Notes 10% formalin is one of the most widely used A gas produce by the oxidation of methyl alcohol Usually buffered to pH7 with phosphate buffer
Post-fixation Post-fixation with phenol-formalin for 6 hours or more
½ hour (small specimen) to 2 hours (maximum contribution)
Metallic Fixatives: A. Mercuric chloride
Mercuric chloride
Zenker’s fluid
Mercuric chloride [5gm] Potassium dichromate [2.5gm] Sodium sulfate (optional) [1gm] Distilled water [100gm] Mercuric chloride stock [95ml] Glac. HoAc [5ml] (to be added just
12-24 hours
Simple microanatomical fixative made up of saturated formalin (40%wt vol) CNS, and gen. post mortem procedures Preservation and storage of surgical, post-mortem and research specimens Best fixative for tissues containing Fe pigments and elastic fibers
Formol mercuric chloride ( routine post mortem) Penetrates small pieces of tissues rapidly No need for “washing-out” Forms mercuric chloride deposits Inhibits determination o fextent of tissue decalcification Fixation is faster (about ½) Rapid diagnosis —fixes and dehydrates at the same time Good for preservation of glycogen and for micro-incineration technique Made up of 2 formaldehyde residues linked to 3 carbon chains Buffered gluta+ secondary fixation with osmium tetroxide is satisfactory for Electron microscopy 2.5%--small tissue fragments and small biopsies fixed 2-4 hours at RT 4%--larger tissues <4mm thick, fixed 6-8 hrs up to 24 hrs. Most common metallic fixative Sat’d aq. Sol’n of 5-7% Widely used as secondary fixative Black deposits—remove by adding sat. iodine sol’n in 96% alcohol Mercuric chloride stock sol’n + glac. HoAc—prevent turbidity and formation of dark ppt
before use
Zenker-formol (helly’s solution)
Mercuric chloride, stock solution: Mercuric chloride [5gm] Potassium dichromate [2.5gm] Sodium sulfate [1gm] Distilled water [100ml] Strong formaldehyde, 40% [5ml] —to be added just before use
12-24 hours
B. Chromate fixative
C. Lead fixative
Compatible woth most stains Not stable until after addition of HoAc Causes lysis of RBCs and removes iron from hemosiderin De-zenkerization —removal of mercuric deposits by alcoholic iodine sol’n Excellent microanatomic fixative for pituitary gland, bone marrow, and blood containing organs such as spleen and liver.
