Quantifying SIMS of Organic Mixtures and Depth Profiles—Characterizing Matrix Effects of Fragment Ions
Sets of matrix factors, Ξ, are reported for the first time for secondary ions in secondary ion mass spectrometry for several binary organic systems. These show the interplay of the effects of ion velocity, fragment chemistry, and the secondary ion point of origin. Matrix factors are reported for negative ions for Irganox 1010 with FMOC or Irganox 1098 and, for both positive and negative ions, with Ir(ppy)2(acac). For Irganox 1010/FMOC, the Ξ values for Irganox 1010 fall with m/z, whereas those for FMOC rise. For m/z < 250, Ξ scales very approximately with (m/z)0.5, supporting a dependence on the ion velocity at low mass. Low-mass ions generally have low matrix factors but |Ξ| may still exceed 0.5 for m/z < 50. Analysis of ion sequences with addition or loss of a hydrogen atom shows that the Ξ values for Irganox 1010 and FMOC ions change by − 0.026 and 0.24 per hydrogen atom, respectively, arising from the changing charge transfer rate constant. This effect adds to that of velocity and may be associated with the nine times more hydrogen atoms in the Irganox 1010 molecule than in FMOC. For Irganox 1098/Irganox 1010, the molecular similarity leads to small |Ξ|, except for the pseudo molecular ions where the behavior follows Irganox 1010/FMOC. For Ir(ppy)2(acac)/Irganox 1010, the positive secondary ions show twice the matrix effects of negative ions. These data provide the first overall assessment of matrix factors in organic mixtures necessary for improved understanding for quantification and the precise localization of species.
KeywordsAnalysis Matrix factors Organic solid mixtures Quantification Secondary ion mass spectrometry SIMS
The authors would like to thank M. Wywijas and S. A. Smith for the preparation of the samples used in this study and A G Shard for helpful comments. This work forms part of the “3D OrbiSIMS” project in the Life-science and Health programme of the National Measurement System of the UK Department of Business, Energy and Industrial strategy. This work has received funding from the 3DMetChemIT project of the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.
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Conflict of Interest
The authors declare that they have no competing interests.
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