How to test whether soybean meal is mixed with urea or other protein-enhancing substances?

I plant into a batch of soybean meal, the protein is very good, but suspected mixed with urea. -- can be observed under a microscope It's best to send the quality inspection station to measure the content of non-protein nitrogen-- you can do the urea setting test-- do the true protein and microscopic examination. Do the qualitative analysis of urea-formaldehyde polymer-consult the master: the building owner said, "do a true protein and microscopic examination." Can the solubility of the so-called real protein explain this kind of problem in an ordinary laboratory?-- Thank you for your guidance. Urea has been qualitatively analyzed, and the result is not contained. Let's take a look at the real protein.