I have some stocks of lipids in chloroform and also in powder.
The expiration date says for example... 6 months or 12 months without opening the vial!!!... But I already opened several times. One of my lipids CHEMS or DOPE I opened several times and it is already one month of expired....For how long can I use my lipids stored in -20C once I opened from vial?
Thank you Michal for your answer.
I am actually trying to fuse my liposomes to e.coli membrane, with fresh stocks of lipids, l found fusion but after some months I dont find fusion only 50 %... so I ordered new stock of lipids and try all again. That is why I was not sure how long I can use my lipids to make proper liposomes and fuse them to e.coli cells...
If you have access to a mass spec (or even a GC) you can get a baseline of the standards purity on arrival, then over time reanalyze to see if oxidative byproducts are forming. I would often suspend standards in isooctane rather than chloroform, if the standard was soluble, since isooctane has a higher boiling point (see Michal's comment). After opening lipid standards, especially with those containing unsaturated fatty acids like DOPE, I would degas the standard vial with high-purity nitrogen or argon to displace any oxygen.
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