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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Kimisti on February 28, 2020, 01:08:51 PM

Title: Total nitrogen determination in chemical fertilizers ( N P K )
Post by: Kimisti on February 28, 2020, 01:08:51 PM

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!

Title: Re: Total nitrogen determination in chemical fertilizers ( N P K )
Post by: shchavel on March 06, 2020, 08:02:59 AM

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.

Title: Re: Total nitrogen determination in chemical fertilizers ( N P K )
Post by: Kimisti on March 07, 2020, 10:31:20 AM

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