Switchable 1,8-diazabicycloundec-7-ene and 1-hexanol ionic liquid analyzed by liquid ToF-SIMS

Switchable ionic liquids (SWIL) play an important role in green chemistry. Due to the nature of SWIL chemistry, such as air sensitivity, pressure, and temperature dependence, it is difficult to characterize SWIL using vacuum-based surface techniques. The fully CO₂ loaded 1:1 mixtures of 1,8-diazabicycloundec-7-ene (DBU) and 1-hexanol (a SWIL system) and non-CO₂ loaded DBU and 1-hexanol mixture were analyzed by in situ time-of-flight secondary ion mass spectrometry (ToF-SIMS) coupled with the system for analysis at the liquid vacuum interface (SALVI), respectively. The DBU/1-hexanol/CO₂ SWIL was injected into the microchannel before liquid secondary ion mass spectrometry analysis. Bi₃ ⁺ primary ion beam was used. The positive and negative spectra of the SWIL chemical components are presented. The characteristic peaks m/z 153 (protonated DBU) in the positive mode and m/z 101 (deprotonated 1-hexanol) in the negative mode were observed. In addition, ion pair peaks including m/z 253, 319, 305, and 451 in the positive mode and m/z 145, 223, and 257 in the negative mode are first observed using this approach. These results demonstrate that the SALVI microfluidic reactor enables the vacuum-based surface technique (i.e., ToF-SIMS) for in situ characterization of challenging liquid samples such as ionic liquids.