[D_A_M_H]

I'm a chemist working in refinery site in the water lab
I have to analyse a caustic sample and determine mercaptide in it using method UOP-209
Breifly I take a known volume (or weight) of caustic sample and add 100 ml of mixed solvent (1 N NaOH, Iso-propanol and ammonia with different portions) then titrate it potentiometry using silver nitrate as titrant
I was reading about this method and found that the reason to add the 1 N NaOH is to neutralize the medium and make mercaptan extract easily...but when increasing the NaOH concentration (for example 2 N or 3 N), a salting out will occur
Anyone have an idea what's the meaning of (salting out will occur)??
If you have a page from book or an article talking about that, it will be better for me
Thanks in advance

[Arctic-Nation]

The reason, I believe, is that while mercaptide/thiolate is more or less soluble in lower base concentrations, it starts to form all kinds of insoluble salts with metal ions that might be present when the amount of base increases. Any insoluble salt will precipitate and not partake in the titration, thus skewering the results.