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CB / CB-UL, CBF / CBF-UL (E7) 07/2021 Page 145/197
19. Reference measurements
Reference measurements of the temperature, CO
2
, O
2
(chamber with O
2
control), and humidity can be
performed via the silicone measuring port (N) located on the inner glass door. Reference temperature
measurements always take place under equilibrated conditions with both doors closed.
19.1 CO
2
reference measuring
There are three possibilities to perform CO
2
test measurements between the recommended annual
maintenance procedures. To test the CO
2
concentration inside an incubator, see chapters 19.1.1 to 19.1.3.
19.1.1 Measuring CO
2
concentration indirectly via the pH of the cell medium
By using the indirect determination of CO
2
concentration via the pH-value of the nutrient, it is possible to
check the CO
2
concentration inside the chamber. This is a simple method to test the correct CO
2
concentration without any special CO
2
measuring equipment. You need only use an accurate pH indicator
or a pH-measuring electrode, which are standard equipment in cell culture laboratories.
This method is based on the acid base equilibrium of the buffer system in the culture media. NaHCO
3
buffers the common media. From the pH value of the medium, it is possible to conclude its CO
2
concentration. Figure 38 shows the relationship between CO
2
concentration in vol.-% and the pH of different
NaHCO
3
buffered media.
These test systems are not suitable for calibrating the BINDER sensor system.
Recommended procedure:
• Incubate an empty sample with medium for 1/2 day under the same conditions as the cells. You can
perform the incubation in a cell culture cylinder or in a 50 ml Falcon tube with open lid.
• After gassing, remove the empty sample from the incubator and within 5 minutes measure the pH-value
with a glass electrode.
During the measurement, the medium should have the least possible surface contact with the ambient
air, so that the CO
2
can evaporate only slightly. A significant downward movement will happen only after
5 minutes, permitting sufficient time for measurement.
• In addition, you can of course use pH-test strips (pH range 6 to 8, not bleeding).
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