Patent Description:
This specification relates to method for determining a concentration of a chemical species of interest.

Reduction and oxidation reaction is a commonly utilized method to control or measure the concentration of a chemical species of interest. It is widely employed in process control in paper/pulp industry, sanitation control such as swimming pool and drinking water safety, and waste water management. A noble metal sensor, such as platinum and gold is the most commonly used sensor for providing such a measurement. This measurement is commonly known as the oxidation reduction potential (ORP) measurement.

Although generally effective, prior art ORP measurement methods suffer from slow response speed, uncertainty of which of chemical reaction from several that may be occurring gives rise to the oxidation reduction potential, and the lack of ability to distinguish sensor fouling or memory effect from the measurement of the species of interest. For example, a known redox process centering at the intended control point may provide an ORP value of <NUM> mV. However, if the sensor is fouled, then it is hard to tell the difference between a reading of <NUM> mV as the actual response or the sensor is fouled such that the reading is compromised. Since there is no other independent measurement to differentiate a fouled sensor versus a good sensor, the user can only assume the reading is a true indication of the reaction rate. Another example of the short comings of prior art methods, these methods can have slow response times when measuring the ORP of species in which the reaction measured involves a two-step electron transfer process. In prior art methods, there is no convenient way to tell if a slowly increasing response is caused by the sensor or by the complexity of the two electrons transfer process. Previously, there was no known method for those skilled in the art to overcome these challenges.

<CIT> discloses methods of determining concentrations and/or amounts of redox-active elements at each valence state in an electrolyte solution of a redox flow battery. Once determined, the concentrations and/or amounts of the redox-active elements at each valence state can be used to determine side-reactions, make chemical adjustments, periodically monitor battery capacity, adjust performance, or to otherwise determine a baseline concentration of the redox-active ions for any purpose.

<CIT> discloses a method for the determination of chlorine dioxide, chlorite and/or acid in aqueous solutions.

<CIT> discloses methods, devices and systems for rapidly measuring analytes within a biological sample.

<CIT> discloses method for measuring the antioxidant capacity and/or the amount of a specific antioxidant in a sample.

<CIT> discloses a method and apparatus for conditioning a sensor to measure an oxidation reduction potential of an aqueous solution such that the time to obtain a reliable oxidation reduction potential measurement is substantially reduced. Such conditioning is often necessary when the sensor is moved from potentiometric equilibrium (e.g., the sensor is cleaned, the sensor is exposed to air, and the like). The method may comprise generating a current through a measurement electrode and a reference electrode of the sensor for a duration of time. A reliable oxidation reduction potential measurement can be made as the voltage across the measurement electrode and the reference electrode stabilizes after the duration of time. Depending on the aqueous solution, the stabilized value can be constant or variable.

<CIT> method for the in-situ detection of a change in the quality of water of a site to be tested, that comprises using: a sensor including a work electrode made of boron-doped diamond and a reference electrode; an electronic device including a potentiostat for applying a predetermined potential to the work electrode and for measuring the resulting current on said electrode, and an electronic circuit for controlling the steps of said method. The detection method comprises the following steps: - obtaining and storing at least one current-potential reference curve of the water of the site to be tested; continuously scanning in a cyclical manner the potential of the work electrode relative to the reference electrode, between the water oxidation and reduction potential, in order to cover the oxidation-reduction potentials of a plurality of chemical species, thus providing at least one current-potential curve representative of the water quality; carrying out a qualitative comparison of the current-potential curve with the reference curve by subtraction of the reference curve from the current-potential curve thus obtained; analysing the optional differences resulting from the comparison relative to predetermined boundary values; and optionally initiating an alarm response.

The invention is set forth in the independent claim. Embodiments result from the dependent claims and the below description.

The present invention provides a method in which a concentration of a chemical species of interest is obtained. The method comprises measuring a property of a reagent to obtain a baseline measurement. The method continues with adding the reagent to the solution under test, then measuring the property of the solution under test post reaction with the first reagent to obtain a post reaction measurement, and then determining the concentration of the chemical species of interest based on the baseline measurement and the first post reaction measurement. Typically, this is done by calculating a difference of the baseline measurement and the post reaction measurement, then using the difference and a pre-determined conversion table to determine the concentration of the chemical species of interest.

A baseline measurement process effectively calibrates the sensor of the test instrument every time by using the reagent before reacting with the species of interest. This provides an unambiguous performance verification of the sensor. Furthermore, any offset in the sensor response is factored in every measurement of the species of interest.

According to the invention, a method for measuring a concentration of a chemical species of interest in a solution under test in accordance with claim <NUM> is provided. The method comprises the steps of:.

According to a preferred embodiment, determining the concentration of the chemical species of interest utilizes a set of data set, in particular a set of pre-determined data set.

According to a preferred embodiment, determining the concentration of the chemical species of interest utilizes baseline measurements, in particular pre-determined baseline measurements.

According to a preferred embodiment, determining the concentration of the chemical species of interest further comprises.

According to a preferred embodiment, the method further comprises:.

According to a preferred embodiment, determining the concentration of the chemical species of interest further comprises:.

The property measured may be an oxidation reduction potential (ORP), but could also be temperature, pH, conductivity, viscosity, turbidity, gas solubility, or color. The reagent may be based on a simple, single electron, redox couple, such as Fe<NUM>+ and Fe<NUM>+, but may be other reducing or oxidizing reagents.

Using a reagent based on a single electron redox couple provides a rapid response in an ORP measurement compared to a more complex redox process and the response time of the measurement is improved significantly. Furthermore, the instability of the chemical reaction is also being factored out as the simple redox couple will now be the dominant ORP indicator.

For example, the ferrous (Fe<NUM>+) and ferric (Fe<NUM>+) ions is a single electron redox couple with a readily reversible reaction. A reagent based on such a single electron redox couple may be used to measure the concentration of a more complex oxidizing reagent such as hypochlorous acid using an ORP measurement. Due to the single electron reversible conversion between Fe<NUM>+ and Fe<NUM>+, the ORP of the combined reagent and solution under test will reflect closer to the value predicted by Nernst equation, making the measurement more repeatable and reliable.

The surface of the noble metal in an ORP sensor, such as Pt and Au, can be poisoned when exposing to high ORP conditions. For example, with the chemistry system of OCl- and HOCl, at neutral pH, the oxidizing disinfectant can easily boost the ORP to above 700mV even at low concentration, making the electrode "poisoned," leading to sluggish or even false readings. This poisoning can remain on the noble metal electrode, causing a "memory effect" when measuring subsequent species, leading to false measurements. When using the ferrous and ferric redox reagent, the ORP will be brought down to much lower values. This mitigates the "poisoning" and the "memory effect. " The redox reagent concentration can also be adjusted to measure the oxidizing disinfectant in different ranges.

The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the inventive subject matter and, together with the detailed description, explain the principles and implementations thereof. Like reference numbers and characters are used to designate identical, corresponding, or similar components in different figures. The figures associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy.

<FIG> is a flow chart of a representative embodiment of a method for measuring a concentration of a chemical species of interest in a solution under test.

In describing the one or more representative embodiments of the inventive subject matter, use of directional terms such as "upper," "lower," "above," "below", "in front of," "behind," etc., unless otherwise stated, are intended to describe the positions and/or orientations of various components relative to one another as shown in the various Figures and are not intended to impose limitations on any position and/or orientation of any component relative to any reference point external to the Figures.

In the interest of clarity, not all the routine features of representative embodiments of the inventive subject matter described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve specific goals, such as compliance with application and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Those skilled in the art will recognize that numerous modifications and changes may be made to the representative embodiment(s) without departing from the scope of the claims. It will, of course, be understood that modifications of the representative embodiments will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the representative embodiments is essential. In addition to the embodiments described, other embodiments of the inventive subject matter are possible, their specific designs depending upon the particular application. As such, the scope of the inventive subject matter should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof.

<FIG> shows a flow chart of a representative embodiment of a method <NUM> for measuring a concentration of a chemical species of interest in a solution under test. The solution under test is an aqueous solution of an oxidizer, such as chlorine. Water from a swimming pool or domestic water supply would be typical sources.

The method <NUM> uses a test instrument that can measure oxidation reduction potential (ORP), temperature, and pH. In other embodiments, the test instrument measures conductivity and/or some other property. The instrument is configured with a sensor well to hold the solution under test. The measurements and the overall method are controlled by an embedded microcontroller, with some user input.

The representative embodiment method <NUM> uses a reagent based on a redox couple. The reagent will reduce any oxidizer in the sample solution. In the representative embodiment, the reagent is based on a redox couple of Fe<NUM>+ and Fe<NUM>+.

The first step of the representative embodiment method <NUM> is a baseline measurement step <NUM>. The baseline measurement step <NUM> comprises measuring a property of the reagent to obtain a baseline measurement. This baseline measurement step <NUM> begins with the sub-steps of rinsing the sensor well with the reagent, then filling the sensor well with the reagent. The baseline measurement step then continues with the sub-steps of measuring the oxidation reduction potential (ORP) of the reagent (typically in millivolt (mV)), then recording this ORP measurement as a baseline measurement. The baseline measurement step <NUM> then ends with emptying the sensor well.

The second step is a sample pretreatment step <NUM>. The sample pretreatment step <NUM> comprises adding a first reagent to the solution under test. This sample pretreatment step <NUM> begins with the sub-step of measuring out a pretreatment amount of the sample solution, sufficient to fill the senor well (about <NUM>). The sample pretreatment step <NUM> then continues with the sub-step of adding an amount of a selection agent, sufficient to make the pretreatment amount of the sample solution have a pH in the range of <NUM> - <NUM>, resulting in a pretreated sample solution. In the representative embodiment, the selection agent is <NUM>. 09N Sulfuric Acid, but other reagents and concentrations may be used. This step removes interference species, such as forms of bicarbonate species (NaHCO<NUM>, HCO<NUM>--).

The third step is a sample measurement step <NUM>. The sample measurement step <NUM> comprises measuring the property of the solution under test post reaction with the reagent to obtain a post reaction measurement. The sample measurement step <NUM> begins with the sub-step of adding a quantity of the reagent to the pretreated sample solution in a ratio predetermined to be sufficient for accelerating the measurement process. In the representative embodiment, a ratio of <NUM> to <NUM> (e.g. <NUM> to <NUM>) is used, but in other embodiments, other ratios may be used. The sample measurement step <NUM> then continues with the sub-steps of mixing the pretreated sample solution and reagent for sufficient time to produce a mixture solution, then allowing the mixture solution sufficient time to stabilize. In the representative embodiment, the pretreated sample solution and reagent are mixed for <NUM> minute, and the mixture solution is allowed to stabilize for <NUM> minute, but other times may be used in other embodiments of the method for other species of interest and reagents. The sample measurement step <NUM> then continues with the sub-steps of rinsing the sensor well with the mixture solution (typically filling and emptying three times), filling the sensor well with the mixture solution, then measuring the ORP of mixture solution (typically in mV), then recording the measurement as the post reaction measurement.

The fourth step is a conversion step <NUM>. The conversion step <NUM> comprises determining the concentration of the chemical species of interest based on the baseline measurement and the post reaction measurement. The conversion step <NUM> uses a conversion table with two sets of related values. The table is generated in advance, typically in a laboratory, cross-checking the values with higher sensitivity equipment. The first set of values are property measurement values (ORP values in the first embodiment, typically in mV) and the second set of values is concentration of the species of interest (typically in parts per million (ppm)). Each of the property measurement values is associated with one of the concentration values. The conversion step <NUM> begins with calculating a delta-measurement value based on a difference between the baseline measurement and the post reaction measurement. The conversion step <NUM> then continues with obtaining concentration of the chemical species of interest in the solution under test by using the delta-measurement value to obtain an associated concentration value from the conversion table, which is designated as the (uncompensated) concentration of the chemical species of interest.

The fifth step is a temperature compensation step <NUM>. The temperature conversion step <NUM> begins with measuring the temperature of the mixture solution. This is followed by determining the (compensated) concentration of the chemical species of interest based on the (uncompensated) concentration of the chemical species of interest (determined in the conversion step) and the temperature. The compensated concentration is the value corrected to standard temperature, typically <NUM>. In the first exemplary method, a temperature compensation formula is used, but in other embodiments, a table may be used. The temperature conversion step <NUM> continues with presenting the compensated concentration of the chemical species of interest, typically by displaying it on an electronic display. The temperature conversion step <NUM> ends with accepting a final compensated concentration of the chemical species of interest after <NUM>-<NUM> seconds or when the value of the compensated concentration stabilizes.

The representative embodiment of a method described above may be used for measuring a rate of reaction of a chemical species of interest in a solution under test, which is outside the scope of the present set of claims. The solution under test may be an aqueous solution of an oxidizer, such as chlorine.

This alternative method uses a test instrument that can measure oxidation reduction potential (ORP), temperature, and pH. In other embodiments, , the test instrument measures conductivity and/or some other property. The instrument is configured with a sensor well to hold the solution under test. The measurements and the overall method are controlled by an embedded microcontroller, with some user input.

The alternative method uses a reagent based on a redox couple. The reagent will reduce any oxidizer in the sample solution. In the representative embodiment, the reagent is based on a redox couple of Fe<NUM>+ and Fe<NUM>+.

The first step of the alternative method is a baseline measurement step The baseline measurement step comprises measuring a property of the reagent to obtain a baseline measurement. This baseline measurement step begins with the sub-steps of rinsing the sensor well with the reagent, then filling the sensor well with the reagent. The baseline measurement step then continues with the sub-steps of measuring the property of the reagent, then recording this measurement as a baseline measurement. The baseline measurement step then ends with emptying the sensor well.

The second step is a sample pretreatment step. The sample pretreatment step comprises adding a first reagent to the solution under test. This sample pretreatment step begins with the sub-step of measuring out a pretreatment amount of the sample solution, sufficient to fill the senor well (about <NUM>). The sample pretreatment step then continues with the sub-step of adding an amount of a selection agent, sufficient to make the pretreatment amount of the sample solution have a pH in the range of <NUM> - <NUM>, resulting in a pretreated sample solution. In the alternative embodiment method, the selection agent is <NUM>. 09N Sulfuric Acid, but other reagents and concentrations may be used. This step removes interference species, such as forms of bicarbonate species (NaHCO<NUM>, HCO<NUM>--).

The third step is a sample measurement step. The sample measurement step comprises measuring the property of the solution under test post reaction with the reagent to obtain a post reaction measurement. The sample measurement step begins with the sub-step of adding a quantity of the reagent to the pretreated sample solution in a ratio predetermined to be sufficient for accelerating the measurement process. In the alternative embodiment method, a ratio of <NUM> to <NUM> (e.g. <NUM> to <NUM>) is used, but in other embodiments, other ratios may be used. The sample measurement step then continues with the sub-steps of mixing the pretreated sample solution and reagent for sufficient time to produce a mixture solution, then allowing the mixture solution sufficient time to stabilize. In the representative embodiment, the pretreated sample solution and reagent are mixed for <NUM> minute, and the mixture solution is allowed to stabilize for <NUM> minute, but other times may be used in other embodiments of the method for other species of interest and reagents. The sample measurement step then continues with the sub-steps of rinsing the sensor well with the mixture solution (typically filling and emptying three times), filling the sensor well with the mixture solution, then measuring the property of mixture solution, then recording the measurement as the post reaction measurement.

The fourth step is a conversion step. The conversion step comprises determining the reaction rate of the chemical species of interest based on the baseline measurement and the post reaction measurement. The conversion step uses a conversion table with two sets of related values. The table is generated in advance, typically in a laboratory, cross-checking the values with higher sensitivity equipment. The first set of values are property measurement and the second set of values is reaction rate of the species of interest. Each of the property measurement values is associated with one of the reaction rate values. The conversion step begins with calculating a delta-measurement value based on a difference between the baseline measurement and the post reaction measurement. The conversion step then continues with obtaining concentration of the chemical species of interest in the solution under test by using the delta-measurement value to obtain an associated reaction rate value from the conversion table, which is designated as the (uncompensated) reaction rate of the chemical species of interest.

Claim 1:
A method for determining a concentration of a chemical species of interest in a solution under test with a reagent, comprising the steps of:
measuring a property of a first reagent to obtain a first baseline measurement, wherein the first reagent is based on a redox couple that utilizes a single electron transfer process, wherein the property is one of a group of pH, oxidation reduction potential, conductivity, viscosity, turbidity, gas solubility, and color;
adding the first reagent to a first portion of the solution under test to produce a first mixture solution;
measuring the property of the first reagent of the first mixture solution to define a first post-reaction measurement; and
determining the concentration of the chemical species of interest based on the first baseline measurement and the first post-reaction measurement.