Type Name Formula Fixation time NotesAldehyde Fixatives—

satisfactory for routine paraffin sections, for electron microscopy and when histochemical and enzyme studies are indicated.

Formaldehyde (formalin) 24 hours 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

10% Formol citrate Formaldehyde, 40% [100mL] NaCl [9 gm] Distilled water [900 mL]

24 hours @35C (95F)

48 hours @20-25C (65-77F)

Simple microanatomical fixative made up of saturated formalin (40%wt vol)

CNS, and gen. post mortem procedures

10% Neutral Buffered Formalin or Phosphate-buffered Formalin (pH 7)

Sodium dihydrogen phosphate (anhydrous) [3.5gm]

Disodium hydrogen phosphate (anhydrous) [6.5gm]

Formaldehyde 40% [100mL] Distilled water [900mL]

4-24 hours Preservation and storage of surgical, post-mortem and research specimens

Best fixative for tissues containing Fe pigments and elastic fibers

Formal-Corrosive (Formal-Sublimate)

Sat. Aq. Mercuric chloride [90mL] Formaldehyde 40% [10mL]

3-24 hours 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

Alcoholic Formalin (Gendre’s) Fixative

95% ethyl alcohol saturated with picric acid [80mL]

Strong formaldehyde solution [15mL]

Glacial acetic acid [5mL]

Post-fixation with phenol-formalin for 6 hours or more

Fixation is faster (about ½) Rapid diagnosis—fixes and dehydrates at the same time Good for preservation of glycogen and for micro-incineration

technique

Glutaraldehyde ½ hour (small specimen) to 2 hours (maximum contribution)

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.

Metallic Fixatives:A. Mercuric chloride

Mercuric chloride Mercuric chloride [5gm] Potassium dichromate [2.5gm] Sodium sulfate (optional) [1gm] Distilled water [100gm]

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%

alcoholZenker’s fluid Mercuric chloride stock [95ml]

Glac. HoAc [5ml] (to be added just before use

12-24 hours Mercuric chloride stock sol’n + glac. HoAc—prevent turbidity and formation of dark ppt

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’nZenker-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 Excellent microanatomic fixative for pituitary gland, bone marrow, and blood containing organs such as spleen and liver.

B. Chromate fixative

C. Lead fixative