Stable Isotope Ratio Mass Spectrometers –
(ThermoFinnigan DeltaPlus and DeltaPlusXL)
The light stable isotope facility houses two ThermoFinnigan isotope ratio mass spectrometers that are fed by four analytical streams. An elemental analyzer (EA) is connected to the DeltaPlus mass spectrometer. The ThermoFinnigan Gas Bench, thermal combustion elemental analyzer (TC/EA) and gas chromatography combustion interface (GC-C) are connected to the DeltaPlusXL. The EA, TC/EA and GC/C are connected via Finnigan ConFlo III interfaces. The DeltaPlusXL is also equipped with a Dual Inlet interface for off line analysis and developmental work. Recently a home-built preparation line for analysis of N2 and N2O in nitrates has been added to the DeltaPlusXL.
The Gas Bench is used for automated acid digestion and analysis of 13C and 18O isotopes in carbonate minerals (calcite, dolomite, magnesite, hydromagnesite, siderite, ankerite) and analysis of gases, dissolved inorganic carbon (DIC) in fluids, and archeological samples such as bone. Sample and standard mineral powders are treated with phosphoric acid in sealed glass exetainers that have been flushed with helium. The CO2 produced is introduced into the mass spectrometer in continuous flow mode, using helium as the carrier gas. The gas from the sample is analysed along with reference CO2 gas of known composition. DIC is analysed on the gas bench by acidification of the sample water in sealed exetainers that have been flushed with helium. The CO2 produced is introduced into the mass spectrometer in continuous flow mode.
The TC-EA is used for sample pyrolysis and continuous flow analysis of 2H and 18O water and 2H in minerals. The TC/EA is at present only being used for liquid samples, although solids can also be analysed. Liquids are introduced by autosampler into the furnace tube at 1450 °C and pyrolyzed. The component hydrogen and oxygen gases are carried to the mass spectrometer in helium carrier, via a Finnigan Conflo III interface. Experiments are currently underway to allow analysis of 18O in silicates.
The EA is used for analysis of 13C and 15N in solid samples, including organisms, hair, sediments, and coal. Samples are placed in tin cups and introduced to the elemental analyzer with an AS autosampler. The sample is combusted in the presence of oxygen at 1000 °C. Combustion gases are then carried in a stream of helium through a reduction column, a water trap and finally a GC column where the gases are separated. Final combustion products N2 and CO2 are introduced to the DeltaPlus by the Conflo and δ15N and δ13C are determined. For some δ13Corg analyses, samples are treated first with 10% HCl and dried before placing the samples into tin cups.
The GC/C system measures compound specific stable isotope ratios of carbon, nitrogen, oxygen and hydrogen in gases, liquids, organic volatile compounds and biomolecules. It is includes a HP 6890 gas chromatograph, a micro combustion furnace, a reduction furnace, a reactor for thermo-chemical conversion of gas chromatograph uluates, and an autosampler.