3
Preparation
10
3.2 Sterilisation of the
Membrane Filtration Unit
Upon receipt of your water test kit the
Membrane Filtration Unit (MFU) must be
washed thoroughly and then dried with a clean
cloth or paper towel.
Prior to use, the MFU must also be sterilised.
This
is to reduce the risk of cross contamination
of the
water sample. It should be re-sterilised
each time
a new sample of water is analysed.
Sterilisation in the field can be difficult. A simple
way of carrying out this sterilisation is
with the
use of Methanol (Methyl Alcohol).
Items Required:
• Membrane Filtration Unit
• Methanol (Methyl Alcohol)
- not supplied with kit
• Cigarette Lighter/Matches
- not supplied with kit
• Paper Towels - not supplied with kit
• Plastic 1ml Pasteur Pipette
Procedure:
1
Using the Pasteur pipette add approximately
1ml of methanol into the stainless steel
sampling cup.
2 Swirl the methanol around the inside of the
sampling cup, coating as much of the internal
surface as possible.
3 Holding the sampling cup facing away from
you, use a lighter/match to ignite the methanol.
The methanol will ignite instantly. Always
exercise caution during this step. The methanol
will burn with a pale blue flame; in bright
sunlight it can be
difficult to see this
flame. However,
the heat
produced
should confirm it
has ignited.
4 Place the sampling cup base down on a flat
surface while the methanol burns.
5 Assemble the filter funnel and silicone
rubber base components of the MFU.
Ensure that the filter funnel is inserted
in the rubber base in the correct position
for sterilisation (see below), which will leave
a small gap between the bottom of the filter
funnel and the silicone base.
Once the flame has virtually extinguished,
invert the filter funnel and silicone rubber
base components of the MFU and insert into
sampling cup as shown below.
6
Under these conditions, formaldehyde gas is
produced, which has excellent bactericidal
properties. With the MFU in this position,
formaldehyde gas can penetrate all contact
areas, ensuring optimal coverage.
7
Leave for 15 minutes to ensure the formaldehyde
gas carries out a complete sterilisation.
8 Remove filter funnel and base assembly from
the sampling cup.
9 Pour any residual solution in the sampling
cup away and re-insert the filter funnel and
base assembly.
The Membrane Filtration Unit is now sterile
and ready for use. It should be kept in the kit
case until required.
IMPORTANT: This sterilisation procedure
should be repeated each time a new water
sample is to be analysed.
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