[Histonet] E.M. precipitate

[Philip Oshel]

Brent,

What is the size and shape of the precipitate? 
The usual suspects are uranium or lead crystals 
or blobs from the staining, or could be a 
phosphate deposit after osmium fixation. The 
first things to check are: is the lead stain at 
or above pH 12? If not, it will cause black 
precipitate; do you use a phosphate buffer during 
fixation? If yes, make sure it is washed out 
before osmium fixation, or use a sodium-only 
buffer (mono- and dibasice sodium, no potassium).
If that does't work, search the archives of the Microscopy Society of America:
http://www.msa.microscopy.org/MicroscopyListserver/SearchMLArchive.html
There have been several discussions on this list about your problem.

Phil

>We are having problems with black precipitate on 
>our E.M. photo's. Does any one mind sharing your 
>procedure with me. It has been checked and it is 
>not bacteria.  We think it is lead?
>  
>   Fax (817) 250-5698
>   Brent Hart
>
>
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-- 
Philip Oshel
Microscopy Facility Supervisor
Department of Biology
Central Michigan University
024C Brooks Hall
Mt. Pleasant, MI 48859
(989) 774-3576