Dissolved Oxygen Electrode: Optical and Polarographic Determination

Dissolved Oxygen Electrode

Optical and Polarographic Electrodes for Proper Determination of Dissolved Oxygen

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Reliable Meters

pH Meters

We offer durable meters in our SevenExcellence portfolio that support reliable dissolved oxygen measurements. Our portfolio has options to meet your needs for compliance and routine measurements, and it includes economical models for those working under tight budgets.

SevenExcellence Meters

Effective Calibration Standards

pH Solutions

We also offer standards for reliable results at low dissolved oxygen levels. Zero-oxygen tablets that make the preparation of a zero-oxygen solution fast and easy are also available for DO electrode calibration.

More about DO Electrode Standards

Expert Application Support

Expert Application Support

Our pH Competence and Support Center (pH CSC) offers you easy access to dedicated application specialists for your pH, ORP, ion, conductivity, and DO measurements. These specialists provide know-how and collaborate with product management and development to help ensure a high degree of success in all your critical electrochemical analyses.

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Analytical Instruments

Products and Specs

 
Products and Specs
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Connector
Shaft Material
Sensor Type
Shaft Diameter
Temperature probe
Material No.: 51344621
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ConnectorMini-LTW (IP67)
Shaft MaterialPC/ABS
Sensor TypeOptical
Shaft Diameter16 mm
Temperature probeNTC 30 kΩ
SampleGeneral Purpose
Material No.: 51344622
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ConnectorMini-LTW (IP67)
Shaft MaterialPC/ABS
Sensor TypeOptical
Shaft Diameter16 mm
Temperature probeNTC 30 kΩ
SampleGeneral Purpose
Material No.: 51344623
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ConnectorMini-LTW (IP67)
Shaft MaterialPC/ABS
Sensor TypeOptical
Shaft Diameter16 mm
Temperature probeNTC 30 kΩ
SampleGeneral Purpose
Material No.: 51344611
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ConnectorBNC/RCA (Cinch) IP67
Shaft MaterialPPS
Sensor TypePolarographic
Shaft Diameter12 mm
Temperature probeNTC 22 kΩ
SampleGeneral Purpose
Material No.: 51344612
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ConnectorBNC/RCA (Cinch) IP67
Shaft MaterialPPS
Sensor TypePolarographic
Shaft Diameter12 mm
Temperature probeNTC 22 kΩ
SampleGeneral Purpose
Material No.: 51344613
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ConnectorBNC/RCA (Cinch) IP67
Shaft MaterialPPS
Sensor TypePolarographic
Shaft Diameter12 mm
Temperature probeNTC 22 kΩ
SampleGeneral Purpose
Material No.: 51340291
See details
ConnectorBNC/RCA (Cinch) IP67
Shaft MaterialPPS
Sensor TypePolarographic
Shaft Diameter12 mm
Temperature probeNTC 22 kΩ
SampleGeneral Purpose
Material No.: 51340298
See details
ConnectorBNC/RCA (Cinch) IP67
Shaft MaterialPPS
Sensor TypePolarographic
Shaft Diameter12 mm
Temperature probeNTC 22 kΩ
SampleGeneral Purpose
Material No.: 51340292
See details
ConnectorBNC/RCA (Cinch) IP67
Shaft MaterialPPS
Sensor TypePolarographic
Shaft Diameter12 mm
Temperature probeNTC 22 kΩ
SampleGeneral Purpose
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InLab® Sensors
The manufacturing of high quality sensors with outstanding performance not only requires technical skills and expertise but also a profound understand...

Applications

Biochemical Oxygen Demand From Theory to Practice
One important analysis to assess water quality is determining the BOD (biochemical oxygen demand). BOD is an indicator of the amount of organic matter...

FAQ


 

1. What types of electrodes can be used for measuring dissolved oxygen (DO)?

The following types of dissolved oxygen sensor technologies are available for laboratory and field applications:

a. Optical dissolved oxygen electrode (InLab OptiOx)

b. Polarographic dissolved oxygen electrode (InLab 605)

c. Galvanic dissolved oxygen electrode (LE621)


 

2. How does an optical dissolved oxygen electrode work?

Cross-section of an optical DO sensor


 

3. How does a polarographic DO electrode work?

Cross-section of a polarographic DO sensor


 

4. How does a galvanic DO electrode work?

Cross-section of a galvanic DO sensor


 

5. What are the differences between polarographic and galvanic dissolved oxygen electrodes?

Characteristic

Galvanic DO Electrode

Polarographic DO Electrode

  • Anode Material
  • Cathode Material
  • Polarization
  • Polarization Time
  • Anode Depletion
  • Oxidation Product’s Fate
  • Inherent Consequences of the Working Principle
  • Zinc or lead
  • Silver
  • Self-polarization
  • None
  • All the time
  • Precipitates in the electrolyte
  • Precipitate covers the membrane and reduces its permeability to oxygen
  • Anode is depleted regardless of whether sensor is in use or not
  • Mostly silver
  • Gold or platinum
  • Instrument-promoted polarization
  • Some hours (approx. 6)
  • Only during measurement
  • Accumulates on the anode
  • Oxidation product coats the anode and reduces the sensitivity of the sensor
  • Needs several hours of polarization time prior to measurement

 

Therefore, in summary, galvanic sensors require no warm-up time and are more stable at a lower level of dissolved oxygen as compared to polarographic probes. On the contrary, polarographic sensors have longer lifetime. For more information on the working principles of individual sensors, please refer to questions 3 and 4 above.


 

6. Is there any electrode preparation required for laboratory DO sensors prior to a measurement?

a. Electrochemical sensors must be checked for membrane integrity. Additionally, it must be ensured that the electrolyte is properly replenished, if electrolyte refilling is applicable.
b. When using a polarographic sensor, the proper polarization of the sensor needs to be ensured.
c. Optical laboratory DO sensors do not require any preparation prior to their usage.


 

7. Is it necessary to calibrate an optical dissolved oxygen electrode before performing measurements?

For standard oxygen measurements, a 1-point calibration at 100% oxygen saturation (water-saturated air) is sufficient for many applications. For low oxygen concentration measurements (below 10% or 0.8 mg/L) it is recommended to have a second calibration point using an oxygen-free standard solution (this corresponds to 0% oxygen saturation). For this purpose, zero oxygen tablets are dissolved in water, in order to eliminate all the dissolved oxygen in it.


 

8. Is it necessary to stir the sample while measuring it with a laboratory DO sensor?

For the electrochemical laboratory DO sensors, stirring is necessary because the sensors consume oxygen while measuring. The stirring should be kept at a constant speed. In contrast to electrochemical sensors, optical DO electrodes do not require stirring because they do not consume oxygen. In order to reduce the measurement duration, the sensor tip should be submerged into the sample before starting the measurement. This procedure will allow the oxygen concentration and temperature to equilibrate. Air bubbles at the sensor tip must be avoided. Otherwise, the oxygen concentration of the air bubbles will also be measured, leading to false results.


 

9. How should I store the laboratory DO sensors?

General storage tips:
After a measurement, the sensor should be cleaned with water and wiped with a soft tissue. Especially when measuring biological samples, microbiological growth should be carefully avoided. For optimal performance, a sensor should be stored in a safe environment at temperatures between 5 and 45 °C, fast temperature changes should be avoided.

Galvanic DO sensor for laboratory applications:
For short-term storage, it should be rinsed with deionized water and placed in a storage solution. For long-term storage, it should also be short-circuited (to prevent deterioration due to continuous self-polarization) and stored in a cool place.

Polarographic DO sensor for laboratory applications:
During short-term storage, avoid the 6-hour polarization requirement, it can be left connected to the instrument. For long term storage, it should be detached from the instrument because continuous polarization will gradually reduce its lifetime. Provided the sensor is filled with inner electrolyte and the protective cap is placed over the membrane, it can be stored for several months. However, to use the sensor again after more than 3 months of storage, the electrolyte should be replaced. If storage of more than 6 months is intended, the electrolyte should be removed.

Optical laboratory DO sensor:
An optical sensor should be stored dry. Sensors with a replaceable membrane module should have it exchanged as soon as the sensor shows signs of reduced performance.


 

10. Are METTLER TOLEDO's laboratory DO sensors waterproof?

Most are IP67 certified, ensuring that the entire portable system is able to withstand wet and demanding environments.


 

11. Can METTLER TOLEDO's laboratory DO probe measure temperature as well?

Most of our laboratory DO probes come with an integrated temperature probe that helps measure the right temperature of a sample.


 

12. Can an InLab 605 laboratory DO sensor be used for field applications too?

Indeed, it is equipped with a glass fiber reinforced PPS shaft and a measuring membrane protected by a steel mesh making this sensor optimal for tough applications.


 

13. What is the Biological oxygen demand (BOD) and why is it necessary to measure BOD?

Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic conditions at a specified temperature. BOD is an important parameter in water treatment plants indicating the degree of organic pollution in water. To learn more, you can refer to our guide dedicated to this topic: Biochemical Oxygen Demand From Theory to Practice. With the SevenExcellence DO meter setting up your own BOD determination process is possible in no time.


 

14. Can the laboratory optical DO probe be used for measuring BOD as well?

Yes, the InLab OptiOx is perfectly equipped for measuring BOD. The special OptiOx BOD adapter makes the sensor perfectly suited for measurements in all common BOD canisters.

 OptiOx BOD adapter


 

15. Can the optical DO sensor only be used for lab applications?

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