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General Test Procedure (GTP) for Residue on Ignition/Sulphated Ash

PURPOSE
To lay down the procedure for Loss on drying of the materials.

APPARATUS
Muffle furnace with temperature controller capable of achieving up to 800°C
Silica, Platinum, Porcelain or Quartz crucibles
Graduated pipette – 1ml
Bunsen Burner
Desiccator
Nickel tongs

REAGENTS
Sulphuric Acid: AR grade


PROCEDURE
  • Ignite the crucible in a muffle furnace at 600 ± 50°C for 30 min. Allow to cool in a desiccator over silica gel or other suitable desiccants to ambient temperature and weigh accurately. Note down the weight in g as W1.
  • Transfer the sample about 1.0 g or as specified, into the crucible and weigh accurately. Note down the weight of the crucible with a sample in g as W2.
  • Moisten the sample with a small amount of Sulphuric acid (usually 1 ml), and heat gently over a Bunsen burner, at a temperature as low as practicable, until the sample is thoroughly charred.
  • After cooling, moisten the residue with a small amount of Sulphuric acid (usually 1 ml) and heat gently until white fumes are no longer evolved.
  • Ignite at 600 ± 50°C in the muffle furnace until the residue is completely incinerated.
  • Allow the crucible to cool in a desiccator and weigh accurately. Note down the weight in g as W3.
  • If the amount of the residue so obtained exceeds the limit specified; repeat the moistening with Sulphuric acid, heating, and ignition as before, until constant weight is attained or until the percentage of residue complies with the limit.

CALCULATION
Where,
W1 = Weight in g of empty crucible
W2 = Weight in g of the crucible with sample before ignition.
W3 = Weight in g of the crucible with the residue of the sample after ignition.

REFERENCES
USP
BP 
EP

Note: Ensure that flames are not produced at any time during the procedure.

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