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WO2009055093A1 - Procédés électrochimiques pour une détection sélective de chlore libre, de monochloramine et de dichloramine - Google Patents

Procédés électrochimiques pour une détection sélective de chlore libre, de monochloramine et de dichloramine Download PDF

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Publication number
WO2009055093A1
WO2009055093A1 PCT/US2008/063190 US2008063190W WO2009055093A1 WO 2009055093 A1 WO2009055093 A1 WO 2009055093A1 US 2008063190 W US2008063190 W US 2008063190W WO 2009055093 A1 WO2009055093 A1 WO 2009055093A1
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Prior art keywords
fluid sample
free chlorine
value
monochloramine
amount
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PCT/US2008/063190
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English (en)
Inventor
Eve Fabrizio
Glenn Martin
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Veolia WTS Analytical Instruments Inc
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GE Analytical Instruments Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
    • G01N27/4045—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for gases other than oxygen

Definitions

  • the present application relates to electrochemical methods for detecting free chlorine, monochloramine, and/or dichloramine in a fluid sample.
  • the present application also relates to electrochemical methods for quantifying the amount of free chlorine, monochloramine, and/or dichloramine in a fluid sample.
  • Chlorine It is common to disinfect drinking water using a combination of chlorine and ammonia. Chlorine, unfortunately, undergoes time-dependent, irreversible degradation into non-active forms (i.e., forms incapable of disinfecting water). Monitoring of actual free chlorine levels in water has therefore become very important in maintaining safe potable water. For human health and safety reasons, potable water must be closely monitored for chlorine content. The optimum chlorine disinfection level has a narrow operating window: too little chlorination presents the risk of microbial growth, and over-chlorination leads to the formation of chlorinated byproducts that are mutagenic.
  • Free chlorine in water is defined as the concentration of residual chlorine in water present as one or more of dissolved gas (Cl 2 ), hypochlorous acid (HOCl) 3 and hypochlorite ion (OCF).
  • dissolved gas Cl 2
  • hypochlorous acid HOCl
  • OCF hypochlorite ion
  • chloramines such as monochloramine (NH 2 Cl), dichloramine (NHCl 2 ) and trichloramine (NCl 3 ).
  • Trichloramine is very rarely formed. It is also important to monitor the amount of monochloramine and dichloramine present in the potable water. Dichloramine imparts an undesirable odor and taste to potable water, disappears faster from the water system because it is unstable, and can produce undesirable disinfection byproducts because it is a stronger oxidizer than monochloramine.
  • monochloramine is a more stable form, and has less effect on the odor and taste of the potable water.
  • the present disclosure describes electrochemical methods for detecting free chlorine, monochloramine, and/or dichloramine in a fluid sample.
  • the present disclosure also provides electrochemical methods for quantifying the amount of free chlorine, monochloramine, and/or dichloramine in the fluid sample.
  • methods are described for detecting free chlorine and monochloramine in a fluid sample.
  • the method comprises: (a) adjusting a pH of a fluid sample to a value less than about 4.0; (b) applying a potential difference to said fluid sample; (c) measuring a current generated in said fluid sample; and (d) correlating a magnitude of said current generated to an amount of free chlorine and monochloramine in said fluid sample.
  • the method comprises: (a) adding an amount of a nitrogen-containing solute to a fluid sample; (b) adjusting a pH of said fluid sample to a value less than about 4.0; (c) applying a potential difference to said fluid sample; (d) measuring a current generated in said fluid sample; and (e) correlating a magnitude of said current generated to an amount of free chlorine and monochloramine in said fluid sample.
  • the pH is adjusted to a value of about 3.3.
  • a potential difference having a magnitude of about 470 mV is applied to the fluid sample.
  • the method comprises: (a) adjusting a pH of a fluid sample to a value greater than about 4.0, such that an electrochemically detectable amount of hypochlorous acid is present in said fluid sample; (b) measuring the value of said adjusted pH of said fluid sample; and (c) correlating the value of said adjusted pH to an amount of free chlorine in said fluid sample.
  • the method comprises: (a) adjusting a pH of a fluid sample to a value of about 6.2; (b) applying a potential difference to said fluid sample; (c) measuring a current generated in said fluid sample; and (d) correlating a magnitude of said current generated to an amount of free chlorine in said fluid sample.
  • a potential difference having a magnitude of about 470 mV is applied to the fluid sample.
  • a method for detecting free chlorine and dichloramine in a fluid sample comprises: (a) adjusting a pH of a fluid sample to a value of about 4.0; (b) applying a potential difference to said fluid sample; (c) measuring a current generated in said fluid sample; and (d) correlating a magnitude of said current generated to an amount of free chlorine and dichloramine in said fluid sample.
  • a potential difference having a magnitude of about 400 mV is applied to the fluid sample.
  • the method comprises: (a) performing a first measurement on a first portion of a fluid sample, comprising: (i) adjusting a pH of said first portion to a value less than about 4.0; (ii) applying a potential difference to said first portion; and (iii) measuring a current generated in said first portion; (b) performing a second measurement on a second portion of said fluid sample, comprising: (i) adjusting a pH of said second portion to a value greater than about 4.0; (ii) applying a potential difference to said second portion; and (iii) measuring a current generated in said second portion; (c) taking a difference between said first measurement and said second measurement; and (d) correlating said difference to an amount of monochloramine present in said fluid sample.
  • a potential difference having a magnitude of about 470 mV is applied to the first portion and the second portion of the fluid sample.
  • the pH of the first portion is adjusted to a value of about 3.3.
  • the pH of the second portion is adjusted to a value of about 6.2.
  • a method for quantifying an amount of dichloramine in a fluid sample comprises: (a) performing a first measurement on a first portion of a fluid sample, comprising: (i) adjusting a pH of said first portion to a value of about 4.0; (ii) applying a potential difference to said first portion; and (iii) measuring a current generated in said first portion; (b) performing a second measurement on a second portion of said fluid sample, comprising: (i) adjusting a pH of said second portion to a value greater than about 4.0; (ii) applying a potential difference to said second portion; and (i ⁇ ) measuring a current generated in said second portion; (c) taking a difference between said first measurement and said second measurement; and (d) correlating said difference to an amount of dichloramine present in said fluid sample.
  • a potential difference having a magnitude of about 400 mV is applied to the first portion of the fluid sample.
  • a potential difference having a magnitude of about 470 mV is applied to the second portion of the fluid sample.
  • the pH of the second portion is adjusted to a value of about 6.2.
  • Figure 1 shows a flow diagram of an exemplary embodiment of the disclosed methods.
  • the fluid sample is potable water.
  • Other non-limiting examples of fluid samples are raw or waste water, or the fluids used for performing dialysis.
  • the forms of chloramines need to be closely monitored, as some forms can be harmful to the body.
  • Figure 1 shows a flow diagram of an exemplary embodiment of the disclosed methods.
  • the pH of the fluid sample can be adjusted to a value less than about 4.0 prior to measurements being performed on the fluid sample (step 102 of Fig. 1).
  • a pH of less than about 4.0 herein refers to a pH preferably between 2.5 and 3.99. More preferably, a pH of less than about 4.0 refers to a pH between 2.7 and 3.75.
  • the measurements being performed are vo ⁇ tammetric measurements. Alternatively, the measurements may be oxidation-reduction measurements using an open-circuit electrode potential.
  • an amount of a solute is added to the fluid sample to convert the free chlorine to monochloramine (step 100 of Fig. 1).
  • the solute is preferably a nitrogen-containing solute, such as ammonia, cyanuric acid, glycine, etc.
  • the nitrogen-containing solute is an amine.
  • the monochloramine in the fluid sample is converted into a form of chlorine that is electrochemically (i.e., amperometrically or voltammetrically) active at a certain applied voltage.
  • Dichloramine is not detected under these conditions, nor under neutral or alkaline pH conditions.
  • trichloramine i.e., nitrogen trichloride
  • a measurement of the current generated is then performed at an applied potential of about +47OmV relative to a reference electrode (steps 104 and 106 of Fig. 1).
  • an applied voltage of about +47OmV herein refers to an applied voltage between +450 and +500 mV.
  • the magnitude of the current generated in the fluid sample can be correlated to the amount of free chlorine and monochloramine in the fluid sample (step 108 of Fig. 1).
  • the reference electrode is a saturated KCl, Ag/AgCl reference electrode. However, other reference electrodes are known in the art.
  • the magnitude of the current generated in the fluid sample is found to be proportional to the amount of free chlorine and monochloramine present in the fluid sample.
  • the measurement serves to detect the presence of the free chlorine and monochloramine in the fluid sample.
  • one or more calibration curves or tables may be used to correlate the magnitude of current generated in the sample to the amount of the molecule of interest in the sample.
  • one or more fluid standards may be used to generate the calibration curves (or tables) of measured current versus the known amount of the molecule of interest in the standard (e.g., current vs. ppm calibration curves).
  • separate calibration curves are generated for the different molecules of interest described herein, i.e., free chlorine, monochloramine, or dichloramine.
  • a standards addition technique may be employed to correlate the magnitude of current generated in the sample to the amount of the molecule of interest in the sample.
  • the sample would be measured as described herein, then a volume of a standard containing a known content of the molecule of interest can be added to the sample, and the measurement can be repeated on the sample plus standard mixture. The amount of the molecule of interest in the sample could then be determined based on the two measurements.
  • the standards technique may be preferable for a sample that gives a suppressed response from that of the pure calibration standard.
  • the pH of the fluid sample may be adjusted by any method known in the art.
  • the pH can be adjusted using a concentrated buffer solution, for example, 2.2 mol/L of a phosphate buffer. Adjusting the pH of the fluid sample shifts the equilibrium of the reactions among the different forms of chlorine and chloramines. For example, a pH of 5.7 for results in a greater concentration of free chlorine, while a pH of 2.9 results in a greater concentration of monochloramine.
  • a given fluid sample may be divided into multiple portions, herein also referred to as aliquots, and the pH of each portion can be adjusted to a different value prior to performing the measurements described herein.
  • Each such portion (or aliquot) of the fluid sample can be of the same fluid volume; or each portion can be a different fluid volume.
  • one aliquot of a fluid sample may be adjusted to a pH of about 6.2 for the free chlorine measurements
  • a second aliquot may be adjusted to a pH of about 4.0 for the dichloramine plus free chlorine measurement
  • a third aliquot may be adjusted to a pH of about 3.3 for the monochloramine plus free chlorine measurement.
  • pH may vary by ⁇ 0.5.
  • the methods described herein may be performed on a single fluid sample, or on a single aliquot of a fluid sample.
  • a potential of less than about +47OmV relative to a reference electrode may be applied to the fluid sample to detect the presence of the free chlorine and monochloramine in the fluid sample.
  • the pH of the fluid sample can be adjusted to a different value less than about 4.0 in order to convert the monochloramine to an electro chemically active form before performing the measurements.
  • the pH of the fluid sample can be adjusted to a value less than about 4.0 prior to measurements being performed on the fluid sample.
  • the fluid sample is adjusted to a pH between 2.5 and 3.99. More preferably, the pH is adjusted to a pH between 2.7 and 3.75.
  • methods are also described for detecting and/or quantifying the free chlorine content of a fluid sample.
  • the pH of the fluid sample can be adjusted to a value such that sufficient hypo chlorous acid can be present to be detectable in the fluid sample by electrochemical measurements.
  • the pH of the fluid sample after the adjustment, i.e., the adjusted pH, is then measured.
  • the total amount of free chlorine present in the fluid sample can be quantified by calculating the fraction of free chlorine, hypochlorite, and hypochlorous acid present in the fluid sample at the time of measuring the pH.
  • a pH of greater than about 4.0 herein refers to a pH preferably between 4.01 and 7.0. More preferably, a pH of greater than about 4.0 refers to a pH between 5.5 and 6.95. In some examples, a pH of greater than about 4.0 refers to a pH of 6.2 ⁇ 0.5.
  • a measurement of the current generate can be then performed at an applied potential of about +47OmV relative to a reference electrode (steps 104 and 106 of Fig. 1). Preferably, the applied voltage is between +450 and +500 mV.
  • the magnitude of the current generated in the fluid sample is found to be proportional to the amount of free chlorine present in the fluid sample (step 108 of Fig. 1).
  • a measurement of the current generated is then performed at an applied potential of about +40OmV relative to a reference electrode (steps 104 and 106 of Fig. 1).
  • an applied voltage of about +40OmV herein refers to an applied voltage between +350 and +445 mV.
  • the magnitude of the current generated in the fluid sample is found to be proportional to the amount of free chlorine and dichloramine present in the fluid sample (step 108 of Fig. 1).
  • methods are also described for quantifying an amount of monochloramine in a fluid sample.
  • the amount of monochloramine in a fluid sample is proportional to the difference between (i) the value of current generated in a fluid sample under conditions for quantifying the amount of monochloramine plus free chlorine present in the fluid sample, as described above, and (ii) the value of current generated in a fluid sample under conditions for quantifying the amount of free chlorine present in the fluid sample, as described above.
  • the free chlorine content of the fluid sample can be directly calculated from the current measurement at a pH of about 6.2 with an applied potential of +47OmV relative to a reference electrode, such as an Ag/AgCl electrode.
  • the value of pH of about 6.2 may vary by ⁇ 0.5.
  • the current measurement at a pH of about 3.3 provides a measure of the monochloramine plus free chlorine concentrations in the fluid sample.
  • the value of pH of about 3.3 may vary by ⁇ 0.5.
  • the current due to free chlorine can be subtracted from the total current of the monochloramine plus free chlorine measurement.
  • the remaining current can be attributed to monochloramine and can be used to calculate the monochloramine concentration of the fluid sample,
  • the amount of dichloramine in a fluid sample is proportional to the difference between (i) the value of current generated in a fluid sample under conditions for quantifying the amount of dichloramine plus free chlorine present in the fluid sample, as described above, and (ii) the value of current generated in a fluid sample under conditions for quantifying the amount of free chlorine present in the fluid sample, as described above.
  • the free chlorine content of the fluid sample can be directly calculated from the current measurement at a pH of about 6.2 with an applied potential of +47OmV relative to a reference electrode, such as an Ag/ AgCl electrode.
  • the value of pH of about 6.2 may vary by ⁇ 0.5.
  • the current measurement at a pH of about 4.0, and an applied potential of about +40OmV, is proportional to the free chlorine plus dichloramine concentrations in the fluid sample.
  • the value of pH of about 4.0 may vary by ⁇ 0.5. Therefore, based upon the free chlorine measurement at a pH of about 6.2, the portion of the current attributable to the free chlorine can be subtracted and the remaining current can be used to calculate the concentration of dichloramine in the fluid sample.
  • methods for quantifying an amount of monochloramine and dichloramine through time-dependent measurements on a fluid sample.
  • the electrochemically (i.e., amperometrically or voltammetrically) active form of monochloramine that can be detected at a pH of less than about 4.0, and at a certain applied voltage, is found to be time-dependent.
  • the electrochemically active form of monochloramine is believed to convert to a form of dichloramine after a certain period of time. Therefore, a method is described that takes advantage of the time-dependent nature of the electrochemically active form of monochloramine to quantify the amount of both monochloramine and dichloramine in the fluid sample.
  • a fluid sample, or an aliquot of the fluid sample is adjusted to a pH of 6.2, and measurement Ml is performed at an applied potential of about +47OmV relative to a reference electrode to quantify the amount of free chlorine in the fluid sample or aliquot.
  • an amount of a nitrogen-containing solute such as ammonia, cyanuric acid, glycine, etc., may then be added to the fluid sample or aliquot of the fluid sample, to convert the free chlorine to monochloramine.
  • the nitrogen-containing solute is an amine.
  • the pH of the fluid sample, or an aliquot of the fluid sample is adjusted to a value less than about 4.0; measurement M2 is performed shortly after the pH is adjusted to less than about 4.0.
  • Measurement M2 provides a measure of the amount of monochloramine and free chlorine in the fluid sample or aliquot.
  • measurement M2 is performed at a pH of about 3.5 ⁇ 0.5 and at an applied voltage of about +47OmV relative to the reference electrode.
  • measurement M3 is performed on the fluid sample, or an aliquot of the fluid sample, at a time interval Tl after the pH of the sample is adjusted, or after measurement M2 was performed.
  • time interval Tl is sufficiently long so that the electrochemically active form of monochloramine converts to a form of dichloramine.
  • Time interval Tl may be about 0.01 seconds or less, about 0.5 seconds, about 1 second, about 30 seconds, about 1 minute, or about 5 minutes or more.
  • Measurement M3 provides a measure of the amount of dichloramine and free chlorine in the fluid sample or aliquot. Measurement M3 may be performed at the same applied potential that was used for measurement M2, or at a different applied potential. For example, measurement M3 may be performed at an applied potential of about +40OmV relative to the reference electrode.
  • the fluid sample or aliquot is maintained at the same value of pH for both measurements M2 and M3.
  • the pH may be adjusted to different values before each measurement M2 and M3.
  • the free chlorine measurement Ml can be subtracted from measurement M2 to provide a measure of the amount of monochloramine in the fluid sample or aliquot.
  • the free chlorine measurement Ml can be subtracted from measurement M3 to provide a measure of the amount of dichloramine in the fluid sample or aliquot.
  • measurements Ml, M2, and M3 are voltammetric measurements.
  • measurements Ml, M2 and M3 may each be performed on different aliquots of the fluid sample.
  • Such sensors can include one or more of, for example, electrodes and ion-selective membranes acting as ion- selective electrodes (ISEs), amperometric and potentiometric sensing elements that may or may not have electrode coatings on the electrode surfaces, conductivity sensing elements, reference electrodes, to name a few.
  • ISEs ion- selective electrodes
  • Other suitable sensor devices include those disclosed in United States Patent No. 4,743,954 ("Integrated Circuit for a Chemical- Selective Sensor with Voltage Output") and United States Patent No. 5,102,526 (“Solid State Ion Sensor with Silicone Membrane”), the disclosures of which are incorporated herein by reference.
  • Such sensors can be fabricated using known lithographic, dispensation and/or screen printing techniques (e.g., conventional microelectronics processing techniques). Such techniques can provide sensors having sensing elements with micron-sized or sub-micron- sized features, e.g., sensor elements having dimensions below 5 ⁇ m, 2 ⁇ m, 1 ⁇ m, or 0.5 ⁇ m.
  • the sensing elements may be integrated at the chip level, and can be integrated with low-cost electronics, such as ASICs (applications specific integrated circuits).
  • Exemplary sensors can be fabricated on silicon substrates or can be fabricated on other types of substrates such as, for example, ceramic, glass, SiO 2 , or plastic substrates, using conventional processing techniques.
  • Exemplary sensors can also be fabricated using combinations of such substrates situated proximate to one another.
  • a silicon substrate having some sensor components e.g., sensing elements
  • a ceramic, SiO 2 , glass, plastic or other type of substrate having other sensor components e.g., other sensing elements and/or one or more reference electrodes.
  • Conventional electronics processing techniques can be used to fabricate and interconnect such composite devices.
  • the fluid sample may be delivered to, or injected onto, a sensor device by any suitable fluid control device known in the art.
  • the fluid sample may be delivered to the sensor device by pumps, valves, microfluidics, or other means known in the art.
  • different aliquots of the fluid sample may be delivered to the sensor device by pumps, valves, microfiuidics, or other suitable means known in the art. Examples of such fluid control devices, and suitable sensors, are described in copending United States Patent Application Ser. No. 10/840,628 ("Monitoring Systems and Methods for Fluid Testing") and United States Patent Application Ser. No. 10/840,639 ("Fluid Monitoring Systems and Methods with Data Communication to Interested Parties”), as well as United States Patent No.
  • the methods described herein may be implemented on many different types of processing devices by program code comprising program instructions that are executable by a device processing system.
  • the software program instructions may include source code, object code, machine code, or any other stored data that is operable to cause a processing system to perform methods described herein.
  • Other implementations may also be used, however, such as firmware or even appropriately designed hardware configured to carry out the methods described herein.
  • a computer processor performs the steps of manipulating the data from the measurements in order to correlate the magnitude of current to the amount of the molecule of interest in the fluid sample.
  • the sensors are coupled to the computer processor.
  • a computer system receives the measurements from the sensors to perform the steps of the methods described herein.
  • the systems' and methods' data may be stored and implemented in one or more different types of computer-implemented ways, such as different types of storage devices and programming constructs (e.g., data stores, RAM, ROM, Flash memory, flat files, databases, programming data structures, programming variables, IF-THEN (or similar type) statement constructs, etc.).
  • data structures describe formats for use in organizing and storing data in databases, programs, memory, or other computer-readable media for use by a computer program.
  • the systems and methods may be provided on many different types of computer- readable media including computer storage mechanisms (e.g., CD-ROM, diskette, RAM, flash memory, computer's hard drive, etc.) that contain instructions for use in execution by a processor to perform the methods' operations and implement the systems described herein.
  • the methods are performed using an electrochemical sensor employing a platinum electrode as the working electrode, and a saturated KCl silver/silver chloride reference electrode.
  • electrode materials are gold, indium-doped tin oxide, and boron-doped diamond.
  • a three electrode arrangement is preferred, including separate reference and auxiliary electrodes.
  • the platinum surface can be kept in a highly reproducible state in order to achieve consistent sensitivity, by method known in the art. For example, this may accomplished by electrochemically renewing the surface of the platinum electrode by anodic and cathodic current steps, followed by poising the platinum electrode at the detection potential prior to each fluid sample measurement.
  • the surface of the platinum electrode is renewed through the steps of oxidizing, reducing, and the partially oxidizing the electrode, which results in a partial monolayer of oxide forming on the electrode. It is found that renewing the electrode surface allows for more reliable measurements.
  • the surface of the electrodes are preferably renewed prior to each measurement being performed.

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Abstract

L'invention porte sur des procédés électrochimiques pour détecter une ou plusieurs parmi les différentes formes de chlore qui peuvent exister dans diverses proportions dans un échantillon de fluide, à savoir, le chlore libre, la monochloramine et la dichloramine. La proportion de chlore libre, de monochloramine et de dichloramine dans l'échantillon de fluide peut être amenée à varier par l'ajustement du pH de l'échantillon de fluide. La présente invention porte également sur des procédés électrochimiques pour quantifier la quantité de chlore libre, de monochloramine et/ou de dichloramine dans un échantillon de fluide, par l'ajustement variable du pH de l'échantillon de fluide.
PCT/US2008/063190 2007-10-24 2008-05-09 Procédés électrochimiques pour une détection sélective de chlore libre, de monochloramine et de dichloramine Ceased WO2009055093A1 (fr)

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WO2017083698A1 (fr) * 2015-11-12 2017-05-18 Hach Company Mesure de chlore libre et combiné par microcapteurs électrochimiques
GB2551084A (en) * 2012-10-22 2017-12-06 Baxter Int Total chlorine water detection system and method for medical fluid treatments
WO2018005952A1 (fr) * 2016-06-30 2018-01-04 Pax Water Technologies Inc. Procédés et système pour évaluer et maintenir des niveaux de désinfectant dans un approvisionnement en eau potable
CN110006965A (zh) * 2019-04-11 2019-07-12 厦门英仕卫浴有限公司 一种实时检测余氯的智能淋浴器
US10766796B2 (en) 2015-06-12 2020-09-08 Ugsi Solutions, Inc. Chemical injection and control system and method for controlling chloramines
US10800685B2 (en) 2017-05-31 2020-10-13 Ugsi Solutions, Inc. Chemical injection control system and method for controlling chloramines
US10836659B2 (en) 2017-09-19 2020-11-17 Ugsi Solutions, Inc. Chemical control systems and methods for controlling disinfectants

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