Determination of the nitrogen abundance in organic materials by NanoSIMS quantitative imaging†

Aurelien Thomen (1) , François Robert (2) , Laurent Remusat (2)

1 Cosmochemistry Laboratory, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Manoa
2 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

We describe a procedure to determine precise and accurate elemental abundance by means of quantitative imaging using secondary ion mass spectrometry (on images covering 10 10 mm2) applied to natural Insoluble Organic Matter (IOM). Dynamic SIMS conditions are reached for a 16 keV Cs+ fluence of >2.0 1017 Cs+ cm 2 implanted at the surface of the IOM. Once the sample surface is saturated in cesium, steady-state implantation and sputtering yield are reached: constant secondary ion count rates are then observed. Two calibrations of the nitrogen abundance are presented. The nitrogen abundance is expressed either as [N] or N/C atomic ratio calibrated by means of 12C14N /12C or 12C14N /12C2 ionic ratios respectively. The 12C14N /12C uncertainty is always larger than the uncertainty of 12C14N /12C2 . At a smaller scale inside an image ( 1 1 mm2), a little larger than the primary beam size, processes induced by topographic irregularity of the IOM powder result in a variation of the 12C14N ,12C2 and 12C count rates and increase the variability of the ionic ratios. The chemical contrast produced by a rough sample surface exposed to the Cs+ rastering is evaluated with a scratched epoxy resin for 12C14N /12C and 12C14N /12C2 elemental ratios. Owing to similarities in emission parameters, the determination of the N/C ratio in rough organic surfaces is improved by using 12C 14N /12C2 instead of 12C 14N /12C .

Aurelien Thomen, François Robert, Laurent Remusat. Determination of the nitrogen abundance in organic materials by NanoSIMS quantitative imaging†. Journal of Analytical Atomic Spectrometry, 2014, 29, pp.512. ⟨10.1039/c3ja50313e⟩. ⟨hal-00984384⟩