An evaluation of static ToF-SIMS analysis of environmental organics

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been extensively used in surface analysis due to its high mass resolution, sensitivity, and mass spectral imaging capabilities. Static ToF-SIMS has mainly been used for solid material analysis; however, its application in environmental organics is limited. During SIMS spectral analysis, relative mass accuracy and measurement repeatability are key factors for obtaining reliable speciation and acquiring chemical insights of the specimens. Herein, we provide an evaluation of four environmentally relevant organic systems, including glyoxal, pyruvic acid, oil-in-water emulsion, and carbon dioxide (CO₂) capture solvent (i.e., N-2-ethoxyethyl-3-morpholinopropan-1-amine, EMMPA), to show the spectral measurement repeatability when using static ToF-SIMS. First, sample preparation is essential in acquiring accurate and reproducible results in ToF-SIMS analysis. The mass spectral results show that characteristic peaks observed can be distinguished with reasonable confidence by comparing the observed mass to charge ratios (m/z) to theoretical ones. The statistical analysis of peak areas indicates that the peak area and/or peak height measurement ratios are satisfactory among replicates. Compared with previous studies, the bismuth cluster primary ion beam, namely Bi₃ ⁺, has less fragmentation than Bi⁺. Therefore, Bi₃ ⁺ is deemed more suitable for organic analysis using static SIMS. Our results show that ToF-SIMS offers a viable approach to study environmental organics including but not limited to aqueous aerosols, wastewater emulsions, and CO₂ capture solvents. It is expected that future studies will expand organic speciation with high fidelity due to the continued advancement of SIMS as a sensitive analysis technique.