Abstract:
A method of analyzing for the presence or concentration of an analyte in a liquid in microgravity is disclosed. The method includes removing a first quantity of the liquid from a first container and passing the removed liquid through a porous pad that includes a reagent that is responsive to the analyte. The presence or concentration of the analyte in the liquid is determined based on a response of the reagent. The removed quantity of liquid is transferred back to the first container or to a second container, and followed by disposal of the first or second container.

Description:
BACKGROUND 
     Through the many years of manned exploration of outer space, the composition and properties of water and other on-board liquids have typically been subject to a monitoring protocol that includes only periodic monitoring for some tests, and lack of monitoring at all for some components. Of course, water and other liquid management systems on board spacecraft tend to be robust, so it has typically been practiced that, absent outward signs of malfunction, testing for contaminants or properties that are out of specification has been thought to be necessary only periodically. This has meant that for short duration flights, no on-board monitoring is typically used. For long duration flights in Earth orbit, the periodic monitoring can be accomplished with samples being collected on-board and sent back to Earth for testing. 
     Notwithstanding the robustness of on-board water or other liquid management systems, there can be components in water or other liquids that can have a profound effect on personnel or on-board systems so that more frequent on-board monitoring is needed. This was demonstrated recently when silica buildup on spacesuit water separators caused a buildup of water inside the suit, necessitating an emergency abort of an astronaut spacewalk on the International Space Station. Additionally, the prospect of manned exploration of deep space will preclude the use of terrestrial testing, again necessitating that testing be conducted on-board. 
     BRIEF DESCRIPTION 
     In some aspects of this disclosure, a method of analyzing for the presence or concentration of an analyte in a liquid in microgravity comprises removing a first quantity of the liquid from a first container and passing the removed liquid through a porous pad comprising a reagent that is responsive to the analyte. The presence or concentration of the analyte in the liquid is determined based on a response of the reagent. The removed quantity of liquid is transferred back to the first container or to a second container, and followed by disposal of the first or second container. 
     In some aspects of this disclosure, a system for analyzing for the presence or concentration of an analyte in a liquid from a liquid source in microgravity includes a sealed sample collection container that includes a first port adapted for connection to the liquid source. The system also includes a test cassette comprising a sealed housing that includes an inlet port and an outlet port. The test cassette also includes a porous pad within the sealed housing comprising a reagent that is responsive to the analyte. The cassette is also configured to provide a flow of liquid from the inlet port through the porous pad to the outlet port. The system also includes a pump configured to transfer liquid from the sample collection container to the cassette inlet through the porous pad to the cassette inlet, and to the sample collection container or a second container. 
     In some aspects of this disclosure, a method of analyzing for the presence or concentration of an analyte in a liquid comprises passing a first quantity of the liquid through a porous pad comprising a reagent that is responsive to the analyte, and determining the presence or concentration of the analyte in the liquid based on a response of the reagent to the first quantity of liquid. If the first quantity of the liquid does not produce a measurable response by the reagent, an additional quantity or multiple quantities of the liquid are passed through the porous pad until the reagent produces a measurable response or a null response is noted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter that is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
       The FIGURE is a schematic depiction of an exemplary system according to this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the FIGURE, an exemplary system  10  and process for testing a liquid such as water is depicted and described further below. As schematically depicted in the FIGURE, water  12  from a water source (not shown) is transferred into a first container  14  for testing. The container  14  can be any sort of container, although a polytetrafluoroethylene bag can be conveniently used and is very clean and impermeable. The container can include any sort of opening port/closure and fitting, and container  14  is depicted with a first female luer lock fitting  16  with tethered cap  17  for connecting to the water source, and a second female luer lock fitting  18  with tethered cap  19  for drawing and returning test samples. A test sample of a first quantity of the liquid is drawn from the container  14  and passed through a test cassette  20 . Test cassette  20  has a sealed housing  22  with an inlet port  24  and outlet port  26 . A test pad  28  is disposed within the sealed housing. Test pad  28  is a porous pad comprising a reagent that is responsive to the analyte being tested for. 
     The liquid is tested by passing it through the test pad  28 . With continued reference to the FIGURE, the test cassette inlet port  24  is connected, either directly or with a connector, to the fitting  18  on container  14 . A sampling syringe (i.e., pump)  30  has a one-way inlet valve  32 , a one-way outlet valve  34 , and a plunger  36 . The sampling syringe inlet valve  32  is connected to the test cassette outlet port, and an outward stroke of the plunger  36  is used to draw liquid from the container  14 , through the test cassette  20  and test pad  28 , into the syringe  30 . The test pad  28  can then be examined for a response such as a colorimetric response that can be compared to a reference chart  38 . If the test cassette housing  22  is opaque, inspection of the test pad  28  would require disassembly of the cassette or opening of a viewing hatch. Alternatively, test cassette housing  22  can be transparent or can contain a transparent viewing window for the test pad  28 . 
     An inward stroke of the plunger  36  will eject the test quantity of liquid from the syringe through one-way outlet valve  34 . As depicted in the FIGURE, the syringe outlet valve  34  is connected to the second fitting  18  on container  14  to return the liquid to container  14  for disposal after a single-pass test by test pad  28 . In some embodiments, however, a method is contemplated where additional quantities of test liquid are passed through test pad  28  to test for smaller quantities of the analyte. Some test protocols may be tolerant of re-use of the test liquid without significantly impacting the results. However for test protocols that require unadulterated liquid samples for testing, the syringe outlet valve  34  can be connected to a second (disposal) container (not shown) so that additional unadulterated samples of liquid can be drawn from container  14  for testing. 
     Varying the quantity of water passed through the test pad  28  can be used to expand the sensitivity of the test method. This can be accomplished if the reagent/analyte reaction is such that the response is proportional to the quantity of analyte that has reacted with the reagent. In this case, when the concentration of the analyte in the liquid is below the calibration threshold of the test pad so that no observable response is produced by the first quantity of liquid contacting the test pad, additional quantities of liquid can be passed through the test pad to increase the quantity of analyte that has reacted with the reagent. Such additional quantities can be repeated multiple times with intervening observations of the test pad until an observable result is produced or a null result (i.e., a determination that the level is effectively zero or below a level of concern). In such a case, the reference chart  38  can have multiple rows of numbers below each colorimetric sample, with each row corresponding to a concentrations represented by the reference circles for different total quantities of liquid passed through the test pad  28 . 
     It should be noted that the system depicted in the FIGURE is exemplary in nature and should not be viewed as limiting. For example, embodiments are contemplated where test cassette  20  could be connected directly to a water source (first container) that is pressurized by a pump, and pressurized water then transferred through the cassette  20  to a second (disposal container) through a control valve that is used to control the quantity of liquid passed through the test pad  28 . 
     Various types of materials can be used for the porous pad used to make test pad  28 , including polymers such as polyether sulfone, cellulose acetate, mixed cellulose esters (MCE), polyethylene (PE), polyethylene/polyester (PE/PET), and styrene-based polymers, or inorganic materials such as porous ceramics. Various reagents can also be used as well, depending on the analyte being tested for. For example, one analyte of interest is silica, and exemplary reagents to test for silica can be selected according to the molybdosilicate method of the Standard Method 4500-SiO2 Silica (Editorial Revisions 2011) of the Standard Methods for the Examination of Water and Wastewater. Examples of such reagents include ammonium molybdate and oxalic acid. Other analytes can also be tested for, including but not limited to nickel, iron, ammonia, orthophthalaldehyde, dimethylsilanediol (DMSD), and iodine, as well as more mundane analytes such as ionic species associated with pH. Reagents to test for such analytes are known to those skilled in the art. The liquid being tested can comprise water (e.g., potable water, service water, ethylene glycol/water blends, or water-based borate/carbonate buffers), or non-aqueous liquids such as fluorocarbon refrigerants. 
     While the present disclosure provides detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various details of embodiments have been described, it is to be understood that some embodiments may include only some of these details. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.