Accelerated Degradation Experiment
Conditions
Procedure A1: |
10 days exposure at 50 °C and 100% relative humidity. |
Procedure A2: |
30 days exposure at 50 °C and 100% relative humidity. |
Procedure B: |
30 days exposure at 50 °C and 100% relative humidity followed by 5 days at 70 °C and 100% relative humidity. |
Appearance of the substance
The substance, originally in the form of fine, white granules changes after procedure A1 into a slightly yellow coloured powder with some agglomeration on the surface and having a light perceptible odour of mercaptone. No further change is observed after procedures A2 and B.
Gain of moisture
After procedures A and B: |
practically no change. |
Chromatographic test
Adsorbent: Silica gel F-254
Solution applied to the plate: Substance dissolved in pyridine/methanol (1:4). Use freshly prepared solutions.
Solvent system:
n-butanol .......................... 60 volumes
ethane 95%...................... 40 volumes
concentrated ammonia ...... 5 volumes
Development conditions: The solvent is allowed to migrate until the front reaches a line 15 cm from the starting line.
Detection: After drying the plate until the odour of ammonia has disappeared, it is left in a chromatographic chamber containing some iodine crystals until spots appear.
Results: The spots obtained from the solution of the sample subjected to procedure A1 and the spots obtained from the reference solution of melarsoprol display the same chromatographic characteristics of migration and detection, except of the spot remaining on the starting line being much more intense. The results remain the same after procedures A2 and B.
Solution in pyridine/methanol
After procedure A1 a strong opalescence is observed in the solution even after addition of methanol, whereas the reference solution remains clear.
Ultraviolet spectrophotometry
Prepare a 0.5% solution of the sample subjected to procedure A1 in 1 N hydrochloric acid/methanol (1:9); a slight precipitate is formed, whereas the reference solution of melarsoprol remains clear. The spectrum of the filtered test solution is similar to that of the reference solution with a maximum at 285 nm and a shoulder at 255 nm.
Conclusion
Melarsoprol is subject to decomposition after procedure A1, which does not seem to increase after procedures A2 and B. It is not possible to estimate the percentage of degradation.
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