Dissolved oxygen measurement
Summary
TLDRThis script delves into the critical role of dissolved oxygen measurement in various liquids for quality assurance. It introduces the amperometric method, pioneered by Leland C. Clark, using a Clark electrode to gauge oxygen levels in solutions, and discusses its maintenance challenges and improvements with reference electrodes. The optical method, relying on fluorescence quenching, offers fast, stable readings with minimal maintenance. Both techniques are vital for industries such as water treatment, food and beverage, and life sciences, ensuring process control and product quality.
Takeaways
- š§ Liquids such as water, beverages, and chemicals are vital in daily life and their quality is determined by their chemical and physical properties.
- š To assess the quality of liquids, various measurement principles are employed, including the measurement of dissolved oxygen which is crucial for many applications.
- š± Oxygen penetrates liquids through various means like plants, waves, and gas exchange with the atmosphere, and it distributes evenly in the water.
- š¬ The amperometric and optical measurement principles are established for determining oxygen concentration in liquids.
- š„ In 1954, Leland C. Clark developed the Clark electrode for measuring oxygen concentration in blood, which is also applicable to various solutions.
- š An amperometric sensor consists of a gold cathode and a silver anode, with a DC voltage applied, and is separated from the medium by a porous membrane that allows oxygen to diffuse into the sensor.
- š The current generated by the reduction of oxygen at the cathode is proportional to the oxygen concentration and is displayed after processing by the transmitter.
- š Over time, a silver bromide layer can form on the anode, potentially causing measurement errors, but this can be mitigated with sensors that have reference electrodes.
- š”ļø The amperometric measuring principle is suitable for a wide range of oxygen pressures and concentrations, including trace levels.
- š The optical oxygen sensor operates on the principle of fluorescence quenching, using an LED and a photodiode to measure the attenuation of fluorescence light by oxygen molecules.
- š ļø Optical sensors with reference LEDs are used in high-temperature applications to ensure reliable results despite the aging of the measurement LED.
- š The optical method offers fast, stable measurements with low maintenance requirements, which is advantageous for industries such as water treatment, food and beverage, and life sciences.
Q & A
What are some examples of liquids that are essential in our daily life?
-Examples of essential liquids in daily life include water, beverages, dairy products, chemicals, acids and bases, and pharmaceutical products.
How is the quality of liquids determined?
-The quality of liquids is determined by their chemical and physical properties.
What is the significance of measuring dissolved oxygen in liquids?
-Measuring dissolved oxygen in liquids is significant for assessing their chemical and physical properties, which is crucial for quality assurance and process control.
How does oxygen penetrate liquids?
-Oxygen penetrates liquids through various means such as oxygen-producing plants, waves, or gas exchange with the atmosphere.
Who developed the Clark electrode and for what purpose?
-Leland C. Clark, an American biochemist, developed the Clark electrode in 1954 to measure the oxygen concentration in blood.
What are the main components of an amperometric sensor?
-An amperometric sensor mainly consists of a gold cathode (working electrode), a silver anode (counter electrode), a reaction chamber filled with an electrolyte, and a porous membrane that separates the chamber from the medium.
How does the amperometric oxygen measuring principle work?
-The amperometric oxygen measuring principle works by applying a DC voltage to the electrodes, allowing dissolved oxygen to diffuse through the membrane into the sensor, where it is reduced at the gold cathode, resulting in a current flow proportional to the oxygen concentration.
What issue can arise with the silver anode over time and how is it addressed?
-Over time, a silver bromide layer can form on the silver anode, reducing the effective voltage and potentially causing measurement error. This layer is regularly removed in applications with high temperatures, or reference electrodes are used to compensate for the increasing silver bromide layer.
What is the advantage of using a reference electrode in amperometric sensors?
-The reference electrode compensates for the increasing silver bromide layer via an internal regulating circuit, reducing maintenance requirements for the sensor and ensuring accurate measurements.
How does the optical oxygen sensor operate?
-The optical oxygen sensor operates using the fluorescence quenching principle. It contains an LED, a photodiode, and a separating section covered by an oxygen permeable layer with marker molecules. Oxygen molecules quench the fluorescence light emitted by the marker molecules, and the attenuated light is detected and processed to display the oxygen concentration.
Why are reference LEDs used in optical oxygen sensors for applications involving higher temperatures?
-Reference LEDs are used in optical oxygen sensors for applications involving higher temperatures to compensate for the aging of the measurement LED, ensuring reliable results even in demanding conditions.
In which industries is oxygen measurement essential for quality assurance and process control?
-Oxygen measurement is essential for quality assurance and process control in industries such as water and wastewater, food and beverage, life sciences, chemical, and power industry.
Outlines
š Dissolved Oxygen Measurement Principles
This paragraph introduces the importance of measuring the quality of various liquids, such as water and beverages, through their chemical and physical properties. It focuses on dissolved oxygen measurement, explaining how oxygen enters water through different means and the two main principles for measuring oxygen concentration: amperometric and optical methods. The amperometric method is detailed, describing the Clark electrode invented by Leland C. Clark in 1954, which uses a gold cathode and silver anode to measure oxygen levels in solutions. The process involves oxygen diffusion through a porous membrane and reduction at the cathode, generating a current proportional to the oxygen concentration. The paragraph also discusses the formation of silver bromide on the anode, which can cause measurement errors, and the use of reference electrodes to compensate for this issue. The optical method is briefly mentioned, utilizing fluorescence quenching to measure oxygen levels.
š¬ Applications and Further Information on Oxygen Sensors
The second paragraph discusses the application of amperometric and optical oxygen measurement in various industries, including water and wastewater treatment, food and beverage production, life sciences, chemical, and power industries. It emphasizes the significance of these measurement techniques for quality assurance and process control. The paragraph concludes by directing interested viewers to the Endress+Hauser YouTube channel or their official website for more information on liquid analysis and oxygen sensors featuring Memosens technology, suggesting a resource for further exploration into this topic.
Mindmap
Keywords
š”Liquids
š”Chemical and Physical Properties
š”Dissolved Oxygen
š”Amperometric Measurement
š”Clark Electrode
š”Electrolyte
š”Membrane
š”Partial Pressure
š”Optical Measurement
š”Fluorescence Quenching
š”Quality Assurance and Process Control
Highlights
Liquids like water, beverages, dairy, chemicals, acids, bases, and pharmaceuticals are essential in daily life and their quality is determined by chemical and physical properties.
Dissolved oxygen measurement is a key principle for assessing liquid quality, with oxygen penetrating liquids via plants, waves, or gas exchange with the atmosphere.
Oxygen molecules migrate from the atmosphere into water at the surface and distribute evenly to achieve uniformity.
Amperometric and optical measurements are established principles for determining oxygen concentration in liquids.
Leland C. Clark developed the Clark electrode in 1954 to measure oxygen concentration in blood, which can also be used for various solutions.
An amperometric sensor consists of a gold cathode (working electrode), silver anode (counter electrode), and an electrolyte-filled reaction chamber separated from the medium by a porous membrane.
The partial pressure difference of oxygen across the membrane causes diffusion through the membrane and reduction at the gold cathode, generating a current proportional to the oxygen amount.
The current is processed and displayed as oxygen concentration, partial pressure, or saturation percentage.
A silver bromide layer can form on the silver anode over time, reducing effective voltage and oxygen flow, potentially causing measurement errors.
Reference electrodes are used in applications with high temperatures to compensate for the silver bromide layer and reduce sensor maintenance.
The amperometric principle offers linear measurement across the full range, suitable for high and low oxygen pressures and trace concentrations.
Optical oxygen sensors use the fluorescence quenching principle with an LED, photodiode, and oxygen permeable layer containing marker molecules.
Oxygen molecules quench the fluorescence light of the marker molecules, and the attenuated light is detected and processed to display oxygen levels.
Reference LEDs are used in high-temperature applications to compensate for measurement LED aging and ensure reliable results.
Optical oxygen measurement offers fast, stable readings and extremely low maintenance.
Both amperometric and optical oxygen measurement are crucial for quality assurance and process control across industries like water, food, life sciences, chemicals, and power.
For more information on liquid analysis and oxygen sensors with Memosens technology, visit the Endress+Hauser YouTube channel or website.
Transcripts
Many liquids are essential in our daily life.Ā They may include water, beverages, dairy products,Ā Ā
chemicals, acids and bases or pharmaceuticalĀ products. The quality of these liquids isĀ Ā
determined by their chemical and physicalĀ properties. To assess these properties, variousĀ Ā
principles of measurement are used. One of theseĀ principles is the measurement of dissolved oxygenĀ Ā
in liquids. Oxygen penetrates liquids in differentĀ ways. For example via oxygen producing plants,Ā Ā
waves, or gas exchange with the atmosphere. AtĀ the water surface oxygen molecules migrate fromĀ Ā
the atmosphere into water and vice versa. OnceĀ the oxygen is in the water, it distributes evenlyĀ Ā
to achieve a uniform distribution in space. TheĀ established measuring principles the determinationĀ Ā
of oxygen concentration are the amperometric andĀ optical measurements. Let's take a look at howĀ Ā
the amperometric oxygen measuring principle works.Ā In 1954, Leland C. Clark, an American biochemist,Ā Ā
developed the so-called Clark electrode toĀ measure the oxygen concentration in blood.Ā Ā
This type of amperometric oxygen sensor canĀ be used to measure the oxygen concentrationĀ Ā
in many different solutions. An amperometricĀ sensor usually consists of a gold cathode,Ā Ā
also called working electrode, and a silverĀ anode, the counter electrode. A DC voltageĀ Ā
is applied to both electrodes. The cathode andĀ anode are located in a reaction chamber that isĀ Ā
filled with an electrolyte. The reaction chamberĀ is separated from the medium by a membrane. ThisĀ Ā
porous membrane allows dissolved oxygen to diffuseĀ into the sensor. When the sensor is immersed in aĀ Ā
medium containing oxygen, the difference in theĀ partial pressure of oxygen between the inner andĀ Ā
the outer membrane walls leads to the diffusion ofĀ oxygen through the membrane, that if used oxygenĀ Ā
is reduced at the gold cathode in the reactionĀ chamber, resulting in a current flow that isĀ Ā
proportional to the amount of transformed oxygen.Ā The current is processed by the transmitterĀ Ā
and displayed as oxygen concentration,Ā partial pressure or percentage saturation.
After a certain period of time, a silverĀ bromide layer forms on the silver anode. ThisĀ Ā
layer reduces the effective voltage and thus, theĀ oxygen flow, which can lead to measurement error.Ā Ā
In applications with high temperatures duringĀ cleaning or sterilization, the silver bromideĀ Ā
layer is regularly removed. At moderateĀ temperatures, however, it remains permanent.Ā Ā
That's why sensors with reference electrodesĀ are used in these applications. The referenceĀ Ā
electrode compensates for the increasing silverĀ bromide layer via an internal regulating circuit,Ā Ā
considerably reducing the maintenance forĀ the sensor. The amperometric measuringĀ Ā
principle offers a linear measurement via theĀ complete measuring range and is thus suitableĀ Ā
for high and low partial oxygen pressuresĀ and concentrations down to trace level. TheĀ Ā
optical oxygen sensor uses the fluorescenceĀ quenching measuring principle. This sensorĀ Ā
is equipped with an LED, a photodiode, andĀ a separating section that is covered by anĀ Ā
oxygen permeable layer. In this layer, thereĀ are as many oxygen molecules as in the medium.Ā Ā
This means the partial oxygen pressure in theĀ layer is equal to the pressure in the medium.
The layer contains marker molecules that areĀ excited by an orange light and respond with aĀ Ā
dark red fluorescence light. Oxygen moleculesĀ attached to the marker molecules and attenuateĀ Ā
the fluorescence light, which is calledĀ quenching. The light signal is detected byĀ Ā
the photodiode processed in the transmitterĀ and displayed in the required units. InĀ Ā
applications that involve higher temperatures,Ā for example during sterilization or cleaning,Ā Ā
sensors with reference LEDs are used.Ā This LED compensates for the aging ofĀ Ā
the measurement LED and delivers reliableĀ results even in demanding applications.
The advantage of optical oxygen measurement isĀ Ā
fast availability of stabled measuredĀ values and extremely low maintenance.
Amperometric and optical oxygen measurementĀ is essential for quality assurance and processĀ Ā
control in many industries, such as water andĀ wastewater, food and beverage, life sciences,Ā Ā
chemical and power industry. For furtherĀ information on liquid analysis and oxygenĀ Ā
sensors featuring Memosens technology, visit theĀ Endress+Hauser Youtube channel or www.endress.com.
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