Isotope
The Stable Light Isotope Laboratory at the University of Cape Town (UCT) forms part of the BIOGRIP Node for Isotope Biogeochemistry. The lab is one of only a few on the African continent that can measure stable light isotope ratios (¹³C/¹²C, ¹⁵N/¹⁴N, ¹⁸O/¹⁶O, ²H/¹H and soon ³⁴S/³²S) for users from the South African research community and abroad. Stable isotope ratios provide natural tracers of biological and geological processes in the world around us, across scales ranging from intracellular metabolism to earth and atmospheric cycles. Important applications include studies of the flows of nutrients (e.g. carbon and nitrogen) through food webs, enabling one to track the diets of consumers eating isotopically varied foods. Environmentally induced variations in stable isotope ratios are an important tool in detecting illicit trade in endangered wildlife species and natural products. Measurement of water isotopes aids in characterising aquifers, especially estimating recharge rates.
At present, the bulk of our analyses are of C and N isotopes in organic materials. We also measure C and O isotopes in carbonates (or carbon dioxide). We will soon be expanding our capacity to measure (a) Sulphur isotopes (b) nitrogen and oxygen isotopes in oceanic nitrates (c) the rare isotope oxygen 17 in carbonates and carbon dioxide.
The laboratory is equipped with a full complement of sample preparation facilities, including microbalances, centrifuges and freeze-dryers. Its staff are well trained and skilled, enabling a range of support and guidance where needed.
Laboratory equipment
Isotope Ratio Mass Spectrometers (IRMS)
Delta V Plus (ThermoFinnigan, 2010)
The Delta V Plus is used to analyse carbon and nitrogen isotopes in materials such as plant and animal tissues, soils and filter papers. Samples are weighed into tin cups using a microbalance, then combusted in a Flash 2000 series elemental analyser (Thermo Finnigan) to convert them into CO₂ and N₂. The gases are passed into the mass spectrometer via a Conflo IV gas control unit (Thermo Finnigan, Bremen, Germany).
Sample requirements:
Sample requirements differ depending on the user’s requirements. It is recommended users contact the lab in advance to discuss their particular needs.
Samples should be submitted prepared, dried, homogenised and (if possible) weighed, ready to be run.
Delta V Plus (2020)
The new Delta V Plus is used to analyse carbon and nitrogen and sulphur isotopes in materials such as plant and animal tissues. This new instrument will add sulphur isotopes to our suite of possible analyses. Samples are weighed into tin cups using a microbalance, then combusted in a EA Isolink series elemental analyser (Thermo Finnigan) to convert them into CO₂ and N₂ and SO2. The gases are passed into the mass spectrometer via a Conflo IV gas control unit (Thermo Finnigan, Bremen, Germany).
Delta Plus XP (2004)
Used in combination with a ThermoFinnigan Gasbench to analyse carbon and oxygen isotopes in carbon dioxide, or in carbonates such as carbonate rocks, tooth enamel, or ostrich eggshell. Dual inlet capability is also used to measure C, O and H isotopes in silicates and waters which have been prepared offline in the Department of Geological Sciences.
Samples are weighed into 12 ml borosilicate tubes closed with screw top lids containing a septum. The tubes are placed in a temperature-controlled sampler tray set to 72°C, then flushed with helium to remove the atmospheric gases. Five to seven drops (according to sample size) of warm (72°C) phosphoric acid are added to each sample tube by manual injection through the septum, using a 1 ml syringe, then left to react for a minimum of two and a half hours. The evolved gas is sampled by the autosampler and passed through a Nafion water removal unit, then a GC column to separate the gases and then through a second Nafion water trap. The purified gas is then passed into a Delta Plus XP isotope ratio mass spectrometer (IRMS) controlled by Isodat software.
Sample requirements:
Sample requirements differ according to the material analysed and the user’s requirements. It is recommended that users contact the lab in advance to discuss their particular needs.
Affiliated centres
Marine Biogeochemistry Lab (MBL)
The Marine Biogeochemistry Lab in the Department of Oceanography at the University of Cape Town (UCT) is one of the labs affiliated with the BIOGRIP Node for Isotope Biogeochemistry.
Read more about the MBL here.
Multicollector ICP-MS Lab
The Multicollector ICP-MS Lab in the Department of Geological Sciences at the University of Cape Town (UCT) is affiliated with the BIOGRIP Node for Isotope Biogeochemistry.
Read more about the lab here.
