Capillary Electrophoresis for Spacecraft Drinking Water Analysis: Methods and Breadboard Development

This report describes the first two parts of a three-phase project to develop and test a spacecraft-compatible capillary electrophoresis (CE) instrument. This instrument is designed to monitor the quality of recycled potable water aboard spacecraft such as the International Space Station. Phase I involved selecting and validating methods for low mass-to-charge ratio (m/z) cations and anions by using a slightly modified commercial CE instrument as a model. The analytical performance of several published CE methods was assessed for their ability to detect targeted anions and cations listed in a NASA water quality standard. Direct and indirect UV absorption detection at a single wavelength (214 nm) was used, and separation selectivity and sensitivity were optimized at the expense of analysis time. Phase II focused on building a breadboard CE instrument and flight-testing it on NASA's KC-135 parabolic aircraft. Phase I results showed that 91% of the target ions can be separated and detected, and the required minimum detection limits (MDL) for 52% of NASA's target ions can be met by using a 75 cm x 50 μm bubble-cell capillary and three different separation schemes. Phase II results verified that that the instrument can function in parabolic flight but that further tests are needed to optimize separation and to confirm detection limits in microgravity.