Tritium (3H)
Definition
A radioactive hydrogen isotope used as an alternative label in RIA, particularly for small organic molecules such as steroids and drugs where iodination would alter binding properties. Tritium emits beta particles detected by liquid scintillation counting. Its half-life is about 12.3 years, giving tritium-labelled reagents a longer shelf-life than iodine-125 preparations.
- Isotope
- Radioactive hydrogen, symbol 3H
- Half-life
- About 12.3 years
- Decay type
- Beta particle emission
- Detection method
- Liquid scintillation counting
- Typical use
- Labelling small organics such as steroids and drugs in RIA
Common questions
Why choose tritium over iodine-125 for some RIA targets?+
Iodination adds a bulky iodine atom that can distort the binding site of a small molecule, changing how it reacts with the antibody. Tritium substitutes for a hydrogen already in the molecule, so the labelled compound behaves almost identically to the natural analyte.
Does tritium's long half-life create a practical advantage?+
Yes. Because it decays slowly, tritium-labelled reagents remain usable for longer storage periods than iodine-125 reagents, which decay much faster and need more frequent replacement in a working laboratory.
Related terms
- Calibration Curve
- In RIA, a set of standards containing known concentrations of unlabelled analyte that are run alongside test samples. Bound radioactivity is measured...
- Chemiluminescent Immunoassay (CLIA)
- A non-radioactive immunoassay that uses enzyme-catalysed chemiluminescent reactions to generate the detection signal. CLIA instruments measure light output in relative light units....
- Competitive Binding Assay
- An immunoassay format in which labelled and unlabelled forms of the same analyte compete for a fixed, limiting number of antibody binding...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Iodine-125 (125I)
- The radioisotope most commonly used in RIA. It emits gamma radiation, has a half-life of approximately 60 days, and can be covalently...