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!