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Biologists often use a CO2 incubator - it's a chamber that not
only maintains a constant chamber, but also maintains a
constant CO2 concentration, typically around 5%. This is
necessary because many cultured cells grow best at these
higher CO2 concentrations.
A CO2 incubator is normally fed
from a CO2 cylinder. A
solenoid valve opens to let CO2 in, when necessary, and the
chamber itself is more-or-less airtight to limit the loss of
However, this is a huge faff. You have to have a big (eg
CO2 cylinder, which is typically rented from a supplier; it
to have a leak-free connection to the incubator; and you
to replace the cylinder when it gets low. If it runs out over
weekend, it can be bad news for your cells. So an ideal
has _two_ cylinders connected to a gadget that
switches from the empty cylinder to the full one, ensuring
continuity of supply.
Now, all this is a bit silly. CO2 is very easy to make by
combustion. So, I suggest a better way.
Inside the incubator, we place a little battery-powered or
mains-fed gizmo consisting of a alcohol burner, an electronic
ignition, and a snuffer. It also has a CO2 sensor (like current
CO2 incubators). When the CO2 level falls, the electronic
igniter lights the wick, burning alcohol to produce CO2.
a couple of seconds, the snuffer drops down over the wick to
extinguish the flame. If the CO2 level is still too low, the
process repeats every few minutes.
One problem is that the burning will raise the temperature
the incubator, which would be very bad. However, if the
small flame is active for only a couple of seconds every few
minutes, the heater control of the incubator will
and the temperature deviation will be negligible.
A level sensor can warn the user when the alcohol needs
topping up. No CO2 cylinders or automated changeover
are needed. It also means that you can run a CO2 incubator
in locations too remote for regular cylinder deliveries.
[bs0u0155, Aug 26 2019]
||Potential bun, but I want to see some math about how much
the flame will affect the carbon dioxide concentration and
||Well, I don't have the math but I do have an experiment.
Burning an alcohol-soaked tissue in my CO2 incubator for
about 5 seconds sent the CO2 concentration up into the 10s
of percent, and caused a brief blip of about 5°C. +5°C is
completely unacceptable, but I also produced far too much
CO2. I think a much smaller flame for a couple of seconds
would give me 5% CO2 for a temperature rise of maybe
0.5°C. An even smaller flame in short bursts would reach
5% CO2 without a significant temperature change.
||If you were really worried about temperature fluctuations,
you could have the burner thermally isolated from the
chamber, and just chimnify the resulting CO2-rich gas into
the chamber. But I don't think that would be necessary.
||A look at the numbers, Aigas charge us about $1.80/kg for
CO2, Decon charge about $15/kg for EtOH, now a kg of
EtOH = 2 kg of CO2 when combusted, but it still turns out
dramatically expensive. Then there's doing the
combustion in a clean way, you'll have water to deal
with, and worse there's non-CO2 combustion products,
just a little CO for example could mess things up.
||Now, HCl is cheap, and baking soda can be bought for
~$1/kg. Dosing is a microcontroller and a cheap
peristaltic pump. No flames, purity guaranteed.
||One problem I have with incubators, they can only INCREASE
CO2. A total pain, I blame the cancer people who have cells
that can't be bothered actually doing any real respiration.
Consequently, if you have a full incubator of cells that
actually use their mitochondria, the CO2 can go above 5%
over the weekend.
||Another tactic, used by labs with relaxed attitudes, is to
have a nice healthy bacterial colony living in the water at
the bottom. Always an interesting smell come monday.
||//$15/kg for EtOH// Jeezus that's cheap! Where exactly
did you find that? I pay a fortune for 96% ethanol, even
without duty. But, we can use methanol instead, which I
believe is much cheaper.
||Agreed, CO would be bad - but how much CO is produced
when burning alcohol in what is essentially air? As for water
- many incubators are humidified anyway.
||The baking soda/HCl option is sort of nice, but not as simple
as an alcohol burner. And the main consideration was not
cost (which won't be great in any case) but faff.
||See link, we get it even cheaper via the hospital
pharmacy, but the lady who orders is on hols, so I have no
idea exactly how much. It still involves a fax machine for
||I know many incubators are humidified, but you have to
be able to deal with an excess. Actually, there needs to
be an auto-top up on incubators. I have one on my fish
tank, they're not pricey.
||HCl/Limestone? Could use an XYZ controlled dropper to
slowly acid etch your own face into a block of stone.
||Or, how about using Pd/Pt catalysis for oxidation of the
natural gas? no flame, entirely gaseous. The only problem
I can think of is the sulfur compounds they put in the gas.
Buggers a lot of catalysts right up and probably cells too.
||Ah, America. Land of the home and the brave of the free. I
guess high ethanol prices are a UK thing. I forget the last
price I paid but it was over £200 for 2.5l of 96%.
||Natural gas - does bottled gas have sulphur? I guess it must
have a sulphur-containing odorant (since it still smells bad).
Otherwise it would be a good solution; you could use the same
camping-gas cylinders that you use for lab bunsens.
||They put the stinky stuff in everything that might get near a
consumer. Still, a great commercial opportunity to sell
activated charcoal filters. No CO2, just recurring filters...