Accelerated Degradation Experiment

Conditions

Appearance of the substance

The substance, originally in the form of a white or pale brownish yellow powder, changes after procedure A into a hard yellow-golden compact mass turning to an orange colour after procedure B. During testing, a strong odour of sulfur dioxide can be detected.

Gain of moisture

Chromatographic test

Adsorbent: Silica gel 60 F-254

Solution applied to the plate: Substance dissolved in a mixture of methanol and water (1: 1).

Solvent system:

n-butanol: .................................50 volumes
ethanol 95%: ..........................15 volumes
water: ......................................20 volumes
acetic acid: ..............................15 volumes

Development conditions: The solvent is allowed to migrate until the front reaches a line 15 cm from the starting line.

Detection: The plate is examined under ultraviolet light at a wavelength of maximum output at about 254 nm, and then left in a chromatographic chamber containing some iodine crystals until spots appear. A second plate is sprayed with a 0.2% solution of triketohydrindene hydrate in acetone, then heated at 100 - 105 °C for 15 minutes.

Results: The reference solution of bacitracin zinc shows numerous spots of different intensities. The solutions of each of the samples subjected to procedures A and B show diminished intensities of the main spots as well as additional spots.

Ultraviolet spectrophotometry

A reference solution in 0.05 M sulfuric acid shows 2 absorption maxima at 252 nm and 290 nm. The absorption values of the solutions of each of the samples subjected to procedures A and B and recalculated to the dried substance, remain similar at the wavelength of 252 nm, but increase significantly at 290 nm.

Differential scanning calorimetry

No significant change is observed after procedures A and B.

Conclusion

Bacitracin zinc is subject to decomposition under accelerated degradation conditions.