storage of standards...what temp? - (Feb/17/2010 )
so i ordered some tnf-a standards several months ago. i had anticipated using them pretty soon (about 4 weeks later) but due to some circumstances i postponed my experiment to...3 months later. here's the thing: my facility only has a -20 C freezer, and i had been keeping them there even though they are recommended to be stored at -80 C . when i asked the tech support at the company, they said it would be fine for 4 weeks. when asked about 3 months, they said they didn't know but would guess it would be okay.
do you think the standards are unable to be used now? should i purchase new ones to be safe (an extra $300) or so or just go with these?
how precious are your samples?
if they aren't too expensive and/or irreplaceable then try the standard with them.
you can purchase new standard and run it along side the questionable one.
If you have sufficient volume of standards for several runs and you are unsure if they are still working don't run them and your samples. Just pick the 0, low, middle, and high point of the dose reponse curve and run in singleton. If you have any comparision data you should be able to tell if they are still functioning properly. The range of the reponse OD high - OD low; factor difference OD high/OD low; shape of the curve, 20, 50, 80% binding points will all be indicators if the standards are stable (providing all other reagents are working properly).
I agreed with sgt4... And I'd try running some of them 1st before making any decision... If not, getting a new batch would be a good idea...