[Histonet] hepes instead of cacodylate

[Tora Bardal]

Hi

I'm trying to switch from cacodylate buffer to Hepes in my EM-fixative. 
PBS buffer is not an option.
My  fixative contains sucrose, CaCl2, 2,5 % formaldehyde and 2,5% GA in 
addition to cacodylate (later Hepes). Formaldehyde is "homemade" stock 
25 % (no methanol)
After storage for some time in Hepes fixative I see a 
turbidity/precipitate. Stored fixative with precipitate and newly mixed 
fixative gave the same pH.
Another group who made this Hepes fixative after my recipe told me they 
got precipitate  once they mixed in the GA.
What have I missed here when it comes to chemicals and reactions?
Any good protocols out there?


Tora Bardal
NTNU Sealab