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SIMS21, Poland 2017 - Matthias Lorenz abstract

Matthias Lorenz oral presentation (PB2-Mon4-1-3)

In Situ Sputter Deposition of Molecular Matrix Compounds for ME SIMS

Matthias Lorenz1, Alex G. Shard2, Jean-Luc Vorng2, Ian S. Gilmore2

1 University of Tennessee, Knoxville, 1 Bethel Valley Rd MS 6493, TN 37831-6493 Oak Ridge, United States
2 National Physical Laboratory, Hampton Road, TW11 0LW Teddington, United Kingdom

We present an alternative approach for the in situ application of molecular matrices in matrix enhanced secondary ion mass spectrometry (ME SIMS). Our technique can substitute the commonly applied ex situ techniques of wet application from solutions or physical vapor deposition. In situ sputter deposition enables to prevent the direct contact of the sample with liquids such as solvents, and the resulting analyte delocalization. The technique is compatible with sputter erosion for sample clean-up and depth profiling for 3D chemical imaging.

The in situ transfer of intact molecular matrix compounds from an adjacent reservoir for bulk material onto the sample surface is facilitated by the use of gas cluster ion beams for sputter deposition. Beams of these projectile species have been shown to enable the ejection of organic material with a large fraction of intact molecules.[1] They further facilitate a pronounced directed ejection of organic material, which can be utilized for the deposition of the ejected intact molecules on the sample surface, directly in the field of view of a SIMS analysis. Effectively, this is a molecular version of sputter deposition.

We demonstrate the technique’s potential to transfer complex organic molecules from the matrix reservoir onto the sample surface. We show the in situ deposition of the established ME SIMS matrix 2,5-dihydroxybenzoic acid, and a correlation of the signal enhancement with the amount of deposited matrix.

We use routine SIMS cryo capabilities for the vacuum introduction of highly volatile compounds and their use as ME SIMS matrices. We show the signal enhancement of the quasimolecular ions of the drug compounds chloroquine, haloperidol, and amiodarone embedded in bovine liver tissue homogenate by deposition of a frozen aqueous solution of formic acid, and 3-nitrobenzonitrile as matrices.

We show the alternating application of matrix sputtering and sample erosion cycles for the controlled in situ application and removal of matrix compounds to enable the multi-modal analysis by SIMS and ME SIMS.

[1] M. Lorenz, A. G. Shard, J. D. P. Counsell, I. S. Gilmore, J. Phys. Chem. C, 120, 2016, 25317.