Instructions

TECHNICAL NOTE
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Drying tube
Venting stopper for microfilters
with Luer cone:
Bottle-top dispensers and bottle-top burettes come with a
ventilation channel, which ensures that the pressure inside the
media bottle is the same as the ambient pressure.
If the inside of the bottle were to be hermetically sealed from
the ambient atmosphere, a vacuum would be created in the
bottle as removal of the medium increases. Depending on the
vapor pressure of the medium, it would begin to evaporate
as a result. At the very least, the dispensing process would be
impaired by the vacuum in the bottle.
The drying tube is used when the medium must be protected
from the penetration of moisture or carbon dioxide from the
air. The drying tube is a plastic tube with a screwed-on elbow
piece and removable closure cap with hose nozzle.
The tube is screwed onto the valve block of the dispensette or
titrette where the ventilation channel is sealed with a perforat-
ed plug on delivery.
Binding water:
Water content in organic solvents that increases over time
can have a disturbing eect on the chemical reaction or the
analytical procedure. In hygroscopic aqueous media, such as
concentrated sulphuric acid, the concentration changes.
Silica gel (made from silicone dioxide) and a molecular sieve
with pore size 4Å (made of zeolites), used individually or in
combination, are a good drying agent for air since they do not
dissolve when the water content increases. Silica gel in com-
bination with a humidity indicator is also referred to as blue
gel or orange gel. As the water content changes, the changing
color makes it easy for the user to tell when the drying tube
filling has expired.
Binding CO
2
:
When CO
2
from the air dissolves in water, carbonic acid forms.
If the solution is a base, for example an aqueous sodium or
potassium hydroxide solution, the CO
2
is bound as a carbon-
ate, which changes the content of the base via a neutralization
reaction. This is particularly a problem when the base solution
is a titration medium, since titrating a solution with an un-
known content leads to erroneous results. In addition, carbon-
ates that are by comparison poorly soluble can break down in
the solution – for example in an ethanolic potassium hydroxide
solution. In turn, the precipitates then form salt crystals which
can wear out the piston of the instruments faster and lead to
leaky ball valves.
To bind the CO
2
from the air, granulated absorbers such as
soda lime can be used. Soda lime consists primarily of calcium
hydroxide and sodium hydroxide, with an indicator also mixed
in.
Binding odors:
The Dispensette® is a laboratory instrument and should
therefore also be operated in a laboratory environment that
includes technical ventilation with suicient air exchange. In
practice; however, local and temporary exposure to strong
smelling compounds may occur. A drying tube filled with acti-
vated carbon can provide relief in these situations.
If you use the Dispensette® bottle-top dispenser to dispense
sterile media, for example nutrient solutions for cultivating
microorganisms, the instrument should first be autoclaved.
Instructions on preparing instruments can be found in the
operating manual. The venting stopper for microfilters with
Luer cone is used to attach a microfilter over the Luer cone.
If you use the Dispensette® bottle-top dispenser to dispense
a sterile media, such as a nutrient solutions for cultivating
microorganisms, the instrument should first be autoclaved.
The drying tube must be filled with a solid reagent that is
suitable for the application. Adding a bit of mineral wool into
the tube is recommended as a filter material so that the solid
material or its dust cannot enter the bottle.
Venting stopper with Luer cone
without filter attached
Dispensette® with drying tube
With filter attached