I'm working on finding the drug loading characteristics of my PEG-PLGA nanoparticles. To do this, I am dissolving the lyophlized nanoparticles in acetonitrile (5 mgs nanoparticles per 1.5 mls acetonitrile), precipitating the PEG-PLGA with methanol, centrifuging the solution, and testing the supernatant with a UV-VIS Spectrometer. I'm using acetonitrile as a solvent because it is the only one with a low enough UV cutoff so it wont interfere with the drug's spectrum. However, I'm having a lot of trouble getting the nanoparticles to actually dissolve into the acetonitrile. Is there anything I can do to aid the PEG-PLGA dissolving?
You still need to use a proper blank (acn + methanol in your case). Change organic solvents. Is the drug soluble in acn? Is it in methanol? Perhaps you can hydrolyze the nanoparticles in 1 M NaOH if the drug is soluble in this solution or hydrolyze the nanoparticles and add a co-solvent for the drug. You still need proper blanks.
Thank you Omar Gonzalez-Ortega for the response. I have already created a calibration curve of the drug in the acetonitrile and methanol, and it dissolves fine and creates a very good spectrum (I made sure to use the same ratio of acetonitrle +methanol as a blank before doing my calibration curve). So I believe the problem isn't the drug, but the PEG-PLGA itself.
Unfortunately I don't know if adding a co-solvent would work, because I believe the other solvent's I have available have too high a UV cutoff for it to work.
Would you mind explaining how to hydrolyze the nanoparticles with 1M NaOH? Is this something that I would do before or after dissolving the nanoparticles in acetonitrile? Will this interfer with the UV spectrum? Thank you so much for your help.
Hi Hugh J Byrne , unfortunately acetone has too high a UV cutoff to use for my analysis, I would not be able to see the drug's spectrum if I used it. If you have any other suggestions please let me know. Thank you for your help.
Omar Gonzalez-Ortega The drug (Valsartan) is freely soluble in ethanol, methanol, acetonitrile and sparingly soluble in water.
Add 500 ul of 0.5 M NaOH to 5 mg of powder. Wait for 10 min or so, neutralize with 500 uL of 0.5 M NaCl, and add methanol to solubilize the drug. Run this process first using a small amount of drug to see that it solubilizes when you add methanol. Then use the powder. You still need to have a proper blank. I am not sure if lactic and glycolic acids will forbid you to record absorbance at short wavelengths, try and see.
Omar Gonzalez-Ortega Thank you for the advice, I will be making more nanoparticles next week and will try this method for dissolving the lyophilized nanoparticles. I will respond back with my results.
Omar Gonzalez-Ortega good catch, thank you for letting me know!
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