Patent Application
20230074431
The present disclosure relates to devices and methods for detecting phosphate levels in a fluid (e.g., natural water), and more particularly relates to the use of one or more molybdenum (Mo) electrodes to allow for in situ reagent generation to measure such phosphate levels in a small, transportable device.
Phosphorus is an essential nutrient element used by all living organisms for their growth and energy transport. Humans and all other vertebrates need phosphorus to build their bones and teeth which contain up to 50% by volume and 70% by weight of hydroxyapatite, Ca10(PO4)6(OH)2. Additionally, many other phosphorus compounds play important roles in fundamental biochemical functions. For instance, nucleotides act as precursors in DNA and RNA, adenosine triphosphate (ATP) can be an important source of energy to many biological systems, phospholipid is often considered the main characteristic component of a cell wall membrane, and the buffering capability of phosphate ions (PO43−) can be important in maintaining the pH of intracellular environment.
Despite its importance to many living organisms, excess level of phosphorus in aquatic environment can be detrimental, since phosphorus, along with nitrogen and carbon, is understood to be the main nutrient that causes eutrophication in water. Eutrophication is one of the six major environmental problems in lakes, estuaries and coastal waters throughout the world. It describes the phenomenon in water where the rate of supply of organic matter to an ecosystem is increased. The over-supply of the organic matter to the water can stimulate the growth of different types of micro-organisms including dense nuisance and toxic algae causing decrease of the light penetration and beneficial submerged aquatic vegetation. Further, the growth of micro-organisms can reach the state where it cannot be balanced by the consumption from species in the higher rank of the food web, and that excess organic matter sinks to the bottom of water. As a result, the oxygen level in the water decreases as it is decomposed by bacteria which consumes oxygen in the process. The oxygen can be critical to every living organism in water and the decrease of it (hypoxia, <3 milligrams/Liter of O2 in water) or the absence of it (anoxia) can significantly disturb the ecosystem in water by causing the death of fish and other important organisms, the degradation of their habitat, and the alteration of their migration pattern. Moreover, from an economic perspective, it can lead to the decrease in fishery production and negatively impact the life pattern and tourism of local communities, among other problems.
The importance of the monitoring of phosphorus level in natural waters mainly comes from the effect of phosphorus control on the management of the eutrophication. In water, phosphorus never exists by itself. It forms either inorganic orthophosphate (phosphate), condensed polyphosphate, or organic phosphate. Even with its variously defined forms, the total phosphorus level in natural water is typically determined by decomposing all the different phosphorus-related compounds into inorganic phosphate and measuring its concentration. Numerous studies have developed technologies to detect phosphate or other types of phosphorus-related compounds. The detection mechanisms of these technologies include spectrophotometry, electrochemistry, fluorescence spectroscopy, infrared/Raman spectroscopy, NMR spectroscopy, and enzyme-based biology. Although the detection range of each technology and the type of water to which the technologies can be applied cover a wide range, one method for determining phosphorus level in natural water is a spectrophotometric determination of phospho-molybdenum blue (PMB) molecule (PMB method). In this method, phosphate ions and acidified molybdate ions form 12-molybdophosphoric acid (12-MPA) in an acidic environment. 12-MPA is further reduced by the reductant into the PMB molecule of which intensity is correlated with the concentration of phosphate ions.
Despite the fact that the PMB method can be applied to most natural waters with a good sensitivity and selectivity to phosphate ions, there are still great demands for the improvement of the technology. For example, the demands for a reliable in situ and portable measurement device has dramatically increased as obtaining the temporal and spatial information of the phosphorus level can be important in water quality management. However, the current technology typically requires manual sampling, and the transport and storage of the sample, followed by laboratory-based analysis. To the extent any portable phosphate measurement devices exist, these devices suffer from several problems, including that the footprint of the device increases with the increase of its working time. This is simply because an increase in the number of measurements yields an increase in the volume of reagents for the PMB method.
While attempts have been made to overcome the limitations of existing phosphate level detection devices, such devices have included complications such as complex mechanical parts and/or electrical systems that do not allow for such devices and systems to be used in an easy, portable manner. For example, some existing devices that utilize molybdenum oxidation for in situ reagent generation include devices having chambers with volumes of 365.4 μL and 91 μL. Such devices can require significant energy (e.g., 18 Joules of energy per measurement), and time (e.g., 180 seconds) to induce the level of oxidation necessary for measurements to be made. In other words, most of the energy is consumed in generating a considerable amount of protons through the oxidation to lower the pH of the reaction environment for the formation of 12-MPA. A reaction environment with high pH can easily lead acidified molybdate ions to form 12-molybdosiliacid (12-MSA), instead of 12-MPA, under the presence of silicate ion, a major interference ion in the PMB method. Because 12-MPA and 12-MSA exhibit similar electrochemical behaviors, preventing such interference by providing excess protons, thereby increasing the energy consumption, becomes inevitable in designing these devices.
Additionally, the time to actually make a measurement can be on the order of about 80 minutes, at least because the slow diffusion of acidified molybdate ions and 12-MPA makes it difficult to have a homogeneous reaction environment and detection environment for 12-MPA. To the extent devices have been developed capable of reducing the 80-minute wait time, they often utilize additional mechanical and/or electrical components (e.g., a pump) to mix or homogenize the resulting solution to make the analysis, and that still can take at least 5 minutes. This increase in complexity to improve wait times is not an ideal trade-off, as in addition to extra components, it causes the volume of the device to increase and raises the energy consumption of the device. Limiting factors of existing devices that may be considered to be portable include the number of measurements a device can make without requiring a reagent refill, and, relatedly, the volume of reagents that can be loaded in the device.
Accordingly, there is a need for devices and methods that allow for phosphate levels of a fluid (e.g., natural water) to be measured in situ using transportable, easy to use devices that make quick measurements, are energy-efficient, and minimize an amount of reagent used on a per-measurement basis so that the shelf-life of the device without requiring a refill is extended beyond current capabilities.
The present disclosure provides for phosphate level measuring devices that have a minimal footprint with respect to size, energy consumption, time to make measurements and phosphate level determinations, and the amount of reagent needed per measurement, meaning more measurement can be made with the same device. The devices provided for herein utilize in situ reagent generation by anodic dissolution of molybdenum and detecting 12-molybdophosphoric acid (12-MPA) to make determinations about phosphate levels of the fluid being tested. The devices and methods provided for herein are useful with respect to natural water, and are particularly useful with respect to fresh water. Phosphate levels in other waters can also be measured, including but not limited to surface water from bodies such as ponds or lakes, seawater, and drinking water. Still further, the teachings of the present disclosure can be adapted for use with measuring phosphate levels in other fluids, typically liquids.
The devices, and related methods, allow for in situ generation and/or supply of the reagents for making phosphate level determinations (e.g., molybdate and protons) by the anodic dissolution of molybdenum metal. At least three different designs of phosphate level measuring devices are provided for in the present disclosure. One illustrated device (see, e.g.,
The method of using the devices involves supplying the fluid, which includes phosphate ions, to a device that includes a molybdenum electrode. The molybdenum electrode is oxidized to supply molybdate ions to the fluid, the ions having a low pH to form 12-molybdophosphoric acid (12-MPA). A redox response results and is measured using an electrochemical measurement that includes one or more of a working electrode(s), a reference electrode(s), and a counter electrode(s). In at least some of the provided embodiments, the working electrode is disposed near a molybdenum electrode, typically near the second molybdenum electrode in embodiments that use at least two molybdenum electrodes, the second molybdenum electrode being disposed further downstream from a reaction that occurs by way of oxidation of a first molybdenum electrode (as shown in at least some of the embodiments, distal of the first molybdenum electrode).
One exemplary embodiment of a phosphate level detection device includes a first chamber, a first molybdenum electrode, and a working electrode. The first molybdenum electrode is at least partially disposed with the first chamber, and the working electrode is also at least partially disposed within the first chamber. Further, the working electrode is positioned within about 100 micrometers of the first molybdenum electrode. The device is configured such that oxidation of the first molybdenum electrode in the presence of a fluid that includes phosphate ions results in the formation of a 12-molybdophosphoric acid. Notably, the first chamber can have an enclosed configuration or an open configuration, depending on the desired set-up.
In some embodiments, the device can include a second chamber, a second molybdenum electrode, and a proton exchange membrane. In at least some such embodiments, each of the first and second chambers can be enclosed chambers, the second molybdenum electrode can be at least partially disposed in the second chamber, and the proton exchange membrane can be disposed between the first and second chambers. Further, the device can be configured such that oxidation of the second molybdenum electrode in the presence of a fluid results in protons migrating from the second chamber, across the proton exchange membrane, and to the first chamber to reduce a pH level of fluid disposed in the first chamber. More specifically, in some embodiments, the device can be configured such that the protons that migrate from the second chamber, across the proton exchange membrane, and to the first chamber reduce the pH level to a range of about 0.8 to about 1.2, such as to about 1. In embodiments that include a proton exchange membrane disposed between first and second chambers, the first molybdenum electrode and the working electrode can be disposed directly adjacent to the proton exchange membrane.
The phosphate level detection device can also include a reference electrode and/or a counter electrode. The reference and/or counter electrodes, in conjunction with the working electrode, can be configured to make electrochemical determinations of a phosphate level of a fluid disposed in the first chamber when the first molybdenum electrode is oxidized. In at least some embodiments that include both a reference electrode and a counter electrode, the first chamber can be an open chamber and each of the first molybdenum electrode, the working electrode, the reference electrode, and the counter electrode can be at least partially disposed within bounds defined by walls of the first chamber. In such instances, the device can be configured to operate in an open-cell configuration.
In some embodiments the device can have a total chamber volume of about 6 microliters or less. This volume can be about 1.5 microliters or less in some instances. In some embodiments a molybdenum consumption level can be approximately 0.08 milligrams or less per measurement. This consumption level can be approximately 0.0008 milligrams or less per measurement in some instances. In some embodiments an energy consumption level for oxidation of the first molybdenum electrode can be approximately 0.2 Joules or less per measurement for each 1 millimeter2 of exposed first molybdenum electrode surface area. This consumption level can be approximately 0.00025 Joules or less per measurement for each 1 millimeter2 of exposed first molybdenum electrode surface area in some instances. In some embodiments a phosphate level detection time of the device can be approximately two minutes or less in the absence of stirring the 12-molybdophosphoric acid. This time can be approximately 30 seconds or less in the absence of stirring the 12-molydophosphoric acid in some instances, or even approximately 10 seconds or less in the absence of stirring the 12-molydophosphoric acid in some instances.
One exemplary method for determining phosphate levels in a fluid includes oxidizing a first molybdenum electrode that is at least partially disposed in a first chamber of a phosphate level detection device to form a 12-molybdophosphoric acid from a fluid having phosphate ions disposed in the fluid, and determining a level of phosphate ions present in the fluid from which the 12-molybdophosphoric acid is formed. The determination is done using an electrochemical set-up, and the electrochemical set-up includes a working electrode disposed within about 100 micrometers of the first molybdenum electrode. Notably, the first chamber can have an enclosed configuration or an open configuration, depending on the desired set-up.
The method can further include causing the fluid having phosphate ions disposed therein to enter the first chamber. The fluid can come from a fluid source that is at a location at which the oxidizing and determining actions are performed such that determining a level of phosphate ions present in the fluid from which the 12-molybdophosphoric acid is formed occurs in situ.
In some embodiments, the method can further include oxidizing a second molybdenum electrode that is at least partially disposed in a second chamber to cause protons to migrate from the second chamber, to the first chamber, to reduce a pH level of the fluid disposed in the first chamber. In such embodiments, the first and second chambers can be enclosed. In at least some such embodiments, the method can further include causing the fluid having phosphate ions disposed therein to enter the second chamber. The fluid can come from a fluid source that is at a location at which the oxidizing and determining actions are performed such that determining a level of phosphate ions present in the fluid from which the 12-molybdophosphoric acid is formed occurs in situ.
The migration of the protons from the second chamber to the first chamber can reduce the pH level of the fluid disposed in the first chamber to a range of about 0.8 to about 1.2, for example to about 1. In at least some embodiments, the first molybdenum electrode and the working electrode can be disposed directly adjacent to the second chamber.
In some embodiments a total chamber volume of the phosphate level detection device can be about 6 microliters or less. This volume can be about 1.5 microliters or less in some instances. In some embodiments approximately 0.08 milligrams of molybdenum or less is consumed per measurement. This consumption level can be approximately 0.0008 milligrams or less per measurement in some instances. In some embodiments approximately 0.2 Joules or less of energy for each 1 millimeter2 of exposed first molybdenum electrode surface area can be consumed per measurement. This consumption level can be approximately 0.00025 Joules or less of energy for each 1 millimeter2 of exposed first molybdenum electrode surface area per measurement in some instances. In some embodiments determining a level of phosphate ions present in the fluid from which the 12-molybdophosphoric acid is formed using an electrochemical set-up consumes approximately two minutes or less of time in the absence of stirring the 12-molybdophosphoric acid. This time can be approximately 30 seconds or less in the absence of stirring the 12-molydophosphoric acid in some instances, or even approximately 10 seconds or less in the absence of stirring the 12-molydophosphoric acid in some instances.
Another exemplary method for determining phosphate levels in a fluid includes sampling a fluid having phosphate ions disposed in the fluid from a fluid source. The method further includes generating a reagent from the fluid having phosphate ions disposed in it due to anodic dissolution of molybdenum metal and determining a level of phosphate ions in the fluid from which the reagent is generated. The actions of sampling, generating, and determining are all performed at the location of the fluid source. Thus, determining a level of phosphate ions in the fluid from which the reagent is generated occurs in situ. Notably, the method can be performed using set-ups with closed or open configurations, depending on the desired set-up.
The action of generating a reagent from the fluid having phosphate ions disposed in it due to anodic dissolution of molybdenum metal can include oxidizing a first molybdenum electrode that includes the molybdenum metal that is dissolved. In some such embodiments, a working electrode used in conjunction with determining a level of phosphate ions in the fluid from which the reagent is generated can be disposed within about 100 micrometers of the first molybdenum electrode.
The first molybdenum electrode can be disposed in a first enclosed chamber of a phosphate level determination device. In some such embodiments, the method can further include oxidizing a second molybdenum electrode disposed in a second enclosed chamber of the phosphate level determination device. A proton exchange member can be disposed between the first enclosed chamber and the second enclosed chamber, with the proton exchange member being able to cause protons to migrate from the second enclosed chamber to the first enclosed chamber to reduce a pH level of the fluid disposed in the first enclosed chamber. The migration of the protons from the second enclosed chamber to the first enclosed chamber can reduce the pH level of the fluid disposed in the first chamber to a range of about 0.8 to about 1.2, for example to about 1. In at least some embodiments, the first molybdenum electrode and the working electrode can be disposed directly adjacent to the second chamber.
In some embodiments a total chamber volume of the phosphate level detection device can be about 6 microliters or less. This volume can be about 1.5 microliters or less in some instances, for example when the first molybdenum electrode is disposed in a first chamber of a phosphate level detection device. In some embodiments approximately 0.08 milligrams of molybdenum or less is consumed per measurement. This consumption level can be approximately 0.0008 milligrams or less per measurement in some instances. In some embodiments approximately 0.2 Joules or less of energy for each 1 millimeter2 of exposed first molybdenum electrode surface area can be consumed per measurement. This consumption level can be approximately 0.00025 Joules or less of energy for each 1 millimeter2 of exposed first molybdenum electrode surface area per measurement in some instances. In some embodiments determining a level of phosphate ions present in the fluid from which the reagent is generated consumes approximately two minutes or less of time in the absence of stirring the 12-molybdophosphoric acid. This time can be approximately 30 seconds or less in the absence of stirring the fluid during the generating and determining actions in some instances, or even approximately 10 seconds or less in the absence of stirring the fluid during the generating and determining actions in some instances.
This disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure.
To the extent features, sides, objects, electrodes, steps, or the like are described as being “first,” “second,” “third,” etc., such numerical ordering is generally arbitrary, and thus such numbering can be interchangeable. For example, in configurations that include two molybdenum electrodes, the electrode closest to the working electrode is often referred to as the second molybdenum electrode, but that electrode may be referred to in the claims as a first molybdenum electrode. Still further, the present disclosure includes some illustrations and descriptions that include prototypes or bench models. A person skilled in the art will recognize how to rely upon the present disclosure to integrate the techniques, systems, devices, and methods related to such prototypes and/or bench models provided for into a product, such as a transportable, phosphate level measuring device.
The present disclosure generally provides for small, transportable devices that can be used to make in situ determinations about the level of phosphates in a fluid (e.g., natural water). The fluid is typically a liquid. A molybdenum electrode is used in conjunction with a working electrode, also referred to as a sensing electrode, such that once the molybdenum electrode is oxidized, a reagent is generated that can be measured by an electrochemical set-up to determine how the phosphate level of the fluid being tested. The working electrode is disposed very close to the molybdenum electrode (e.g., within about 100 micrometers or less), and phosphate measurements can be made quickly after the reagents are generated (e.g., within about two minutes, within about thirty seconds, within about ten seconds, depending on the embodiment). Various embodiments of phosphate level determination devices that include one or two molybdenum electrodes are provided. In some instances, the electrodes are disposed in an enclosed chamber through which the fluid being tested is pumped or otherwise driven through, while in other instances an open-cell configuration, i.e., an open chamber, is provided such that the phosphate level determination device can be placed directly in the fluid being measured and operated to make phosphate level determinations. Use of the term “chamber” herein can apply to both an enclosed or closed chamber (e.g., the chambers illustrated in
The second chamber 104b also includes a working electrode 112 and a reference electrode 114, the working electrode 112 being more proximate to the second Mo electrode 102b than the reference electrode 114 is to the second Mo electrode 102b. The working electrode 112 can also be referred to as a sensing electrode. In some embodiments, a distance D between the working electrode 112 and the second Mo electrode 102b, with the distance D being measured between adjacent surfaces of the working electrode 112 and the second Mo electrode 102b, can be approximately in the range of about 10 micrometers to about 1000 micrometers, including some instances where the distance be approximately 100 micrometers or less, or approximately 100 micrometers. In contrast, known devices that includes Mo electrodes and a working electrode are separated into different chambers (see, e.g., “First Deployment and Validation of in Situ Silicate Electrochemical Sensor in Seawater” by Barus, et al., in Marine Science, published Feb. 26, 2018), which thus typically leads to them having a much greater distance between them as compared to the distance between the Mo electrode and working electrode 112 in the present disclosures. Fluid can be passed into the first and second chambers 104a, 104b by respective first and second inlets 116a, 116b and outlets 118a, 118b. As described with respect to
One non-limiting exemplary embodiment of measuring phosphate levels in a fluid is illustrated by
Mo(s)+4H2O→MoO42−+6H++6e− (1),
while at the counter electrode 120, the reaction can be depicted as:
2H2O+2e−→H2+2OH− (2).
Protons 132 resulting from oxidation of the first Mo electrode 102a can migrate, in this instance diffuse, across the first PEM 106 and into the second chamber 104b. The protons 132 can help decrease a pH level of the second chamber 104b. For example, the pH level of the second chamber 104b can be reduced to a range approximately between about 0.8 to about 1.2, and in some embodiments the pH level can be reduced to about 1.
As shown in
Mo(s)+4H2O→MoO42−+6H++6e− (1), and
2H2O+2e−→H2+2OH− (2).
The generation of reagent in the second chamber 104b results in the formation of 12-MPA, as shown in
PO43−+12MoO42−+27H+→H3PMo12O40+12H2O (3).
The generation of 12-MPA can then be used to measure phosphate levels in the fluid.
More specifically, an electrochemical sensing set-up 132 can be used to detect the 12-MPA, and thus sense the level of phosphates in the fluid. In the illustrated embodiment in
Redox 1: PMo12O403−+2e−+2H+↔H2PMo2VMo10VIO403− (4), and
Redox 2: H2PMo2VMo10VIO403−+3e−+3H+↔H5PMo5VMo7VIO403− (5).
To the extent devices and methods exist that can detect 12-MPA in fluid samples, such devices and methods generally require manual sampling, followed by transport and/or storage of that sample before conducting a laboratory-based analysis of the sample. The present embodiments, in contrast, provide reliable, in situ measurement of 12-MPA in fluid samples.
The configuration of this device parts differs from the device 100 of
In the illustrated embodiment, the working electrode 212 is an approximately 50 micrometer diameter wire, having a total surface area that is approximately 0.337 millimeters2, although other diameters, surface areas, structures (i.e., not necessarily a wire), and configurations are possible. For example, in some embodiments a diameter of the wire can be approximately in the range of about 10 micrometers to about 200 micrometers and a total surface can be approximately in the range of about 0.1 millimeters2 to about 1.5 millimeters2 The configurations of the reference and counter electrodes 214, 220, as well as the background solution, are also provided in
The second Mo electrode 202b and the working electrode 212 can be disposed proximate, or directly adjacent, to the first PEM 206, which is to say they can be disposed at a top of the diffusion barrier. In some embodiments, to constitute being directly adjacent to the first PEM 206, a distance between the first PEM 206 and at least one of the second Mo electrode 204b and the working electrode 212 is approximately in the range of about 0 micrometers and about 1 millimeter, and in some embodiments it is approximately 500 micrometers. Generally, in accordance with the present disclosures, the closer the second Mo electrode 202b can be to the working electrode 212, the better.
Fluid can be passed into the first and second chambers 204a, 204b by respective first and second inlets 216a, 216b and outlets 218a, 218b. Similar to the configuration of
It will be appreciated that when using the instant device 200 on the surface water of a pond or lake, which typically has a conductivity approximately 100 times smaller than that of seawater, up to 100 times more energy for the oxygenation of molybdenum may be used. However, if the decrease in the energy consumption coming from the decrease of the test volume is significant enough, the increase in the energy consumption caused by using the lower conductivity might not be significant enough compared to the total energy consumption of the device. Moreover, the decrease of the test volume per measurement makes the device more portable and/or extends the working time of the device. Further, the complexation time of 12-MPA can be greatly reduced as the small volume can facilitate the homogenization of molybdate ions. Under these assumptions, the device can be applied to various types of natural water without a huge disadvantage.
A method of using the double molybdenum detection device 200 can be similar to the method described above with respect to
After fluid 230 enters the chambers, the first Mo electrode 202a can be oxidized. The oxidation can occur for a time period approximately in the range of about 20 seconds to about 60 seconds (e.g., 20 seconds, 40 seconds, 60 seconds), although other values of time less or greater than that are possible. The current density supplied to the first Mo electrode 202a can be approximately in the range of about 0.1 milliampere/millimeters2 to about 2 milliamperes/millimeters2, for example about 0.5 milliamperes/millimeters2, although other values of current density less or greater than that are possible. An oxidation time period and a current density can be linked such that a small current density can be used in conjunction with a longer oxidation time period or a larger current density can be used in conjunction with a shorter oxidation time period. Further, these values can also depend on the size and shape of the components of the device and/or the device itself. Accordingly, as a volume of the chamber 204a and/or a surface area of the first Mo electrode changes 202a, so too can the oxidation time period and/or the current densities to achieve desirable results. After oxidation of the first Mo electrode 202a occurs, protons subsequently migrate (e.g., diffuse) across the first PEM 206 and into the second chamber 204b, which can decrease a pH level in the second chamber (e.g., to a value approximately in the range of about 0.8 to about 1.2, including to about 1, as described above with respect to
The second Mo electrode 204b can then be oxidized. This can occur for a time period approximately in the range of about 1 second to about 20 seconds (e.g., 2 seconds), although other values of time less or greater than that are possible. The current density supplied to the second Mo electrode 202b can be approximately in the range of about 0.001 milliamperes/millimeters2 to about 1 milliampere/millimeters2, for example about 0.05 milliamperes/millimeters2, although other values of current density less or greater than that are possible. That is, similar to the first Mo electrode 202a, an oxidation time period and a current density for the second Mo electrode 202b can be linked such that a small current density can be used in conjunction with a longer oxidation time period or a larger current density can be used in conjunction with a shorter oxidation time period. Further, these values can also depend on the size and shape of the components of the device and/or the device itself. Accordingly, as a volume of the chamber 204b and/or a surface area of the second Mo electrode changes 202b, so too can the oxidation time period and/or the current densities to achieve desirable results. In at least some embodiments, after approximately two seconds, 12-MPA formation can begin.
Moreover, the instant configuration of device 200 differs from the device 100 in that the device 200 includes a diffusion barrier 222 disposed between the first chamber 104a and the second chamber 104b. As shown, the diffusion barrier 222 can be in the form of a vertical column that leads from the first chamber 204a to the second chamber 204b, though it will be appreciated that a size and shape of the diffusion barrier 222 can vary based, at least in part, on the shape of the device, the substances used, and/or other design parameters known to one skilled in the art. For example, during oxidation of the first Mo electrode 202a, the diffusion barrier delays the diffusion of protons from the first chamber 204a to the outside environment 210 to create a diffusion gradient along the second chamber 204b, with the first chamber having the lowest pH and gradually increasing through the diffusion barrier 222 and through the second chamber 204b, a bottom of the second chamber 204b having the highest pH values. Having such a gradient reduces the time and amount of energy used to lower the chamber pH as it provides a local area with a pH that is low enough for 12-MPA formation rather than decreasing the pH of an entire volume of the chamber. As a result, the working electrode 212 and the second molybdenum electrode 202b are placed in the upper part of the second chamber 204b so that they can experience the lowest possible pH along the chamber.
Use of two separate molybdenum oxidations allows for control of the pH of the reaction environment because it can determine the efficiency of the formation of both 12-MPA and 12-MSA. 12-MSA, 12-molybdo-silicic-acid, can be a major interference molecule in the detection of 12-MPA, which is formed between silicate, molybdates, and protons. Optimization of the formation of 12-MPA to maximize the amount of 12-MPA while minimizing that of 12-MSA, which can avoid the interference from silicate ion, can occur when there exists approximately 70 times excess molar concentration of protons than that of molybdate. Optimization of the oxidation of the first molybdenum electrode 102a is therefore desired to realize optimum conditions in the second chamber 104b.
Testing of the device 200 illustrated in
The detection time and range is also vastly improved by the present disclosures. For example, while existing devices for phosphate level determinations can take about 70 minutes to perform their analysis without stirring the fluid (i.e., the 12-MPA) and about 5 minutes with stirring the fluid (such as by using a pump, as described above), the present device can detect phosphate levels (i.e., a phosphate level detection time) approximately in the range of about 1 minute to about 10 minutes without stirring the fluid (i.e., the 12-MPA), and in some embodiments about 2 minutes or less without stirring the fluid. These times may be even faster if the fluid is stirred. Still further, a linear detection range of existing devices can be approximately in the range of about 0.1 μM to about 1 μM or about 0.25 μM to about 4 μM, while the linear detection range of the present device 200 can be approximately in the range of about 1 μM to about 25 μM. Other linear detection ranges, including those that exceed about 25 μM, may also be possible in view of the present disclosures.
Similar to the device of
Fluid 330 can be passed into the chamber 304 by the illustrated inlet 316 and outlet 318. A total chamber volume of the present device 300 can be significantly smaller than existing analysis devices. For example, a total chamber volume for existing devices can be at least 275 microliters in typical embodiments, while the device 300 of
A method of using this single molybdenum detection device can arguably be even simpler than the device 200 of
There are a number of operating conditions that separate the device 300 from the device 200, which can allow the device 200 to outperform both existing devices and that of device 200. For example, an amount of oxidation of Mo in the device 300 can be sufficiently high to supply a sufficient amount of protons for 12-MPA formation, which is much higher than the oxidation of the second Mo electrode 204b in the device 200. In fact, the device 300 can oxidize an amount of molybdenum that is so large so as to achieve both a PH reduction due to the proton generation and a formation of the 12-MPA in presence of orthophosphate ions in the same chamber and at the same time. The device 200 instead uses a smaller current than that of device 300, with the current being passed through the second Mo electrode because the function of the electrode is only towards the formation of 12-MPA. The pH is being regulated by a separate molybdenum oxidation chamber in the configuration discussed with respect to the device 200.
Testing of the device 300 illustrated in
The detection time is also vastly improved by the present disclosures. For example, while existing devices for phosphate level determinations can take about 70 minutes to perform their analysis without stirring the fluid (i.e., the 12-MPA) and about 5 minutes with stirring the fluid (such as by using a pump, as described above), the present device can detect phosphate levels (i.e., a phosphate level detection time) approximately in the range of about 10 seconds to about 2 minutes without stirring the fluid (i.e., the 12-MPA), and in some embodiments about 30 seconds or less without stirring the fluid. These times may be even faster if the fluid is stirred. The device can have a non-linear relation, as opposed to a linear detection range as described above. While linear detection ranges can sometimes be preferable, non-linear relations will typically also work for the intended purposes of the present disclosure.
As shown, each of an Mo electrode 402, working electrode 412, reference electrode 414, and counter electrode 420 are provided as part of a device that is associated with the fluid to be tested. Rather than an enclosed chamber, as described in earlier embodiments, the device includes an open chamber 404, sometimes referred to as a mounting component or mounting plate, with which the electrodes are coupled or otherwise associated. The illustration in
In the illustrated embodiment, the Mo electrode 402 has a surface area that is approximately 4 millimeters2, and the working electrode 412 is an approximately 50 micrometer diameter wire having a total surface area that is approximately 1.13 millimeters2, although other sizes and configurations are possible. For example, in some embodiments a diameter of the wire can be approximately in the range of about 10 micrometers to about 200 micrometers and a total surface can be approximately in the range of about 0.5 millimeters2 to about 5 millimeters2 The configurations of the reference and counter electrodes 414, 420, as well as the background solution, are akin to those from
A method of using this single molybdenum detection device 400 can arguably be even simpler than the devices 200, 300 of
Testing of the device 400 illustrated in
The detection time is also vastly improved by the present disclosures. For example, while existing devices for phosphate level determinations can take about 70 minutes to perform their analysis without stirring the fluid (i.e., the 12-MPA) and about 5 minutes with stirring the fluid (such as by using a pump, as described above), the present device can detect phosphate levels (i.e., a phosphate level detection time) approximately in the range of about 1 second to about 1 minute without stirring the fluid (i.e., the 12-MPA), and in some embodiments about 10 seconds or less without stirring the fluid. These times may be even faster if the fluid is stirred.
Although the embodiments described herein are sometimes referred to as double or single molybdenum detection devices, such devices can include additional electrodes without departing from the spirit of the present disclosure.
A person skilled in the art will recognize that a benefit of the present disclosures is the minimal amount of components that are needed to make phosphate level detections, and the resulting size of the devices that allows them to be transportable and used in situ directly on-site. An important aspect of the design strategy of the device 100 is to minimize a thickness of the chambers 104a, 104b while maximizing the cross-sectional area of each layer. The thin layers of the chambers 104a, 104b will compensate the increase in ohmic resistance caused by the volume reduction, and decrease the diffusion length between the first and second chambers 104a, 104b, resulting in faster transfer/diffusion of protons across the first PEM 106. Moreover, performance is increased when the surface area of the molybdenum electrode in the chambers is maximized. For the molybdenum electrode 102a in the first chamber 104a, the larger surface area will generate more protons under the same current density, which can result in less time needed to reach the desired pH. Similarly, the larger surface area of the second molybdenum electrode 102b can facilitate the homogenization of molybdate ions for the faster formation of 12-MPA. Still further, a smaller distance between the second molybdenum electrode 102b and the working electrode 112 decreases the diffusion length of the 12-MPA reducing the response time. It will be appreciated that although this is being discussed with respect to the embodiment of the device 100, these concepts can apply to all of the devices 200, 300, 400 of the present disclosure.
Each of the devices 100, 200, 300, 400 discussed herein can be portable, autonomous, and capable of in situ measurements.
Oxidation of the first Mo electrode 202a, with the first Mo electrode 202a being installed at the bottom of the first layer in the first chamber 204a can provide protons through the third layer having the first PEM 206 into the second chamber 204b. The second chamber 204b, as shown, can include a fourth layer having a second chamber upper conduit 205, a fifth layer having the second Mo electrode 202b, a sixth layer having a connection board 207, and a seventh layer having a second chamber lower conduit 209. The device 200 can further include an eighth layer having a second PEM 208, a ninth layer having a sealing gasket 211, and a tenth layer including a separator 213. In some embodiments, the second chamber 204b can include a gold wire electrode as a working electrode. The gold wire electrode can be positioned on top of the second Mo electrode 202b without contacting the second Mo electrode 202b. Additional details related to a gold wire electrode are described below with respect to the device 300 of
Examples of the above-described embodiments can include the following:
1. A phosphate level detection device, comprising:
One skilled in the art will appreciate further features and advantages of the disclosure based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.
The present application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/972,994, filed Feb. 11, 2020, and titled “Devices and Methods for Determining Phosphate Levels in Natural Water,” and which is incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/017733 | 2/11/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62972994 | Feb 2020 | US |
