Technical Review: Comparison of IC and CE for Monitoring Ionic Water Contaminants on SSF

The measurement of ionic contaminants in samples from the potable water system on Space Station Freedom is one of the basic functions of the Crew Health Care System (CHeCS). The U. S. Environmental Protection Agency has identified ion chromatography as the analytical method of choice for measurement of anions and cations in water as described in USEPA method numbers 300.0 and 300.7, respectively. For this reason, ion chromatography was the technology initially identified to perform the ion contaminant monitoring function in the CHeCS Water Quality Subsystem. Subsequently, mass, size, and maintenance restrictions have led to a reevaluation of method options. Capillary electrophoresis (CE) has emerged as one of the more promising alternatives. CE is inherently microgravity compatible and uses an order of magnitude less reagent volume than ion chromatography. The major drawback to CE is its present state of development. To date only anion analysis has been commercially developed as a standard method using CE technology. The selection of CE for ion contaminant monitoring on SSF will be largely dependent upon the development of standard methods for cation and transition metal analyses.