If the separate packages of XTOL are of developer components and alkaline, which would be the logical way to package them, they should have longer shelf-life if you dissolve them separately. I don't know what the alkaline component in XTOL is, but most alkaline solutions will last a very long time and don't need a preservative.(posted 8220 days ago)By the way, if you're feeling the slightest bit daring and would like to mix your own developer from scratch, check out Pat Gainer's vit-c developers on the unblinkingeye.com website. I've been very impressed with the results I've gotten using his formula--decidedly better than XTOL. See related threads for details.