Water Environment Federation (WEF) Discussion ForumsWater Environment Federation (WEF) Discussion Forumshttp://www.wef.org/TechnicalDiscussions/jfuller@wef.orgMon, 08 Sep 2008 08:46:54 GMT20http://www.wef.org/TechnicalDiscussions/Topic9056-15-1.aspxRelated to that -- Are you using a glass fume aspirator with your Foss Tecator digester? If so--do you turn the water flow down from high to low once your lower-temperature water boil-off step is completed? Manufacturer recommends this in order to avoid excessive loss of sulfuric acid. Acid loss could lead to higher ratio of salt to acid, which could lead to higher boiling temperature, which could lead to N loss.</P><P>I have to add, though--My own Foss Tecator system really does not seem to be too sensitive to this. If I space out on turning the water down, everything's generally OK anyway! But then, I use the old mercury-catalyzed digestion, which has a higher ratio of acid to salt than the copper-catalyzed method does.Thu, 17 Jul 2008 20:59:41 GMTLois Herringhttp://www.wef.org/TechnicalDiscussions/Topic9056-15-1.aspxYour 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.Thu, 22 May 2008 13:16:39 GMTtpirondinihttp://www.wef.org/TechnicalDiscussions/Topic9056-15-1.aspxWe 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. </P><P>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.</P><P>Any suggestions would be welcome.Mon, 05 May 2008 13:10:19 GMTSuenoir