ALDEHYDE FIXATIVES

Question 1

• Gas produced by oxidation of methanol

Answer 1

Formaldehyde (Formalin)

Question 2

Formaldehyde

Concentrations:
_____ gas form

______- stock concentration (causes overhardening of the external surfaces of tissues)

_____working solution; most commonly used

Answer 2

100%

• 37% to 40%

• 10%

Question 3

Formaldehyde

Usually buffered to pH 7 with____

Answer 3

phosphate buffer

Question 4

Advantages of formaldehyde

Answer 4

Cheap, readily available, and easy to prepare

Compatible with many stains

Penetrates tissue well

Allows natural tissue color to be restored

Question 5

Disadvantages of formaldehyde

Answer 5

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

Question 6

Formaldehyde prolonged storage

EFFECTS

REMEDY

Answer 6

White formaldehyde ppt

• Filter
• Add 10% methanol (but dentures proteins thus unsuitable for EM)

Question 7

Formaldehyde unbuffered

EFFECTS

REMEDY

Answer 7

Formation of Formic acid

Buffer or Methanol

• 10% formol saline + Mg** / Ca** carbonate in jar with marbles

Question 8

Formaldehyde action of formic acid w excess blood

EFFECTS

REMEDY

Answer 8

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)

Question 9

10% Formol-Saline

Answer 9

Saturated formaldehyde + 10% NaCl

Question 10

Recommended for fixation of CNS tissues and general post mortem tissues for histochemical examination

Answer 10

10% Formol-Saline

Question 11

Advantage: Ideal for Silver impregnation staining technique

Disadvantage: Slower; tissue shrinks during alcohol dehydration

Answer 11

10% Formol-Saline

Question 12

10% Neutral Buffered Formalin (NBF)

Answer 12

Formaldehyde +

Na Dihydrogen Phosphate +

Disodium Hydrogen Phosphate

Question 13

pH 7
Best general tissue fixative

Answer 13

10% Neutral Buffered Formalin (NBF)

Question 14

Best for iron-containing pigments and elastic fibers which do not stain well after Susa, Zenker, or Chromate fixation

Answer 14

10% Neutral Buffered Formalin (NBF)

Question 15

Disadvantage: Longer to prepare, inert to phospholipids and neutral fats

Answer 15

10% NBF

Question 16

10% NBF

o Fixation Time:

Answer 16

4 to 24hrs

Question 17

4. Formol-Corrosive (Formol Mercuric Chloride)

Answer 17

Saturated aq. Mercuric chloride + 40%
Formaldehyde

Question 18

Recommended for routine post mortem tissues and Silver Reticulum staining methods

Answer 18

Formol-Corrosive (Formol Mercuric Chloride)

Question 19

Advantage: does not need washing, fixes lipids

Disadvantage: Forms mercuric chloride deposits

Answer 19

Formol-Corrosive (Formol Mercuric Chloride)

Question 20

Has 95% ETOH, Picric acid, and GHAc

Answer 20

Gendre’s (Alcoholic Formalin)

Question 21

o
Advantage: good for microincineration techniques; Fixes sputum

Answer 21

Gendre’s (Alcoholic Formalin)

Question 22

For gastrointestinal (GI) tissues, prostate biopsies, and bone marrow (BM)

Answer 22

Hollande’s

Question 23

• Made up of 2 formaldehyde residues linked by 3 carbon chains; Container must be refrigerated

Answer 23

Glutaraldehyde

Question 24

For enzyme histochemistry and electron microscopy

Answer 24

Glutaraldehyde

Question 25

Advantage: more pleasant and less irritation compared to formalin Disadvantage: less stable and more expensive than formalin

Answer 25

Glutaraldehyde

Question 26

Glutaraldehyde Concentrations: For immune electron microscopy For small TSE fragments Most common For large TSE fragments

Answer 26

0.25% 2.5% 3% 4%

Question 27

• Polymer of Formalin Powder in form, used in 4% Plastic embedding • For ultrathin and electron microscopy

Answer 27

Paraformaldehyde

Question 28

Acrolein in glutaraldehyde or formalin For Electron Histochemistry & Electron Immunocytochemistry

Answer 28

Karnovsky's Paraformaldehyde / Glutaraldehyde

Question 29

• Advantage: no smudging of nuclei and distortion of staining compared with formalin • Disadvantage: reduced staining capacity Remedy: increase staining time

Answer 29

40% Aqueous Glyoxal