I know that urea will be decomposed to NH3 and CO2 when it is heated (NH2COONH4(s) 2NH3(g) + CO2(g)). But if we add urea to the solution containing enough concentration of NH3 (e.g. solution with dissolved NH4Cl), does existing NH3 in solution prevent decomposition of urea?
Since NH3 will go into the gas phase (especially at higher temperatures) I doubt that. In fact this might drive the reaction forward. But you can sterile filter the solution without problems. Use a 0,2uM filter diameter for it.
I saw in many credible papers that they mixed urea with a solution containing NH4Cl and NaHCO3 and then autoclaved. they could also filter-sterilize but they didn't. why?
(See page 88 of the highly referred thesis https://smartech.gatech.edu/handle/1853/19720)
I would say they do it because autoclaving is easier. Obviousky the stabilty is not a problem, otherwise this wouldn't be recommended.
Filter sterilisation is a whole lot easier. There are papers where urea is autoclaved with ammonium chloride but what they don't seem to do is analyse the urea in the final mixture. You might also want to think about the Cl- concentration.
can i ask about the exact size of the filter used for sterilisation of urea ??
Depends.. look at the Millipore and Satorious commercial sites. A 0.2 μm membrane removes bacteria ..usually.
I would be cautious abot heating urea solutions above 35C. In the presence of heat, urea will break down to form isocyanate, which can lead to carbamylation of
proteins. Sigma recommends that you not allow the temperature of urea solutions to rise above 30C. (see their website). We always used sterile filtration.
Best wishes
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