Methylation
For the Periodic Acid-Schiff Reaction
This procedure is used to block acid groups, particularly carboxyl groups. As a consequence, basophilic staining materials cease to be basophilic. Extended treatment destroys Periodic Acid-Schiff (PAS) positivity of some carbohydrates. This may be used as a means of identifying them, particularly if done in conjunction with other blocking procedures.
Solution
| Material | Amount | |
|---|---|---|
| Methanol | 99.17 | mL |
| 0.1N Hydrochloric acid, conc. | 0.83 | mL |
Procedure
Place dewaxed sections into the solution in a sealed container at the temperature specified for the time given.
| Tissue | Temperature | Time | State |
|---|---|---|---|
| Glycogen | 58°C | 3 days | Complete |
| Epithelial mucin | 58°C | 3 days | Complete |
| Glycogen | 37°C | 7 days | Not complete |
| Epithelial mucin | 37°C | 7 days | Not complete |
It should be noted that methylation is more commonly used to abolish metachromasia or cytoplasmic basophilia. Treatment of sections at 37°C with 1% hydrochloric acid in methanol for 2 days will usually accomplish this, while not affecting PAS reactivity.
Safety Note
Prior to handling any chemical, consult the Safety Data Sheet (SDS) for proper handling and safety precautions.
References
- Lillie, R.D., (1954)
Histopathologic technique and practical histochemistry Ed.2
Blakiston, New York, USA
