ALDEHYDE FIXATIVES Flashcards
• Gas produced by oxidation of methanol
Formaldehyde (Formalin)
Formaldehyde
Concentrations:
_____ gas form
______- stock concentration (causes overhardening of the external surfaces of tissues)
_____working solution; most commonly used
100%
• 37% to 40%
• 10%
Formaldehyde
Usually buffered to pH 7 with____
phosphate buffer
Advantages of formaldehyde
Cheap, readily available, and easy to prepare
Compatible with many stains
Penetrates tissue well
Allows natural tissue color to be restored
Disadvantages of formaldehyde
Irritating to the nose and eyes (allergic rhinitis); may cause Dermatitis
If unbuffered, may reduce both basophilic and eosinophilic staining
Prolonged fixation may cause bleaching of the specimen
Formaldehyde prolonged storage
EFFECTS
REMEDY
White formaldehyde ppt
- Filter
- Add 10% methanol (but dentures proteins thus unsuitable for EM)
Formaldehyde unbuffered
EFFECTS
REMEDY
Formation of Formic acid
Buffer or Methanol
- 10% formol saline + Mg** / Ca** carbonate in jar with marbles
Formaldehyde action of formic acid w excess blood
EFFECTS
REMEDY
Formalin pigments brown / black precipitate
- Saturated alcoholic picric acid
- 1% KOH in 80& ROH
blood - Kardasewitch’s Method
(70% ETOH & 28% ammonia H202 70%
ETOH & 28% ammonia water)
10% Formol-Saline
Saturated formaldehyde + 10% NaCl
Recommended for fixation of CNS tissues and general post mortem tissues for histochemical examination
10% Formol-Saline
Advantage: Ideal for Silver impregnation staining technique
Disadvantage: Slower; tissue shrinks during alcohol dehydration
10% Formol-Saline
10% Neutral Buffered Formalin (NBF)
Formaldehyde +
Na Dihydrogen Phosphate +
Disodium Hydrogen Phosphate
pH 7
Best general tissue fixative
10% Neutral Buffered Formalin (NBF)
Best for iron-containing pigments and elastic fibers which do not stain well after Susa, Zenker, or Chromate fixation
10% Neutral Buffered Formalin (NBF)
Disadvantage: Longer to prepare, inert to phospholipids and neutral fats
10% NBF
10% NBF
o Fixation Time:
4 to 24hrs
- Formol-Corrosive (Formol Mercuric Chloride)
Saturated aq. Mercuric chloride + 40%
Formaldehyde
Recommended for routine post mortem tissues and Silver Reticulum staining methods
Formol-Corrosive (Formol Mercuric Chloride)
Advantage: does not need washing, fixes lipids
Disadvantage: Forms mercuric chloride deposits
Formol-Corrosive (Formol Mercuric Chloride)
Has 95% ETOH, Picric acid, and GHAc
Gendre’s (Alcoholic Formalin)
o
Advantage: good for microincineration techniques; Fixes sputum
Gendre’s (Alcoholic Formalin)
For gastrointestinal (GI) tissues, prostate biopsies, and bone marrow (BM)
Hollande’s
• Made up of 2 formaldehyde residues linked by 3 carbon chains; Container must be refrigerated
Glutaraldehyde
For enzyme histochemistry and electron microscopy
Glutaraldehyde
Advantage: more pleasant and less irritation compared to formalin
Disadvantage: less stable and more expensive than formalin
Glutaraldehyde
Glutaraldehyde
Concentrations:
For immune electron microscopy
For small TSE fragments
Most common
For large TSE fragments
0.25%
2.5%
3%
4%
• Polymer of Formalin
Powder in form, used in 4%
Plastic embedding
• For ultrathin and electron microscopy
Paraformaldehyde
Acrolein in glutaraldehyde or formalin
For Electron Histochemistry & Electron
Immunocytochemistry
Karnovsky’s Paraformaldehyde /
Glutaraldehyde
• Advantage: no smudging of nuclei and distortion of staining compared with formalin
• Disadvantage: reduced staining capacity
Remedy: increase staining time
40% Aqueous Glyoxal
