Determination of NH4-N by Steam Distillation

Reagents
  1. 40% NaOH solution (w/w) (16.67 N NaOH)
  2. BORIC ACID INDICATOR SOLUTION - Dissolve 400 g H3B03 in about 2 L of hot deionized water (use a 4 L beaker, heat and stir on a hot plate). When H3BO3 is dissolved, transfer to 20 L carboy. Dilute to approximately 18 L with dH20. Add 200 mL of mixed indicator solution and dilute to 20 L. Adjust pH to 5.0 using 2 mL of 1.67 N NaOH.
  3. STOPPER TIGHTLY!
  4. STANDARDIZED H2S04 SOLUTION - Dilute 64 mL conc. H2S04 to 20 L with deionized H20. Be sure to standardize solution by following the standardization of acids and bases procedure. (Final concentration should be close to 0.1142 N.)
  5. MIXED INDICATOR SOLUTION - Weigh 0.33 g Bromocresol green and 0.165 g Methyl red. Transfer weighings to a 500 mL volumetric flask using an ethanol squirt bottle. Dilute to volume with ethanol. Carefully slide a stir bar into flask and stir until the bromocresol green and methyl red are dissolved. Remove stir bar and store solution in plastic bottle.
  6. NITROGEN STANDARD - Accurately weigh 4.6445 g (NH4)2S04 (dried and stored in desiccator), dissolve in deionized water, then dilute to 100 mL. This will give you a 1% N solution. To check distillation procedure, pipet 1 mL into digestion tube, dilute with about 80 mL deionized water and follow the distillation procedure. For calculation, 1 mL = 1 g.

Apparatus

  1. KJELTEC 2300 DISTILLATION UNIT
  2. 250 mL DIGESTION TUBES