Oxygen flask Combustion Method

The definition of the Oxygen flask combustion method says that the method is useful in identifying or determining if sulphur or halogens are produced when organic compounds are combusted. These compounds contain iodine, fluorine, bromine, chlorine, or sulphur in a flask that is filled with oxygen. When these compounds are combusted they give out inorganic products which are soluble in water. The inorganic materials then produced are determined as bound for the individual element. Another name for the method is the Schöniger flask test. The test should be performed with extreme care. The flask used must be completely clean from any trace of organic solvent.

Oxygen flask combustion Apparatus

The oxygen combustion apparatus that is used in the procedure is a colourless flask with thick walls. The upper part of the flask is made like a saucer. The flask has a capacity of 500 ml. For the determination of fluorine, the flask used should be made of quartz. The ground stopper is made up of hard glass. When using the procedure for the determination of fluorine then a stopper made up of quartz must be used.

Preparation of test solution

The following method must be used unless otherwise specified.

Preparation of sample

•   For solid samples: The quantity of the sample that is specified in the monograph should be placed in the centre of the filter. The sample must be weighed precisely and the sample should be wrapped along the dotted line and make sure it does not scatter. Then the parcel should be placed in a platinum basket and its fuse-strip is left outside.
•   For liquid samples: use a filter paper to roll an appropriate amount of absorbent cotton that should be 50 mm lengthwise and 5 mm breadthwise. It should be rolled in a way that around 20mm of paper on the end part should be left as a fuse strip. The parcel should be placed in a platinum basket. The sample must be weighed precisely and placed in a suitable glass tube. The cotton should be moistened with the quantity of the sample that is specified in the monograph and the edge of the sample is brought in contact with the cotton.

Method of Combustion

The absorbing liquid specified in the monograph should be placed in flask A. Then the flask should be filled with oxygen and the ground part of the stopper should be moistened with water, and the fuse strip is ignited and transferred to the flask immediately. The flask should be kept airtight until the combustion is finished. The flask should be shaken occasionally so that the white smoke completely vanishes. Let it stand for 15 to 30 minutes and then the resulting solution would be labelled as a test solution.

Procedure of determination

1. Chlorine and bromine

A small amount of water should be applied to the upper part of A then, C is pulled out carefully and the test solution is transferred to a beaker. C, B, and the inner side of A should be washed with 15 ml of 2-propanol and the washings should be combined with the test solution. 1 drop of bromophenol blue TS is added to this solution and dilute nitric acid is added dropwise until a yellow colour develops. Then, 25 ml of 2-propanol is added and 0.005 mol/ L silver nitrate is used to titrate it.

2. Iodine

A small amount of water is applied to the upper part of A and C is pulled out carefully. 2 drops of hydrazine hydrate are added to the test solution and C is put on A. The solution is decolourised by shaking vigorously. The contents of A should be transferred to a beaker and C, B, and the inner side of A is washed with 25ml of 2-propanol and the washings should be transferred to the above beaker. 1 drop of bromophenol blue TS is added to this solution and then dilute nitric acid is added dropwise until a yellow colour develops. Then it is titrated with 0.005 mol/ L silver nitrate VS according to the potentiometric titration under the Electrometric Titration.

Conclusion

The definition of the Oxygen flask combustion method describes it as a method which is used to identify and determine halogens by combusting an organic compound in a flask filled with oxygen. The organic compounds used could be Iodine, chlorine, bromine, fluorine or sulphur. The apparatus used to perform the procedure is known as the oxygen flask combustion apparatus. The capacity of the flask is 500 ml and it is made up of hard glass. The procedure must be performed with utmost care and the flask should be completely clean without any residue of another compound. The oxygen flask combustion technique is used to trace analysis.