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At present, spacecraft water quality is assessed when samples collected on the International Space Station (ISS) are returned to Earth. Several months, however, may pass between sample collection and analysis, potentially compromising sample integrity by risking degradation. For example, iodine and silver, which are the respective biocides used in the U.S. and Russian spacecraft potable water systems, must be held at levels that prevent bacterial growth, while avoiding adverse effects on crew health. A comparable need exists for the detection of many heavy metals, toxic organic compounds, and microorganisms. Lead, cadmium, and nickel have been found, for instance, in the ISS potable water system at amounts that surpass existent requirements. There have been similar occurrences with hazardous organic compounds like formaldehyde and ethylene glycol. Microorganism counts above acceptable limits have also been reported in a few instances.

We are developing a drinking water test kit based on colorimetric-solid phase extraction (C-SPE) for use onboard the International Space Station (ISS) and on future Lunar and/or Mars missions. C-SPE involves measuring the change in diffuse reflectance of indicator disks following their exposure to a water sample. We previously demonstrated the effectiveness of C-SPE in measuring iodine in microgravity. This analytical method has now been extended to encompass the measurement of total I (i.e., iodine, iodide, and triiodide). This objective was accomplished by introducing an oxidizing agent to convert iodide and triiodide to iodine, which is then measured using the indicator disks previously developed for iodine. We report here the results of a recent series of C-9 microgravity tests of this method. The results demonstrate that C-SPE technology is poised to meet the total I monitoring requirements of the international space program.

Aqueous silver(I) is added at trace levels (0.1 – 1.0 mg/L) to spacecraft potable water as a biocide. Development of a method that can be deployed on orbit and in future Lunar and Mars missions is therefore central to maintenance of safe drinking water and crew health. To address this need, our laboratory has created an analytical technique that couples a selective sorption process based on solid phase extraction (SPE) with the quantitative measurement of the extract by a hand-held diffuse reflection spectrophotometer. This technique, referred to as colorimetric-solid phase extraction (C-SPE), enables the low level detection (limit of detection ∼5 ppb) of silver(I) by metering 1.0 mL of a water sample through a reagent-impregnated (i.e., 5-(p-dimethyl-aminobenzylidene)rhodanine, DMABR) SPE membrane. The total workup time for the analysis is only 60-90 s.

Colorimetric-solid phase extraction (C-SPE) is being developed as a method for in-flight monitoring of spacecraft water quality. C-SPE is based on measuring the change in the diffuse reflectance spectrum of indicator disks following exposure to a water sample. Previous microgravity testing has shown that air bubbles suspended in water samples can cause uncertainty in the volume of liquid passed through the disks, leading to errors in the determination of water quality parameter concentrations. We report here the results of a recent series of C-9 microgravity experiments designed to evaluate manual manipulation as a means to collect bubble-free water samples of specified volumes from water sample bags containing up to 47% air. The effectiveness of manual manipulation was verified by comparing the results from C-SPE analyses of silver(I) and iodine performed in-flight using samples collected and debubbled in microgravity to those performed on-ground using bubble-free samples.

Preliminary results on the development of quick, simple analytical method for the low level of lead(II) in water samples are described. The method concentrates lead(II) on a small solid-phase extraction disk, which is then quantified directly on the disk by diffuse reflectance spectroscopy (DRS). This method, termed colorimetric solid-phase extraction (C-SPE), requires only 1–2 min for complete workup and is suitable for use in a wide range of applications, including the microgravity environment on the International Space Station. The procedure first adds an excess of potassium iodide to a 10.0 mL sample at a pH of 3.0–3.5 to produce the anionic PbI42− colored complex, which is exhaustively extracted by the disk that was previously impregnated with cetylpyridinium chloride (CPC). The amount of complex extracted is then determined at 420 nm by a hand-held DRS instrument.

Contamination of spacecraft water by heavy metals, such as cadmium and lead, is of growing concern. As a consequence, there is need for a rapid, on-board, easy-to-use method for the determination of cadmium(II) at low ppb levels in spacecraft drinking water supplies. This paper describes the preliminary development of a method for the selective, low level determination of cadmium(II) based on colorimetric-solid phase extraction (C-SPE) [1, 2]. In C-SPE, an analyte is extracted from a water sample onto a membrane that has been previously impregnated with a colorimetric reagent, and then quantified as its colorimetric complex directly on the membrane surface using diffuse reflectance spectroscopy. Results from preliminary tests that screened the performance of 1-(4-nitrophenyl)-3-(4-phenyl-azophenyl)triazene (cadion), and organic dyes, rhodamine B, brilliant green, and methyl violet as colorimetric reagents for potential use in a C-SPE analysis of cadmium(II) are described.

The need to preserve crew health during space missions, combined with the level of demand on both crew time and cargo space, dictates the development of fast, facile methods capable of monitoring trace quantities of several analytes in spacecraft water. This presentation describes our efforts to address this need by using Multiplexed Colorimetric Solid Phase Extraction (MC-SPE). MC-SPE is a sorption-spectrophotometric platform based upon the extraction of analytes onto membranes impregnated with selective colorimetric agents. Quantification is accomplished using Kubelka-Munk values calculated from the diffuse reflectance spectrum of the complex on the surface of the membrane and calibration curves. In traditional C-SPE, concentration factors of up to 1000 can be realized for a single analysis, yielding low detection limits (ppb – ppm range) with a total analysis time of 75–90 s. Herein, we describe the performance and continued refinement of the MC-SPE platform.

Colorimetric solid-phase extraction (C-SPE) is an integrated technique in which a selected analyte is concentrated onto a disk by SPE and then measured quantitatively by diffuse reflectance spectroscopy (DRS). Although several C-SPE methods have been tested successfully in microgravity simulations, incorporation of air bubbles often makes it difficult to accurately measure the volume of aqueous sample used for the analysis. This paper investigates the application of negligible depletion (ND) to C-SPE. ND is based on reaching an equilibrium in which the concentration of analyte in the original sample and in the outflow from the disk are equal after a minimum volume of sample has passed through the disk. As a result, the amount of extracted analyte is proportional to the sample concentration but independent of sample volume. With this approach, called C-SPE-ND, the precise measurement of sample volume is no longer necessary.

Space exploration by humans requires maintenance of an adequate potable water supply. Biocide levels must therefore be kept within allowable limits to prevent bacterial growth without causing adverse effects on crew health. Likewise, contaminants such as heavy metals and toxic organic compounds must be held at or below acceptable limits. Currently, spacecraft water quality analyses are performed on samples collected on the International Space Station and returned to Earth. Several months, however, can pass between sample collection and analysis, which may compromise sample integrity due to degradation. These delays also inhibit implementation of real time correction scenarios. There is, therefore, a critical need for rapid, on-board methods for monitoring trace quantities of several analytes in spacecraft drinking water supplies.

We are developing a spacecraft water quality monitoring system based on measuring the change in diffuse reflectance of indicator disks following exposure to a water sample. The most widely used approach for deriving quantitative information from a diffuse reflectance spectrum involves an initial Kubelka-Munk transformation of the reflectance data. Provided the assumptions underlying the transformation are satisfied, the magnitude of the resulting function varies linearly with analyte concentration. We measure diffuse reflectance spectra using a commercial-off-the-shelf handheld spectrophotometer designed for color matching applications. Spectra are currently downloaded and transformed to obtain the value of the Kubelka-Munk function at a detection wavelength diagnostic of the analyte. This value is then used to quantify the analyte via a standard response curve.

Archived water samples collected on the International Space Station (ISS) and returned to Earth for analysis have, in a few instances, contained trace levels of heavy metals. Building on our previous advances using Colorimetric Solid Phase Extraction (C-SPE) as a biocide monitoring technique [1, 2], we are devising methods for the low level monitoring of nickel(II), lead(II) and other heavy metals. C-SPE is a sorption-spectrophotometric platform based on the extraction of analytes onto a membrane impregnated with a colorimetric reagent that are then quantified on the surface of the membrane using a diffuse reflectance spectrophotometer. Along these lines, we have analyzed nickel(II) via complexation with dimethylglyoxime (DMG) and begun to examine the analysis of lead(II) by its reaction with 2,5-dimercapto-1, 3, 4-thiadiazole (DMTD) and 4-(2-pyridylazo)-resorcinol (PAR).

One of the long-standing concerns in space exploration is the presence of trace organic contaminants in recycled spacecraft water supplies. At present, water samples on the International Space Station (ISS) are collected at regular intervals, stored in Teflon™-lined containers, and returned to Earth for characterization. This approach, while effective in defining water quality, has several notable problems. First, this method of archiving removes a significant volume of the ISS water supply. Second, the archived water consumes valuable cargo space in returning Shuttle and Soyuz vehicles. Third, the organic contaminants present in the collected samples may degrade upon extended storage. The latter problem clearly compromises sample integrity. Upon return to Earth, sample degradation is minimized by refrigeration. Due to present resource constraints, however, refrigeration is not a viable option in space.

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.

This paper describes the development of a prototype fluid pumping system for incorporation into a miniaturized flow injection analyzer. The strategy couples the well-established capabilities of reagent-based flow injection analyses (FIA) with our novel concepts for the design of a miniaturized, low-power pumping system, i.e., an electrochemically-driven micropump. The basis of pump actuation relies on the electrochemically-induced surface tension changes at the electrolyte/mercury interface, resulting in a “piston-like” pumping process devoid of mechanically moving parts. We present herein the results from the preliminary performance tests of a miniaturized fluid flow system with the micropump. As described, the flow rates and pumping displacement volumes have been studied as a function of the amplitude and the frequency of the applied voltage waveform.

This paper describes the development of a thin-film optical sensor for measuring pH. The indicator behaves as a polyprotic acid with differing optical properties in each of its chemical forms. Together, these properties facilitate the development of an internally calibrated sensor by calculating the ratios of the absorption maximas for each form of the indicator. The covalent immobilization procedure developed demonstrated long term stability of 4 months without recalibration.

This paper focuses on the design, construction, preliminary testing, and potential applications of three forms of miniaturized analytical instrumentation. The first is an optical fiber instrument for monitoring pH and other cations in aqueous solutions. The instrument couples chemically selective indicators that have been immobilized at porous polymeric films with a hardware package that provides the excitation light source, required optical components, and detection and data processing hardware. The second is a new form of a piezoelectric mass sensor. The sensor was fabricated by the deposition of a thin (5.5 μm) film of piezoelectric aluminum nitride (AlN). The completed deposition process yields a thin film resonator (TFR) that is shaped as a 400 μm square and supports a standing bulk acoustic wave in a longitudinal mode at frequencies of ∼1 GHz.