How to Perform Sulfated Ash in pharma?

What is Sulfated Ash:

Sulfated ash is one of the test to perform in the pharmaceutical industry. The test is perform to measure, when the substance is ignited at certain temperature is it volatized or not.

The sulfated ash is used to determine the inorganic impurities present in the substance.

As per USP, General chapter <281> represents Residue on Ignition.

How To Perform Sulfated Ash?

There are two method of analysis of sulfated ash. Method A and Mathod B.

What is Method A of Sulfated ash?

Accurately weigh about 1-2 gm of substance in dry suitable crucible (Usually platinum crucible is used).

Using a gentle heat, remove any excess sulfuric acid, ignite at about 800 °C until all the black particles are gone and moisten again with sulfuric acid (1760 g/l) TS. Then add a little ammonium carbonate R and ignite the mixture to constant weight.

What is Method B of Sulfated ash?

  1. Ignited the crucible at 600°C +/- 50°C. for 30 mins.( Silica, Platinum, Quartz or porcelain crucible).
  2. Cool it in a desiccator at room temperature.
  3. Weigh the crucible (W1).
  4. Add into it 1-2 gm of substance or the weight specified in the individual monograph and weigh the crucible(W2)
  5. Moistened the sample with small amount (generally 1 ml) of sulfuric acid.
  6. Heat the substance gently till the substance completely charred.
  7. Cool it to room temperature.
  8. Again add small amount (1 ml ) of sulfuric acid.
  9. Heat the crucible at specified temperature untill the white fumes are no longer are evolved.
  10. Ignite the substance until the residue is completely incinerated.
  11. Remove the crucible and cool it in a desiccator.
  12. Weigh the bottle with substance (W3).
  13. Calculate the residue percentage of substance.
  14. In this case, repeat the sulfuric acid moistening, heating and ignition procedure it was performed with before, using a 30-minute ignition period, until weighings of residue do not differ by more than 0.5 mg or until the residue percentage exceeds the limit specified in the individual monograph.

How to calculate sulfated ash?





W1 = Empty crucible weight

W2 = Crucible weight with substance

W3 = Crucible weight with substance after drying

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