[Kimisti]

Hello all!

 I am currently encountering a problem when trying to determine total nitrogen in NPK fertilizers, always getting lower results than expected, for example instead of 16% nitrogen, i get around 10%.
The method I'm using involves disolving the sample of NPK in 20mL HCl/H2O 1:3, adding a bit more water and then boiling for about 5 minutes.
After that, I'm using a Kjeltec distilator to measure the ammonia in a receiver solution ( HCl) and then titrating the excess HCl with standard NaOH solution.
Any advice on any method to try?

Thanks in advance!

[shchavel]

Hello! I think you need to use some oxidizer to destroy NPK, just HCl with boiling is not enougn, some nitrogen hiding in the strtructure of NPK.
Often H2SO4 with selenium used.

[Kimisti]

I tried using the dewarda alloy to reduce the nitric nitrogen to -NH2 and it worked, thanks for the tip though!