[saman_Z]

in salt analysis results are not observed if the chlorine water is not freshly prepared..why?

[Arkcon]

It really depends a great deal on your particular analytical method.  Salt analysis is a very common topic, what with the planet being full of it, and it's effects so significant on all life forms.  Your lab write-up may have more information for you.  As a general tip, for a write up, why is anything, in human experience, best freshly prepared?  What are the sorts of things that can go wrong when things are left out for a while?   What sort of reactions can you expect?  See if you can answer those questions, and search for hits in your textbook along those lines.