The first comparison of different ablation environments for elemental analysis using mass spectrometry highlighted the differences in deposited material near the ablation spot and an increase in signal intensities when using helium instead of argon as carrier gas.[1] While ablation rates were reported to be identical for both gases,[2] improved aerosol transport and lower material deposition were assumed to be responsible for the higher sensitivities.[1] Nitrogen Microwave Inductively Coupled Atmospheric-Pressure Plasma Mass Spectrometry (N₂-MICAP-MS), allows for a wider choice of carrier gases [3] and thus nitrogen was recently investigated as carrier gas for laser ablation (LA).[4] A significant surface darkening was observed for LA in a nitrogen environment but the sensitivities differed by 30 % only. As the ablation rates were found to be unchanged as well, aerosol transport was considered to be the main cause of the sensitivity variations obtained between the ablation environments studied.

In order to quantitatively assess differences in laser aerosol deposition in helium, argon and nitrogen, re-ablation of the deposited material from the surface of a NIST SRM 610 glass standard was performed using a laser fluence below the ablation threshold of the substrate. The sensitivities and sensitivity ratios were compared to those during ablation of the craters allowing to calculate the mass balance. As the aerosols in both cases were analysed under same plasma conditions, ICP induced fractionation effects can be separated from effects caused by the LA process. These results will be discussed in relation to previous reports of fractionation phenomena and may improve the understanding of LA for quantitative analysis.


References
[1] S.M., Eggins; L.P.J., Kinsley; J.M.G. Shelley Applied Surface Science, 1998, 127-129, 278-286.
[2] I., Horn; D., Günther Applied Surface Science, 2003, 207, 144-157.
[3] M., Schild, A., Gundlach-Graham; A., Menon; J., Jevtic; V., Pikelja; M., Tanner; B., Hattendorf; D., Günther Journal of Analytical Atomic Spectrometry, 2018, 90, 13443-13450.
[4] D., Käser; R., Kägi; B., Hattendorf; D., Günther submitted manuscript.