Speaking from a human perspective, cocaine has a smell that is unique that smells like, well, cocaine. I can smell the HCl or the citrate and they both smell like cocaine, and I have had citrate in my possession many times in the past, so I know it still smells like coke. So do you really think a dog wont be able to tell? I'm just asking, honestly, not being a smart ass or anything. If its true that the dog is smelling for a very specific nuance that we can't even detect, that would be great news.
Pure cocaine has no smell.