Appendix XI K. Acid-insoluble Ash

Use Method I unless otherwise directed in the monograph.

Boil the ash for 5 minutes with 25 ml of 2m hydrochloric acid, collect the insoluble matter in a sintered-glass crucible or on an ashless filter paper, wash with hot water and ignite. Calculate the percentage of acid-insoluble ash with reference to the air-dried drug.

Ash insoluble in hydrochloric acid is the residue obtained after extracting the sulfated or total ash with hydrochloric acid, calculated with reference to 100 g of drug.

To the crucible containing the residue from the determination of sulfated or total ash, add 15 mL of water R and 10 mL of hydrochloric acid R, cover with a watch-glass, boil the mixture gently for 10 min and allow to cool. Filter through an ashless filter, wash the residue with hot water R until the filtrate is neutral, dry, ignite to dull redness, allow to cool in a desiccator and weigh. Reheat until the difference between 2 consecutive weighings is not more than 1 mg.