Patent Publication Number: US-10309948-B2

Title: Carbon quantifying apparatus and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of U.S. patent application Ser. No. 13/578,451, filed on Aug. 10, 2012 and entitled “Carbon Quantifying Apparatus And Method,” which is a U.S. National Phase application of International PCT Application Serial No. PCT/US2011/024075, filed on Feb. 8, 2011 and entitled “Carbon Quantifying Apparatus And Method,” and which claims priority to U.S. Provisional Application Ser. No. 61/303,388, filed on Feb. 11, 2010, and titled “Apparatus And Method For Quantifying Carbon Materials;” the contents of each prior application are incorporated by reference herein. 
    
    
     FIELD 
     The present invention relates to carbon quantification, and in particular, to a carbon quantifying apparatus and method. 
     BACKGROUND 
     Ultrapure water (UPW) is desirable for a variety of industrial processes, particularly pharmaceutical and semiconductor manufacturing. The semiconductor industry uses UPW as a universal solvent in virtually every step of a production process. Typical acceptable conductivity levels for UPW used in semiconductor industries are about 0.05 micro-siemens per centimeter (μ/cm) and typical acceptable total organic content (TOC) levels are about 1 ppb carbon. Chemical pharmaceutical industries use UPW in the production of drugs and reagents that require high degrees of purity. Typical acceptable conductivity levels for UPW used in pharmaceutical industries can be as high as 1.3 μS/cm at 25° C., and typical acceptable TOC levels can be up to 500 ppb carbon. 
     Ultra low levels of any ionic and non-ionic impurities (or the absence of impurities) therefore are desirable characteristics of UPW. Even small amounts of contaminants or electrolytes can adversely impact the efficacy or yields of the desired products. As semiconductor features decrease in size, smaller amounts of impurities, and certain types of impurities, become less tolerable. 
     For these reasons, determination of the nature of organic contaminants present in an UPW stream would be desirable and could lead to identification of the contaminant source, as well as remediation of the contaminants, which would be an invaluable cost and time saving tool. 
     Conventional TOC analyzers measure the amount of CO 2  produced when organic carbon-containing molecules are oxidized and/or when inorganic carbon-containing molecules are acidified. TOC analyzers are, therefore, unable to identify the organic molecules in UPW. 
     BRIEF SUMMARY 
     In one aspect of the invention, a carbon quantifying cell configured to receive a fluid comprises: two or more electrodes positioned at least partially in the fluid; and meter electronics coupled to the two or more electrodes and configured to place an electrical oxidization, polarization, and/or adsorption program across the two or more electrodes and at least partially oxidize carbon materials in the fluid, apply an AC voltage of a predetermined amplitude across the two or more electrodes, measuring a resulting AC current across the two or more electrodes, wherein a ratio of amplitudes and a phase angle difference provides information for calculating a fluid impedance, receive an electrical response of the fluid to the electrical oxidization, polarization, and/or adsorption program, quantify the carbon materials in the fluid using the electrical response, and detect interfering materials in the fluid using the fluid impedance. 
     Preferably, the two or more electrodes at least partially comprise a titanium dioxide (TiO 2 ) material. 
     Preferably, the two or more electrodes at least partially comprise a boron-doped diamond (BDD) material. 
     Preferably, quantifying the carbon materials includes the meter electronics analyzing the electrical response in order to determine the speciation of the carbon materials and/or speciation of organic materials in the fluid, wherein the speciation detects a presence of carbon material in the fluid. 
     Preferably, quantifying the carbon materials includes the meter electronics determining an identity of the carbon material in the fluid and determining a quantity of the carbon material in the fluid. 
     Preferably, quantifying the carbon materials includes the meter electronics determining relative fractions of two or more carbon materials in the fluid. 
     Preferably, the electrical oxidization, polarization, and/or adsorption program includes one or more of a predetermined DC voltage profile, a predetermined AC voltage profile, or a predetermined current profile. 
     Preferably, placing the electrical oxidization, polarization, and/or adsorption program across the two or more electrodes further comprises applying a varying DC voltage program across the two or more electrodes, thereby preferentially adsorbing and/or oxidizing and/or polarizing a predetermined carbon solute. 
     In one aspect of the invention, a method for quantifying carbon materials in a fluid comprises: placing an electrical oxidization, polarization, and/or adsorption program across two or more electrodes positioned at least partially in the fluid and polarizing and/or adsorbing and/or at least partially oxidizing the carbon materials in the fluid; applying an AC voltage of a predetermined amplitude across the two or more electrodes; measuring a resulting AC current across the two or more electrodes, wherein a ratio of amplitudes and a phase angle difference provides information for calculating a fluid impedance; quantifying the carbon materials in the fluid using an electrical response of the fluid to the electrical oxidization, polarization and/or adsorption program; and detecting interfering materials in the fluid using the fluid impedance. 
     Preferably, quantifying the carbon materials includes analyzing the electrical response in order to determine the speciation of the carbon materials and/or speciation of organic materials in the fluid, wherein the speciation detects a presence of carbon material in the fluid. 
     Preferably, quantifying the carbon materials includes determining an identity of the carbon material in the fluid and determining a quantity of the carbon material in the fluid. 
     Preferably, quantifying the carbon materials includes determining relative fractions of two or more carbon materials in the fluid. 
     Preferably, the electrical oxidization, polarization, and/or adsorption program is maintained for at least a predetermined polarization time period without oxidation of the organic species. 
     Preferably, the electrical oxidization, polarization, and/or adsorption program is maintained for at least a predetermined adsorption time period without oxidation of the organic species. 
     Preferably, the electrical oxidization, polarization, and/or adsorption program includes one or more of a predetermined DC voltage profile, a predetermined AC voltage profile, or a predetermined current profile. 
     Preferably, the electrical oxidization, polarization, and/or adsorption program includes applying a varying DC voltage program across the two or more electrodes, thereby preferentially adsorbing and/or oxidizing and/or polarizing a predetermined carbon solute. 
     In one aspect of the invention, a method for quantifying carbon materials in a fluid comprises: applying an AC voltage of a predetermined amplitude across the two or more electrodes; measuring a resulting AC current across the two or more electrodes, wherein a ratio of amplitudes and a phase angle difference provides information for calculating a fluid impedance; applying a varying DC voltage program across the two or more electrodes, thereby preferentially adsorbing and/or oxidizing and/or polarizing a predetermined carbon solute; quantifying the carbon materials in the fluid using an electrical response of the fluid to the electrical oxidization, polarization and/or adsorption program; and detecting interfering materials in the fluid using the fluid impedance. 
     Preferably, quantifying the carbon materials including analyzing the electrical response in order to determine the speciation of the carbon materials and/or speciation of organic materials in the fluid, wherein the speciation detects a presence of carbon material in the fluid. 
     Preferably, quantifying the carbon materials including determining an identity of the carbon material in the fluid and determining a quantity of the carbon material in the fluid. 
     Preferably, quantifying the carbon materials including determining relative fractions of two or more carbon materials in the fluid. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The same reference number represents the same element on all drawings. It should be understood that the drawings are not necessarily to scale. 
         FIG. 1  is an exploded view of a carbon quantifying cell according to an embodiment of the invention. 
         FIG. 2  shows a carbon quantifying cell having replaceable and/or disposable thin film electrodes according to an embodiment of the invention. 
         FIG. 3  shows a carbon quantifying cell having three electrodes according to an embodiment of the invention. 
         FIG. 4  is a graph showing the electrochemical stability of boron-doped diamond electrodes versus other representative conventional electrodes. 
         FIG. 5  is a conductance versus time graph illustrating the selective oxidation of formic acid by boron-doped diamond electrodes at various potentials in the presence of acetic acid. 
         FIG. 6  is a graph showing impedance versus potential profiles for UPW, 1 parts-per-billion (ppb) formic acid, and 1 ppb acetic acid. 
         FIG. 7  shows a carbon quantifying system according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-7  and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
       FIG. 1  is an exploded view of a carbon quantifying cell according to an embodiment of the invention. The carbon quantifying cell  20  may be used for speciation of organic materials in a fluid. Two or more electrodes  22  are positioned at least partially in thee fluid. The electrochemical cell  20  includes a supporting body  26  including a cavity  24 . The electrochemical cell  20  further includes two cover plates  28 A and  28 B that are configured to be assembled to the supporting body  26  and close off the cavity  24 . An inlet  42  and an outlet  44  communicate between the cavity  24  and the exterior, wherein fluid may flow into and out of the cavity  24  (see arrows  40 , for example). Fluids are received in the cavity  24  and tested therein. 
     The cavity  24  and the supporting body  26  may be made from polytetrafluoroethylene (PTFE) in some embodiments, or any suitable material coated by PTFE. Skilled persons will appreciate that other materials and coating can be used. 
     Insulators  30 A and  30 B are positioned between the supporting body  26  and the cover plates  28 A and  28 B. Electrodes  22 A and  22 B are held inside the cavity  24 . Electrodes  22 A and  22 B may be received on shoulders or in grooves in the cavity  24  (not shown). The insulators  30 A and  30 B are positioned so that the electrodes are electrically isolated from the cover plates  28 A and  28 B. The electrodes  22 A and  22 B are in contact with electrical leads  34  that pass through the cover plates  28 A and  28 B and through the insulators  30 A and  30 B. Consequently, an electrical field can be placed across the two electrodes  22 A and  22 B, wherein a resulting electrical current can be generated through the fluid under test. 
     The electrochemical cell  20  can further include a UV source  53  in some embodiments. The UV source  53  can be positioned to transmit UV light into the cavity  24 , such as through a UV translucent panel (not shown). The UV light can radiate into the cavity  24  and interact with the fluid. For example, the UV light may initiate, cause, enhance, accelerate, or otherwise participate in oxidization of the fluid and material within the fluid. 
     The electrochemical cell  20  can include a thermistor  52  in some embodiments. The thermistor  52  can be positioned to measure a temperature of the cavity  24 . The temperature measurements can be used in analyzing the fluid and the material within the fluid. The thermistor  52  can measure the before, during, and after the application of direct current (DC) voltage and during impedance measurement. 
     The electrochemical cell  20   a  may employ specialized electrodes, such as metal oxides or modified or unmodified doped diamond electrodes, to selectively oxidize and sense organic compounds in water streams, such as those of manufacturing processes. 
     The electrochemical cell  20  can be used to perform online measurements to determine organic compound speciation and TOC, if desirable. The online speciation can be performed in either a flow mode or stopped flow mode in the cavity  24 . 
     The cover plates  28  can be made from aluminum or stainless steel, for example, and may be threaded with holes to receive screws  32  for assembling the electrochemical cell  20 . The electrodes  22  may be connected through the electrical leads  34  to an external power supply that may be used for applying a voltage program to the electrodes  22  in the electrochemical cell  20 . 
     A sample UPW solution that may contain one or more organic impurities or analytes may be directed in a flowing stream, or diverted from a stream, in a flow direction  40  through an inlet  42  into the electrochemical cell  20  and through an outlet  44  that leads back to the fluid stream, to one or more additional electrochemical cells  20 , or to a waste stream. While in the electrochemical cell(s)  20 , the sample solution is exposed to the electrodes  22 . A voltage program can then be applied that causes only a specific molecule or class of molecules to adsorb to the electrode and then undergo an oxidation-reduction (redox) process. 
     An alternating current (AC) field superimposed on the voltage program may allow concurrent impedance detection during the adsorption and electrochemical process. Impedance, conductivity, and/or resistance can also be measured by separately applying the AC field, including applying the AC field before, after or during the voltage program. The conductivity, resistance and/or impedance-potential profiles obtained can be used as a “fingerprint” to differentiate organic species. Alternatively, a current program may be applied to the electrodes  22  for oxidation and/or adsorption purposes and the voltage is measured between the additional electrodes  52  in contact with the UPW. 
     In some embodiments, the voltage measurement electrodes  52  are made from a metal or alloy such as stainless steel stainless steel and/or titanium. An electrochemical cell  20  having four electrodes (two of each type, oxidation and measurement electrodes) may reduce possible in-situ impedance measurement errors caused by any undesirable bubble formation during the oxidation process. AC impedance can be measured before, after and during the oxidation of the sample by UV radiation. 
     A DC voltage program is applied to the two electrodes  22  for oxidizing any organic compounds within a fluid. Impedance is measured before, after and during the DC voltage program by applying a superimposed AC voltage. 
     In operation, a fluid to be tested is admitted into the cavity  24 . The fluid can be flowing or static, as previously discussed. A voltage program is applied to the electrodes  22 A and  22 B in order to oxidize the fluid and material within the fluid. Characteristics of the applied electrical voltage, and the resulting electrical current, may be tracked and logged. Further, an AC voltage may be applied in order to measure an impedance of the fluid and the AC voltage and/or AC current can be tracked and logged. The resulting electrical response information may be analyzed in order to detect organic materials in the fluid and in order to speciate the organic materials (i.e., determine the species of organics present). 
     In some embodiments, the electrochemical cell  20  and associated meter electronics may be configured to place an electrical oxidization program across electrodes positioned at least partially in the fluid and at least partially oxidizing the carbon materials in the fluid, quantify the carbon materials in the fluid using an electrical response of the fluid to the electrical oxidization program, and detect interfering materials in the fluid using the electrical response. 
     Electrochemical selectivity techniques that have been used to determine the nature of some organic contaminants in aqueous solutions have been investigated. Such electrochemical techniques require various concentrations of electrolytes to conduct the analysis. In particular, conventional electrochemical systems achieve selective oxidation by scanning or stepping a DC voltage across a predetermined voltage range in presence of electrolytes (typically 100 mill molar). Organic identification is achieved by measuring the current generated due to oxidation of the organic compounds. This oxidation-generated current is known as Faradaic current which can be detected against a small background charging current (due to charging of the electrodes) that is present in all electrochemical systems. The charging and background currents may be small due to the presence of electrolytes. 
     Because of the high resistance (18.2 MS2 cm) of UPW, a large background charging current would be present in UPW systems. Therefore, obtaining a meaningful Faradaic current that is separated from the large background current during the electrochemical oxidation of parts-per-billion (ppb) levels of organic compounds in UPW samples would be extremely difficult These electrochemical techniques cannot work under low electrolyte or no electrolyte conditions. As a result, there is no cost effective technique for on-line electrochemical TOC speciation, such as detecting ppb organic analytes in ultrapure de-ionized water samples. 
     An organic impurity analyzer or TOC analyzer with speciation capabilities therefore would provide significant advantages over existing TOC analyzers, especially for on-line analyses. 
     Some embodiments for effecting electrochemical speciation of ppb-level organic compounds in UPW samples (especially samples with low or no electrolyte content) may include, but are not limited to, one or more of the following techniques: using metal or metal oxide electrodes, doped-metal oxide electrodes, doped-mixed metal oxide electrodes, or doped-diamond electrodes, using any of the disclosed embodiments to selectively adsorb, pre-concentrate and oxidize the organic compounds; implanting, doping or electrodepositing metals or metal oxides on inert substrates like titanium dioxide or doped-diamond substrate for selective adsorption and/or oxidation of organic molecules; performing organic or TOC speciation based on the rate and/or energy of organic oxidation; using specialized geometries of the sensing and/or oxidizing electrodes to provide a well-defined relationship between the electrodes to facilitate analytical electrochemistry in high resistance media (the electrode geometries in conventional TOC applications are of little consequence); employing a compact design of an electrochemical cell to enable efficient online and real-time detection and quantification of organic compounds; providing DC and/or AC voltage programs to facilitate measurement of the interfacial, bulk, and/or diffusional impedance of the electrochemical cell to obtain online species specific information about the TOC in high resistance media; or measuring the TOC on modified or unmodified doped-diamond electrodes during and after speciation. 
     In some embodiments the electrode design, such as a close parallel arrangement of the electrodes, may limit the voltage drop caused by the high resistance media such as UPW, may efficiently expose the organic compounds to the electrodes, and may displace bubbles that might otherwise be formed at the electrode/solution interface. In some embodiments, microelectrodes or metal regions implanted on an inert substrate like doped-diamond substrate may enhance electrochemical detection. In some embodiments, selective adsorption and/or pre-concentration of organic molecules using modified doped-diamond electrodes may enhance detection. 
     In some embodiments, monitoring the variation of the electrochemical cell&#39;s impedance during oxidation/adsorption of the organic molecules may be an efficient detection method in a high resistance system like UPW. In some embodiments, employing in-situ impedance as a detection method may facilitate use of fewer sensors. Fewer inert metal oxide/metal electrodes can suffice for detecting various families/classes of organic molecules using impedance techniques. If conventional electrochemical techniques are used, then each family or each organic compound should need an individual sensor for detection purposes. 
     In some embodiments, stopped flow and/or flow techniques can be used to expose the sample solution to the electrodes. 
     In some embodiments, electrochemical speciation may include analysis without the addition of electrolytes or reagents. 
     In some embodiments, electrochemical speciation can be determined in the absence of a TOC measurement. 
       FIG. 2  shows a carbon quantifying cell  20  having replaceable and/or disposable thin film electrodes  22 A and  22 B according to an embodiment of the invention. The disposable thin film electrodes  22 A and  22 B can be used to measure in-situ impedance of the electrochemical cell  20  during, before and after a DC voltage program. The insulating material  30  has guide pins  31  in this embodiment. These guide pins are used to align the position of the electrodes with the inlet and outlet of the electrochemical cell. The insulator  30  is used to hold the electrodes  22 A and  22 B and the thermistor  52 . Electrodes  22 A and  22 B, and optionally thermistor  52 , can be produced on the insulator  30  by screen printing, laser ablation, electrode position, chemical vapor deposition, chemical bath deposition or other techniques. The electrodes  22 A and  22 B are designed to adsorb, oxidize and measure the organic molecules. Gasket  33  is made of inert material like PTFE and is used to seal the cover plates  28 A and  28 B to the supporting body  26  and complete the cavity  24 , where the sample is exposed to the electrodes  22 A and  22 B. The guide pins  31  maintain the position of the flexible substrate  30  and the gasket. The electrodes  22  may be connected through the electrical leads  34  to an external supply and monitor that may be used for applying a voltage program to the electrodes  22  and measure the current response in the electrochemical cell  20 . The thermistor  52  may be connected through the electrical leads  35  to an external meter that may be used to monitor the temperature of the contents of the cell. 
       FIG. 3  shows a carbon quantifying cell  20   c  having three electrodes according to an embodiment of the invention. The carbon quantifying cell  20   c  can be used for online speciation of organic compounds. The electrochemical cell  20   c  includes two working electrodes (anodes)  22  and a counter electrode (cathode)  62  housed within a quartz or glass cell  66  that functions like the body  26  to contain moving or stationary samples of UPW that may contain organic impurities. Other materials known to skilled practitioners may be used to form the cell  66 . It is preferable to use inert materials like quartz, titanium or diamond as the material which is in contact with the sample solution. The material which is not in contact with the sample can be produced with any convenient material. 
     In some embodiments, in addition to the inlet  42  and the outlet  44  for the UPW samples, the electrochemical cell  20   c  has an inlet  72  and an outlet  74  to support the flow of nitrogen or an inert gas through, or the containment of the gas within, the electrochemical cell  20   c  to prevent atmospheric contamination. As with the other embodiments of electrochemical cells, a DC voltage with a superimposed AC voltage can be applied. 
     In some embodiments, the electrodes  22  are arranged in a close and generally parallel configuration or planar configuration. In general, the electrodes  22  are spaced far enough apart to ensure electrical isolation and close enough together to minimize the voltage drop across the electrodes  22  because of the high resistance of UPW (e.g., 18.2 MΩ cm). In particular, the DC voltage applied to the electrodes for oxidizing and detecting the organic species may largely depend on distance between the electrodes in a high resistive media like UPW. The voltage drop across the electrode decreases with a decrease in the distance between the electrodes  22 . However, if the distance between the electrodes  22  is too small, then exposure of the organic compound impurities to the electrodes would be less efficient. Hence, an optimal distance between the electrodes  22  is desirable to minimize the voltage drop and maximize delivery of organic compounds to the electrodes  22 . 
     In some embodiments, the distance between the electrodes  22  is within a range of about 0.1 mm to about 1 cm. More preferable spacing distances are within a range of about 0.1 mm to about 2 mm. In some embodiments, the distance between the electrodes  22  is within a range of about 1 mm to about 2 mm. In some embodiments of  FIG. 1 , the distance between the electrodes  22  is 1-2 mm. In some embodiments of  FIG. 2  the distance between the electrodes  22  is fixed at 0.1 mm or 1 mm. In some embodiments of  FIG. 3 , the distance between the electrodes  22  is fixed at about 1 mm. 
     The preferred distance or range of distances between electrodes may also vary as a consequence of one or more of the dimensions, surface area, and composition of the electrodes  22  or the nature of the electrode coatings as well as may vary as a consequence of one or more of the amount of the ranges of applied voltage or current, the amount of expected organic impurities, the flow rate of the samples through the electrochemical cell  20 , the geometry of the electrochemical cell  20 , and the particular application of the electrochemical cell  20 . 
     In general, larger surface areas and smaller distances for the electrodes  22  enhance the signals obtained during interfacial measurements and enable measurements of very low concentrations of organic molecules in UPW. The dimensions of the working electrodes  22  may be the same size as each other and the same size as the non working or counter electrode  62 , or one or more of the electrodes  22  or  62  may be different sizes. The preferred dimensions or range of dimensions of electrodes may also vary as a consequence of one or more of the spacing, surface area, and composition of the electrodes  22  or the nature of the electrode coatings as well as may vary as consequence of one or more of the amount of the ranges of applied voltage or current, the amount of expected organic impurities, the flow rate of the samples through the electrochemical cell  20 , the geometry of the electrochemical cell  20 , and the particular application of the electrochemical cell  20 . 
     In some exemplary embodiments, one or more electrodes  22  have an active or coated surface area within a range of about 0.0001 cm 2  to about 100 cm 2 . In some exemplary embodiments, one or more electrodes  22  have an active or coated surface area within a range of about 0.1 cm 2  to about 100 cm 2 . In some exemplary embodiments, one or more electrodes  22  have an active or coated surface area within a range of about 0.0001 cm 2  to about 0.1 cm 2 . In some exemplary embodiments, one or more electrodes  22  have an active or coated surface area within a range of about 0.01 cm 2  to about 10 cm 2 . 
     In some embodiments, the electrodes  22  have dimensions of about 1 cm diameter and 0.2 mm thick to about 3 cm diameter 0.2 cm thick are coated on one or both sides, and have an electrode surface area exposed to the solution of about 1.5 cm 2  to about 10 cm 2 . In some embodiments of  FIGS. 1-3 , the electrodes  22  have dimensions of 1 cm diameter by 0.2 cm thick and are coated on one side and have an electrode surface area exposed to the solution of about 1.5 cm 2 . In some embodiments of  FIGS. 1-3 , the electrodes  22  have dimensions of 1 cm diameter and 0.2 cm thick and are coated on both sides such that an embodiment of  FIG. 1  would have an electrode surface area exposed to the solution of about 6 cm 2  and an embodiment of  FIG. 3  would have an electrode surface area exposed to the solution of about 12 cm 2 . In some embodiments of  FIG. 3 , the working electrode  22  has an electrode surface area exposed to the solution of about 10 cm 2  and the counter electrode  62  has an electrode surface area exposed to the solution of about 5 cm 2 . 
     In some embodiments, each electrode  22  is coated on only a single side (monopolar), the surface area of each electrode  22  is 0.84 cm 2 , and the distance between the electrodes is 1 to 2 mm. In some embodiments, each electrode  22  and  52  are coated on both sides (bipolar), the surface area of each electrode  22  is 10 cm 2 , the surface area of the counter electrode  52  is 5 cm 2 , the distance between the electrodes  22  and  52  is 1 to 2 mm, and the volume of the electrochemical cell  20   c  is 2 mL. 
     Skilled persons will appreciate that numerous combinations of electrode spacing, dimensions, surface area, composition, and coating and electrochemical cell  20 , geometry are possible and are contemplated. The examples given herein are given merely for illustration and the carbon quantifying cell  20  is not limited by any of the included examples. Additionally or alternatively, a microelectrode array (not shown) containing hundreds or even thousands of micron-sized electrodes may be employed. Such a microelectrode array can be employed in an electrochemical cell  20  such as in a UPW supply stream, or such a microelectrode array can be dipped in a sample solution containing an organic compound for oxidation and detection. In some embodiments, the microelectrode arrays may be employed in the form of interdigitated arrays (IDAs) or interdigitated ultramicroelectrode arrays (IDUAs) with uniform distances between the electrodes in a generally coplanar fashion. In an exemplary embodiment, a microelectrode array may include  106  electrodes that are about 5 μm in diameter and that are spaced about 150 μm away from each other. 
     Each array of electrodes  22  may contain only identical electrodes  22  or a one or more different electrodes  22  having one or more different properties of electrode spacing, dimensions, surface area, composition, or coating. 
     Additionally or alternatively, electrochemical cells  20  or arrays of electrodes  22  may be positioned in series in an UPW flow stream. Such electrochemical cells  20  or arrays of electrodes  22  may have the same or different configurations or properties. For example, each electrode  22  could be modified with different active materials, such as conducting polymer or active metals like Cu, Pt, as later described. 
     Another exemplary alternative embodiment employs concentric mesh electrodes  22  that provide a high surface area and a tendency to minimize the trapping of bubbles. Such mesh electrodes  22  may employ porous titanium dioxide or diamond substrates such that the UPW fluid can flow through the electrodes  22  during the selective oxidation/adsorption process. 
     Another exemplary alternative embodiment of an electrochemical cell or system  20  employs a concentric hollow tube with a solid cylinder at the center of it to maximize the surface area of the electrodes  22 . The UPW fluid that may contain organic analyte impurities flows between the cylinder and the hollow tube. The inner part of the hollow tube may be coated with a TiO 2  or boron-doped diamond (BDD) material, which is described later. In some embodiments, an exemplary distance between such concentric electrodes  22  can be within the range from 0.1 mm to 1 cm. Skilled persons will once again recognize that numerous alternative variations are possible, especially in view of the number of discussed variables. 
     In some exemplary embodiments, the UPW fluid containing the analyte is trapped or flowed between the electrodes  22  at a rate in the range of 0.16 mL/min to 16 mL/min. Some exemplary electrochemical cells  20  have a cell volume of about 2 mL. In embodiments where flowing conditions are used, the flow rates required to oxidize the most difficult organic is identified. This is used as a standard to measure the impedance before, after and during the oxidation. The flow rate may depend on a number of factors, such as one or more of the particular application, electrochemical cell geometry, or electrode parameters. 
     In some embodiments, the electrodes  22 ,  52 , and  62  (collectively electrodes  22 ) may be made from TiO 2  or BDD material. The BDD electrodes  22  contain a thin polycrystalline diamond layer on a conductive substrate material. BDD coatings are a relatively new material for the electrodes  22  and exhibit exceptional chemical stability as well as high wear resistance. The BDD electrodes  22  also exhibit high oxygen and hydrogen over-potentials. The electrochemical window in which meaningful processes can be observed is governed by the reduction and oxidation of the solvent. In this invention, primarily water is the solvent in which organic speciation is performed. The reduction of water produces hydrogen, and oxidation of water produces oxygen. The energy required to oxidize or reduce water strongly depends on the electrode substrate. On inert BDD electrodes, the energy required to produce oxygen and hydrogen is relatively higher than most of the electrodes in aqueous solvents. This results in very low background noise, which is another attractive feature of BDD electrodes. 
     With reference to  FIG. 4 , the BDD electrodes exhibit the greatest electrochemical stability. This figure shows the electrochemical window of various electrode materials. BDD clearly has the largest electrochemical window. The hydrogen and oxygen evolution occurs outside the horizontal bars indicating the electrode material. 
       FIG. 4  is a graph showing the electrochemical stability of BDD versus other representative conventional electrodes. Electrodes that are comparable to BDD include doped and undoped iridium oxide (IrO 2 ) electrodes, tin oxide (SAnO 2 ) electrodes, antimony oxide (Sb 2 O 5 ) electrodes, lead dioxide (PbO 2 ) electrodes, niobium or tantalum doped titanium dioxide (Nb/TiO 2  or Ta/TiO 2 ) electrodes, and dimensionally stable anodes (DSA), typically stable metal alloys and TiO 2 . Any of these electrode materials may be suitable for use as electrodes  22  in many of the embodiments and applications discussed herein. 
     The BDD electrodes  22  evoke particularly low background noise, a property which is especially useful for obtaining meaningful electrochemical signals arising from the oxidation or adsorption of the organic compounds in UPW. The BDD electrodes can be selectively modified to enhance selectivity for particular organic groups or compounds, as later discussed. 
     An embodiment of an exemplary electrode  22  may include a base material of niobium or any other suitable metal or alloy. An exemplary thickness of the base material is about 2 mm, but the thickness may be changed to suit the variables previously mentioned and/or manufacturing considerations. An exemplary thickness of the diamond coating is within a range of about 1 to 20 An exemplary standard thickness is about 5 μm with homogeneity of ±10%. An exemplary boron doping level is within a range of about 100 to 8000 ppm. In some exemplary embodiments, the boron doping level is about 1019-1021 boron atoms per cm 3 . 
     An exemplary resistivity of an electrode  22  may be within the range of about 10 to 100 mΩ cm, with current density limitations up to about 500 mA cm − . The BDD may be coated on one or all the sides of the niobium substrate (bipolar BDD electrodes). An exemplary distance between the electrodes  22  tailored to these parameters is about 1 to 2 mm. 
     Modifying BDD can impart selectivity to produce functionalized BDD electrodes  22 . Such functionalized BDD electrodes  22  can be prepared by several methods. Implanting, or electrochemical deposition of BDD with active materials in the form of metals, such as copper (Cu), nickel (Ni), or platinum (Pt), palladium (Pd), silver (Ag), ruthenium (Ru), zinc (Zn), or metal oxides, such as cupric oxide (CuO) or iridium oxide (IrO 2 ), can provide means for selective detection of organic molecules. The implanted active material acts as a microelectrode on BDD. Due to the difference in diffusion processes between the microelectrode(s) and “macro” electrode  22  selective detection is possible. 
     For example, Ag modified BDD electrodes  22  are selective towards amines; IrO 2  modified BDD are selective towards alcohols; Zn modified BDD are selective towards trihalomethanes, and ionic molecules like organic acids can be identified by measuring the change in the bulk conductivity without any modifications to the BDD. Bulk conductivity can be directly obtained from the impedance measurements as later discussed. 
     BDD can also be modified with functionalized polymers, which can be tuned to impart selectivity towards specific organics. Oxidation/reduction of the BDD substrate in the presence of desired functional groups can introduce the functional groups directly on to the BDD substrate. These functional groups can selectively react with organic compounds. The selection of the functional groups can be tailored to reactions with known or anticipated organic contaminants. 
     Organic compounds commonly found in UPW include urea, carboxylic acids, such as formic acid or acetic acid; resin amines or their derivatives, such as trimethyl amine or trimethyl ammonium hydroxide, alcohols, such as isopropyl alcohol or methanol, and trihalomethanes, such as chloroform. Table I presents a list organic compounds and classes of compounds and electrode modifications for selectively detecting them. 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Electrode Modifications for Selective 
               
               
                 Detection of Organic Compounds 
               
            
           
           
               
               
            
               
                 Organic 
                   
               
               
                 compounds 
                 Metals/metal oxides/conductive polymers 
               
               
                   
               
               
                 Urea 
                 Titanium/platinum-iridium (70:30::Pt:Ir) , titanium/(tantalum  
               
               
                   
                 oxide or iridium oxide)70:30, platinum, enzyme modified  
               
               
                   
                 poly-thiophene 
               
               
                 Carboxylic  
                 Tin/tungsten oxide, titanium/tin oxide, lead oxide, ruthenium  
               
               
                 acids 
                 oxide, polypyrrole, titanium suboxide (Ebonex) 
               
               
                 Amines 
                 Silver-lead oxide, silver-lead alloys 
               
               
                 Alcohols 
                 Copper (II) oxide, cobalt (III) oxide, cobalt (IV) oxide/  
               
               
                   
                 hydroxide, iridium oxide, silver oxide, platinum, poly-N 
               
               
                   
                 (2-pyridyl pyrrole) 
               
               
                 Trihalo- 
                 Zinc, platinum, gold, silver, zinc (II) porphyrin polyaniline,  
               
               
                 methanes 
                 poly (o-ethoxyaniline, poly(3,4-diphenylpyrrole) 
               
               
                   
               
            
           
         
       
     
     In some embodiments, a series or array of electrodes  22  or microelectrodes, in which each BDD electrode is modified with different active materials (different conductive polymers, different active metals, and/or different active metal oxides), can be used to cover a wide range of organic compounds that may be present as impurities. Similarly, the same or different electrodes  22  may be subjected to the same or different DC and/or AC voltage programs including the same or different voltages, waveforms, frequencies, increments, and/or timing schemes. 
     All these approaches can be tailored to selectively detect and/or quantify specific organic compounds at ppb levels in a mixture of organic compounds in UPW by measurement of interfacial and bulk properties of the electrochemical cells  20  with or without application of DC voltages. 
     DC voltage can be applied to the electrodes to oxidize organic molecules or to enhance the interaction between organic molecules and the electrodes  22 . Application of specific voltages oxidizes or facilitates the adsorption of specific organics. Hence by varying DC voltages, specific organic compounds or specific classes of organic compounds can be oxidized or adsorbed selectively. The electrode geometries discussed permit on-line analysis in the absence of reagents or electrolytes and permit very small signals arising from oxidation and/or adsorption of ppb levels of organic molecules. 
     In addition, functionalized electrodes  22  can spontaneously adsorb specific organic compounds without the application of DC voltage. This adsorption will cause a change in the interfacial properties. Measuring the interfacial properties of the electrochemical cell  20  will provide qualitative and quantitative information about specific organic molecules present in the electrochemical cell  20 . 
     In particular, impedance measurement techniques can be used to discriminate organic species in UPW. In some embodiments, a single impedance measurement can be used to obtain various interfacial and bulk parameters of an electrochemical system or cell  22 . Obtaining various parameters such as interfacial capacitance, charge transfer resistance (Rct), surface potential, solution resistance, phase angle, dielectric property, dissipation factor, and bulk capacitance with a single impedance scan and measurement can provide unique 2D and 3D profiles for specific organic compounds. The organic species can be both quantified and identified by such an approach. 
     Double layer/series/interfacial capacitance, an interfacial parameter, arising from the electrostatic, adsorption or charge stored at the heterogeneous interface between solid electrode and liquid sample solution, can be determined by measuring the impedance quantities. Heterogeneous charge transfer resistance is another interfacial parameter which arises from the resistance encountered by the charge which is transferring from the electrode (solid phase) to the solution (liquid phase). When a metal oxide semiconductor (TiO 2 ) is used a the electrodes,  22 , charge separation occurs and confines to the surface of the electrode. This causes a surface potential to develop. This potential can be calculated by determining the charge stored at the interface by impedance measurement. Solution resistance can be determined by applying an appropriate frequency to the electrodes, which eliminates other interfering electrical parameters and can be easily measured by impedance techniques. Phase angle between the applied AC voltage and the measured AC current will provide information of the capacitive components and the resistive components present in the electrochemical cell. The dissipation factor of the system is the ratio of the energy dissipated by a system due to resistive heating to the energy stored by the system by capacitive and inductive mechanisms. The dissipation factor reaches a maximum when the energy stored by the capacitive/inductive mechanism tends to be zero. At high frequencies (10 MHz to 1 GHz) a maxima is observed for the dissipation factor. This impedance quantity can be determined by applying high frequencies. The capacitance of the sample solution depends on the dielectric properties of the solution. The dielectric properties depend on the nature of the species. 
     In some embodiments, DC voltages (or DC voltage ranges) in a wide range of potential from about 0 to about 100 V can be used for samples containing a mixture of organic impurities. For some embodiments, various fixed DC voltages within the range of 0 to 10 V can be used. 
     Depending on flow rate, the DC voltage can be slowly continuously increased (or decreased) or stepped up (or down) in gradual increments or jumped to specific voltages or voltage ranges where known impurities can be identified. In some embodiments, the increment of DC voltage may be within the range of about 0.01 V to 1 V. In some embodiments, the increment of DC voltage may be about 0.05 V. The increment values may be influenced by the size of the DC voltage range and predetermined voltage differentiation points. The increment values need not be the same and any subsequent voltage increment may be smaller or larger in size than a previous voltage increment. 
     In some voltage stepping embodiments, the voltage may be maintained at each voltage level for a period within the range of about 10 seconds to about 10 minutes subject to flow rates and other considerations. Such considerations include, but are not limited to, the parameters of the superimposed AC current program including its waveform, range of frequencies, and duration of each frequency. 
     In some embodiments, the voltage at each step may be maintained for a period within a range of about 1 minute to about 5 minutes. The voltage at each step need not be maintained for the same period of time. For example, steps at voltages where distinctive data for common organic impurities can be obtained may be maintained for longer periods of time than for steps at voltages where data for rare or unknown organic impurities may be obtained. One or more libraries of electrochemical data for each type of organic impurity with each type of electrode  22  or modified electrode  22  and/or electrochemical cell  20  can be developed over time so that the voltage programs can be tailored to be as quick and efficient as possible. The voltage program can be adjusted by an operator or automatically adjusted when samples exhibit changes in the nature of the organic impurities. 
     In some embodiments, a fixed DC current may be applied from within an exemplary range of 0.001 mA to 10,000 mA. In some embodiments, the fixed DC may be within a range of 0.001 mA/s to 100 mA/s. In some embodiments, the DC may be applied in a stepped linear ramp between 0.001 mA/s to 100 mA/s. This type of profile can be used in a four electrode system, for example, where DC current can be applied between the first set of electrodes  22  and the voltage developed across the system can be measured by the second set of electrodes  52 . 
     In some embodiments, AC amplitudes or amplitude ranges in a wide range of potential from about 0 to about 100 V can be used, and various frequencies or frequency ranges within a range of 0.001 Hz to 1 GHz of an AC sine wave, with or without a fixed DC base voltage, can be used to establish and detect the impedance profiles. In some embodiments, AC amplitudes or amplitude ranges in a range of potential from about 0 to about 10 V can be used with various frequencies or frequency ranges within a range of 0.001 Hz to 1 GHz of an AC sine wave. In some embodiments, AC amplitudes or amplitude ranges in a range of potential from about 0 to about 10 V have been used with various frequencies or frequency ranges within a range of 10 Hz to 100 Hz of an AC sine wave. 
     The frequency of the AC waveform can be slowly continuously increased (or decreased) or stepped up (or down) in gradual increments or jumped to specific frequencies or frequency ranges where known impurities can be identified. In some embodiments, the increment of AC waveform frequency may be within the range of about 0.001 Hz to 1000 Hz. In some embodiments, the increment of AC waveform frequency may be about 10 Hz. The increment values may be influenced by the size of the AC waveform frequency range and predetermined frequency differentiation points. The increment values need not be the same and any subsequent frequency increment may be smaller or larger in size than a previous frequency increment. 
     Other AC waveforms could be employed such as square waveforms, triangle, saw tooth, or differential square wave ramp waveforms. Furthermore, more than one AC waveform may be tested at any given AC or DC voltage. 
     For some exemplary embodiments, an AC sine waveform of 0.005 V amplitude with fixed frequencies within a range of 10 Hz to 100 KHz has been superimposed on various fixed DC voltages in the range of 0 to 10 V to detect selective organic compounds. 
     In some experiments concerning exemplary embodiments, the DC voltage was applied in increments of 0.05 V from an initial potential of 0 V to a final potential of 10 V. A sequential AC sine waveform of 0.005 V amplitude was superimposed on the base DC potential. The frequency was fixed at 10 Hz. The current and potential were sampled and analyzed to obtain real and imaginary impedance. The experiments show that the resultant impedance-potential profiles are unique for different organic acids in ultra pure water in cell  20   a  and  20   c.    
     In one set of experiments, a fixed base DC voltage was applied typically for 2 minutes while the AC voltage of amplitude 5 mV at a fixed frequency of 10 Hz was superimposed on the base DC voltage. 
     In another set of experiments, the DC voltage was scanned from 0 to 10 V in increments of 0.05 V. The AC voltage of amplitude 5 mV at 10 Hz was superimposed on the base DC voltage. In this set of experiments, after each increment of the DC voltage, the CH instrument 760 C potentiostat was operated to wait for a stable response and measure the AC current. This measurement was used to calculate the impedance parameters. The duration for one scan between DC voltages 0 and 10 was 3 minutes at a frequency of 10 Hz. 
     The applied frequency affected the duration of the experiments and affected the duration of the steps and scam in general. Typically the duration of the experiments was shorter for higher frequencies and was longer for lower frequencies. At lower frequencies the instrument takes a longer time to produce a stable measurement. 
     Ion chromatographs were obtained to confirm selective oxidation at specific electrical potentials. In-situ impedance measurements were performed during the application of a DC voltage program in a UPW solution containing formic and acetic acids to confirm the efficacy of the techniques discussed herein. 
       FIG. 5  is a conductance versus time graph illustrating the selective electro-oxidation of formic acid and acetic acid by unmodified BDD electrodes  22  at various potentials in the presence of each other in a solution made using UPW. With reference to  FIG. 5 , formic acid and acetic acid were present at levels of 78 ppb each, and the electro-oxidation time was 1 minute. 
     At lower potentials, such as 50 to 70 V, the graph shows significant reduction of the formate concentration with minimal change to the acetate concentration. Above 100 V, the graph shows complete elimination of formic acid from the solution. As the potential is increased, the oxidation of formic acid is enhanced. If the electrical potential or oxidation time is increased further, acetate can also be efficiently electro-catalyzed. The kinetic and thermodynamic selection is may provide the basis of the electrochemical selection. 
       FIG. 6  is a graph showing impedance versus potential profiles for UPW, 1 ppb formic acid, and 1 ppb acetic acid. Formic acid is shown in (black) circles, acetic acid is shown in (pink) triangles, and UPW is shown in (red) diamonds as a reference. The onset of a decrease in impedance for a solution containing formic acid started at  ˜ 6.8 V and peaked at  ˜ 7.8 V with a half wave potential at  ˜ 7.3 V. For a solution containing acetic acid, the onset for the decrease in impedance appeared at  ˜ 7.2 V and peaked at  ˜ 8.6 V with a half wave potential at  ˜ 8.0 V. (The impedance peak for the solution containing formic acid was at  ˜ 7.8 V, and the impedance peak for the solution containing acetic acid was at  ˜ 8.6 V.)  FIG. 6  demonstrates the impedance versus potential profiles for C1 and C2 carboxylic acids are unique with speciation being possible between two similar molecules. 
     The subject matter disclosed in any sentence or paragraph herein can be combined with the subject matter of one or more of any other sentences or paragraphs herein as long as such combinations are not mutually exclusive or inoperable. For example, any of the types of electrochemical cells  20  disclosed may employ any combination of DC and AC voltage programs. Similarly, any of the types of electrochemical cells  20  disclosed may employ any type electrode  22 , and moreover, with any combination of DC and AC electrical programs. 
       FIG. 7  shows a carbon quantifying system according to the invention. The carbon quantifying system comprises a carbon quantifying electrochemical cell  20  and meter electronics  21  coupled to the cell  20 . The cell  20  can comprise any Of the herein discussed embodiments. The meter electronics  21  provides a means for supplying energy in a programmable manner for inducing an electrical oxidization and/or polarization and/or adsorption of the organic species at the electrodes in the cell  20 . The meter electronics  21  also provides a means to measure the resulting electrical signal arising from the electrochemical (oxidation, polarization and/or adsorption) phenomenon occurring in the cell  20 . The cell  20  receives a fluid and receives the electrical oxidization program and at least partially oxidizes the fluid. The meter electronics  21  receives an electrical response of the fluid to the electrical oxidization program. The meter electronics  21  is configured to place an electrical oxidization program across electrodes positioned at least partially in the fluid and at least partially oxidizing the carbon materials in the fluid, quantify the carbon materials in the fluid using an electrical response of the fluid to the electrical oxidization program, and detect interfering materials in the fluid using the electrical response. 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims. 
     The apparatus and method according to the invention can be employed according to any of the embodiments in order to provide several advantages, if desired. The apparatus and method advantageously detects carbon in a fluid. The apparatus and method quantifies carbon or carbon materials in a fluid. The apparatus and method quantifies carbon or carbon materials in a fluid regardless of interfering materials. The apparatus and method identifies any interfering materials in a fluid. The apparatus and method quantifies any interfering materials in a fluid. 
     The apparatus and method can select for a predetermined carbon material or materials. The apparatus and method is capable of being configured to select for predetermined carbon compounds, including organic carbon compounds. The apparatus and method advantageously can distinguish electrical signals generated from carbon materials from electrical signals generated from interfering materials. The apparatus and method advantageously can distinguish electrical signals generated from carbon materials from electrical signals generated from interfering materials by controlling electrical parameters and electrode characteristics. 
     The apparatus and method does not require complete oxidization of carbon in a fluid in order to detect and quantify the carbon. The apparatus and method may polarize carbon compounds in a fluid, wherein the polarization can contribute to a quantification process of the carbon. The apparatus and method may polarize organic molecules in a fluid, wherein the polarization can contribute to a quantification of the organic molecules. 
     The apparatus and method may include a direct current (DC) electrical oxidization that performs one or both of the oxidization of the carbon and polarization of carbon-including compounds, wherein non-oxidized carbon compounds may still be detected and/or measured. 
     The apparatus and method does not require a membrane that can become clogged, torn, or damaged or that requires calibration. 
     The apparatus and method enables the detection, quantifying, and/or tracing of sources of contamination of the fluid. 
     The apparatus and method may include two or more electrodes. The apparatus and method may include four electrodes. The apparatus and method may include electrodes for separately performing operations in the fluid. The apparatus and method may include multiple electrodes for separately performing operations in the fluid. The apparatus and method may include multiple electrodes for separately performing oxidization and polarization operations in the fluid. The apparatus and method may include multiple electrodes for separately performing oxidization and impedance measuring operations in the fluid. The apparatus and method may include multiple electrodes for separately performing oxidization, polarization, and impedance measuring operations in the fluid. The apparatus and method may include four electrodes for separately performing oxidization, polarization, and impedance measuring operations in the fluid. 
     Unlike in the prior art, complete oxidization of all carbon-including compounds is not necessary. Unlike in the prior art, interfering materials do not need to be eliminated from a fluid. Unlike in the prior art, interfering materials do not need to be separated out beforehand or later screened out of an oxidization and/or polarization result. Unlike in the prior art, interfering materials can also be identified in the fluid. Unlike in the prior art, interfering materials can also be quantified in the fluid.