[Breaking Bad] the reason Walt consistently outperforms everyone in terms of purity is due to his buying phenylacetic acid.
Edit: Grey Matters was not a Chem supply company
Just an idea from the scene where the guys say that they synthesize it and how simple it is to do so. Even with Walt siphoning his methylamine from a train, which seems easy to contaminate, he makes the best product ever in just an RV. What if the purity stems partly from his knowing that it's nearly impossible, or super difficult or time consuming, to make the acid perfectly, and so Walt simply buys his?
This might explain something - Gale, and most of the other cooks we see, are trained chemists but may not have experience in the economic side of it, like how they get certain precursors to come out pure. In contrast, Walt actually founded a chemical supply company, and had experience separate from his classroom experience.
So what if the cartel cooks and the other professionals are overstepping their abilities, don't check the phenylacetic acid, and are simply adding in an unknown number of variables when they make their own precursors?
Also helps to show that a textbook chemist in the show - Gale - is much more oriented to simply following instructions from the textbook, as opposed to Walt, who knows the market inside and out.