Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) provides molecular information with high spatial resolution, making it well suited for imaging the distribution of individual organic molecules. However, most of the applications are limited to low molecular weight ions. Unfortunately, many compounds lack characteristic peaks in the low mass range. In the low mass range, the major peak of PEG (polyethylene glycol) appears at m/z 45, but this ion can also come from any compound containing the C2H5O+ group. In this research, PEG retained in the cross-section of ink-printed paper was studied. The distribution of PEG in the cross-section of two different kinds of paper was examined by imaging high molecular weight ions, which are characteristic peaks for PEG.
SIMS spectra and images were obtained using a 69Ga+ ion source was operated at both 15kV and 25kV. Charge compensation was accomplished with a low energy electron beam. The surface and the cross-section of the unprinted and printed paper were analyzed. Both high mass resolution spectra and high spatial resolution images were obtained.
The spectra in the mass range m/z 400-600 obtained from the cross-sections, both non-printed and printed smooth paper, are compared in Figure 1.