Electrospray Ionization for Water Monitoring

Current methods for monitoring the water used on the International Space Station (ISS) rely heavily on ground analysis of archival samples. Air monitors presently on board the ISS could be used for trace analysis of the water samples. Electrospray ionization (ESI) is a powerful and widely used ionization technique for analysis of bio-molecules in solution and provides a potential means for introducing water into the current monitors. Ions are formed in liquid droplets and these droplets behave differently depending on the composition of the liquid. A ground study is important to characterize the spray produced from different liquid compositions in an ESI source as a first step to proposing an ESI flight experiment. This study will serve as the baseline for the flight experiment, where the effect of microgravity on electrospray is unknown. Different liquid compositions will be used in an attempt to affect the surface tension and conductivity, and, therefore, the power requirements to form an electrospray. Solutions mimicking the ISS water samples will be tested to determine if the sprays produced require different parameters from those produced using different dopants. The intended product of this project will be a report detailing the effects of solution composition, needle size, and solution flow rate using the ESI source. These results will provide a baseline for an on-orbit ESI experiment, which might eventually lead to a new ionization source for water sample analysis. A successful completion of this project will lead to a proposal aimed at studying ESI as a station detailed test objective. As ESI is currently used in ground-based studies of biomolecules, further testing of this technique for on-orbit medical monitoring may be pursued. More »