Sensor
Inventors
Assignees
Publication Number
US-11313821-B2
Publication Date
2022-04-26
Expiration Date
2038-06-28
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Abstract
A sensor for the in situ detection of a target chemical species, comprising a gas permeable membrane having a sampling side and an opposing analytical side, wherein the sampling side of the membrane is capable of receiving a sample and the membrane is permeable to target chemical species present in the sample. A weak acid or a weak base is in contact with the analytical side of the membrane, and a conductivity detector is in contact with the weak acid or weak base. In use, target chemical species present in the sample permeate through the membrane and react with the weak acid or weak base, producing ionic species and changing the conductivity.
Core Innovation
The invention relates to a sensor for the in situ detection of a target chemical species, particularly free ammonia, in aquatic, air, or agricultural environments. The sensor comprises a gas permeable membrane with a sampling side exposed to the sample and an opposing analytical side in contact with a weak acid or weak base. A conductivity detector is arranged in contact with the weak acid or weak base on the analytical side. Target chemical species permeate through the membrane and react with the weak acid or weak base, producing ionic species that increase the conductivity measurable by the detector.
The problem addressed is the lack of sensors capable of performing real-time, in situ, continuous monitoring of chemical species such as ammonia in environmental samples. Existing methods require sample collection and laboratory analysis, which are impractical for large-scale, long-term monitoring and management of ecosystem health. The invention seeks to provide a simple, sensitive, accurate, and reliable sensor system that continuously monitors ammonia concentrations by exploiting the permeation of NH3 through a hydrophobic PTFE membrane and its reaction with boric acid, allowing conductivity-based detection without the need for ongoing calibration.
The sensor operates by converting free ammonia in a sample into ammonium ions at the analytical side via reaction with boric acid, increasing the conductivity of the receiving phase. The gas permeable membrane is hydrophobic and selectively permeable to free ammonia gas, eliminating interference from other species. The sensor includes a reservoir with weak acid or base, a 4-electrode conductivity detector, and may include temperature and pH sensors to correct measurements. It provides both instantaneous ammonia measurements and an average concentration over deployment time by integrating conductivity changes.
Claims Coverage
The patent contains five independent claims covering a sensor for in situ detection of target chemical species and associated systems incorporating these sensors. The independent claims focus on the structural features of the sensor and its operational principle.
Sensor for in situ detection with gas permeable membrane and conductivity detection
A sensor comprising a gas permeable membrane with a sampling side for receiving a sample and an analytical side in contact with a reservoir containing a weak acid or weak base, along with a conductivity detector located in the reservoir to measure conductivity changes caused by ionic species generated when the target chemical species permeate through the membrane and react with the weak acid or weak base.
Sensor utilizing a hydrophobic PTFE membrane and boric acid for free ammonia detection
A sensor configured for free ammonia detection comprising a hydrophobic PTFE membrane permeable to free ammonia, a reservoir containing boric acid on the analytical side of the membrane, and a conductivity detector including an electrode in contact with the boric acid to detect conductivity changes from ionic species formed by ammonia reacting with boric acid.
Sensor housing with defined opening for sample contact
A sensor in which the gas permeable hydrophobic PTFE membrane is supported in a housing with an opening allowing the sample to contact the sampling side of the membrane.
Sensor capable of detecting low concentrations of target chemical species
A sensor capable of determining at least about 1 μg L−1 of the target chemical species in a solution, with the conductivity change detectable at levels as low as about 0.5 μS/cm.
System for in situ detection using multiple sensors and data acquisition
A system comprising a support structure under water holding multiple sensors spaced to provide a three-dimensional concentration profile of a target chemical species, a floater on the water surface, an anchor, a data acquisition unit receiving data from the sensors, and wherein each sensor includes a gas permeable membrane, a reservoir of weak acid or base, and a conductivity detector measuring conductivity changes due to ionic species generated by interaction with the permeated target chemical species.
Data acquisition unit programmed with threshold for alerts and process control
The system includes a data acquisition unit programmed with a pre-determined threshold concentration of the target chemical species, capable of comparing detected concentrations and raising alerts when differences exceed a specified level, optionally integrated with a programmable logic controller to control a chemical process generating the target species.
The independent claims collectively cover a sensor with a gas permeable membrane and conductivity detection of ionic species formed from reaction with a weak acid or base, a specific configuration for free ammonia detection using hydrophobic PTFE membrane and boric acid, housing features facilitating sample contact, sensitivity to low concentration detection, and systems employing multiple such sensors with data acquisition and automated alert and process control capabilities.
Stated Advantages
The sensor enables real-time, in situ, continuous monitoring of target chemical species such as ammonia directly at the sampling location.
It provides both instantaneous concentration measurements and average concentrations over deployment time through integrated conductivity changes.
The sensor design eliminates the need for ongoing calibration once the sensor constant is determined, reducing maintenance and operational costs.
It exhibits high sensitivity, capable of detecting low levels of ammonia (as low as about 1 μg L−1) and small conductivity changes (down to about 0.5 μS/cm).
The use of a hydrophobic PTFE membrane provides selectivity to free ammonia by preventing interference from other ions or gases.
The sensor is low cost, easy to maintain, reusable, and suitable for mass production.
The system facilitates spatial profiling of target chemical species concentrations through deployment of multiple sensors.
Inclusion of temperature and pH sensors allows for real-time corrections, improving measurement accuracy.
Documented Applications
Real-time in situ monitoring of free ammonia in aquatic environments including rivers, streams, ponds, reservoirs, drinking water, and seawater.
Detection and monitoring of ammonia concentrations in soil and atmospheric environments, including monitoring ammonium evaporation from agricultural soils.
Use in environmental impact assessments by determining large-scale, long-term average concentrations and temporal variations of ammonia.
Deployment of arrays of sensors in aquatic environments to create 2D or 3D profiles of ammonia concentration distributions for source identification.
Integration in process control systems where detected concentrations above or below thresholds automatically trigger adjustments in chemical-generating processes.
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