Halogens, determination Oxygen flask combustion

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Application of the oxygen-flask combustion method to the determination of fluorine in organic combination has now been made by a number of workers. The fluoride in solution after combustion may be determined by thorium nitrate titration or colorimetrically as the alizarin complexan chelate or with a chloranilate (see Halogen Acids and Salts, p. 302). A method based upon the alizarin complexan chelate is given in Appendix IV. 

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. 

Three basic types of methods exist for the determination of chlorine and other halogens in polymers. These are based (i) on fusion of the polymer in a groimd form with sodium carbonate, followed by subsequent determination of the sodium halide (Method 75), (ii) combustion of the polymer in an oxygen flask containing an absorbing solution followed by determination of halide ion (Methods 76 - 78) and (iii) non-destructive methods based on x-ray fluorescence spectrometry of the polymer. 

Combustion of the sample in an oxygen combustion flask (Alcino et al., 1965) followed by ion chromatography is an attractive method for the analysis of sulfur in humic substances. Not only does the method require relatively little sample and provide high sensitivity, but it also allows simultaneous determination of halogens. One must be sure that sulfur is not rendered insoluble by ash constituents such as calcium. 

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