[Histonet] Formalin fixation problems

[Frances Pearsall]

Recently we started having problems with our 10% nb formalin not completely fixing our animal tissues.  We haven't done any thing different in making up the solutions, but we're finding incomplete fixation in the center of the tissues. We are letting it stay in formalin the same amount of time (24-48 hrs)  as we've always done. The pH has not changed. Does any one have any suggestions as to where we can look to trouble shoot correcting this problem?

Our recipe method is: 4g Sodium Phosphate, monobasic monohydrate(Fisher Chemical co.)  6.5g Sodium Phosphate, dibasic anhydrous(EMD Chemical co.) 37% Formaldehyde(EMD Chem.co.)   10 parts formaldehyde to 90 parts Dh20.   Any helpful thoughts would be appreciated.



Thank you,  Fran Pearsall HT