I highly doubt anyone will have a readily available household method that can determine the purity of methylone but we can give this a little time to see if anyone has information.
What does your powder look like and what is the concistency of it? Ive seen very pure Methylone ( 99% ) and it was a very fresh white with a flourery concistency; the crystals are very light. Brown/beige powder is a sign of left over sovlents used in the synthesis process.
Short answer: No.
To get any kind of reliable answer you need advanced analytical equipment, but I guess you could do some simple TLC tests at home.
It will not give you a percentage but it could maybe show some impurities.
testing the melting point which i cant seem to find, solubility 357 mg/mL (20 °C), and it's density could give a you a rough estimate of it's purity before you decide to ingest it for further research.