Stable Isotope Laboratory

Researchers:

Attila Demény (DSc, director)

István Fórizs (PhD)

Gabriella Barna

Sándor Kele

Zoltán Siklósy

Technicians:

Katalin Kovács-Varga

Noémi Szász

The laboratory was established in 1990. There are two senior researchers running the laboratory, Attila Demeny (geologist, isotope geochemistry) and István Fórizs (physicist, isotope hydrology), and three Ph.D.students.

Until 2005 the stable isotope laboratory was equipped with a Finnigan MAT delta S isotope ratio mass spectrometer that has a collector system for ¹³C/¹²C, ¹⁸O/¹⁶O, ¹⁵N/¹⁴N and ³⁴S/³²S ratio determinations in CO₂, N₂ and SO₂ gases, and a collector system for D/H ratio determination in H₂ gas. In 2005 a new continuous-flow Finnigan delta plus XP mass spectrometer was purchased and installed. It can analyse the same isotope compositions, but the required sample amount is very low down to 1 micromole.

The laboratory is capable to analyse the following types of materials. This description contains some observations that might be useful to the reader interested in the stable isotope preparation techniques.

Water. Oxygen isotope compositions are measured using automatic on-line CO₂-H₂O equilibration devices (Roether 1970). Hydrogen isotope compositions are measured using the Zn-reduction method described by Vennemann and O'Neil (1993) in the case of the traditional dual-inlet mass spec. A strong fractionation effect between the evolved H₂ gas and the hydrogen absorbed by the zinc has been observed for most commercially available zinc alloys (Demény, 1995). The fractionation effect can be corrected for provided that the relative amounts of H₂O and Zn is recorded. However, this amount effect has been eliminated in the case of a recently produced Zn alloy (A. Schimmelmann, Indiana University, personal communication).

In the case of the delta plus XP type mass spec, the D/H ratios of waters are determined by H₂-H₂O exchange using an on-line equipment.

Carbonate. δ¹³C and δ¹⁸O values are determined in calcite, dolomite, ankerite, siderite and magnesite using the traditional off-line (with the delta S) or automated on-line (delta plus XP) H₃PO₄-carbonate reaction.

Organic matter. Organic matter is oxidized using CuO at ~500 °C. The sample is mixed with CuO, placed into pyrex glass tubes, vacuum-pumped and sealed, then reacted overnight. δ¹³C and δD are measured in CO₂ and H₂ produced from the evolved H₂O separated by vacuum distillation.

Fluid inclusions. Inclusion fluids are analysed by thermal decrepitation or - in case of H-bearing contaminant - vacuum crushing.

CO₂ in air. CO₂ is usually analysed for ¹³C/¹²C and ¹⁸O/¹⁶O ratios by freezing at liquid nitrogen temperature. However, N₂O - with the same molecule mass - is frozen together with CO₂ and hence a correction factor is applied. Another method involves separation of CO₂ and N₂O by gas chromatography and analysing the CO₂ separately. Since one of our projects dealt with polluted urban air that may contain anthropogenic N₂O from different sources, the gas chromatographic separation is chosen.

Research areas

Isotope geochemistry (Attila Demény)

- isotope geochemistry of the upper mantle (Canary Islands, Pannonian Basin, carbonatites)

- isotope geochemistry of mass extinction events (joint project with József Pálfy)

Isotope hydrology (István Fórizs)

- protection of water resources

- secular variation of River Danube

- cave dripping water, and thermal waters

CO₂ in air (Attila Demény). 1998-1999: Academy Research Project; 2000-2003: joint NWO-OTKA project with the Hungarian Meteorological Service (László Haszpra) and the University of Groningen.

Stable isotope geochemistry of speleothemes (Zoltán Siklósy), freshwater limestones (Sándor Kele) and mollusc shells (Gabriella Barna).

The methods of stable isotope geochemistry are also applied in soil geochemistry studies (Bernadett Bajnóczi).

The GEOCHEMISTRY & PALEOCLIMATE Research Group has been established to coordinate research activities within the Institute for Geochemical Research related to paleoclimatology.