I wouldn't recommend the last two, KNO3 especially.  You might have some luck with NaOCl but it's most likely limited.  Your best bet would be oxidation with a chromate, or H2O2.  I've always had problems with H2O2 oxidations for a couple reasons: 1) They don't always work when you want them to, usually needing a catalyst of some sort. 2) far too many variables, especially for an experimental trial.  A lot of times, if your H2O2 is below a certain concentration, it wont do what you want.  I've got a bottle of hydrogen peroxide, not more than 4 or 5 months old and it all of the sudden refuses to oxidize stuff.  I bought a fresh bottle, and it works flawlessly.  It was stored in the fridge with it's cap tightly on too, imagine that.