Isotope Ratio Mass Spectrometers
Five different mass spectrometers (MS) are used at the Center of Isotope Research to determine stable isotope ratios. The MS are optimized for different types of samples and the way that the samples are supplied, as explained below. The MS are named: ZwOptima, AirOptima, DI-Optima, MM10 and Pyroh-Heka.
Analysis of 13C isotope ratio is needed for a correction on 14C isotope ratio to calculate the age of a sample. The 13C and 15N ratios are determined with the IsoPrime100 before a sample is analyzed on 13C and 14C ratios using the Acceleration Mass Spectrometer (AMS). Thus, 13C isotope ratios are measured both by IsoPrime100 and AMS and the results are compared to check the quality of both instruments. In case of good agreement, the data of IsoPrime100 are used for further analysis, because the IsoPrime100 is most accurate for the stable isotope 13C whereas the AMS is specially designed for an accurate determination of the 14C isotope ratio. The 15N isotope ratio is a supplementary measurement that informs on animal diet.
The isotope ratios of atmospheric CO2: 13C and 18O, in particular samples from our Lutjewad monitoring station, are determined using the DI-Optima MS in combination with the AMS. As above, results of 13C measurements from both instruments are also used for quality control. The 18O isotope ratio informs on the temperature and the isotope ratios of C inform on fossil fuel fraction of atmospheric CO2.
Changes in atmospheric CO2 concentration –as measured with the DI-Optima- are commonly accompanied by changes in O2 concentrations because CO2 and O2 are inversely exchanged in important global processes: fossil fuel combustion, photosynthesis and respiration. However, oceanic uptake of CO2 is not related to O2 uptake as solubility of CO2 largely exceeds O2 solubility, due to equilibrium of CO2 with (bi)-carbonate in water. The Air-Optima is specially designed to measure the atmospheric O2/N2 concentration ratio to determine global oceanic CO2 uptake. The measurements are performed with very high precision as relative changes in O2/N2 are very small.
All other 13C and 18O isotope ratios, for example from water samples are measured with the general purpose instrument MM10 MS. The water is equilibrated with CO2 of known isotopic composition. The MM10 MS is then used to measure changes in the CO2 isotopic composition before and after equilibration and this result in the determination of the isotopic composition of CO2 in the water sample.
Isotope ratios of small (from 0.12 µl onwards!) water samples: 2H and 18O are measured using the Pyroh-Heka. The Pyroh reduces water on a chromium oven and the Heka pyrolysis water to get H2 and CO for analysis at the MS. The instrument is mainly used for measurements on artificially enriched isotope ratios in biological samples, but also enriched ice from Greenland has been measured.
|Laatst gewijzigd:||15 april 2019 16:36|