Isotope-ratio mass spectrometry (IRMS) is a real forensic-materials technique, distinct from checking which elements are present (elemental composition) or how atoms vibrate (molecular spectroscopy). Instead it measures the ratio of two isotopes of the same element — say ¹³C to ¹²C — and reports it as a per-mille (‰) deviation from an international reference standard, called delta notation.
δ = (R_sample / R_standard − 1) × 1000‰
R = (heavy isotope) / (light isotope)
Natural processes (biology, rock formation, solar-system chemistry) fractionate isotopes in narrow, well-catalogued ranges. A sample's δ value is compared against known terrestrial and meteoritic reference bands — if it falls outside both, that's the "anomalous" case worth a closer look, though in practice it almost always means instrumental drift or contamination, not an exotic origin.
- Isotope system — δ¹³C (carbon, standard VPDB), δ¹⁸O (oxygen, standard VSMOW) or δ¹⁵N (nitrogen, standard AIR — atmospheric air). Real IRMS labs run all three plus δD and δ³⁴S for a full fingerprint.
- Sample δ value — the true isotope ratio of the "unknown" sample, expressed directly in delta notation (a real instrument reports the raw ratio R and computes δ from it automatically).
- Measurement noise — per-replicate scatter from real IRMS counting statistics; the simulator draws several replicate measurements and averages them, exactly as a lab reports a mean ± standard deviation rather than a single reading.
- Reference range — quick-loads a representative δ from the terrestrial, meteoritic or clearly out-of-range "anomalous" zone so you can see how each classifies.
Real-world relevance: this is genuinely how labs distinguish terrestrial contamination from extraterrestrial material — e.g. carbonaceous-chondrite organics show a δ¹³C signature distinct from terrestrial biology, and presolar grains in meteorites carry δ¹⁵N values enriched by hundreds of per mille, far beyond anything biological.