Cell culture media generally comprise amino acids, salts,
vitamins, other substances, and an anorganic buffer substance
(NaHCO3). To allow cell cultures to grow, the pH
value should be balanced and stable. Starting values of
pH 7.2–7.4 are ideal for nearly all cells; these values can
vary from cell type to cell type during cultivation. The
pH value of NaHCO3 buffered media depends strongly
on the CO2 content of the incubator atmosphere.
Depending on the selected medium, it is necessary to add
a corresponding amount of CO2 concentration. A continuous
supply of CO2 is required for pH stability.
How a CO2 incubator
guarantees pH stability
Figure 1 - BINDER CB CO2 incubator.
Figure 2 - Rapid stabilization of the pH value after door opening in a BINDER
CB chamber with an IR sensor versus long recovery times in models with thermal
conductivity sensor technology.
For successful cell cultivation, it is absolutely necessary
that the pH stability be maintained throughout the
entire culturing process. For example, even a slight disturbance,
such as the opening of an incubator door, can
cause a disturbance. This is a common occurrence, particularly
if several persons are using the same incubator.
Even if the door is opened for only 30 sec, the parameters
temperature, humidity, and CO2 concentration in the
chamber interior are affected. The CO2
concentration immediately drops to
about 0.3% (normal atmosphere), which
in itself causes a pH value shift within the
growth medium. If the system does not
counteract this immediately, it may have
negative consequences for cell growth.
Only a highly dynamic and adaptive
system with an IR sensor, such as the
BINDER CB (Binder GmbH,
Tuttlingen, Germany) (Figure 1), can
rapidly compensate for such disturbances
in the climate balance—generally
within a few minutes. The advantage
is that the measurement is
independent of the air moisture content
and can be made correctly at any
time, and the CO2 content can be
immediately regulated. The buildup of
humidity in the air is usually relatively
slow after disturbances such as a door
opening, due to the physical conditions.
However, as a result of the rapid
recovery times in a BINDER CB with IR sensor technology, the pH value
remains within the neutral range,
while long recovery times in units
with thermal conductivity sensors can
lead to cell-damaging values (see
Figure 2). This effect is further
increased by frequent door openings.
Figure 3 - Possible consequences of a disturbance in the CO2 supply on the pH
value of a cell culture: The pH value could shift into the alkaline range with insufficient
gas supply (low CO2 level), or into the acid range with excessive gas supply
(high CO2 level). Intelligent Fail Safe ensures rapid stabilization.
The above example demonstrates how
cell cultures react to a disturbance in
CO2 concentration. Ensuring a constantly
regulated CO2 supply is critical
to the safety of the cells in an incubator.
At any time during the long cultivation
period, it is important to prevent
shifts in the pH value into the
acid or alkaline range beyond the tolerance
limits (see Figure 3). After a shift
of only 4 hr, negative effects on growth
can be expected. The consequence is
slowed cell division, which can eventually endanger
projects and even lead to complete cell death.
Figure 4 - Rapid adaptation of the CO2 supply due to activation of Intelligent Fail Safe.
It is not often that the CO2 content in an incubator
changes unnoticed, but it happens more often than one
would think. There can be numerous reasons
for this. A problem that occurs over
the weekend, when, for example, there is
no one in the laboratory, may prove irreversible.
A good solution is the Intelligent
Fail Safe system (Binder). During normal
incubator operation, it stores information
on gas consumption, which is normally
necessary to obtain the selected CO2 concentration.
During continued operation
of the unit, the actual gas supply is then
constantly compared to the saved value. If
there are deviations in the CO2 injection,
i.e., too much or too little gas, Intelligent
Fail Safe takes over control of the CO2
supply and returns the value to the original
concentration (see Figure 4). The system
reacts immediately to any change in
the gas supply, and it does so before an
alarm for CO2 over- or underconcentration is triggered
(±1 vol % of the target value). The pH value is rapidly
stabilized again. The stability of the pH value is therefore
guaranteed in every case, even during a controller or sensor
defect. The Fail Safe system is referred to as “intelligent”
because it independently and continuously monitors
the CO2 concentration.
Cell culture safety
The Intelligent Fail Safe system for monitoring CO2 concentration
in a Binder CO2 incubator works in a similar
way to overtemperature protection systems incorporated
in any general laboratory instrument today. It is an effective
safety function for pH stability in CO2 incubators
that protects valuable work or samples. The system is
suitable for cell culture specialists who cannot afford to
leave anything to chance in their applications.
Mrs. Maurer is Product Manager, Binder, Bergstr. 14, D-78532, Tuttlingen, Germany; tel.: +49 7462 2005 0; fax: +49
7462 2005 100; e-mail: firstname.lastname@example.org; home page: www.binder-world.com.