Ammonia loss during block TKN digestion

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Ammonia loss during block TKN digestion

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Suenoir

Posted 5/5/2008 1:10:19 PM

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We are using a FOSS tecator to digest TKN. We use 25 mL sample with 10 mLs digestion reagent. The digestion is 1hr @ 160 raising to 380 over one hour, then 30 minutes at 380.

We run a 20 ppm NH4Cl standard and a 25ppm Urea standard. We get about 18ppm recovery of the NH4Cl standard and 22 recovery for Urea. Our TKNs are lower than the ammonias on the same samples sometimes.

Any suggestions would be welcome.

Post #9056

tpirondini

Posted 5/22/2008 1:16:39 PM

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Your recoveries are not too bad, just a little low (90% NH4Cl and 85% Urea). If the Urea was much lower than NH4Cl, then I would suspect incomplete digestion. Since recoveries are close for both free and complexed nitrogen, I would focus on endpoint of the digestion possibly boiling down too much = resulting in some loss of NH4. Extra H2SO4 may help the digestion endpoint.

Post #9226

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