Heat a silica or platinum crucible to redness for 10 minutes, allow to cool in a desiccator and weigh. Unless otherwise specified in the individual monograph, transfer to the crucible 1 g of the substance under examination and weigh the crucible and the contents accurately. Ignite, gently at first, until the substance is thoroughly charred. Cool, moisten the residue with 1 ml of sulphuric acid, heat gently until the white fumes are no longer evolved and ignite at 800° ± 25° until all black particles have disappeared. Conduct the ignition in a place protected from air currents. Allow the crucible to cool, add a few drops of sulphuric acid and heat. Ignite as before, allow to cool and weigh. Repeat the operation until two successive weighings do not differ by more than 0.5 mg.
Method AFor crude vegetable drugs Unless otherwise stated in the individual monograph, weigh accurately 2 to 3 g of the air-dried crude drug in a tared platinum or silica crucible and incinerate, gently at first, and gradually increase the temperature to 675 ± 25°, until free from carbon, cool and weigh. If a carbon-free ash cannot be obtained in this way, extract the charred mass with hot water, collect the insoluble residue on an ashless filter paper, incinerate the residue and filter paper until the ash is white or nearly so, then add the filtrate, evaporate it to dryness and heat the whole to a temperature of 675 ± 25°. If a carbon-free ash cannot be obtained in this way, cool the crucible, add 15 ml of ethanol (95 per cent), break up the ash with a glass rod, bum off the ethanol, and again heat the whole to a temperature of 675 ± 25°. Cool in a desiccator, weigh the ash, and calculate the percentage of ash with reference to the air-dried crude drug.
Method BFor all other substances Heat a platinum or silica crucible to red heat for 30 minutes, allow to cool in a desiccator and weigh. Unless otherwise specified in the individual monograph, weigh accurately about 1 g of the substance under examination and evenly distribute it in the crucible. Dry at 100° to 105° for 1 hour and ignite to constant weight in a muffle furnace at 600° ± 25°. Allow the crucible to cool in a desiccator after each ignition. The material should not catch fire at any time during the procedure. If after prolonged ignition a carbon-free ash cannot be obtained proceed as directed in method A. Ignite to constant weight.
Calculate the percentage of ash on the dried basis.
Use Method C unless otherwise directed.
Method CBoil the ash (Method A or B) with 25 ml of 2 M hydrochloric acid for 5 minutes, collect the insoluble matter in a Gooch crucible or on an ashless filter paper, wash with hot water, ignite, cool in a desiccator and weigh. Calculate the percentage of acid-insoluble ash on the dried drug basis.
Method DPlace the ash (Method A or B), or the sulphated ash, as directed in the individual monograph, in a crucible, add 15 ml of water and 10 ml of hydrochloric acid, cover with a watch glass, boil for 10 minutes, and allow to cool. Collect the insoluble matter on an ashless filter paper, wash with hot water until the filtrate is neutral, ignite to dull redness, cool in a desiccator and weigh. Calculate the percentage of acid-insoluble ash on the dried basis.
Boil the ash (Method A or B) for 5 minutes with 25 rnl of water, collect the insoluble matter in a Gooch crucible or an ashless filter paper, wash with hot water, and ignite for 15 minutes at a temperature not exceeding 450°. Subtract the weight of the insoluble matter from the weight of the ash; the difference in weight represents the water-soluble ash. Calculate the percentage of water-soluble ash on the dried basis.
Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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