Isotope Ratio Mass Spectrometry (IRMS)
Definition
Specialised MS that measures precise ratios of light stable isotopes (delta values of 2H, 13C, 15N, 18O, 34S) on a continuous-flow combustion or pyrolysis interface.
- Measures
- Light stable isotope ratios (delta values)
- Isotopes covered
- 2H, 13C, 15N, 18O, 34S
- Interface
- Continuous-flow combustion or pyrolysis
- Reported as
- Delta notation relative to a reference standard
Common questions
How does IRMS differ from the ICP-MS-based isotope work used on bullet lead?+
IRMS targets light elements common in organic material, such as carbon, nitrogen, hydrogen, oxygen and sulfur, using combustion or pyrolysis to convert the sample to a simple gas before measurement. ICP-MS instead ionises the sample directly and is suited to heavier elements like lead or strontium, so the two techniques serve different classes of forensic isotope questions.
What kinds of forensic samples does IRMS actually work on?+
It is applied to organic evidence where the delta values encode information about origin or authenticity, such as drug samples, food and beverage products, and questioned documents, since the isotopic signature can reflect the geographic or manufacturing source of the material.
Related terms
- Atmospheric Pressure Chemical Ionisation (APCI)
- A complementary atmospheric-pressure source that vaporises the LC eluent and uses a corona discharge to ionise a reagent gas, which transfers charge...
- Electrospray Ionisation (ESI)
- A soft atmospheric-pressure ionisation source that sprays the LC eluent through a charged capillary into a heated counter-current gas, producing protonated or...
- Hyphenation
- Online coupling of a separation technique (GC, LC, ICP) with a spectrometric detector (MS, FTIR) so identification happens within the same run....
- ICP Plasma
- Inductively coupled argon plasma at 6,000 to 10,000 K that atomises and ionises samples in ICP-MS, generating singly charged elemental ions for...
- Interface
- The hardware bridge that transfers analyte from the separation stage to the detector while removing the unwanted mobile phase (carrier gas, solvent,...
- Internal Standard / Deuterated Standard
- A chemically similar (often perdeuterated) compound spiked into the sample to correct for matrix effects and ionisation suppression. Standard practice in forensic...
- Jet Separator
- Early GC-MS interface (Ryhage, 1964) that used differential pumping through a nozzle to enrich analyte and bleed helium. Replaced by direct capillary...