Stable Isotope Ratio Analyses of Light Elements

Welcome & What can we offer

The Stable Isotopes Laboratory (SIL), affiliated to the Centrum for System Biology (C4Sys), provides stable isotope ratio analyses of light elements C, O, H, and N in solid (mainly organic) and liquid samples using a continuous flow isotope ratio mass spectrometer (IRMS). The laboratory exists from year 2001 and accomplishes more than three thousand analyses per year for many research projects mainly from biology, plant and animal ecology, and geology but also for food authenticity control and nature and environment protection. In addition to our in-house research, a custom-base service is offered. The laboratory promotes cross-disciplinary research and education, develops and supports the infrastructure of stable isotope ratio analyses and related techniques.

The SIL offers education and training in stable isotope techniques and their applications in a graduate and postgraduate international course in cooperation with the Technical University in Munich (

The SIL is housed in the building B of the Faculty of Science, University of South Bohemia in České Budějovice and administrated by the Department of Experimental Plant Biology.

How can you access

General questions

Jiří Květoň,,

Ladislav Marek,

phone: +420 7772351, +420 7772354, +420 7772353

Head: Jiří Šantrůček (

IRMS operators: Jiří Květoň, Ladislav Marek

Staff: Petra Fialová, Jiří Kubásek, Jitka Neuwirthová,

Customer registration

Please, fill in the short registration form

The information will be used (i) for your identification as a customer of our infrastructure (ii) for contacting you in case we will need more information about your samples.

Analytical services

The SIL can provide analyses of solid, liquid, or gaseous samples for determination of stable isotope ratios of carbon (13C/12C), nitrogen (15N/14N), hydrogen (1H/2H), and oxygen (18O/16O) in bulk material. In future, we aim to extend our services to compound-specific IRMS analyses.

Carbon (13C) and Nitrogen (15N) Analysis of Solids by EA-IRMS

Plant materials and soils are typical representatives of solid samples that can be analysed using an isotope ratio mass spectrometer (IRMS) coupled with an elemental analyser (EA). The isotopic label (13C or 15N) of enriched samples must be brought to a maximum content not  exceeding twice as much the natural abundance of the isotope (by “dilution” with a proper material) in order to make the samples measurable. Samples must be dry, ground to a very fine powder (like flour), weighed to tin capsules, and air-tightly wrapped. Samples are catalytically flash-combusted in a burst of oxygen in an oxidation reactor at a temperature of 1020 °C. Carrier gas (helium) takes the combustion gases into a reduction reactor where nitrogen oxides are reduced to molecular nitrogen at 650 °C. The measured analytes are therefore CO2 and N2. After removing H2O from the gas stream, it enters the IRMS. A sample isotope ratio is expressed relative to the international standard VPDB (Vienna PeeDee Belemnite) for carbon and Air for nitrogen.

Oxygen (18O) and Hydrogen (2H) Analysis of Water by TC/EA-IRMS

Water is thermally decomposed at a temperature of 1450 °C to its constituents – hydrogen and oxygen – in a high temperature conversion elemental analyser (TC/EA). Hydrogen flows through the system without change whereas oxygen reacts with the filling of the reactor – carbon – and forms carbon monoxide. So, analytes that leave the TC/EA in a stream of carrier helium and enter the IRMS are H2 and CO. When to be analysed water samples enriched with either 2H or 18O, the samples must be finally diluted with an isotopically suitable water to a maximum label content not exceeding twice as much the natural abundance of the isotope in order to be the samples measurable. This procedure can be accomplished in the SIL. A sample isotope ratio is expressed relative to the international standard VSMOW (Vienna Standard Mean Ocean Water) for the isotopes of both the elements.

Carbon (13C) and Oxygen (18O) Analysis of Carbon Dioxide by GasBench-IRMS

Gas samples are analysed using the Gas bench. The analysed gas – carbon dioxide – can either be present as an original gas sample or be liberated from a liquid or solid phase into the headspace of a sample container by different sample preparation methods. The gas in a stream of helium is got rid of water and injected into the IRMS. If required, gas samples with a concentration of carbon dioxide below the measuring limit can be concentrated using a cryo-concentrating equipment upstream. For samples enriched with either 13C or 18O, a proper dilution with an inert gas (helium, nitrogen, etc.) of an appropriate isotopic composition must be performed. For correct analysis, a maximum content of both the labels must not significantly exceed the natural abundance of the isotope more than twice. A sample isotope ratio is expressed relative to the international standard VPDB for carbon and VSMOW or VPDB for oxygen.

Compound Specific Isotope Analysis (CSIA) by GC-C-IRMS

The SIL intends to start with Compound specific 13C analyses in frame of the C4Sys Research Infrastructure project. At present, we are out-sourcing the facility for our in-house research. For more details, contact Jitka Neuwirthová (

Sample size and respective international reference standards

Isotopes Sample type Sample form Sample delivery Amount of element* International standard
minimum working range
13C/12C solid fine powder tin capsules 15 μg 37 – 53 μg
260 – 360 μg
gas gaseous gas container 0.05 % 0.30 – 0,40 % VPDB
carbonates fine powder vial 80 μg 150 – 250 μg VPDB
15N/14N solid fine powder tin capsules 20 μg 40 – 200 μg air
2H/1H water liquid vial 25 μl 50 – 200 μl
1 – 2 ml
18O/16O water liquid vial 25 μl 50 – 200 μl
1 – 2 ml
18O/16O carbonates fine powder vial 80 μg 150 – 250 μg VSMOW

VPDB – Vienna PeeDee Belemnite
VSMOW – Vienna Standard Mean Ocean Water
* The most common sample sizes are given. Amounts depend on the type of the sample.