APPLICATION DIGESTION INSTRUMENTS AND VAPODEST Pace 1 oF § TOTAL NITROGEN IN WATER 4. Principle wine Ritfogen content ofthe sample is digested in acid solution, The reduction ofthe tate nitrogen is achieved wa Dawvarda's alloy. The dgested sample is made alkaline wth caustic soda. the thas hace ‘ammonia is Separated by dstilation, received in boric acid and determined volumetrically 2. Method Based on * German Standard Method for the examination of water, sewage, and sludge; Dinesmination of bound nivogen: method ater reduction with Devarda’s sey and catalytic digestion H28 DIN 38409 Teil 28, April i992, * AOAC Official Method 973.48, Nitrogen Total in Water, Kjeldahl Method, 1973, Amount of Sample Content or Recover 1 1-500 mi [>From 0.1 mg N to 100 mgN — a [eluates OT Extracts (Geraci ~ a 4. Chemicals quality: p.a. 4.1 Sulphuric acid H»S0., 98 % min., density 1.84 gim! 42.Catalyst tablets Kjeltabs CX, cat.no. 12-0328, or similar 4.3.Caustic soda solution NaOH, 32% 4.4Indicator MS or similar 4.8.Boric acid solution H580., 2 to 3.% 46 Buhurc acid solution c(H;$0,) = 0,05 mo alternatively hydrochloric acid c(HC)) = 0.1 mold & for low contents sulphuric acid o(H.S0,) 4.7.Aquadest 48. Devarda's alloy 4.8.Boling stones AN) (005 moi atemnatively hydrochloric acid c(HC!) = 0.01 mo (= 0.01N 5. Instruments 5.1 Digestion instruments fora sample size up to 60 mi Cat. No. [System Places Tor Digestion 7 Size of glasses Digestion apparatus Kjeldahl (with serial Task heater) 6x260 mi EL DATS destion system (lock system) {8 280m ——~ [KJELDATHERW digestion system Bloc steeny 20.x250 mi 08 TURBOTHERM digestion unt automatic 6x 250 mi rTé “TURBOTHERM digeston unt automate [ya as0 mt} Trace Hon instruments for sample sizes more than 80 ml >| Syston T Pies Tor Bigston | ‘Size of glasses, Digestion apparatus Kjeldahl (with sera ask heatey 4500 mi Digestion apparatus Kjeldahl with serial fask heater) [+ eopo 2033 _ Digestion apparatus Kjeldahl wit sel Task hecee |x boom 10-0034 "| Digestion apparatus Keldahl (wih serial face roses x 750 mi ——? {2.0064 KJELOATHERIT ages ae stem) ~~ Sx-400 mr BS TURBOTHERM digestion unit, automatic [4400 mit 1085_|TURBOTHERM digestion unit. automatic [4x00 mi ‘A144 Total Nirogen in Water. doe 2082014APPLICATION DIGESTION INSTRUMENTS AND VAPODEST Pace 20 TOTAL NITROGEN IN WATER 5.3, VAPODEST 105-508 5.4 Erlenmeyer flask 300 mi (wide neck), burette 5. Analysis ‘The homogenized water sample is carefully pipetted into a digestion tube Depending on the expected content the following sample size s suggested | Amount of Sample [mill] Range of Concentration mig) N 500 <1 250 1105 100 5 to approx. 35, 50 20 to approx. 70 20 50 to approx. 175 10 100 to approx. 350 300 to approx. 700 hoy (28) nan id (4.1), 1 catalyst tablet (6.2) and 2-3 boing stones (4.9) as well as 02 9 Devarda's alloy (48), 5.1. Digestion seer oxdation ofthe organic components with oxygenated water is also poseble and can be found very uring the second step of the digestion the organic components of the sample carbonate, ‘meaning that the Colour of the sample changes to black and white steam develops ceaen:' SF After about 20 to 40 minutes the aigest assumes a translucent appearance andthe white steam another 10 ensvestion solution should be translucent to light green. Now, the heating should conn ge ‘nother 10 minutes and then the digestion is finished, ae Goelng off period takes about another 30 minutes and then the flask can be inserted int the distilation instrument 5.1.4, Digestion with KJELDATHERM The prepared samples are put into the insert rack and the later is connected tothe exhaust device ims Water Jt pump oF the Turbosog scrubber system is tumed on Then, te rack oot a samples is inserted into the (to 250 °C) pre-heated block ‘A141. Total Nirogen in Water doe 282014APPLICATION DIGESTION INSTRUMENTS AND VAPODEST Pace 30r5 TOTAL NITROGEN IN WATER Progra suggested for heating - {Time {min) J Temperature “Cj [Comments 30 250 inser the digestion tubes info the preheated block, desiccate te | samples, | j APetex. 20 mi, the digestion souiton i clear (oxidation) Svagested program for erdinary samples: —__ [Time fminj Power [%| omment 010 120, 100] Desiccation evaporation | 2 30160 approx. 20 i 501060] the sampie, also see table ‘showing times for clear (oxidation) he digestion souion pabending on the sample tube andthe amount of sample diferent ime ig ‘Needed for the concentration Process. The following table gives some guidelines Suggested time for evaporation [Beeston tube "Amun of Sample | Bag aor appro Concentration time BG 250 oom | Bi comin XKTG-250 ml) 400m 9 min 85 min 80D a00'm 200 mi Sen | (4k a00 mi} S09 18min 1 15min | ted program for heavily foaming samples Ste Power) Tete Soom ——————— 00 | Heating un ofthe syst til he digestion soutone —, botingyfoaming TBreak, zl { Foaming, strong reaction? —] Break Foaming, strong reaction? —| [Break —| ‘fie 20 fo 30 minutes the digestion solution should Be ‘translucent ‘A141 Toll Nvopen Water doc zoazoiaAPPLICATION DIGESTION INSTRUMENTS AND VAPODEST Pace 4 oF TOTAL NITROGEN IN WATER should heavy foaming occur. In that case, lft the insert rack ‘This program was tested at 230 V, Since the power supply depends a lot on the voltage an amendment of the program might be advisable. {pader all circumstances i is important to continue with the digestion for atleast 90 minutes after the clearing of the digestion solution and that the sulphuric acid is boiling. 5.4.3 Digestion using Serial Heating Units The prepared samples are pipetted into 500 mi Kjeldahl flasks and the chemicals are added. ‘Any Sample residues in the neck of the flask are rinsed back with sulphuric acid. Then, the flasks are put in Position on the heating unt and are connected to the exhaust device. The water jet pump or the Turbosog ‘scrubber system is turned on, Each individual flask is heated up carefull and slowly so that the black foam stays in the bulb of the flask When the foaming subsides and white foam is forming the heating can be intensified, Condensate wil then form in the neck ofthe flask, which should stop at around the middle of the neck (you might have to redues the ower). After 60 minutes at maximum, there should not be left any carbonized particles in the flask After clearing ofthe digestion solution the heating process must be continued for another 90 minutes. The Sulphuric acid must be kept boiling This program can only be a suggestion, it might have to be adapted particulary 5.1.4, Suction of the Digestion Gases During the entire digestion period the scrubber TURBOSOG should be working, About 1200 ml of a 15 % caustic soda solution is recommended for the washing bottle; his amount is sufficient to neutralize digestion gases of about 60 digestions. The cooling period after iting the insert rack or the cooling period after turning Off the heating is about 30 minutes; during this time the scrubber should continue working, 5.2. Distillation Use the VAPODEST following the instruction manual, As a start run a blank distilation in order to heat up and Clean the instrument, Check whether all chemicals are present in the required quantiies! Alter the digested sample has cooled down, the water steam disilaton is effected according to the following program: [Program Parameter ~~ [VAP Was] VAP Zoe ca [Program Parameter VAP 101s [VAP 20s] VAP 30s | VAP-455 J VAP 508 | den [sas {as | anf ge ae SA =40 mr =40 mi =40 mi} - ei Os 38 20s | 240 s 00% ies 400% | ae 40 mi 70 - 80m 70= 80 ml ‘manual 303 | manual — ‘manual 308) - ‘mandal ‘manual — | automate” | automatic | ‘manual “manual |" manual automatic 2, All activities that have to be done manually are wuiten in italic print * extemal trator apcamle is diluted with Aquadest (4.7,) (only VAP 10s and VAP 20s, ) and the sample tube is put into the VAPODEST. The 300 mi Erlenmeyer flask containing 60 - 70 ml boric acid (4.5) is used as a recover Tre ule tubing ofthe distillate must be immerged inthe boric acid solution. Then the program is started and the distilation is run. The amount of distilate should be approx, 100 ml ‘After the distilation is terminated, the receiver is taken out and the outlet tubing is rinsed with dstiled water. ‘A141 Total Nirogen in Water doe 2082014APPLICATION DIGESTION INSTRUMENTS AND VAPODEST Pace 5 or § TOTAL NITROGEN IN WATER 5.3. Titration A titration to the end point is performed. At pH 5, the mixture indicator M5 (4.4.) changes its colour from {green to gray. When using an electrode for titration, the pH-value of the undiluted boric acid is measured first, then it is back titrated to this value and the amount of titration solution (3.6,) needed is noted (VAP 10s to VAP 30s). 5.4. Calculation ‘The mass per unit volume of the nitrogen BIN in mg/l is calculated using the following equation: BN = (c+ (V-V) * M)/E © -H' ion concentration ofthe tation solution [moll] V__ - amount of titration solution sample [mi] Vg. amount of titration solution blank value [ml} M™ molar mass of nitrogen - 14007 mg/mol E initial sample volume (mi 5.5, Determination of Blank Value For the determination ofthe blank value a sample tube without sample but wit all chemicals is run through the whole analysis and the amount of ttration solution is determined, This amount is then subtracted from the consumption of the sample. The reason for doing so is the need to detect any impurities in the ‘chemicals and instruments as well as to take the factor of dilution for the boric acid. The consumption with a 0.1 molf titration solution should be around 0.1 to 0.2 ml 6. Comment Using the Kjeldahl method as well as the water steam distilation, the concentration of ammonium can be determined as well as the nitrate and the organically bound nitrogen, These 3 nitrogen compounds make the total N-content of a sample: Total N = ammonium content + nitrate/nitrite content + organically bound nitrogen For the analysis of the respective compounds the following procedure can be applied: ~ First, the sample is homogenized and split into 3 even parts ~ An ammonium determination is done by water steam distillation from a buffer solution or with magnesium oxide, alternatively calcium oxide to alkalfy it (also see application C.2.2. Ammonium in Liquid Samples) ~ Then the nitrate/nitrite determination is done. The nitrate-nitrogen content of the sample is reduced using Devarda and is dstiled as ammonia (also see C.3, Nitrate in Liquid Samples). At the same time the ammonium content is detected and has to be deducted from the result. ~ After that, the determination ofthe total N with Devarda's alloy has to be done, following the procedure described above. The portion of organically bound nitrogen can be determined by deducting the respective nitrogen portions. Determination of Organic Nitrogen Portions in Water [The procedure is comparable to the one used for total-N determination, withthe exception, that Devarda's alloy 's not used in this case. All other things are identical: the relevant data for the sample. program parameters and instruments. Since this method determines the content of ammonium at the same time, its vale must be known in order to deduct it for the calculation ofthe organic nitrogen content ‘A114 Total Nizogen in Wistar doe 2082014