I'm considering various lab supplies for a protocol we're going to be running, and have been struck by the remarkable difference in price for different quality levels of the same basic substance.
Sigma will sell you water, for example, for anything from \$15/L to \$500/L and even over \$10,000/L, depending on what level of purity is guaranteed. Obviously, one doesn't want to use inferior tools and guaranteed unreliable results, but also it would be foolish to use a reagent that's far pricer than one's actual tolerances.
Most of the actual protocols that I encounter, however, don't seem to actually specify what grade of purity they need, and I'm trying to figure out how to navigate the problem. Trial and error is definitely not a good option, since (a) it can waste a lot of time, and (b) good and bad results in a trial don't actually tell you what you need (a good result could be an unusually good batch of poor reagent; a bad result could be from an entirely different problem). Asking the authors is also not a great solution, for a number of similar reasons.
To make this concrete, let's consider a very simple and typical case that I am currently encountering. The protocol I'm setting up for right now cultures E. coli in LB media. Sigma will sell me LB media powder as "quality 100" L3152 for \$139/kg and "quality 200" L3522 for \$182/kg. Both say they are "good for E. coli".
Is there any reason not to pick the cheaper media? How should one decide how much quality their media needs to have for a typical bacterial culture experiment?