Schoniger oxygen flask technique

Ion chromatography has been successfully applied to the quantitative analysis of ions in many diverse types of industrial and environmental samples. The technique has also been valuable for microelemental analysis, e.g. for the determination of sulphur, chlorine, bromine, phosphorus and iodine as heteroatoms in solid samples. Combustion in a Schoniger oxygen flask (Section 3.31 )is a widely used method of degrading such samples, the products of combustion being absorbed in solution as anionic or cationic forms, and the solution then directly injected into the ion chromatograph. 

For the determination of sulfur contents of residual fuels a variety of procedures are available. The bomb (ASTM D-129, IP 61) and quartz tube (ASTM D-155, IP 63) combustion methods have long been established. Other, more rapid techniques are becoming increasingly available, including high-temperature combustion (ASTM D-1552), X-ray absorption and fluorescence methods, and the Schoniger oxygen flask procedure. 

Traces of chlorine have been determined in polyolefins [17] at levels between 0 and 500 ppm. The Schoniger oxygen flask combustion technique requires a 0.1 g sample and the use of a 1 litre conical flask. Chlorine-free PE foil is used to wrap the sample, which is then supported on a platinum wire attached to the flask stopper. Water is used as the absorbent. Combustion takes place at atmospheric pressure in oxygen. The chloride formed is potentiometrically titrated in nitric acid/acetone medium with 0.01 M silver nitrate solution. 

Mittenberger and Gross " determined chlorine in PVC by fusion with sodium peroxide followed by silver nitrate titration of the chloride produced. Tanaka and Morikawa described a semimicro technique for the determination of total chlorine in PVC using a semimicro method based on the Schoniger oxygen flask and Fajans method. 

Combustion in an oxygen flask, commonly called the Schoniger technique, offers advantages when readily volatilized elements such as halogens, Se, S, P, B, Hg, As, or Sb are to be determined. The combustion is performed with oxygen in a sealed container and the reaction products are absorbed in a suitable solvent before the reaction vessel is opened. 

In the Schoniger technique, the sample is dried in a cellophane bag or on filter paper and placed in a basket made of platinum or nichrome. After insertion of the basket the flask which may range in capacity from 500 ml to 2 litres is flushed with oxygen and sealed. The sample is then ignited by means... 

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