Patrick Arnold is a very different guy--a highly regarded, industry known chemist. He says the isomer thing is bullshit, but I am not sure what I think about it simply because no one has yet been able to provide an explanation as to how two different brands can pass a lab test, yet produce very different results. Until I do, I am not going to discard the isomer theory.
I will also say that other chemists have said the opposite of Patrick when it comes to this subject, but these were people who supposedly had a hand in making the "alpha" version for various OTC companies (when SD was still legal). So, it could have just been marketing bullshit. Regardless, no one has been able to provide an explanation for how 2 different, lab tested versions can produce very different results--drastically differnt.