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8.3 MIcro KJeldahl system 8.3 1 8 3 2 8 3 3 8.34 8 3 5 Place 500 ml of sample or an ahquot dIluted to 50 ml m a 100 ml KJeldahl flask and add 10 ml sulfunc aCId-mercunc sulfate-potassIUm sulfate solutIOn (7 3) Evaporate the mIxture m the KJeldahl apparatus untIl S03 fumes are gIven off and the SolutIon turns colorless or pale yellow Then digest for an addItional 30 mmutes CooltheresIdueandadd30mldistIlledwater Make the digestate alkahne by careful addItion of 10 ml of sodIUm hydroxIde- thIosulfate solution (7 4) Without mIxmg Do not mIX untIl the dIgestIOn flask has been connected to the dIstillatIOn apparatus Connect the KJeldahl flask to the condenser with the tIp of condenser or an extension of the condenser tiP below the level of the bonc aCId SolutIon (76) m the receIvmg flask or 50 ml short-form Nessler tube SteamdIStill30mlattherateof6-10mllmm,mto5mlof2%boncacid(76) DIlute the dIstillate to 50 ml For concentratIons above 1mg!l the ammoma can be determtned tItnmetncally For concentratIons below thIS value, It IS determmed colonmetncally The potentiometnc method IS apphcable to the range 005 to 1400 mg/1 8.4 DetermtnatIOn of ammoma m dIstIllate Determme the ammoma content of the dIstIllate tItnmetncally, colonmetncally, or potentiometncally, as descnbed below 84 1 Tltnmetnc determmatIOn Add 3 drops ofthe mIxed mdicator (7 5) to the dIstIllate and tItrate the ammoma with the 002 N H2S04 (77), matchmg the endpomt agamst a blank contammg the same volume of dIstIlled water and H3B03 (7 6) solution 8 4 2 Colonmetnc determmatIOn Prepare a senes of Nessler tube standards as follows ml of Standard 8 4.3 8 4 4 DIlute each tube to 50 ml with ammoma free water, add 1 ml of Nessler Reagent (7 10) and mIX After 20 mmutes read the absorbance at 425 nm agamst the blank From the values obtamed for the standards plot absorbance vs mg NH3-N for the standard curve Develop color m the 50 ml dIluted dIstIllate m exactly the same manner and read mg NH3-N from the standard curve Potentiometnc determmatIOn Consult the method entItled NItrogen, Ammoma PotentIOmetnc, Ion SelectIve Electrode Method, (Method 350 3) m thIS manual It IS not ImperatIve that all standards be treated m the same manner as the samples It IS recommended that at least 2 standards (a hIgh and low) be dIgested, dIstIlled, 10 ml = 001 mg NH3-N 00 05 10 20 40 50 80 100 mg NH3-N!50 0 ml 00 0005 0010 0020 0040 0050 0080 010 351 3-4PDF Image | Methods for Chemical Analysis of Water and Wastes
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