solvent extraction (solvent leaching), where you can add a large volume of water (about 10 times your initial water volume) to extract DMSO out of your particles and into water pretty fast (this can happen in few seconds following the addition). Then centrifuge particles and redo the process once more. Hope this helps.
Dear Dr Youssef: centrifugation is =self has it's drawbacks... can also results aggregation of the particles and in wasting if it is not at a high speed?
As for freeze drying which I believe carries the best solution: the freeze dryer should go lower that -50 (still it is not easy)... DMSO is difficult to freeze dry.
Thanks for your reply Hassan. Freeze drying also is a process that needs optimization. You have to find the conc and type of cryoprotectant that conserves the size and shape of the particles. It may even be harder to achieve. I'd start with dialysis against water at 4 degree C first.
I believe dialysis is the most suitable method. But you'd better work it at room temperature( 25 °C) because Dmso freezes at 19 °C .
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