O-A-445C
4.4.5 Oil determination. Extract the residue in the round bottom flask with four 10 ml portions of carbon tetrachloride. Add the solvent from a 10-ml pipette and while adding each portion, run the tip of the pipet around the inside neck of the flask as the latter is rotated, to completely wash the inside wall of the flask. Carefully transfer each 10 ml portion of carbon tetrachloride (and any water present in the residue) to a separatory funnel, combining the extracts in the same funnel. The funnel should have a dry stopcock (no lubricant) and should have been previously rinsed with carbon tetrachloride. After shaking allow the water phase of the combined extract to separate and draw off the organic bottom layer through a dry filter paper into a weighed evaporating dish. Rinse the filter paper with two 10 ml portions of carbon tetrachloride. The filter paper should be washed previously with carbon tetrachloride and dried. Place the evaporating dish on a steam bath and evaporate the carbon tetrachloride. As the last of the solvent is evaporated, wipe the outside of the dish with a piece of absorbent tissue and cool the dish in a desiccator. Finally weigh the dish and residue to the nearest
0.1 mg. Make a blank evaporation of 60 ml of carbon tetrachloride for each lot of the solvent used.
4.4.5.1 Reagents and equipment. a. Reagents.
1. Carbon tetrachloride, ACS reagent.
2. Calcium chloride, anhydrous, for use as desiccant. b. Equipment.
1. Evaporation flask, 1 liter capacity, round bottom.
2. Evaporation dish, 100 ml capacity, glass flat bottom.
3. Pipet, 10 ml capacity.
4. Funnel, separatory, 125 ml capacity.
5. Paper, filter, Whatman No. 5 or No. 41 or equivalent.
6. Desiccator.
7. Analytical balance, accurate to 0.1 mg.
4.4.5.2 Calculations. Calculate the oil content of the sample by means of the following equations: Oil content, ppm = (1.47)(A-B)(F)
Where:
A = Weight of oil residue, mg
B = Weight of carbon tetrachloride blank, mg
F = Evaporation factor derived from the chart (figure 1) relating evaporation factor to the pressure (or temperature) of ammonia in the tank from which the sample was drawn
1.47 = 1000 (1000 ml)(0.682 g/ml)
where 0.682 g/ml is the density of liquid ammonia at atmospheric pressure (14.7 psig).
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