No! You can only mitigate uncertainty to an acceptable level.

Better to purchase them as it involves lot of analysis. You can get them with CoA.

If you are an analytical chemist, and have instrumentation to characterize and have resources for all other requirements, you may do so.

The best it is to purchase them.

Standard reference material is prepared by purifying the material to the highest degree and then qualify and characterize it to obtain the least uncertainty in its potency, but not equal to zero.

Secondly, you can compare your standard reference material with well established standards.

It is impossible preparing SRM with zero uncertainty

By doing characterization of mass/NMR etc. and should match with the desired requirement of that particular material