Really i have three questions, if i can get answers about it!

1- First One, Usually researchers used Sodium Azide with concentrations (1-5 mM or 0.01-0.1%) with long time (15-20 hour) on pH=7, or same concentration with (6 Hours) on pH=3, Many paper said Sodium Azide is more active on acidic pH (3-3.5) for inducing mutations, why they didn't write what is the pH solution some times? is that mean, they preparing Sodium Azide in pH=7 in distillated water?

2- Second Question, Researchers using phosphate buffer when they preparing sodium azide, some of them use Citrate or Acetate buffers, why they prefer phosphate buffer in most of researches?

3- Third Question, when i prepare (phosphate buffer) 0.1M (as they said in many papers) from KH2PO4 (1.36g in 100ml), i need 0.5ml phosphoric acid (85%) to rich pH=3, so when i set bean (Phaseolus vulgaris) seeds in the solution for 6 hour (as some protocols said), seed germination ratio was 5-10% (that's without any mutagens), and the seeds germination in distillated water (6 hour) was 90-95%!!, So did you have any comment about this problem, should I have reduce the concentration to less than 0.1 or 0.01M of phosphate buffer?

Thanks anyway,,,