Secondary ion yield enhancement for lipids in frozen hydrated lymphoma tissue samples using water cluster SIMS

The enhancement of secondary ion yields (SI-yields) for lipids by combining frozen-hydrated sample handling and H2O gas cluster ion beams (GCIBs) was investigated in lymphoma tissue sections. Using an Ionoptika J105 time-of-flight secondary ion mass spectrometry instrument equipped with a 40 keV GCIB, H2O and CO2 gas clusters with E/n (kinetic energy per atomic mass for the cluster) ranging between 0.09 and 0.15 eV were compared on frozen-hydrated and freeze-dried tissue sections. The results showed that SI-yields for intact lipids increased while fragmentation decreased with decreasing E/n for H2O and CO2 GCIBs. At similar E/n, the H2O-GCIB had significantly higher SI-yields and reduced fragmentation, but a very similar sputter rate when compared to the CO2 GCIB. Tissue sections analyzed under frozen-hydrated conditions had higher SI-yields and sputter rates compared to freeze-dried samples. Depth profiling combined with atomic force microscopy measurements highlighted that freeze-drying altered the sample condition, affecting the sputter rate and SI-yields. From this study, we conclude that combining frozen-hydrated samples and H2O-GCIB provides the optimum analysis method for ToF-SIMS for studying lipids in tissue sections of this type.