You could help us by giving us your reference to this analytical test. A quick Google of academic copies of the USP NF monographs doesn't give me this test. So I'm left with a What? , Where? and then a Why? question.
What are you doing? The statement "and there is something else which gives it faint yellow color." means what? You added it but don't know what it is? You didn't add it and don't know why it didn't work? Something else?
Where did you hear about doing it?
If you have to identify a pharmaceutical, but you're not using a (not too old copy of) the USP, then why do it that way? Apologies if this test is in the newest USP, or required by another pharmacopoeia.
Please re-read the
Forum Rules{click}. You're casually asking questions about a common drug of abuse. Please keep the discussion theoretical.