Static secondary ion mass spectrometry (S-SIMS) for the characterization of surface components in mineral particulates.

The feasibility of static secondary ion mass spectrometry (S-SIMS) for the detection of molecule specific information from complex materials, such as natural clay and soil samples, has been investigated. Ion trap (IT), as well as triple quadrupole (TQ) instruments, have been used for mass analysis. Secondary ion images have been acquired using time-of-flight (TOF) S-SIMS. The generation of molecular adduct ions from thin and thick layers on the mineral substrates has been investigated using KBr as a simple model system. Results show that molecular adducts of KBr can be indeed detected from the spiked materials. However, the concentrations of the spiking solutions have to be significantly larger than expected from the surface area measured by gas adsorption techniques. In addition imaging analysis has evidenced that the detection of adduct ions in the mass spectra directly relates to the presence of local micro-crystallites.

Feasibility of analyzing molecular pigments in paint layers using TOF S-SIMS.

A first attempt to measure the molecular compositions of pigments in paintings using static SIMS was made. An investigation of pellets of pure pigments such as auripigment and verdigris allowed the detection of numerous high m/z ions useful for molecular identification. Analysis of pigments in embedded paint fragments, on the other hand, only yielded elemental information because of charge build-up and contamination problems. Optimization of the form in which the sample is presented to the analysis method is obviously the price to pay for the ultimate sensitivity and information depth of S-SIMS.

Systematization of the mass spectra for speciation of inorganic salts with static secondary ion mass spectrometry.

The analytical use of mass spectra from static secondary ion mass spectrometry for the molecular identification of inorganic analytes in real life surface layers and microobjects requires an empirical insight in the signals to be expected from a given compound. A comprehensive database comprising over 50 salts has been assembled to complement prior data on oxides. The present study allows the systematic trends in the relationship between the detected signals and molecular composition of the analyte to be delineated. The mass spectra provide diagnostic information by means of atomic ions, structural fragments, molecular ions, and adduct ions of the analyte neutrals. The prediction of mass spectra from a given analyte must account for the charge state of the ions in the salt, the formation of oxide-type neutrals from oxy salts, and the occurrence of oxidation-reduction processes.