Hello, I would assume that it would not be a good idea to premix a stock solution-- even without the amidol. Because of the sodium sulfite's desire to turn into sodium bisulfite(I think that's what it converts to ??---there are others here who know this stuff a lot better than me). When we mix our ABC stock solutions we don't usually mix the B solution unless we know that we will be using it within a few weeks, as it changes. But the amidol stock would also have KBr and Citric Acid---would that stop the Na Sulfite from changing itself ?? I don't know, but I like the idea of using the little baggies to get organized.