Sample preparation for MALDI mass spectrometry of model prebiotic reactions in simulated ocean world environments

The prebiotic potential of ocean worlds such as Europa and Enceladus, while not well constrained, is vital in the search for potential life elsewhere. To better understand this potential, laboratory studies provide experimental insight into the chemical environment(s) of ocean worlds, and any constraints to hold prebiotically relevant systems. However, simulated ocean world solutions present a technical challenge for analytical techniques such as mass spectrometry (MS), as high saline content required for simulating ocean world environments result in ion suppression and reduced sensitivity. Here, we compare three sample preparation techniques – C4 ZipTips, C18 ZipTips, and on-plate washing – for matrix-assisted laser desorption/ionization – time of flight (MALDI-TOF) MS of saline solutions similar to environments expected in ocean worlds. We determined that using C18 ZipTips was optimal when paired with 2,5-dihydroxybenzoic acid (DHB) matrix, whereas on-plate desalting was optimal when paired with alpha-cyano-4-hydroxycinnamic acid (CHCA) matrix. These observations have been attributed to differences in DHB and CHCA hydrophobicity and matrix-analyte mixing. Both approaches resulted in salt suppression from a mixture of selected model prebiotic oligomers and model ocean world solutions, increasing S/N and analyte signals of interest in mass spectra. The methodology described here presents simple, low-volume sample preparation strategies for MALDI-TOF MS of model prebiotic reactions in saline solutions.