Rapid Determination of Biocide Concentrations Using Colorimetric Solid Phase Extraction (C-SPE): Results from Microgravity Testing

A sorption-spectrophotometric platform for the concentration and subsequent quantification of biocides in spacecraft drinking water is described. This methodology, termed Colorimetric Solid Phase Extraction (C-SPE), is based on the extraction of analytes onto a membrane impregnated with a colorimetric reagent. Quantification of the extracted analytes is accomplished by interrogating the surface of the membrane with a commercially available diffuse reflectance spectrophotometer. Ground-based experiments have shown that C-SPE is a viable means to determine biocide concentrations in the range commonly found in water samples from the Space Shuttle and the International Space Station (ISS). This paper details efforts to advance C-SPE closer to space flight qualification and ISS implementation, starting with the modification of the ground based biocide detection platform to simplify operation in a microgravity environment. The modified platform was used during KC-135 reduced gravity flights for the rapid, low level determinations of molecular iodine (I₂) and silver ion (Ag (I)), the biocides used by NASA and the Russian Space Agency, respectively. Iodine is determined as the yellow iodine-poly(vinylpyrrolidone) (PVP) complex and Ag (I) is quantified as the pink silver-5 (p-dimethylaminobenzylidene) rhodanine (DMABR) complex. The results from these flight tests, along with the application of C-SPE to the determination of total iodine in a water sample by employing a pre-extraction Oxone treatment are discussed, along with issues requisite for operational improvements.