Delta Notation (δ)
Definition
A notation expressing the isotope ratio of a sample relative to an international standard in parts per thousand (per mil, ‰). Positive values mean the sample is heavier than the standard; negative values mean it is lighter.
- Unit
- Per mil (parts per thousand)
- Reference
- International isotope standard
- Positive value
- Sample heavier (isotopically enriched) than standard
- Negative value
- Sample lighter (isotopically depleted) than standard
Common questions
Why is delta notation used instead of reporting raw isotope abundance?+
Raw isotope abundances differ by only tiny fractions of a percent between samples, so expressing them as a per mil deviation from a shared standard makes small, meaningful differences easier to compare across laboratories.
Does the same delta notation apply to every isotope system?+
Yes, the notation itself is generic; what changes between systems, such as carbon, nitrogen, oxygen, or strontium, is the specific reference standard each field has agreed to measure against.
Related terms
- Epsilon Notation (ε)
- Similar to delta but expressed in parts per ten thousand, used for radiogenic systems where variation is very small. Epsilon Nd and...
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- TIMS (Thermal Ionisation Mass Spectrometry)
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