Methylation

This procedure is used to block acid groups, particularly carboxyl groups. As a consequence basophilic staining materials cease to be basophilic. Extended treatment destroys 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

Chemical	Amount
Methanol	99.17 mL
Hydrochloric acid, conc.	0.83 mL
Note: This is 0.1N hydrochloric acid.

 

Procedure
Place dewaxed sections into the solution in a sealed container at the temperature specified for the time given.

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.

Tissue	Temp	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

 

Reference

Lillie, R.D., (1954)
Histopathologic technique and practical histochemistry Ed.2
Blakiston, New York, USA.