How It Works
To test whether drinking water is adequately disinfected, space station astronauts will collect galley water in sealed plastic bags, and then use syringes to remove some water from the bags and push it through a cartridge that contains a half-inch-diameter, polymer, porous-membrane disk impregnated with a chemical to detect either iodine or silver. The disks, known as "solid phase extraction membranes," capture either iodine or silver, depending on the chemical in the disk.
Next, the bottom half of the cartridge, which contains the disk, is placed against a German company's handheld "diffuse reflectance spectrometer," which shines light on the disk so it can read the disk's color in about two seconds. Porter says the device was developed to measure the reflectivity or gloss, and thus the quality, of finishes such as automotive paint, industrial surfaces, stainless steel and decorative metals.
Each handheld device two are in the kit taken to the space station weighs 1.1 pounds, runs on four AA batteries, has a readout screen and measures 7 inches by 3.7 inches by 3.2 inches.
To test for iodine, the disk is impregnated with PVP (polyvinylpyrrolidone), a nontoxic chemical in contact lens cleaning solutions. The PVP reacts with iodine, and the intensity of the resulting yellow color reveals the concentration of iodine in the water.
To test for silver in water, the disk is imbued with DMABR, which is short for 5-(dimethylaminobenzylidene)rhodanine. A yellowish color indicates silver is absent, while flesh to brighter pink reveals how much silver is present.
"We can do this whole analysis in about two minutes on the ground or in space," Porter says.
|Contact: Lee Siegel|
University of Utah