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Laser ablation isotope ratio mass spectrometry for enhanced sensitivity and spatial resolution in stable isotope analysis


J. J. Moran, Pacific Northwest National Laboratory, P.O. Box 999, MSIN P7-50, Richland, WA 99352, USA.



Stable isotope analysis permits the tracking of physical, chemical, and biological reactions and source materials at a wide variety of spatial scales. We present a laser ablation isotope ratio mass spectrometry (LA-IRMS) method that enables δ13C measurement of solid samples at 50 µm spatial resolution. The method does not require sample pre-treatment to physically separate spatial zones. We use laser ablation of solid samples followed by quantitative combustion of the ablated particulates to convert sample carbon into CO2. Cryofocusing of the resulting CO2 coupled with modulation in the carrier flow rate permits coherent peak introduction into an isotope ratio mass spectrometer, with only 65 ng carbon required per measurement. We conclusively demonstrate that the measured CO2 is produced by combustion of laser-ablated aerosols from the sample surface.

We measured δ13C for a series of solid compounds using laser ablation and traditional solid sample analysis techniques. Both techniques produced consistent isotopic results but the laser ablation method required over two orders of magnitude less sample. We demonstrated that LA-IRMS sensitivity coupled with its 50 µm spatial resolution could be used to measure δ13C values along a length of hair, making multiple sample measurements over distances corresponding to a single day's growth.

This method will be highly valuable in cases where the δ13C analysis of small samples over prescribed spatial distances is required. Suitable applications include forensic analysis of hair samples, investigations of tightly woven microbial systems, and cases of surface analysis where there is a sharp delineation between different components of a sample. Copyright © 2011 John Wiley & Sons, Ltd.