Calibrating Anaerobic Chamber Oxygen Monitors: A Step-By-Step Guide

Calibrating an oxygen monitor in an anaerobic chamber is a meticulous process that requires careful adherence to specific procedures. The Coy Anaerobic Monitor (CAM-12) is a popular choice for researchers, offering both O2 and H2 monitoring in a single unit. To ensure accurate measurements, it is essential to calibrate the oxygen monitor by comparing its readings to known reference values. This process involves using calibration solutions, such as zero oxygen and high-oxygen solutions, to adjust the meter's readings accordingly. Proper calibration helps to identify and correct any deviations or drifts in the monitor's performance, maintaining its accuracy over time.

Before calibrating, it is crucial to consult the manufacturer's instructions and gather the necessary equipment, including clean containers, calibration solutions, and a magnetic stirrer. The calibration process itself begins with rinsing the probe with distilled water to remove any residue. Subsequently, the probe is immersed in the zero oxygen solution, allowed to stabilize, and adjusted to a zero reading. The next step involves immersing the probe in the high-oxygen solution, stabilizing it, and adjusting the reading to match the known value of the solution.

It is worth noting that dissolved oxygen measurements are temperature-dependent, so controlling the temperature of the calibration solution is essential. Additionally, proper electrode maintenance is critical to preventing inaccurate readings during calibration. Regular calibration of an oxygen monitor in an anaerobic chamber is essential for maintaining accuracy and addressing any potential issues with the equipment.

Calibration solutions and their preparation

Calibration solutions are essential for ensuring the accuracy and precision of your oxygen monitor in an anaerobic chamber. Here is a detailed guide on the types of calibration solutions available and how to prepare them:

Types of Calibration Solutions:

• Standard Calibration Solution: This is typically a solution of known oxygen concentration, usually 20.9% oxygen (atmospheric level). It is used to calibrate the oxygen monitor to a standard reference point.
• Zero Calibration Solution: This solution contains no oxygen (0% concentration) and is used to calibrate the lower end of the oxygen monitor's measurement range.
• Span Calibration Solution: In addition to the standard and zero solutions, you may need a span calibration solution with a known oxygen concentration between 0% and 20.9%. This helps ensure accuracy across the entire measurement range.

Preparation of Calibration Solutions:

• Standard Calibration Solution (20.9% Oxygen): This solution can be prepared by exposing distilled water to atmospheric air. Fill a container with distilled water, leave it open in a room with normal air circulation, and allow the water to equilibrate to room temperature. The dissolved oxygen in the air will saturate the water, resulting in a 20.9% oxygen solution.
• Zero Calibration Solution (0% Oxygen): To prepare a solution with no oxygen, you can use an oxygen scavenger, such as sodium sulphite or sodium bisulphite. Dissolve a small amount of the scavenger in distilled water, and it will react with and remove any oxygen present. Alternatively, you can boil distilled water and then allow it to cool in a closed container. The boiling process will drive off oxygen, creating an oxygen-free environment in the water.
• Span Calibration Solutions: For span calibration solutions with specific oxygen concentrations, you can prepare them by mixing known volumes of the standard (20.9%) and zero (0%) solutions. For example, to create a 10% oxygen solution, mix equal volumes of the standard and zero solutions. Always use precise measurements and clean equipment to ensure accuracy.

Remember to store your calibration solutions in airtight containers to prevent contamination and ensure that they are labelled correctly. Additionally, it is essential to follow the specific instructions provided by the manufacturer of your oxygen monitor for calibration procedures and solutions.

Calibration procedures and their timing

Calibration procedures for an oxygen meter will vary depending on the manufacturer, but there are some general steps that can be followed. Firstly, it is important to read the manufacturer's instructions and familiarise yourself with the specific calibration procedure for your device.

Before beginning the calibration process, ensure you have gathered all the necessary equipment, including the oxygen meter, calibration solutions, clean containers, a magnetic stirrer (if required), and a thermometer or temperature sensor.

The calibration process itself typically involves the following steps:

• Rinse the probe with distilled water to remove any residue or contaminants.
• Immerse the probe in the zero oxygen solution and allow it to stabilise for a few minutes.
• Adjust the reading on the meter to zero.
• Immerse the probe in the high-oxygen solution and allow it to stabilise.
• Adjust the reading on the meter to match the known value of the high-oxygen solution.
• Verify the calibration by checking the readings on the meter against the known oxygen concentrations of the calibration solutions. If the readings are not within the acceptable range, recalibration may be necessary.
• Rinse the probe with distilled water after calibration to remove any residue.
• Store the meter according to the manufacturer's instructions.

It is important to note that dissolved oxygen measurements are temperature-dependent, so it is crucial to control the temperature of the calibration solution during the process and to allow sufficient time for it to reach the desired temperature.

The frequency of calibration will depend on the manufacturer's recommendations, the specific application of the meter, and the environmental conditions in which it is used. For most applications, calibration once a month or every few weeks is recommended. However, more frequent calibration may be necessary if the meter is subjected to harsh conditions or continuous use in high-temperature environments.

Common issues when calibrating

Calibration is a critical process for ensuring the accuracy and reliability of oxygen monitors in anaerobic chambers. While the procedure may vary slightly depending on the specific model and manufacturer, there are several common issues that users may encounter when calibrating their oxygen monitors.

One issue is ensuring proper sensor placement. Sensors should be easily accessible for calibration and replacement, and they should be correctly positioned to detect oxygen levels accurately. Another common challenge is maintaining the correct gas mixture. The gas mixture in the chamber should be calibrated to match the specific background gas mix used in the experiment. This is crucial for safety and accuracy, as an incorrect gas mixture can be dangerous and affect the sensor's performance.

Additionally, users may encounter issues with the catalyst, which is responsible for removing oxygen from the chamber. Over time, the catalyst can become less effective due to poisoning from excess H2S accumulation or other factors. A poorly functioning catalyst can lead to higher oxygen levels in the chamber, affecting the calibration of the oxygen monitor. Regular maintenance and replacement of the catalyst are essential to address this issue.

Furthermore, leaks in the chamber can introduce oxygen and affect the accuracy of the oxygen monitor. It is important to regularly inspect the chamber for any leaks and address them promptly. Finally, user error during calibration or improper use of the chamber can also impact the accuracy of oxygen monitoring. This includes factors such as incorrect use of the passbox cycle, improper arm port usage, or opening the oxygen indicator strip immediately after entering the chamber.

The importance of calibration

Calibration is a critical process that ensures the accuracy and precision of any measuring instrument, including oxygen monitors for anaerobic chambers. Here are several reasons why calibration is essential:

Accuracy and Precision:

Calibration ensures that the oxygen monitor provides accurate and precise readings. Over time, sensors can drift and components can wear out, leading to inaccurate measurements. Calibration allows you to adjust and fine-tune the instrument to meet the required standards and specifications.

Safety:

In many cases, anaerobic chambers are used in environments where safety is a top priority, such as in laboratories and research facilities. Calibration of the oxygen monitor ensures that the chamber maintains the correct oxygen levels, preventing hazardous conditions for both the personnel and the experiment/process.

Cost Savings:

Proper calibration can help optimize gas consumption rates, leading to significant cost savings over time. By understanding the levels of oxygen and hydrogen in the chamber, you can make informed decisions about gas usage and avoid unnecessary expenditures.

Compliance and Standards:

Calibration ensures that your equipment complies with industry standards and regulations. Many organizations require calibration records as proof that instruments are functioning correctly. Regular calibration also helps maintain the validity of any research or experiments conducted using the anaerobic chamber.

Equipment Longevity:

Regular calibration can extend the lifespan of your equipment. By identifying issues early on and making the necessary adjustments, you can prevent equipment malfunctions and reduce the need for costly repairs or replacements.

In summary, calibration of your anaerobic chamber's oxygen monitor is essential to ensure accuracy, safety, and compliance. It also helps optimize gas usage, reduce costs, and extend the lifespan of your equipment. By prioritizing calibration, you can maintain a dynamic and controlled environment that meets the specific requirements of your research or industrial application.

Recommended equipment

The Coy Anaerobic Monitor (CAM-12) is the only analyser that offers both O2 (PPM) and H2 (%) monitoring in one unit. It has been used by researchers to monitor oxygen and hydrogen levels in their anaerobic chambers. The H2 monitor allows each lab to optimise their Gas Mix consumption rate, saving time and operational costs. The Coy Laboratory Products website provides detailed specifications for the CAM-12.

Oxoid sells anaerobic indicator strips that are impregnated with resazurin, a redox indicator that changes colour to indicate partially (pink) and fully (colourless) anaerobic conditions.

Low-cost digital oxygen monitors are used in the brewing and fermentation industries, where oxygen control is important. These can be based on a tunable diode laser or a specific setup like the Endress and Hauser Memosens COS81D.

A DO meter is a device used to measure the amount of oxygen dissolved in a liquid, such as water. It is an essential tool in various industries, including environmental monitoring, aquaculture, and wastewater treatment. There are three main types: handheld, benchtop, and inline DO meters.

The calibration process for a DO meter involves verifying the accuracy of the meter by comparing its readings to known reference values. This ensures the instrument is functioning correctly and provides reliable measurements. Gather the necessary equipment: the DO meter and calibration solutions, clean containers, a magnetic stirrer (if required), and a thermometer/temperature sensor (if temperature compensation is necessary).

For the calibration of oxygen analysers and anaerobic chambers in microbiology labs, the following equipment is required:

• Petriplates/bottles
• Vacuum pump
• Inert gas mixture (Nitrogen gas mixture or Argon gas mixture)
• Palladium canister
• Molecular sieves
• Drying Train switch
• Data loggers temperature probes

Frequently asked questions