STABLE ISOTOPE ANALYSIS TECHNIQUES

Analysis: Carbon-13 & Nitrogen-15 of bulk materials

Technique: EA-IRMS (Elemental Analysis – Isotope Ratio Mass Spectrometry)

For determination of carbon-13 and nitrogen-15 the bulk material must first be converted to pure N² and CO² to permit analysis by IRMS. In this technique, samples are placed in clean tin capsules and loaded into an automatic sampler. They are then dropped into a combustion furnace held at 1000 deg. C where they are combusted in the presence of an excess of oxygen. The tin capsules flash combust causing the temperature in the vicinity of the sample to rise to ca. 1700 deg. C. The gaseous products of combustion are swept in a helium stream over a Cr²O³ combustion catalyst, CuO wires to oxidize hydrocarbons and silver wool to remove sulfur and halides. The resultant gases (N², NOx, H²O, O², and CO²) are then swept through a reduction stage of pure copper wires held at 600 deg. C. This removes any remaining oxygen and converts NOx gases to N². Water is removed by a magnesium perchlorate trap, while removal of CO² is available using a selectable Carbosorb™ trap. Nitrogen and carbon dioxide are separated by a packed column gas chromatograph held at an isothermal temperature. The resultant chromatographic peaks sequentially enter the ion source of the IRMS where they are ionised and accelerated. Gas species of different mass are separated in a magnetic field and simultaneously measured by a Faraday cup universal collector array. For N², masses 28, 29 and 30 are monitored and for CO², masses 44, 45 and 46.

Analysis: Sulphur-34 of bulk materials

Technique: EA-IRMS (Elemental Analysis – Isotope Ratio Mass Spectrometry)

For determination of sulphur-34 the bulk material must first be converted to pure SO² to permit analysis by IRMS. In this technique, samples are placed in clean tin capsules and loaded into an automatic sampler. They are then dropped into a combustion furnace held at 1080 deg. C where they are combusted in the presence of an excess of oxygen. The tin capsules flash combust causing the temperature in the vicinity of the sample to rise to ca. 1700 deg. C. The gaseous products of combustion are then swept in a helium stream through tungstic oxide and zirconium oxide combustion catalysts and then reduced over high purity copper wires. Water is removed by a Nafion™ membrane, permeable to only water. Sulphur dioxide is separated by a packed column gas chromatograph held at an isothermal temperature. The resultant SO² chromatographic peak enters the ion source of the IRMS where it is ionised and accelerated. Gas species of different mass are separated in a magnetic field and simultaneously measured by a Faraday cup universal collector array. For SO², masses 64, 65 and 66 are monitored.

Analysis: Deuterium and Oxygen-18 of bulk materials

Technique: EA-IRMS (Elemental Analysis – Isotope Ratio Mass Spectrometry)

For determination of deuterium and oxygen-18, the bulk material must first be converted to pure H² and CO to permit analysis by IRMS. In this technique, samples are placed in clean silver capsules and loaded into an automatic sampler. They are then dropped into a high temperature furnace where they are converted to H² and CO in the presence of glassy carbon. Residual water is removed by a magnesium perchlorate trap, while any traces of CO² is removed by a Carbosorb™ trap. H² and CO are separated by a packed column gas chromatograph held at an isothermal temperature. The resultant chromatographic peak enters the ion source of the IRMS where it is ionised and accelerated. Gas species of different mass are separated in a magnetic field then simultaneously measured on a Faraday cup universal collector array. For CO, masses 28, 29 and 30 are monitored, while for H2 masses 2 and 3 are monitored.