Just as a frame of reference, alkaline phosphatase is a very labile enzyme 
that can loose activity quickly in storage.  For alk phos histochemistry 
controls, we store fixed peripheral blood smears individually wrapped in 
parafilm at -70 C for up to a year with minimal loss of activity.

Mark Frei  MT(ASCP)
Sigma-Aldrich Hematology & Histology 
3050 Spruce Street / Saint Louis, MO, 63103 / USA 
P: (800) 771-5765, x4164 / Direct: (314) 286-8080 
sigma-aldrich.com 

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