So today I got to do some Proper Lab Work, ie, mixing chemicals to make liquidy chemicals (a buffer today) for putting delicate proteins in. Buffers are solutions that provide the optimum environment for the little cells or proteins or nucleic acids that you work with, so they dont change conformation or otherwise break.I was given the list of ingredients, and being a happy little chemist for the morning set about making the buffer. As always, I got all the tubs of powders and worked out what weight I needed of each to get the right molarity (that's a measure of concentration). Then I proceded to add each of the powders to my glass bottle and poured most of the water I would need into it (If you're going to be pH'ing something, don't put in all the liquid, you might change the volume when you're adjusting the pH with your acid or base). And then, I was utterly confused, the nice solution I was expecting to be clear was a muddy brown... sort of like when the water is turned off for a few hours and turned back on.
Panic! None of the solutions I had used for biological purposes before were this colour! So I went into the neighbouring labs and showed my bottle to the postdocs, and lo, my problem was solved (or at least identified). It turns out that manganese (being an awkward transition element) has variable oxidation states depending on the pH of its environment. So my very basic solution had caused it to turn brown. They tell me the thing to do is to add the MnCl2 after I had corrected the pH, and after redoing the solution like this, I had a lovely clear buffer. \o/ hurrah!
So all in all, beware the oxidation states of transition metals (or add them last), your local postdoc can diagnose problems by looking at a bottle of brown liquid, and that manganese poisoning can lead to a neurological disorder resembling Parkinsons disease (looking at the wikipedia article on manganese is fascinating!).