Residue on ignition
281
Transfer about 50 g, accurately weighed, to a tared crucible, ignite until thoroughly charred, and cool. Moisten the ash with 1 mL of sulfuric acid, and complete the ignition by heating at 800 ± 25

for 15-minute periods to constant weight: the limit is 0.002%.
Add the following:
Related compounds
Potassium ferricyanide solution
Dissolve 50 mg of potassium ferricyanide in water to 10 mL.
Ferric chloride solution
Dissolve 105 mg of ferric chloride in water to 10 mL.
Adsorbent:
0.25-mm layer of chromatographic silica gel mixture.
Test solution
Dissolve an accurately weighed quantity of Butylated Hydroxytoluene in methanol to obtain a solution having a concentration of about 20 mg per mL.
Reference solution
Dilute 1 mL of the Test solution with methanol to 200 mL.
Procedure
Apply separately 10 µL of the
Test solution and the
Reference solution to a suitable thin-layer chromatographic plate (see
Chromatography
621
), and allow to dry. Place the plate in a chromatographic chamber, and develop the chromatograms in methylene chloride until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber. Allow the plate to dry. Spray the plate with a freshly prepared mixture of
Potassium ferricyanide solution, Ferric chloride solution, and water (10:20:70). Observe the spots: any spot in the chromatogram obtained from the
Test solution, apart from the principal spot, is not more intense than the spot in the chromatogram obtained from the
Reference solution (0.5%).
NF27