Abstract:
A method and apparatus measures the presence of total residual oxidant species in aqueous environments. More specifically, the apparatus is operable to measure hypohalites (e.g., hypochlorite and hypobromite) in water containing halide salts using electrochemistry. The apparatus can be a sensor having four electrodes—a reference electrode, a working electrode, and two auxiliary electrodes. The fourth electrode, i.e., the second auxiliary electrode, can be used to generate ionized water near and in contact with the working electrode. The ionized water can clean the working electrode to minimize effects due to scaling or biofilm formation. As such, the working electrode does not need the capability to clean itself. Thus, other elements, originally believed to be unsuitable for use in saline aqueous environments, can be used for the electrodes, for example, gold.

Description:
CROSS REFERENCE TO OTHER APPLICATIONS 
       [0001]    This application claims priority to provisional patent application 61/223,216, filed Jul. 6, 2009, which is incorporated herein by reference in its entirety for all that it teaches. 
     
    
     BACKGROUND 
       [0002]    The practice of eliminating unhealthy/biofouling microorganisms in water dates back to ancient civilizations. There are several methods to disinfect water, including brackish water, waste water and cooling water. Electrochemical methods can produce disinfection agents. Disinfection is not sterilization. Disinfection refers to the deactivation of “pathogen” (disease causing) microorganisms, whereas sterilization refers to the deactivation of all microorganisms present. Mechanisms for microorganism deactivation include the modification of, or attack on: the cell wall (e.g., rupture, property modification, etc.); the cell internal components (e.g., protoplasm or nucleic acid modification, alteration of protein synthesis, fatal induction of abnormal redox processes, etc.); and the enzymatic activity. 
         [0003]    The most common disinfecting agents have properties as oxidants. This makes the disinfectants useful for the deactivation of most microorganisms, but also brings about undesirable effects, such as the discoloration of dyes, the corrosion of some metals, and the attack on some organic substances. These spurious properties of oxidants in some applications create an extra “load” thereby requiring the production of extra amounts of the disinfecting agent, increasing the corresponding costs, or requiring care to maintain the disinfecting agent concentration below levels that can cause damage, increasing collateral costs associated with treatment. Furthermore, some disinfecting agents produce “disinfection by-products” (DBP) upon their addition or reaction with organic substrates. Such DBP&#39;s are frequently toxic, as is the case with most chlorinated hydrocarbons. The main disinfectant agents produced via electrochemistry can be classified according to the oxidizing element: chlorine-based (e.g., chlorine gas, hypochlorite, hypochlorous acid, and chlorine dioxide); oxygen-based (e.g., ozone, hydrogen peroxide, and hydroxyl radicals); and others (e.g., permanganate, ferrate, ions of other transition metal ions (for example, copper and silver), percarbonate, persulfate, other halogens (for example, hypobromite, hypobromous acid) and derivatives (for example, mixed chlorine and bromine oxides), and the electrochemical manipulation of pH (i.e., the production of high levels of acidity or basicity)). 
         [0004]    Reliable measurement of disinfection agents, especially chlorine-based or bromine-based hypohalites, has proven difficult in some circumstances. Automated water sampling systems can grab water samples for manual titration. However, this process is time consuming, does not produce near real-time measurements, and may not be performed in inaccessible systems. In some situations, sensors, based on amperometry, can be used. Amperometry is a generic term for a measurement that consumes the analyte and produces a measurable current that can be correlated to an amount of hypohalite or total residual oxidant in the solution. Total residual oxidant (TRO) measurement is often referred to as the measurement of an oxidant species or, more specifically, the measurement of chlorine using an electrochemical sensor or a titration-based approved standard method. Laypersons refer to electrolytic halogenation as chlorine, chlorination, or electrolytic chlorine generation (ECG) without particular attention to actual speciation. 
         [0005]    However, finding the proper sensor to use for long-term measurement of TRO, especially in saline aqueous environments, has been difficult. Current chlorine amperometry sensors are not able to make functional long-term measurements without frequent and costly maintenance and calibration. In electrochemistry two or more electrodes may make a sensor that provides a measurement. The TRO sensor is a minimum three-electrode sensor that is also an amperometric sensor. Current amperometric sensors have many drawbacks. 
       SUMMARY 
       [0006]    Embodiments presented herein are generally directed to a method and apparatus to measure the presence of total residual oxidant species in saline aqueous environments. More specifically, the apparatus is operable to measure hypohalites (hypochlorite and hypobromite) in water containing halide salts using electrochemistry. The apparatus can be a sensor having four electrodes—a reference electrode, a working electrode, and two auxiliary electrodes. The fourth electrode, i.e., the second auxiliary electrode, can be operated as an alternate working electrode and used to generate ionized water near and in contact with the working electrode. The ionized water can clean the working electrode to minimize effects due to scaling or biofilm formation. As such, the working electrode does not need the capability to clean itself. Thus, other elements, originally believed to be unsuitable for use in saline aqueous environments, can be used for the working electrode, for example, gold. 
         [0007]    The embodiments provide four electrodes, i.e., one working electrode, two auxiliary electrodes, and one reference electrode, that are operated and positioned in a fashion to maximize the surface stability and sensitivity of the working electrode to hypohalites (total residual oxidant). In embodiments, the working electrode is not an active participant in the cleaning steps but is cleaned by being electrically isolated from the electrochemical circuitry and being in intimate proximity to the fourth electrode. 
         [0008]    The use of alternating electrodes allows the working electrode to be isolated from the circuit and, when positioned in substantial proximity to the auxiliary electrode and operated against electrode  4  to create changes in the water, clean the working electrode without degrading the working electrode. The electrical conditions required to clean the working electrode cannot be achieved by the working electrode directly because the metallic surface will dissolve into the saline water when operated at the potentials necessary to affect the water ionization for cleaning. However, by placing the working electrode in substantial proximity to the auxiliary electrode and then operating the auxiliary electrode in conjunction with electrode  4 , with the working electrode electrically isolated, varying pH can be achieved to maintain the surface of the working electrode. Thus, the working electrode can be made from sensitive metals. 
         [0009]    This cleaning of the working electrode maintains the metallic surface of the working electrode in a fairly constant surface condition that provides for long-term measurement stability as a result of stable surface conditions. Typical metallic working electrodes suffer changes in the electrode condition such as surface oxidation, roughening or fouling that cause the measurement calibration to drift over time requiring the sensor to be either routinely cleaned, recalibrated, or both. In other embodiments, amperometric sensors use semi-permeable membranes to isolate the metallic electrodes from the saline water resulting in the need to further maintain the fragile, semi-permeable membrane. 
         [0010]    The apparatus and method provide several advantages:
       1) The ability to measure chlorine and bromine hypohalites (aqueous HOX and OX—, where X═Cl or Br), which hereafter may be referred to as total residual oxidant species;   2) Improved stability and operational life of the precious metal working electrode while either simultaneously or sequentially using the same electrode configuration to assess salinity (a value that is important to electrolytic generator efficiency, generation output, and maintaining sensor stability);   3) The ability to directly and accurately measure total residual oxidant with negligible sensitivity to water flow and thereby eliminate the need for the sensor to be installed in a controlled flow sampling loop;   4) New sensor operational algorithms that compensate the total residual oxidant sensor response based on simple and robust complimentary readings such as salinity and temperature;   5) A sensor package design that allows for electrode substitution at manufacturing to take advantage of both state-of-the-art electrode arrays and low-cost, conventional macro electrodes for the working and auxiliary electrodes;   6) A sensor package that provides for flow insensitive measurement without need for a mechanical means to invoke a controlled flow;   7) Sensor communication to an external device to create a stop flow, or controlled reduced flow, condition that allows for a consistent measurement;   8) A sensor package that provides for a mechanical means to invoke flow, or sample non-flowing water, for a fast response in non-flowing environments;   9) Electrode switching to facilitate cleaning and maintenance of the critical working electrode for stable long-term operation with minimal loss of the electrode surface;   10) Very low pulse measurement of the working electrode to minimize and eliminate measurement sensitivity to varying water flow conditions; and   11) Employment of a micro-scale wire to create a microelectrode at considerably lower cost and complexity to conventional microelectrode arrays (additionally, this novel microelectrode may be placed within the tubular cavity with an auxiliary electrode or a fourth electrode for purposes as previously described).       
 
         [0022]    The phrases “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. 
         [0023]    The term “in communication with” as used herein refers to any coupling, connection, or interaction using electrical signals to exchange information or data, using any system, hardware, software, protocol, or format. 
         [0024]    The term “a” or “an” entity refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, and “having” can be used interchangeably. 
         [0025]    The term “automatic” and variations thereof, as used herein, refers to any process or operation done without material human input when the process or operation is performed. However, a process or operation can be automatic, even though performance of the process or operation uses material or immaterial human input, if the input is received before performance of the process or operation. Human input is deemed to be material if such input influences how the process or operation will be performed. Human input that consents to the performance of the process or operation is not deemed to be “material”. 
         [0026]    The term hypohalite can mean any salt of a hypohalous acid, having a general formula M(OX)n. 
         [0027]    The term analyte can mean any substance undergoing analysis. 
         [0028]    A sensor can mean any arrangement of two or more electrode operable to analyze an analyte. 
         [0029]    An electrode can mean a collector or emitter of electric charge in a sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The present disclosure is described in conjunction with the appended figures: 
           [0031]      FIG. 1A and 1B  are diagrams of an embodiment of a sensor; 
           [0032]      FIG. 2A through 2B  are diagrams of another embodiment of a sensor; 
           [0033]      FIGS. 3A and 3B  are diagrams of still another embodiment of a sensor; 
           [0034]      FIGS. 4A and 4B  are diagrams of an embodiment of microwire electrode; 
           [0035]      FIG. 5  is block diagram of an electric circuit of a sensor; 
           [0036]      FIG. 6  is a flow diagram of an embodiment of a process for measuring total residual oxidant in an aqueous environment; 
           [0037]      FIG. 7  is a flow diagram of an embodiment of a process for manufacturing a microwire electrode. 
           [0038]      FIGS. 8A and 8B  are diagrams of an embodiment of a microdisk and a microwire electrode showing isopotential lines; 
           [0039]      FIG. 9  is a diagram of an embodiment of a microwire electrode showing isopotential lines; 
       
    
    
       [0040]    In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
       DETAILED DESCRIPTION 
       [0041]    The ensuing description provides embodiments only, and is not intended to limit the scope, applicability, or configuration of the claims. Rather, the ensuing description will provide those skilled in the art with an enabling description for implementing the embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the appended claims. 
         [0042]    An embodiment of a sensor  100 , for measuring TRO, is shown in  FIGS. 1A and 1B . The sensor is composed of four electrodes  106 ,  108 ,  110 , and  112 . The four electrodes can be contained within an enclosure  102 . In embodiments, the enclosure  102  is a flow restriction that is substantially formed from of a nonconductive and nonreactive compound (e.g., a plastic or ceramic material). The enclosure  102  may form a barrier between the sensor and the surrounding environment. The example enclosure  102  has the following physical dimensions: external diameter of 25.40 mm (1.0″), internal diameter of 21.43 mm (27/32″), nominal wall thickness of 2 mm, internal height of 18 mm, total cup height of 32 mm, and total internal volume of 6.492 cm 3  (mL) These physical dimensions are exemplary as various other designs for the enclosure are possible. 
         [0043]    The four electrodes include a working electrode  106 , a reference electrode  108 , a first auxiliary electrode  110  and a second auxiliary electrode  112  (also referred to as electrode 4). The working electrode  106  can aid in measuring TRO in the aqueous solution. The working electrode  106  is the location at which reduction of the oxidant species takes place when the working electrode  106  is biased at an appropriate reduction potential with respect to the reference electrode  108 . The working electrode  106  may be a metal, for example platinum or gold. Thus, when the working electrode  106  is biased at a value of less than +0.3 V versus a reference electrode  108 , the working electrode&#39;s  106  surface will reduce hypohalites and produce a current proportional to concentration of the hypohalites and other environmental parameters, such as water flow. A gold surface on the working electrode  106  may be necessary to detect hypochlorite, whereas a graphite surface has been used to detect hypobromite. In an embodiment, the working electrode  106  is a gold microdisk array, such as the ABTECH MDEA 050 gold microdisk array sold by ABTECH Scientific, Inc. The microdisk array may have a diameter of approximately 7.5 mm and contain 5,184 discs each with a diameter of 50 μm producing a total electrochemical area of 10.17 mm 2 . 
         [0044]    The first auxiliary electrode  110  is often called the counter electrode. The working electrode  106  is the electrode on which the reaction of interest occurs, and through which measurements are taken. The auxiliary electrode  110  changes in polarity opposite to that of the working electrode  110 , but the current and polarity of auxiliary electrode  110  are not measured. The auxiliary electrode  110  exists to ensure that current does not run through the reference electrode  108  and often has a surface area much larger than that of the working electrode  106  to ensure that the reactions occurring on the working electrode  106  are not surface area limited by the counter electrode  110 . In the example shown in  FIG. 1B , the auxiliary electrode  110  may be made of platinum black and be at least a 3.6 mm diameter disc having an area of 10.17 mm 2 . 
         [0045]    The reference electrode  108  is an electrode that has a standard, stable electrochemical potential (half-cell potential) that is used as a voltage standard against which voltages are applied to the working electrode  106 . In the example in  FIG. 1A  and  FIG. 1B , the reference electrode  108  can be a mesh of silver wire anodized with Ag/AgCl having an effective height of 10 mm and a width of 7 mm. This robust solid-state reference electrode is optimal for saline waters, such as seawater. In low to non-saline water conditions, a traditional double junction reference electrode may be used with some environmental limitations to the sensor operation with respect to shock, vibration, temperature, pressure and other parameters, known to those skilled in the art. 
         [0046]    The second auxiliary electrode or electrode 4  112  is novel. Electrode 4  112 , at times, acts as a supplemental auxiliary electrode that functions in parallel to the auxiliary electrode  110  (to increase the total surface area of the functional auxiliary electrode). At other times, electrode 4  112  acts as a working electrode in place of the normal working electrode  106  to clean the normal working electrode  106 . Here, electrode 4  112  creates a higher potential, e.g., above 0.7 volts, to ionize the solution that is in contact with the working electrode  106 . The ionized water has attributes of either high or low pH. Thus, the basicity or acidity of the water acts to “clean” the surface of the working electrode  106 . Electrode 4  112  can be made of materials suitable to function as an electrode. In embodiments, electrode 4  112  is made of glassy carbon and is a disk having a diameter of 5 mm with an area of 19.6 mm 2 . 
         [0047]    In prior art sensor development, −0.5 V is used as the negative potential pulse and +0.7 V as the positive potential pulse on the working electrode. The −0.5 V is not sufficient to generate hydrogen, and the +0.7 V is not positive enough to generate oxygen in seawater allowing for a stable long-term cleaning action. Thus, at the prior art voltages, the working electrode would become fouled by biofilm. Further, the working electrode could not be gold if the working electrode was to clean itself, as was common in three electrode systems. The positive potential that may be applied to the working electrode is limited by the gold surface employed for increased sensitivity to chlorine. At a potential more positive than 0.7 V, gold is dissolved (oxidized) away in the presence of chloride. 
         [0048]    To function properly, electrode 4  112  is introduced in close or intimate proximity to the working electrode  106 . In embodiments, electrode 4  112  may be used to clean the surface of the working electrode  106 . The intimate proximity of the working electrode  106  and electrode 4  112  depends on the flow of the solution, the level of potential created at electrode 4  112 , the shape and size of the enclosure  102 , etc. The embodiment shown in  FIG. 1B  includes a separation or barrier  104  that creates two volumes of solution within enclosure  102 . The separation  104  allows electrode 4  112  to change the chemistry of the solution in the first volume and the second volume but in opposite ways. If electrode 4  112  creates an acidic solution in the first volume housing electrode 4  112 , an opposite reaction (e.g., creating a basic solution) will occur in the second volume. The separation design can also affect the functioning of electrode 4  112  with respect to cleaning. The dimensions provided for the embodiment in  FIGS. 1A and 1B  represents one example of an operational sensor  100 . 
         [0049]    Another embodiment of the sensor  100  is shown in  FIGS. 2A and 2B  including the four electrodes  106 ,  108 ,  110 , and  112  and the enclosure  102 . Here, the enclosure  102  includes one or more openings  114  in the bottom of the enclosure  102 . The solution can pass through the openings  114  in this embodiment to allow measurement of a flowing solution. 
         [0050]    Another embodiment of the sensor  100  is shown in  FIGS. 3A-3B  including the four electrodes  106 ,  108 ,  110 , and  112  and the enclosure  102 . Here, the enclosure  102  also includes one or more openings  114  and  116  to allow the mechanically activated flow of solution across the working electrode  106 . The solution can pass through the openings  114  and  116 , in this embodiment, by means of a plunger  120  to allow measurement of a non-flowing, stagnant solution. 
         [0051]    The reference electrode  108  is positioned outside of the enclosure. A unique microwire working electrode  106  is position within a first channel  118   a  while the auxiliary electrode  110  is position within the second channel  118   b.  An embodiment of the microwire electrode  106  is described in conjunction with  FIGS. 4A and 4B . Electrode 4 is also positioned within the first channel further upstream than the working electrode  106 . In this way, ionized solution can flow from electrode 4  112  and to or past the working electrode  106 . 
         [0052]    An embodiment of a microwire electrode  400  is shown in  FIGS. 4A and 4B . The microwire electrode  400  includes a microwire  402  formed into a helix. The microwire can be 50 μm diameter gold wire (Alpha Aesar). The helix has windings  402   a  through  402   j.  A winding can be a single revolution of the wire in the helix. There may be more or fewer windings than those shown in  FIG. 4A . In one embodiment, there are 27 windings. Wrapping microwire into a helix is a much lower cost fabrication means for producing a sensitive measurement microelectrode. 
         [0053]    Further, the microwire electrode  400  can produce greater electrical fields compared to the microdisk electrode. Referring to  FIGS. 8A and 8B , a microdisk electrode  800  is shown in  FIG. 8A . Here, the electrode conductor (e.g., gold electrode)  802  is covered by an insulation insulating layer  804  that has one or more holes or openings  808  formed in the insulation layer  084 . When charged under a potential, the microdisk electrode  800  can create an electrical field (shown as a set of isopotential lines)  806   a  at each opening  808 . 
         [0054]    The a single winding of the microwire electrode  402  is shown in  FIG. 8B . Under the same electrical charge, the microwire electrode can create a larger electrical field (shown as a set of isopotential lines)  806   b  than the opening of the microdisk electrode opening  808 . The winding of the microwire electrode  402  exhibits a large penetration of the isopotential field lines  806   b  into the analyte containing solution. Thus, each winding of the microwire electrode  402  can be more sensitive than each opening  808  of the microdisk electrode  800 . Another diagram of the microwire electrode  402  is shown in  FIG. 9 . Here, the large electrical field, represented by isopotential lines  902 , is compounded or increased because of the several windings used in the microwire electrode. Other shapes are possible for the winding or shaping of the microwire. The microwire can be a conductive substance, for example, gold and platinum. 
         [0055]    In embodiments, the helix may be supported by or affixed on a substructure  404  as shown in  FIG. 4A . The substructure can be a pipe or lumen constructed of a rigid material, for example, plastic. A grove is formed into the substructure  404  in a spiral that holds the helix  402  of microwire. In this way, the microwire maintains the helical shape. A first end of the micro wire may be passed through an opening in the substructure  404 , as shown in  FIG. 4B , to travel through the lumen in the substructure to an electrical connection. The other end of the microwire may also make an electrical connection. As such, the microwire can form a circuit and function as an electrode  106 . 
         [0056]    The dimensions in the microwire electrode dictate how the microwire will perform. The diameter of the microwire, the spacing of the windings of the helix, and the rate of the flow  406  of the solution past the microwire sensor  400 , the potential applied to the microwire, and the measurement duration are important to the function of the microwire electrode  400  based sensor. As the electrode  400  measures hypohalites, the electrical potential created on the microwire  402  can cause some of the hypohalite to be consumed. The consumption of the hypohalite can cause errant readings on windings further downstream if the solution, with the consumed hypohalite, passes the windings. If the measurement time interval (i.e., the period between successive measurements) is set at a predetermined level that is sufficiently short (which is based on flow rate, potential created at the microwire windings, the diameter of the microwire, the distance between the microwire windings, etc.), the microwire electrode  400  can result in measurement insensitivity to flow rate. Thus, the factors mentioned above must be controlled and determined to create a functioning microwire sensor. One skilled in the art will understand how the factors interact and how to change the winding distance to create a functioning sensor. 
         [0057]    An electrical diagram of an embodiment of the sensor  100  is shown in  FIG. 5 . The sensor  100  operates similarly to existing three electrode sensors when measuring hypohalites. One exception is that electrode 4  112  can be used in conjunction with the first auxiliary electrode  110  to create a single “functional” auxiliary electrode with greater surface area. However, the differences with three electrode sensors is more focused on the operation of electrode 4  112 . 
         [0058]    The sensor  100  can include at least one switch  502   a  and  502   b.  Switch  502   a  and switch  502   b  can work in concert to place the sensor  100  either into a measurement configuration or a cleaning configuration. With switch A  502   a  in a position 0 and switch B  502   b  in a position 0 or 1 (table  508 ) the sensor  100  is in a measurement configuration and can measure a current, or a current as a potential, to determine an amount of hypohalite in the solution in which the electrodes reside. With switch A  502   a  in a position 0 and switch B  502   b  in a position 0 (table  508 ) the sensor cleans the working electrode  106 . In this configuration, the working electrode  106  “floats,” that is, the working electrode  106  is neither connected to a power source or to ground. Further, electrode 4  112  is connected to a power source to create a potential at electrode 4  112 . The potential at electrode 4  112  electrolytically creates either an acid or a base solution (depending on whether the potential is positive or negative) that cleans the working electrode  106 . The acidic or basic solution may be alternated during successive or subsequent cleanings. Electrochemical(ly) can mean of or relating to a chemical reaction brought about by electricity. Electrolytically means produced by or used in the process of the producing of chemical changes by passage of an electric current through an electrolyte. The configuration of the sensor  100  can be oscillated or switched back and forth between measurement and cleaning. 
         [0059]    An embodiment of a method  600  for operating the four electrode sensor  100  is shown in  FIG. 6 . Generally, the method  600  begins with a start operation  602  and terminates with an end operation  616 . While a general order for the steps of the method  600  are shown in  FIG. 6 , the method  600  can include more or fewer steps or arrange the order of the steps differently than those shown in  FIG. 6 . Some or all the steps in method  600  can be executed as a set of computer-executable instructions executed by a computer system and encoded or stored on a computer readable medium. Hereinafter, the method  600  shall be explained with reference to the systems, components, devices, etc. described in conjunction with  FIGS. 1-5 . 
         [0060]    The function of the four-electrode, amperometric sensor  100  is to alternate the sensor operation between modes of ( 1 ) oxidant measurement, ( 2 ) conductivity measurement, ( 3 ) proton generation near the working electrode  106  and ( 4 ) hydroxyl generation near the working electrode. Since the working electrode  106  cannot participate in the hydrolysis events (because gold dissolves in chloride environments when energized above +0.7 Volts), the second auxiliary electrode  112  is placed very close to the face of the working electrode  106  and the first auxiliary electrode  110  is placed further away. 
         [0061]    The sensor  100  is introduced into the measurement environment, in step  604 . The sensor  100  is a four electrode sensor  100 . The working electrode  106  of the sensor  100  can be gold. The measurement environment may be a test environment or an actual field environment where the sensor  100  is being used. In embodiments, the environment is a saline aqueous solution that may contain hypohalites, which may be chlorine or bromine based. The saline aqueous solution may be seawater. 
         [0062]    The sensor  100  can take a measurement using the working electrode  106 , in step  606 . In the measurement of total residual oxidant the ideal electrode material for the working electrode  106  is gold. However, gold has an upper bound on the applied potential, if this potential is exceeded, the gold is electrochemically dissolved into the solution as noted above. In the measurement mode, switches  502  are set to the position where the two auxiliary electrodes  110  and  112  are connected in parallel and act as a single larger area auxiliary electrode. In some embodiments, only one of the auxiliary electrodes  110  or  112  is connected. A measurement of total residual oxidant, with a reduction of the analyte at the working electrode  106 , results in a current passing through the working electrode  106  that is proportional to the analyte concentration. This current is converted to a potential, by a current to voltage converter  510 , and subjected to conversion to a digital value for processing by a microprocessor as is understood by those skilled in the art. 
         [0063]    The sensor  100  can transition to a cleaning mode. In the cleaning mode, the analog switches  502  are set to the position where the working electrode  106  is electrically isolated from the circuit. In other words, the sensor  100  configuration floats the working electrode  106 , in step  608 . Further, in the configuration, electrode 4  112  takes on the function of the working electrode. 
         [0064]    An electrical potential is then created on electrode 4  112 , in step  610 . Cleaning of the working electrode  106  (where the halogen reduction occurs) can be performed electrochemically through the application of alternating negative and positive potentials to electrode 4  112 . Calcium and magnesium can solidify onto electrode surfaces but the mechanism for elemental precipitation, as hydroxides, on any surfaces may also apply for the electrodes. The cycling of alkaline and acidic conditions at the electrode surface have been previously shown to prevent hydroxides from precipitating and thus can keep the electrode clean. Hydrogen evolution occurs at a negative potential and oxygen evolution occurs at a positive potential. The change in pH can clean the contaminants precipitated from water onto the working electrode  106 , in step  612 . Thus, the intimate proximity of the working electrode  106  and electrode 4  112  is important to allow the generated hydroxyls and protons to flow over and clean the gold surface of the working electrode  106 . Further, the potential applied to electrode 4  112  may need to be greater than +1.0 V to generate sufficient protons and less than −1.0V to generate sufficient hydroxyls to effect the surface cleaning. 
         [0065]    The system in communication with the sensor  100  may then determine if another measurement is needed, in step  614 . In embodiments, the system takes periodic measurements with the sensor  100 . In this situation, the system determines if the period of time between measurements has elapsed and starts the process of measurement again. In other embodiments, the system is directed by input from a human tester. A human tester may direct a measurement. If a directive is received, the system starts the process of measurement again. If a new measurement is needed, the process  600  flows “YES” back to step  606 . If a new measurement is not needed, the process  600  flows “NO” to end operation  616 . 
         [0066]    Using this process repeatedly, the sensor  100  can reach equilibrium and provide quick and effective measurement of TRO in saline aqueous solutions. The concentration of hypohalites may then be adjusted (by adding chemicals, through electrochemical means, etc.) according to the measurements. The adjustments may then be verified through method  600 . In this way, disinfection, and possibly sterilization, of the aqueous solution can occur. 
         [0067]    An embodiment for manufacturing a microwire electrode  400  is shown in  FIG. 7 . Thread a length of gold wire  402  (e.g., 50 μm diameter gold wire (Alpha Aesar)) through the lumen  408  of the substructure  404  from the top opening  410  through and out a hole formed in the side of the substructure, in step  704 . A stereo microscope is useful. A bent piece of 30 gauge solid wire may be employed to help “fish” the gold wire  402  out of the side hole. Pliers or tweezers should not be used to handle the gold wire  402 . If platinum wire is being used, it may be inserted from the bottom hole instead of the top hole based on the operator preference. Pull a length (e.g., 300 mm) of gold wire  402  out from the bottom side hole, in step  706 . Cut the gold wire  402  leaving about a length (e.g., 30 mm) of gold wire  402  protruding from the top hole  410 , in step  708 . Bend the gold wire  402  protruding from the top hole  410  around substrate  404  so that the gold wire  402  follows the exterior of the substrate  404  and passes the gold wire  402  exiting the bottom side hole, in step  710 . Tools should not be used for this operation; only use clean fingers that have been washed with non-residual soap and water. 
         [0068]    Place the top  410  of the substrate  404  into a rotary tool that is mounted in a fixed position, in step  712 . Optionally, adhere the gold wire  402  by placing a small amount of JB Weld Kwik over the gold wire  402  where the gold wire  402  exits the bottom side hole to hold the gold wire  402  in place, in step  714 . Wind the substrate  404  to create the helical windings of the gold wire  402  in step  716 . In embodiments, step  716  creates  27  turns of gold wire  402  on the substrate  404 . Tack the gold wire  402  into place using JB Weld Kwik, in step  718 . Feed the remaining gold wire  402  through an upper side hole, in step  718 . It may be prudent to apply one turn after the tack location to prevent kinking the gold wire  402  during the termination steps. 
         [0069]    Thread the remaining gold wire  402  into the upper side hole, in step  720 . Thread only the amount necessary for the tip of the gold wire  402  to exit the top hole. Remove the substrate  404  from the rotary tool and pull the slack out of the gold wire  402  to make sure that the gold wire  402  is still properly seated into the upper side hole, in step  722 . Twist the lead gold wires  402  together by rotating the ends of the gold wire  402 , in step  724 . 
         [0070]    Cut a length of wire (e.g., 70 mm piece of 1 mm diameter silver wire), in step  726 . Coat a portion of the cut wire (e.g., 20 mm of the silver wire) with epoxy, e.g., (a thin layer of Ellsworth epoxy), in step  728 . Place the epoxy coated end of the silver wire into the top end  410  of the substrate  404 , in step  730 . Seat the silver wire into the bottom of the substrate  404 , in step  732 . Wrap the protruding gold wire  402  loosely around the silver wire, in step  734 . Solder (e.g., using  0 . 15 ″ diameter  63 / 37  solder) the silver wire to the gold wire  402 , in step  736 . Epoxy, (e.g., using Ellsworth epoxy) the silver wire and open side holes, in step  738 . Cure the epoxy, in step  740 . 
         [0071]    Specific details were given in the description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, elements of the embodiments may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
         [0072]    Also, it is noted that the embodiments were described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function. 
         [0073]    This application contains an appendix with further materials describing the sensor  100 , the microwire electrode  400 , and the operation and methods described herein. The appendix is hereby incorporated as part of the application for all that it teaches. 
         [0074]    While illustrative embodiments of the invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.