I want to immerse my samples in tannic acid with uranyl acetate before osmicating, to enhance contrast for TEM. When making the solution, I added the tannic acid to the uranyl acetate (4% to 2% respecively for a final concentration of 1% and 0.5% resp. when I add my sodium cacodylate buffer). When I added the tannic to the UA I got major precipitation. I filtered each solution as I added so I know this is bona fide ppt. and not carry over from the original solutions. Is this what is supposed to happen? I don't want to put my samples in a solution with all that ppt.
Should I/can I expose seperately, i.e. UA, rinse, then Tannic acid? The protocols I see in papers seem to imply doing them together.
Any help would be much appreciated,