Compound-Specific IRMS (CSIA)
Definition
A technique combining preparative GC separation with isotope ratio mass spectrometry to measure 13C/12C and D/H ratios in individual compounds (e.g. the benzoyl ester of cocaine). Used for geographic source attribution of cocaine seizures.
- Technique
- Preparative GC coupled to isotope ratio mass spectrometry
- Ratios measured
- 13C/12C and D/H
- Target compound
- Benzoyl ester of cocaine
- Application
- Geographic source attribution of cocaine seizures
Common questions
Why measure the isotope ratio of the benzoyl ester specifically rather than the cocaine molecule as a whole?+
The benzoyl group is added during processing from the coca-derived base, and its isotopic signature reflects the specific synthesis chemistry and reagents used, which vary with the region and method of production. This makes it more discriminating for sourcing than measuring the isotope ratio of the intact cocaine molecule alone.
What limits how confidently CSIA can pin a seizure to a specific country of origin?+
Isotope ratios reflect growing conditions, soil, climate and processing chemistry, all of which can overlap between neighbouring coca-growing regions and shift over time. Results are therefore interpreted as consistent with a set of plausible origins using a reference database, not as a unique geographic fingerprint.
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