10
3
Preparation
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.
