Technical data

C 150 (E2) 12/2012 page 55/90
12. Reference measurements
You can take reference measurements of the temperature and CO
2
via the silicone measuring port (8)
located the inner glass door. Reference temperature measurements always take place under equilibrated
conditions with both doors closed.
12.1 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 12.1.1 to
12.1.3.
12.1.1 Measuring the 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
concen-
tration 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 not suitable for calibrating the BINDER FPI sensor system.
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 27 shows the relationship between CO
2
concentration in vol.-% and the pH of dif-
ferent NaHCO
3
buffered media.
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 bottle 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 af-
ter 5 minutes, permitting sufficient time for measurement.
• In addition, you can of course use pH-test strips (pH range 6 to 8, non-bleeding).
4
6
8
10
12
14
16
18
2
3,70 g/l NaHCO
3
2,20 g/l NaHCO
3
0,85 g/l NaHCO
3
6.8 7.0
7.2
7.4
7.6
Value pH
Vo l. % C O
2
0,35 g/l NaHCO
3
1,20 g/l NaHCO
3
Trade names of common media:
DMEM
BME
MEM
Medium 199
Mc Coy
F10
F12
NaHCO
3
[g/l]
3.70
2.20
2.20
2.20
2.20
1.20
1.20
Figure 27: Value pH of NaHCO
3
buffered media as a function of the CO
2
concentration: