Testing of Ion Exchange Chromatography Media for Extraterrestrial in situ Sample Preparation on Liquid Samples

Analysis of liquid samples often includes an initial sample preparation step in which components that are not of interest, or other interfering substances can be removed. Concentration of analytes in a smaller volume is also often important. For samples collected from solar system bodies outside of Earth, it is often not possible to bring the samples back to Earth for analysis, thus the sample preparation method would have to be transported to the liquid sample collection site. The use of ion exchange chromatography as a solid phase extraction method that can be utilized in a remote analysis is investigated in this work. The method developed relied on strong exchangers, with the use of pH changes to elute only analytes while keeping salt ions bound. Method development revealed the need for a pre-elution step in the process to ensure good charge switching of the analytes. Both anion and cation exchange media were evaluated for the capture of analytes from a high salt solution, as would be expected of liquid samples collected on a remote body. Cation exchange media provided the best results, with capture of almost all of the various analytes tested for extraction from simulated ocean water, including amino acids, nucleotides, peptides, and an oligonucleotide. In fact, cation exchange media even captured anionic components such as organic acids, likely through mixed mode hydrophobic based capture. Even though these analytes were released in the wash step, most of the salt removal was completed before release of these analytes, allowing this method to be used for desalting of these analytes. On the other hand, anion exchange media did not capture many of the anionic analytes it was expected to capture when the salt concentration was high. Irradiation exposure, as a model for the solar irradiation expected during deployment of these materials to extraterrestrial locations, did not affect the performance of the ion exchange media tested. Mixed analyte testing showed consistency with individual analyte testing, and coupling of a reverse phase solid phase extraction directly with the ion exchange method was possible.