Solid state amperometric chloramine sensor
Inventors
PRESSMAN, Jonathan G. • Lee, Woo Hyoung • WAHMAN, David G.
Assignees
US Environmental Protection Agency
Publication Number
US-9586814-B2
Publication Date
2017-03-07
Expiration Date
2033-07-11
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Abstract
A monochloramine microsensor includes an elongated housing defining a central axis and an open interior and having a capillary opening at one end. A semi-permeable membrane covers the capillary opening, the semi-permeable membrane allowing diffusion of chloramines there-through while preventing water from entering into the interior of the housing. A chloramine sensitive element in the form of a wire, fiber or nanotube is mounted within the housing, the chloramine sensitive element, when used in conjunction with an anode, outputs current in an amount proportional to the concentration of chloramine present in a liquid sample in which the chloramine sensitive element is immersed. The chloramine sensitive element extends along a length of the central axis to a first end adjacent to and spaced from the semi-permeable membrane. The chloramine sensitive element is a gold wire, a platinum wire, a carbon fiber or a carbon nanotube.
Core Innovation
The invention relates to a solid state amperometric chloramine sensor/microsensor designed for in situ monitoring and quantitative analysis of monochloramine concentrations in aqueous systems, including engineered and natural waters. The sensor comprises an elongated housing with a capillary opening covered by a semi-permeable membrane that allows chloramine diffusion but blocks water ingress. Inside the housing, a compact chloramine sensitive element in the form of a gold wire, platinum wire, carbon fiber, or carbon nanotube is positioned adjacent to and spaced a constant diffusive length from the semi-permeable membrane. When used with an anode, the sensing element generates a current proportional to the chloramine concentration in a liquid sample.
The problem addressed is the interference by dissolved oxygen (DO) in existing amperometric chloramine sensors, which requires complex calibration curves and limits their practical use. Existing sensors are also too large for microscopic applications, such as studying monochloramine penetration in biofilms, and the geometry of electrodes limits sensor linearity at high chloramine concentrations. Conventional sensors have prevented detailed microscopic study of chloramine biofilm kinetics due to the lack of suitable miniaturized needle-type sensors.
The present invention overcomes these problems by providing a compact, needle-like microsensor with tip dimensions around 5-10 microns, allowing microenvironment penetration without structure destruction. The sensor operates at positive applied potentials (e.g., between 0.15 and 0.45 V) to avoid DO interference, simplifying calibration with a single linear curve across varied DO concentrations. This enables accurate, fast (<5 sec), and stable amperometric measurement of monochloramine without interference in pH ranges 6-9 and chlorine-to-nitrogen ratios less than 5:1.
Claims Coverage
The patent includes several independent claims focusing on the structure and function of the chloramine microsensor and its operational characteristics, specifying materials and configurations that avoid dissolved oxygen interference.
Microsensor structure with capillary housing and semi-permeable membrane
An elongated housing with a central axis and capillary opening covered by a semi-permeable membrane that permits chloramine diffusion while preventing water entry.
Chloramine sensitive element in compact wire, fiber or nanotube form
A chloramine sensitive element fashioned as a gold wire, platinum wire, carbon fiber, or carbon nanotube extending inside the housing, spaced a constant diffusive length from the membrane, outputting current proportional to chloramine concentration.
Geometric dimensions enabling microscale sensing
Capillary opening inner diameter between 5-10 microns and spacing of the sensing element end from the membrane at 5-6 microns to enable needle-like microsensor design.
Incorporation of internal reference electrode and electrolyte
An anode serving as a reference electrode mounted within the housing with partial filling of an electrolyte for improved sensor operation.
Operation at positive applied potential to avoid dissolved oxygen interference
Operating conditions with positive applied potentials (e.g., between 0 and 0.25 V or between +0.15 and +0.45 V) that prevent dissolved oxygen from interfering with monochloramine measurement.
The claimed inventive features collectively provide a compact, needle-like amperometric chloramine microsensor with defined geometry and materials that enable sensitive, dissolved oxygen interference-free quantitative analysis of monochloramine in aqueous systems.
Stated Advantages
Eliminates dissolved oxygen interference, allowing use of a single, linear calibration curve regardless of dissolved oxygen concentration.
Compact needle-like sensor tip (~10 microns) enables penetration and in situ measurement in microenvironments such as biofilms without destroying structure.
Fast, highly stable amperometric response with low detection limits and wide measurement range for monochloramine.
Enables spatial and temporal monitoring of chemical profiles with high resolution, aiding kinetic studies in complex aqueous systems.
Simplifies sensor operation and expands potential applications compared to prior macro-scale or non-compact electrodes.
Documented Applications
In situ monitoring and measurement of monochloramine concentration profiles within biofilms for microscopic studies of disinfectant penetration and kinetics.
Use in chloraminated drinking water distribution systems to evaluate nitrification and biofilm control strategies.
Real-time monochloramine monitoring over wide areas integrated with wireless smart grid technology in water utilities.
Potential for multi-analyte detection using microelectromechanical systems (MEMS) combining different sensing techniques and electrodes.
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