Stable Isotope Ratio MS

NOTE: The IRMS lab is undergoing renovation and installation of new instruments. New details will be posted soon. Thanks for your patience. (June 2022)

ThermoFinnigan DeltaPlus and DeltaPlusXL

The light stable isotope facility houses two Thermo Finnigan isotope ratio mass spectrometers that are fed by four analytical streams. A Fisons elemental analyzer (EA) is connected to the DeltaPlus mass spectrometer. A Thermo Finnigan Gas Bench, a thermal combustion elemental analyzer (TC/EA) and a 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 archaeological 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 analyzed along with a reference CO₂ gas of known isotopic 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 in 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 the autosampler into the furnace tube at 1450 °C and pyrolyzed. The component hydrogen and oxygen gases are carried to the mass spectrometer by a helium carrier gas via the 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 such as soil, sediments, plant, insects, fish, hair, fur, and coal, and small amounts of liquids such as fruit juice, honey and biodiesel. Samples are placed in tin cups and introduced to the elemental analyzer by an AS128 autosampler.

The sample is combusted with oxygen at 1000 °C. Combustion gases CO₂ and NO₂ are then carried in a stream of helium through a reduction column that reduces NO₂ to N₂, a water trap that absorbs water vapour, and finally a GC column where the gases are separated. N₂ and CO₂ are introduced to the DeltaPlus by the Finnigan Conflo III interface, and δ¹⁵N and δ¹³C are determined. For δ¹³C_org analyses, samples are treated 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. The GC-C system includes a HP 6890 gas chromatograph with an autosampler, a micro combustion furnace, a reduction furnace, and a reactor for thermo-chemical conversion of gas chromatograph eluates into gas species that the mass spectrometer can analyze.