O-A-445C
4.4.3.1 Routine analysis method. After evaporation is complete (see 4.4.2), determine the volume of the residue remaining in the calibrated centrifuge tubes to the nearest 0.05 ml (corrected to eliminate the volume of the small piece of boiling chip). The composition of the residue will average 28 percent ammonia. The percent by weight of water residue in the sample shall be calculated as follows:
Weight percent moisture = (0.264)(0.72A)(F) Where:
0.264 = [(100)(0.899 Sp. Gr. Residue)] (500ml)(0.682 g/ml NH3)
0.72 = 100 - 28 percent NH3 in the residue
A = ml residue in 500 ml sample
F = Evaporation factor from figure 1
4.4.3.2 Purity. The purity of the ammonia shall be calculated as follows:
100 - weight percent moisture (total residue) = weight percent purity
4.4.3.3 Failure criteria. Nonconformance to 3.1 shall constitute failure of this test.
4.4.4 Referee (Karl Fischer) method. By means of gentle pressuring with dry nitrogen or air, transfer about 25 ml of anhydrous methanol, previously titrated to the dead-stop endpoint, from the aquameter reaction vessel to the tube containing residue (see figure 2). Mix by gentle swirling and then transfer the contents back into the aquameter vessel, by inverting the sample tube. Titrate to the dead-stop endpoint. Repeat the transfer and titration once more and record the total volume of Karl Fischer reagent used. Throughout the transfers and titrations avoid exposing the methanol or the glassware to the atmosphere to avoid absorption of atmospheric moisture.
4.4.4.1 Reagents and equipment. Reagents and equipment shall be in accordance with
ASTM D 4377.
4.4.4.2 Calculations. Calculate the moisture content of the ammonia as follows: Weight percent moisture = CF/W(10)
Where:
C = Karl Fischer reagent required to titrate the sample, ml
F = Water equivalence of Karl Fischer reagent, milligrams (mg)/ml
W = Sample used, g
10 = Factor for converting to percent
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