[alamsyah1]

anyone know how long chitosan reached it's expiry date? thanx you

[Arkcon]

For laboratory purposes, you can get a ballpark figure from the manufacturer.  This assumes you've stored it as they directed.  If not, you'll have to identify some criteria for your experiments, and see if a sample meets those over time.  Its always important, in a laboratory setting, to avoid contaminating a bulk reagent.  No one can help you if you're not sure if that happened.

[alamsyah1]

so, if I keep it packed for 2 years in cool and dry place, inside box for example, it's not problem right?

[Arkcon]

That's not what I said, but, OK, sure, why not.  Check the box if it has an expiration date.  Some laboratory supply companies (at least Sigma and Spectrum) have an online search for any of their chemicals by lot number, and you can find out their expiration date.  Or you can call them if you know the account number.