Determination of Residue and Oil in Anhydrous Ammonia

GBH Enterprises, Ltd.

Plant Analytical Techniques
ANHYDROUS AMMONIA: DETERMINATION OF RESIDUE
AND OIL

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ANHYDROUS AMMONIA: DETERMINATION OF RESIDUE
AND OIL
WARNING AND SAFETY PRECAUTIONS:
VAPOR: CONCENTRATED VAPOR CAN CAUSE SKIN IRRITATION AND
HIGH CONCENTRATIONS MAY GIVE SERIOUS BURNS TO EYES,
RESPIRATORY PASSAGES AND LUNGS.
CAN FORM EXPLOSIVE COMPOUNDS WITH CHLORINE, HYPOCHLORITE
OR MERCURY.

1

SCOPE

This method is suitable for the determination of residue and oil in anhydrous
ammonia.

2

FIELD OF APPLICATION

This method may be applied to standard and premium grade anhydrous
ammonia having residue content in the range 10-5000 micrograms per gram and
oil content in the range l-500 micrograms per gram.

3

PRINCIPLE

Total residue (comprising water and involatile contaminants) is determined
gravimetrically after evaporation of ammonia. Oil is extracted from the
residue using a non-hydrocarbon solvent and its concentration determined by
comparison of infra-red absorption with that of a standard oil solution.


4

REAGENTS AND MATERIALS

4.1 1,1,2

-Trichlorotrifluoroethane : Analytical reagent grade, having < 15
micrograms per gram residue on evaporation.

4.2

Stock standard oil solution: weigh 0.500 + 0.001 g of lubricating oil or
liquid paraffin into a 50 mL beaker. Add approximately 25 mL of
1,1,2-Trichlorotrifluoroethane (4.1), stir to dissolve and quantitatively
transfer to a 250 mL volumetric flask. Dilute to the mark with
1,1,2-Trichlorotrifluoroethane (4.1) and mix. This stock solution is stable
for a period not exceeding 2 months (1 mL = 2 mg oil).

5

APPARATUS

5.1

Infra-red spectrophotometer: A double beam ratio - recording instrument
capable of scanning between 2000-4000 wave numbers (cm-l) and having
a resolution better than 8 cm-l at 3000 cm-l is suitable eg PHILIPS
PU9706 Infra-red Spectrophotometer is suitable

5.2

Optical cells, of path length 30 mm

5.3

Standard volumetric glassware : Class A.

6

SAMPLING

Take 100 g (147 mL) of anhydrous ammonia into a 250 mL conical flask in
accordance with Sampling procedure S2/2/1 of Sampling Procedures Manual
SPL-FE.

7

PROCEDURE

7.1

Analysis for residue

Immerse the sample flask in a continuous stream of cold water and allow the
ammonia to evaporate slowly.
When evaporation is complete, with a fixed air rate of 100 f 5 litres per
hour, blow out traces of ammonia for 30 f 5 seconds.


Allow 30 minutes for the flask to equilibrate to room temperature, dry the
outside of the flask, and weigh to the nearest 0.001 g; record this weight as
'A'g.
Place the flask in an oven heated to 100 + 5OC for 20 minutes. Cool to room
temperature, rinse the flask with several small (approx 5 mL) portions of
1,1,2-Trichlorotrifluoroethane. Transfer the washings to a clean dry 25 mL
volumetric flask and dilute to the mark with 1,1,2-Trichlorotrifluoroethane.
Retain this solution (solution 'A') for the determination of oil.
Rinse the sample flask with 50 % v/v hydrochloric acid, with water and then
with methanol. Heat in an oven at 100 + 5OC for 20 minutes, cool to room
temperature and reweigh. Record this weight as 'B'g.
7.2

Analysis for oil

Measure the absorbance of Solution 'A' from 7.1 at 2990 cm-1 on a scanning
spectrophotometer.
Similarly determine the absorbance of a solution prepared by diluting 0.5 mL
of the stock standard solution (4.2) to 25 mL with 1,1,2-Trichlorotrifluoroethane
(4.1) which contains 40 µg oil per mL.

8

EXPRESSION OF RESULTS

8.1 Method of calculation
The residue, expressed as micrograms per gram, is given by the formula:

Where:
A is the weight, in grams, of the sample flask and residue:
B is the weight, in grams, of the clean, dry sample flask:
100 is the weight, in grams, of anhydrous ammonia taken for analysis.


The residue should be expressed to the nearest 10 micrograms per gram for
results up to 1000 micrograms per gram and to the nearest 100 micrograms per
gram for results between 1010 and 5000 micrograms per gram.
The oil content, expressed in micrograms per gram, is given by the formula:

Where:

A is the absorbance of the standard:
B is the absorbance of the sample, corrected by subtracting the
blank:
100 is the weight in grams of the anhydrous ammonia sample taken
for analysis.

The oil content should be expressed to the nearest microgram per gram for
results between 0 and 30 micrograms per gram, to the nearest 5 micrograms per
gram for results between 31 and 100 micrograms per gram, and to the nearest
10 micrograms per gram for results between 101 and 500 micrograms per gram.
Note: If the absorbance of solution 'A' lies outside the range of calibration
ie> 40 µg oil per mL, dilute a volume V1 mL of solution 'A' to V2 mL with
1,1,2-Trichlorotrifluoroethane (4.1). such that the absorbance of the diluted
solution is within the range of calibration.


8.2

Precision data

8.2.1 Repeatability
The following data was obtained by the analysis of a solution containing
40 tig oil per mL on an infra-red spectrophotometer.
Run Number

Absorbance

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

0.205
0.205
0.205
0.205
0.205
0.210
0.200
0.210
0.210
0.205
0.210
0.205
0.205
0.210
0.205
0.205
0.210
0.205
0.205
0.205

MEAN
STD. DEVIATION
% R.S.D.

0.206
0.0027
1.33


Determination of Residue and Oil in Anhydrous Ammonia

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