Carry out a solubility test on the sample in water at room temperature in the proportion of 2 g per 100 ml.
Weigh 5, 7 or 10 g of the sample to the nearest 0.001 g, as shown in the Table, and place in a 500 ml graduated flask. From the result of the solubility test, proceed as follows:
(a)Products completely soluble in water
Add sufficient water to dissolve the sample; shake, and when completely dissolved, make up to volume and mix thoroughly.
(b)Products not completely soluble in water
Add 50 ml water and then 20 ml hydrochloric acid solution (4.1). Swirl and leave undisturbed until the evolution of carbon dioxide has ceased. Add 400 ml water and shake for half an hour on the rotary shaker (5.2). Make up to volume with water, mix and filter through a dry paper into a dry receiver. Discard the first portion of the filtrate.
7.2 According to the variant chosen, place in the collecting flask a measured quantity of standard sulfuric acid as indicated in the Table on page 21. Add the appropriate quantity of the chosen indicator solution (4.9.1 to 4.9.2) and, if necessary, water to obtain a volume of at least 50 ml. The condenser outlet must be below the surface of the standard acid in the collecting flask.
Transfer by pipette, according to the details given in the Table, an aliquot portion of the clear solution into the distillation flask of the apparatus. Add water to obtain a volume of about 350 ml and several grains of pumice to control the boiling.
Assemble the distillation apparatus and, taking care to avoid any loss of ammonia, add to the contents of the distillation flask 10 ml of concentrated sodium hydroxide solution (4.8) or 20 ml of the reagent in the cases where 20 ml hydrochloric acid (4.1) have been used in order to dissolve the sample. Warm the flask gently and when boiling commences distil at such a rate that about 200 ml are obtained in 30 minutes.
When no more ammonia is likely to be evolved, lower the receiving flask so that the tip of the condenser is above the surface of the liquid.
Test the subsequent distillate by means of an appropriate reagent to ensure that all the ammonia has been completely distilled. Wash the condenser with a little water and titrate the excess acid with the standard solution of sodium or potassium hydroxide prescribed for the variant adopted (see Note).
Standard solutions of different strengths may be used for the titration provided that the volumes used do not, as far as possible, exceed 40 to 45 ml.
7.3 Carry out a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.
7.4 Before carrying out analyses, check that the apparatus is working properly and that the correct application of the method is used by taking an aliquot portion of a freshly prepared solution of ammonium sulfate (4.11) containing the maximum quantity of nitrogen prescribed for the chosen variant.