Measuring CO2 in Life Science Incubators

Cell culture incubators use CO2 to stabilize the culture medium's pH through a bicarbonate buffering system. This note focuses on the specific challenge of measuring CO2 inside an incubator; for the general principles of infrared measurement and temperature/pressure compensation, see the technical note on how to measure CO2.

The central challenge in this environment isn't the measurement principle itself, but the extreme conditions the sensor has to operate reliably in: heat, near-saturation humidity, and periodic sterilization cycles.

This note covers

• Why CO2 is critical for cell culture
• The risk of condensation when measuring in high humidity and temperature
• Why sterilization without removing the sensor is a real advantage

Why CO2 Is Critical in Cell Culture

Most cell culture protocols keep the incubator within a range close to 5% CO2 (some up to 10%, depending on the culture medium used). That CO2 reacts with the medium's bicarbonate to keep the pH stable within the range cells need to grow normally.

A sustained deviation from that range — from a leak, a door that doesn't seal well, or a miscalibrated sensor — shifts the medium's pH and can affect culture viability and growth with no visible sign until the damage is already done. That's why sensor stability and accuracy matter as much here as in any industrial safety application.

The Risk of Condensation When Measuring in High Humidity and Temperature

A typical cell culture incubator operates at 37°C and relative humidity above 95% — conditions the culture needs, but demanding ones for any optical sensor. When a hot, humid gas sample moves to a cooler measurement point (for example, when a pump draws a sample out to a handheld meter), water vapor condenses on the sensor's optical surfaces and skews the reading.

There are two ways to solve this. The first is to measure by diffusion directly inside the chamber, without extracting the sample — avoiding the thermal jump that causes condensation. The second, when extractive sampling is needed (for example with a handheld verification meter), is to use humidity-selective tubing that removes water vapor from the sample before it reaches the measurement chamber.

Vaisala CARBOCAP® probes designed for incubators, such as the GMP231, solve this with a heated sensor head that prevents condensation directly at the measurement point, with no need to extract the sample.