Abstract
The influence of the matrix effect on secondary ion yield presents a very significant challenge in quantitative secondary ion mass spectrometry (SIMS) analysis, for example, in determining the relative concentrations of metabolites that characterize normal biological activities or disease progression. Not only the sample itself but also the choice of primary ion beam may influence the extent of ionization suppression/enhancement due to the local chemical environment. In this study, an assessment of ionization matrix effects was carried out on model systems using C60 (+), Arn (+), and (H2O)n (+) cluster ion beams. The analytes are pure and binary mixtures of amino acids arginine and histidine biological standards. Ion beams of 20 keV were compared with a range of cluster sizes n = 1000-10 000. The component secondary ion yields were assessed for matrix effects using different primary ion beams and sample composition. The presence of water in the cluster beam is associated with a reduction in the observed matrix effects, suggesting that chemically reactive ion beams may provide a route to more quantitative SIMS analysis of complex biological systems.
Highlights
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an established technique for imaging tissues and cells.1,2 Using this technique, the chemical composition of the surface and subsurface can be determined to a high sensitivity and specificity
The component secondary ion yields were assessed for matrix effects using different primary ion beams and sample composition
The presence of water in the cluster beam is associated with a reduction in the observed matrix effects, suggesting that chemically reactive ion beams may provide a route to more quantitative SIMS analysis of complex biological systems
Summary
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an established technique for imaging tissues and cells. Using this technique, the chemical composition of the surface and subsurface can be determined to a high sensitivity and specificity. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an established technique for imaging tissues and cells.. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an established technique for imaging tissues and cells.1,2 Using this technique, the chemical composition of the surface and subsurface can be determined to a high sensitivity and specificity. This study performs an assessment of the matrix effects with different polyatomic ion beams C60þ, Arnþ, and (H2O)nþ, with a range of cluster sizes n 1⁄4 1000–10 000. It examines the effect of water-containing ion beams on the ionization and analysis of a set of pure and binary mixture samples. The pKa values of the resulting conjugate bases are 12.5 and 7.0, respectively.
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