Stable Isotope Lab

The Stable Isotope Lab (SIL) is a hands-on teaching and research facility located on Iowa State University campus in the Department of the Earth, Atmosphere, and Climate. SIL provides analytical services for local, national, and international researchers and supports various disciplines including oceanography, paleoclimatology, geology, ecology, agronomy, and chemistry. SIL offers isotopic (‰) and elemental (%) analyses of carbon, nitrogen, oxygen and hydrogen of organic and inorganic materials at natural abundance by continuous-flow isotope-ratio mass spectrometry (IRMS).

The following analyses are available:

δ¹³C and δ¹⁸O of carbonate
δ¹³C and δ¹⁵N in solid samples, such as soils, plant materials, and dried extracts (combustion)
δD and δ¹⁸O in solid organic samples (pyrolysis)
δD and δ¹⁸O in natural abundance, clean water
δ¹³C of dissolved inorganic carbon in water

The lab’s instrumentation consists of 3 analytical systems and various tools to prepare samples for isotope analysis. There are 2 continuous flow mass spectrometers coupled with several sample introduction systems and a Picarro L2130-i Isotopic Liquid Water Analyzer with an autosampler for rapid measurements of deuterium and oxygen.

Thermo Delta V IRMS

The Thermo Delta V IRMS is coupled with a GasBench II and autosampler allows rapid and automated generation of gases introduced into the mass-spectrometer for isotopic determinations.

Gas Bench II with a CombiPAL autosampler for the automated analyses of carbon and oxygen isotopes. The CO₂ gas is generated through acid digestion of carbonate samples.

The mass spectrometer is configured for high-precision isotope ratio analyses of carbon and oxygen. The long-term precision of this mass spectrometer is ±0.05‰ for δ¹³C and ±0.09‰ for d18O, respectively.

ThermoFinnigan Delta Plus XL IRMS

The ThermoFinnigan Delta XL Plus mass spectrometer coupled with three peripherals. Peripheral devices attached to the Delta Plus XL allow rapid and automated generation of gases introduced into the mass-spectrometer for isotopic determinations.

GasBench with a CombiPAL autosampler for the automated analyses of carbon isotopes in dissolved inorganic carbon.

Costech Elemental Analyzer with zero-blank autosampler attached to a Conflo for the analyses of bulk organic carbon and nitrogen isotopes in plant materials, soils, sediments, and minerals through combustion.

Thermo Finnigan TC/EA (thermochemical elemental analyzer) with zero-blank autosampler attached to a Conflo for the automated analyses of oxygen isotopes in nitrates, sulfates, phosphates, and organic material. This device also allows the determination of hydrogen isotopes in silver encapsulated water and organic samples through high temperature pyrolsis.

The mass spectrometer is configured for high-precision isotope ratio analyses of hydrogen, carbon, nitrogen, and oxygen. The long-term precision of the mass spectrometer is ±0.08‰ for d13C and ±0.14‰ for d15N and ±0.11‰ for δ¹⁸O, respectively.

Sample Preparation Tools

We have 2 fully operational micromilling devices, which facilitate accurate, fine-scale, sampling of carbonate material. The MM2 micromill and Merchantek micromill with digital microscope are capable of several micrometer sampling steps.

The laboratory is equipped with devices to aid in the preparation and purification of samples for isotopic and elemental determinations. These facilities include a ballmill grinding device, freeze-dryer, microbalance, and precision saws.