Isotope Ratio Mass Spectrometry

Isotope ratio mass spectrometry (IRMS) allows for measurements of the stable isotope ratios of light elements such as hydrogen, carbon, nitrogen, oxygen, sulfur, silicon at the natural abundance level in a broad range of samples.

Two Isotope Ratio Mass Spectrometers are used in the NIU Stable Isotope Laboratory (SIL), Thermo Fisher Scientific MAT 253 and Delta Plus Advantage. Samples can be analyzed directly in a dual inlet mode (e.g. CO2, O2, N2 gas) or after conversion to these simple gases using various online techniques. Our laboratory is equipped with Elemental Analyzer (EA, Costech ECS 4010) that converts samples designated for carbon 13C/12C and nitrogen 15N/14N isotope analyzes to CO2 and N2 (Thermo-Finnigan DELTAplus Advantage). Samples frequently analyzed using EA include plant material, animal tissues, soil. In addition to the EA, a Gas Chromatograph (GC) is coupled to the same IRMS via a combustion interface (Thermo Fisher Scientific GC-C III), which allows us to analyze the stable carbon (13C/12C) or hydrogen (2H/1H) isotopes of a single organic compound.

To analyze hydrogen and oxygen stable isotopes in organic samples (e.g. cellulose) or inorganic, for example water, Thermal Conversion/Elemental Analysis (Thermo Finnigan TC/EA) is used. Sample is converted to H2 and CO using pyrolysis reactor and directed to the IRMS for measurements (2H/1H, 18O/16O). Another sample preparation peripheral that is used online is the Gas Bench (Thermo Fisher Scientific), which is used to analyze carbonates, dissolved inorganic carbon or water for their isotope ratios of oxygen and/or carbon (18O/16O and 13C/12C). To analyze oxygen and silicon isotopes (18O/16O and 29Si/28Si, 30Si/28Si ) in quartz samples we first liberate oxygen as O2 and convert Si to SiF4 with the use of a fluorination reaction and a laser  (Photon Machines Fusion 10.6 Laser) before transferring the gasses to IRMS (Thermo Fisher Scientific MAT 253).    

Gas Chromatograph with Mass Spectrometer (Varian Saturn 3800 and 2100 IT Mass Spectrometer)

Gas Chromatograph is used for identification and quantitation of the semi-volatile compounds which are previously extracted from various environmental samples. A mixture of organic compounds in a liquid solvent is injected into an injector kept usually at a temperature between 200-300 °C. The sample instantly vaporizes and is carried in a stream of helium into a capillary column where it undergoes a separation based on the volatility and affinity of a specific compound to a stationary phase of the column. Separated compounds are transferred into an ion trap mass spectrometer, where they undergo the ionization and the detection.   

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Anna Buczynska
Research Associate

Joshua Schwartz
Laboratory Manager