Dissolved oxygen measurement

Summary

This 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

• 💧 Liquids such as water, beverages, and chemicals are vital in daily life and their quality is determined by their chemical and physical properties.
• 🔍 To assess the quality of liquids, various measurement principles are employed, including the measurement of dissolved oxygen which is crucial for many applications.
• 🌱 Oxygen penetrates liquids through various means like plants, waves, and gas exchange with the atmosphere, and it distributes evenly in the water.
• 🔬 The amperometric and optical measurement principles are established for determining oxygen concentration in liquids.
• 🏥 In 1954, Leland C. Clark developed the Clark electrode for measuring oxygen concentration in blood, which is also applicable to various solutions.
• 🔋 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.
• 🔌 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.
• 📉 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.
• 🌡️ The amperometric measuring principle is suitable for a wide range of oxygen pressures and concentrations, including trace levels.
• 🌌 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.
• 🛠️ Optical sensors with reference LEDs are used in high-temperature applications to ensure reliable results despite the aging of the measurement LED.
• 🔄 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

00:00

🌊 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.

05:00

🔬 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.

Keywords

💡Liquids

Liquids are substances that flow and take the shape of their container. In the context of the video, liquids are essential in daily life and include a wide range of substances such as water, beverages, and chemicals. They are important for various applications and their quality is determined by their chemical and physical properties.

💡Chemical and Physical Properties

These are characteristics that define the nature of a substance. Chemical properties describe how a substance reacts with other substances, while physical properties are observable without changing the substance's composition. In the video, these properties are crucial for assessing the quality of liquids.

💡Dissolved Oxygen

Dissolved oxygen refers to the amount of oxygen gas that is dissolved in a liquid, typically water. It is an important parameter in the video as it is measured to assess the quality of various liquids. The process involves oxygen molecules migrating from the atmosphere into the water and achieving a uniform distribution.

💡Amperometric Measurement

Amperometric measurement is an electrochemical technique used to determine the concentration of a substance by measuring the current produced during an electrochemical reaction. In the video, this principle is used to measure dissolved oxygen concentration with the Clark electrode, developed by Leland C. Clark.

💡Clark Electrode

The Clark electrode is a type of amperometric oxygen sensor invented by Leland C. Clark. It is used in the video to measure oxygen concentration in various solutions. The sensor consists of a gold cathode and a silver anode separated by a membrane that allows dissolved oxygen to diffuse into the sensor.

💡Electrolyte

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. In the video, the electrolyte fills the reaction chamber of the amperometric sensor and facilitates the electrochemical reaction that measures dissolved oxygen.

💡Membrane

In the context of the video, a membrane is a porous barrier that separates the reaction chamber of the sensor from the liquid being tested. It allows dissolved oxygen to diffuse into the sensor while keeping other components of the liquid out.

💡Partial Pressure

Partial pressure is the pressure exerted by a component of a gas mixture. In the video, the difference in partial pressure of oxygen between the inner and outer membrane walls drives the diffusion of oxygen through the membrane, which is then measured.

💡Optical Measurement

Optical measurement, as described in the video, involves the use of light to determine the concentration of a substance. The optical oxygen sensor uses fluorescence quenching, where oxygen molecules reduce the intensity of fluorescence emitted by marker molecules, indicating the oxygen concentration.

💡Fluorescence Quenching

Fluorescence quenching is a process where the presence of certain molecules, such as oxygen, reduces the fluorescence emitted by other molecules, known as fluorophores. In the video, this principle is used in optical oxygen sensors to measure dissolved oxygen levels.

💡Quality Assurance and Process Control

Quality assurance and process control are practices used to ensure that products meet certain standards and that processes are carried out correctly. In the video, amperometric and optical oxygen measurements are highlighted as essential for these practices in various industries, such as water treatment and food production.

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.  They may include water, beverages, dairy products,  

chemicals, acids and bases or pharmaceutical  products. The quality of these liquids is  

determined by their chemical and physical  properties. To assess these properties, various  

principles of measurement are used. One of these  principles is the measurement of dissolved oxygen  

in liquids. Oxygen penetrates liquids in different  ways. For example via oxygen producing plants,  

waves, or gas exchange with the atmosphere. At  the water surface oxygen molecules migrate from  

the atmosphere into water and vice versa. Once  the oxygen is in the water, it distributes evenly  

to achieve a uniform distribution in space. The  established measuring principles the determination  

of oxygen concentration are the amperometric and  optical measurements. Let's take a look at how  

the amperometric oxygen measuring principle works.  In 1954, Leland C. Clark, an American biochemist,  

developed the so-called Clark electrode to  measure the oxygen concentration in blood.  

This type of amperometric oxygen sensor can  be used to measure the oxygen concentration  

in many different solutions. An amperometric  sensor usually consists of a gold cathode,  

also called working electrode, and a silver  anode, the counter electrode. A DC voltage  

is applied to both electrodes. The cathode and  anode are located in a reaction chamber that is  

filled with an electrolyte. The reaction chamber  is separated from the medium by a membrane. This  

porous membrane allows dissolved oxygen to diffuse  into the sensor. When the sensor is immersed in a  

medium containing oxygen, the difference in the  partial pressure of oxygen between the inner and  

the outer membrane walls leads to the diffusion of  oxygen through the membrane, that if used oxygen  

is reduced at the gold cathode in the reaction  chamber, resulting in a current flow that is  

proportional to the amount of transformed oxygen.  The current is processed by the transmitter  

and displayed as oxygen concentration,  partial pressure or percentage saturation.

After a certain period of time, a silver  bromide layer forms on the silver anode. This  

layer reduces the effective voltage and thus, the  oxygen flow, which can lead to measurement error.  

In applications with high temperatures during  cleaning or sterilization, the silver bromide  

layer is regularly removed. At moderate  temperatures, however, it remains permanent.  

That's why sensors with reference electrodes  are used in these applications. The reference  

electrode compensates for the increasing silver  bromide layer via an internal regulating circuit,  

considerably reducing the maintenance for  the sensor. The amperometric measuring  

principle offers a linear measurement via the  complete measuring range and is thus suitable  

for high and low partial oxygen pressures  and concentrations down to trace level. The  

optical oxygen sensor uses the fluorescence  quenching measuring principle. This sensor  

is equipped with an LED, a photodiode, and  a separating section that is covered by an  

oxygen permeable layer. In this layer, there  are as many oxygen molecules as in the medium.  

This means the partial oxygen pressure in the  layer is equal to the pressure in the medium.

The layer contains marker molecules that are  excited by an orange light and respond with a  

dark red fluorescence light. Oxygen molecules  attached to the marker molecules and attenuate  

the fluorescence light, which is called  quenching. The light signal is detected by  

the photodiode processed in the transmitter  and displayed in the required units. In  

applications that involve higher temperatures,  for example during sterilization or cleaning,  

sensors with reference LEDs are used.  This LED compensates for the aging of  

the measurement LED and delivers reliable  results even in demanding applications.

The advantage of optical oxygen measurement is  

fast availability of stabled measured  values and extremely low maintenance.

Amperometric and optical oxygen measurement  is essential for quality assurance and process  

control in many industries, such as water and  wastewater, food and beverage, life sciences,  

chemical and power industry. For further  information on liquid analysis and oxygen  

sensors featuring Memosens technology, visit the  Endress+Hauser Youtube channel or www.endress.com.