Abstract

The Elemental Analyser Model EA 1108 (Carlo Erba) enables to determine nitrogen, carbon and sulphur in solid material, in a fast and simple way. The samples are packed into lightweight containers of tin and dropped at preset times into a vertical quartz tube, heated at 1020 degrees C, through which a constant flow of helium is maintained. When the samples are introduced, the helium stream is temporarily enriched with pure oxygen. Flash combustion takes place, primed by the oxidation of the container. Quantitative combustion is then achieved by passing the gases over W2O3. The mixture of the combustion gases is transferred over copper to eliminate excess of oxygen and after drying the water over MgClO4 introduced into a chromatographic column, heated at 57 degrees C. The individual components are then separated, eluted in the order N2, CO2 and SO2, and measured by a thermal conductivity detector (TCD). The instrument is calibrated by combustion of the standard sulphanylamide and the calibration is controlled with the standard reference material (SRM) cystine. The total calibration takes place in 2 hours. The measurement of one single sample takes place in 15 minutes. Every ten samples the instrument is controlled with the standard sulphanylamide. After optimization of the instrument, a Standard Operating Procedure (SOP) for the determination of carbon, nitrogen and sulphur in solid material, has been formulated. The detection limit is for carbon 2 mg/g, for nitrogen 2 mg/g, and for sulphur 5 mg/g. The accuracy for the measurement in cystine is for carbon 3 mg/g (1.0%), for nitrogen 6 mg/g (5.1%), and for sulphur 6 mg/g (2.2%).