Matrix effects in MeV SIMS for modern pigment–binder systems: The influence of binder composition on SOP secondary molecular ion yield

Modern artists’ paints exhibit diverse formulations that both shape artistic expression and pose challenges for cultural heritage preservation. Secondary ion mass spectrometry with MeV primary ions (MeV SIMS) is an increasingly used nuclear analytical technique to identify synthetic organic pigments (SOPs) and dyes. However, successful SOP detection is strongly influenced by the chemical environment, which governs ionization probability. This study investigates how synthetic and natural binders affect SOP secondary molecular ion yields in MeV SIMS, with additional emphasis on sample preparation methodology. Two-component mock-ups were prepared across a selected range of pigment-to-binder ratios by mixing SOPs (PB15:1 and PR254) with pure binders: alkyd, gum arabic, oil, and acrylic. Paints were (i) spin-coated as thin films for direct analysis and UV-aged to evaluate the impact of binder degradation, and (ii) cast on glass slides without aging, followed by dry paint fragment sampling for measurement. Oil-based paints produced the lowest SOP molecular ion yields in both pristine and aged samples, with no correlation to pigment concentration, indicating a strong matrix effect driven by pigment particle encapsulation. In gum arabic, generally the highest yields were obtained, followed by alkyd—especially after aging—with yields increasing with pigment load. Mechanical sampling and pressing into indium substrate enhanced SOP yields by increasing the likelihood of pigment particle exposure at the surface, an effect most evident at low pigment loads. While this approach introduced greater yield variability, it extended the accessible SOP concentration range and confirmed that physical pigment exposure is a key factor in SOP secondary ion yield.