Ammonia and Total Kjeldahl Nitrogen

Ammonia and Total KjeldahlNitrogenD O N S I M M O N S

Overview• Review methods (Part 1)• Why do we distill?• Review methods (Part 2)• Last thoughts

Ammonia Methods• Titration• Ion Selective Electrode• Colorimetric◦ Manual Phenate◦ Automated Phenate(Segmented-Flow Injection Analysis)◦ Flow Injection Analysis• Other Berthelot Reaction Methods (e.g., Timberlineetc)

Titration• Distillation required• Ammonia-free reagent water• Boric Acid Indicator solution• Standardize 0.02 N Sulfuric Acid titrant• Interferences – Residual chlorine• Blank subtraction

Ammonia-Selective ElectrodePros• No colorimetric interferences• Easy to use – quickCons• Not good for dirty samples• Not as sensitive as colorimetric methods

Ammonia-Selective Electrode• >pH 11 and gas-permeable membrane• “Sample distillation is unnecessary.” SM 22 nd Ed.• Table 1B: Footnote 6. Distillation may be required ifany questions arise

Distillation• Manual distillation is not required if comparability data on representativeeffluent samples are on file to show that this preliminary distillation step isnot necessary: however, manual distillation will be required to resolve anycontroversies. In general, the analytical method should be consultedregarding the need for distillation. If the method is not clear, the laboratorymay compare a minimum of 9 different sample matrices toevaluate the need for distillation. For each matrix, a matrix spike andmatrix spike duplicate are analyzed both with and without the distillationstep. (A total of 36 samples, assuming 9 matrices). If results arecomparable, the laboratory may dispense with the distillation step forfutureanalysis. Comparable is defined as < 20% RPD for all tested matrices).Alternatively the two populations of spike recovery percentages may becompared using a recognized statistical test.2012 MUR, Table IB, footnote 6.

Why we distill• Separation of ammonia from interferences• Highly turbid or colored water may interfere withcolorimetric analysis• High dissolved solids may affect determination usingion-selective electrode

Phenate Methods• Phenols react with hypochlorite and ammonia toform indophenol blue compounds that stronglyabsorb in the visible wavelength range (~630-660nm)• Nitroprusside catalyzes the reaction to formindophenol blue enhancing the absorbance

Interferences• Many interferences: Calcium, Magnesium, H2S,Turbidity – needs preliminary distillation.• Alkaline citrate solution will complex cations andkeep them from ppt as hydroxides• Preliminary distillation will help reduce turbidity• Sulfide can be eliminated by acidification andvigorous aeration to remove as H2S.

Automated Phenate• Continuous Flow Injection vs Segmented FlowInjection• Flow Injection is simpler to use• Segmented flow – low dispersion, longer mixingtimes, RSD’s and Sensitivity better.• Discrete Analyzers

ATP procedures• TNT+ methods (epa 350.1)◦ Need comparison to reference method◦ Need distilled vs non-distilled comparison• Timberline methods◦ Do not need to distill….but◦ Good Laboratory Practice recommends you do the distilled vsnon-distilled comparison◦ Footnote 6 – still need to have capability of distilling ifquestions arise

Questions?• Contact information:• Don Simmons – 515-725-1600• donald-simmons@uiowa.edu• Thank you!