The determination of organocarbon in clay materials

Abstract

A dry-combustion method is described for the determination of organocarbon in clay materials. The essential features are the use of purified oxygen; slow insertion of the sample into the furnace to avoid rapid dehydroxylation of the kaolinite and attendant loss of pyrolysis fragments in the atmosphere of steam that is generated; and the use of traps to remove gaseous fluorine compounds, steam and sulphur dioxide. Extensive tests on the apparatus with calcium carbonate and with mixtures of kaolin with glucose and with tannic acid are described. Tests with a commercial kaolin containing organic matter equivalent to about 550 µg of carbon per gram of material indicated a standard error of 8 µg, or ±1·5 per cent. A published method in which the kaolin is heated in a stream of oxygen containing 2 per cent. V/V of ozone has been re-investigated; the organocarbon was only partially oxidised so that the method has no analytical value. Two wet-combustion methods involving the separate use of potassium dichromate and potassium persulphate, which are used in soil analysis, were evaluated. The organic matter on the clay was again only partially oxidised to carbon dioxide under the experimental conditions.