![]() ![]() Portions of this general chapter have been harmonized with the corresponding texts of the European Pharmacopoeia and the Japanese Pharmacopoeia. The portions that are not harmonized are marked with symbols (
![]() ![]() The Residue on Ignition / Sulfated Ash test uses a procedure to measure the amount of residual substance not volatilized from a sample when the sample is ignited in the presence of sulfuric acid according to the procedure described below. This test is usually used for determining the content of inorganic impurities in an organic substance.
Procedure— Ignite a suitable crucible (for example, silica, platinum, quartz, or porcelain) at 600 ± 50 ![]() ![]() ![]() Moisten the sample with a small amount (usually 1 mL) of sulfuric acid, then heat gently at a temperature as low as practicable until the sample is thoroughly charred. Cool; then,
![]() ![]() ![]() ![]() ![]() Unless otherwise specified, if the amount of the residue so obtained exceeds the limit specified in the individual monograph, repeat the moistening with sulfuric acid, heating and igniting as before, using a 30-minute ignition period, until two consecutive weighings of the residue do not differ by more than 0.5 mg or until the percentage of residue complies with the limit in the individual monograph.
![]() ![]() Calibration of the muffle furnace may be carried out using an appropriate digital temperature meter and a working thermocouple probe calibrated against a standard thermocouple traceable to the National Institute of Standards and Technology.
Verify the accuracy of the measuring and controlling circuitry of the muffle furnace by checking the positions in the furnace at the control set point temperature of intended use. Select positions that reflect the eventual method of use with respect to location of the specimen under test. The tolerance is ±25
![]() ![]() Auxiliary Information— Please check for your question in the FAQs before contacting USP.
USP32–NF27 Page 138
Pharmacopeial Forum: Volume No. 31(5) Page 1526
|