Nitrogen, ammonia plus organic, titrimetric, digestion-distillation
Parameter and Code:
Nitrogen, ammonia plus organic, total-in-bottom-material, dry wt, I-5553-85 (mg/kg as N): 00626
1. Application 5.5 Sodium carbonate solution, 0.0357N:
This method may be used for analysis of Dissolve 1.892 g primary standard Na2CO3 in
bottom material containing at least 10 mg/kg of carbon dioxide-free water and dilute to 1,000 mL.
total ammonia plus organic nitrogen. Only that 5.6 Sodium hydroxide-thiosulfate solution:
portion of bottom material that passes a 2-mm Cautiously, dissolve 500 g NaOH in 600 mL
sieve is taken for analysis (method P-0810, sub- ammonia-free water. Add 80 g Na2S2O3·5H2O
sampling, bottom material, coring). and dilute to 1 L.
5.7 Sodium thiosulfate, crystals, Na2S2O3·
2. Summary of method 5H2O.
The sample is subjected to a digestion whereby 5.8 Sucrose.
all organic nitrogen-containing compounds are 5.9 Sulfuric acid, concentrated, sp gr 1.84.
converted to ammonium salts. The resulting 5.10 Sulfuric acid standard solution, approx.
mixture is then made strongly alkaline, and the 0.036N: Cautiously, add 1.0 mL concentrated
ammonia so formed is distilled from the mixture H2SO4 (sp gr 1.84) to 800 mL ammonia-free
into a solution of boric acid and subsequently water and dilute to 1 L. Standardize by titrating
determined by titration with standard sulfuric 25.0 mL 0.0357N Na2CO3 to pH 4.5. Compute
acid solution. normality of sulfuric acid standard solution to
four decimal places.
3. Interferences
There are no known interferences with this 6. Procedure
method. 6.1 Free the distillation apparatus of ammonia
by boiling ammonia-free water until the distillate
4. Apparatus shows no trace using nessler reagent-----
Kjeldahl distillation apparatus, 500-mL flasks. CAUTION: deadly poison.
6.2 Weigh to the nearest milligram, 3 g of
5. Reagents bottom-material sample, prepared as directed in
5.1 Ammonium chloride, crystals. method P-0810, and transfer to the digestion
5.2 Boric acid solution, 20 g/L: Dissolve 20 g flask.
H3BO3 crystals in 800 mL ammonia-free water 6.3 In the same manner prepare a blank, using
and dilute to 1 L. 2.0 g sucrose. Analyze the blank and each sample
5.3 Digestion catalyst: Tablets containing 3.5 g as directed in paragraphs 6.4 to 6.10.
K2SO4 and 0.175 g HgO (Scientific Chemical 6.4 Cautiously, add 25 mL concentrated H2SO4
Technical Sales Inc., SCT Kel-catalyst No. (sp gr 1.84), and under a hood, swirl the contents
KC-M3, or equivalent. of the flask until thoroughly mixed.
5.4 Mixed indicator solution: Dissolve 20 mg 6.5 Add three digestion-catalyst tablets and mix
methyl red and 100 mg bromocresol green in 100 well. Add a few glass beads and begin the
mL 95-percent ethanol. Store in a well- digestion. Continue the digestion until a clear so-
sealed bottle. lution is obtained, and then continue fuming 1 h.
1
6.6 Cool the flask until crystals appear (do not Va X Na X 14,000
cool completely). Add 150 mL ammonia-free ¾¾¾¾¾¾¾¾
Wts
water; mix and allow to cool.
where
6.7 Add 100 mL NaOH-Na2S2O3 solution.
Immediately connect the flask to the distillation
Va = volume of standard H2SO4 used to titrate
apparatus and cautiously mix the contents by
swirling. sample, milliliters, minus volume used
6.8 Distill at a rate of not more than 10 to titrate blank, milliliters,
mL/min and no less than 6 mL/min; collect the Na = normality of standard H2SO4 solution, and
distillate in a 250-mL volumetric flask Wts = weight of sample, grams.
containing 25 mL boric acid solution. The tip of
the delivery tube must be below the surface of 8. Report
the boric acid solution in the receiving flask. Report nitrogen, ammonia plus organic, total-
6.9 Collect approx. 200 mL of distillate, dilute in-bottom-material (00626), concentrations as
to 250 mL with ammonia-free water, and mix. follows: 10 to 100 mg/kg, nearest 1 mg/kg; 100
6.10 To the distillate, add 3 drops mixed mg/kg and above, two significant figures.
indicator solution, and titrate with sulfuric acid
standard solution until the color of the solution 9. Precision
changes from yellow to red. Precision data are not available for this
method.
7. Calculations
Nitrogen, ammonia plus organic (mg/kg) =
