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MI-730, 8-730, 16-730
Oxygen Microelectrodes
Operating
Instructions |
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Included
in the Electrode Kit
1 Oxygen Electrode with membrane
housing
6 Replaceable membrane
housings
1 Bottle of
electrolyte
1 Filling tip
1 Set of instructions
5
Polishing pads
Electrode
Assembly and Preparation
-
Remove
the acrylic housing from the
Oxygen electrode by unscrewing
it from the electrode body.
This housing, with affixed
Teflon membrane, does not
contain the necessary oxygen
electrolyte solution.
-
Add oxygen
electrolyte solution to the
acrylic housing. This is
accomplished by attaching a
filling tip to the bottle of
electrolyte and adding the
electrolyte to the housing to a
minimum height of 6 mm. Gently
place the bubble-free end of the
filling tip against the Teflon
membrane and release the
electrolyte to the minimum
height.
-
Insert the
housing on to the Oxygen
electrode, being careful not to
trap any air bubbles near the
electrode tip. The housing is
screwed clockwise into the body
of the electrode until it
stops. Check the tip of the
electrode for proper seating of
the housing against the
electrode. The electrode is
properly seated if the electrode
protrudes slightly beyond the
end of the housing.
Calibration
Calibration of the electrode
requires the use of two standard
gases with percent values that are
close to the percent values of
Oxygen to be measured. Common
values used are 0% Oxygen for
zeroing and 21% Oxygen (Ambient Air)
for sloping or gain
A. Calibration for
gas samples: When samples
to be measured are gaseous, then
calibration should be performed with
humidified gases. Two possible
setups for calibrating the electrode
are shown below. Keep the tip of
the electrode as far as possible
from the surface of the water. The
bubbling rate of the gas should be
slow (3 - 6 bubbles per second).
Although bubbling at a faster rate
will flush the chamber more quickly,
it will also cause a cooling effect
on the electrode. (Insert Picture)
-
Bubble the 0% gas through the
chamber and adjust the zero of
the meter after a stable reading
is obtained. It may take up to
15 minutes to de-gas the chamber
of contaminants, however
bubbling the gas vigorously will
cause droplets to collect on the
tip of the electrode. This will
make the electrode response time
appear to be slow.
-
Bubble the 21% gas (or any other
percent value you decided to use
for your application) through
the chamber until a stable
reading is obtained. Adjust the
calibration control to 21%.
This procedure of alternating
between the two gases should be
continued until you become
confident of stability and
reproducibility. The electrode
is now ready to use.
B. Calibration for liquid
samples: To decrease
calibration time, two separate
calibration chambers should be
used. One for the 0% gas and
another for the sloping gas such as
21%. When setting up the
calibration chambers initially, it
will take up to 30 minutes to flush
each chamber to obtain a steady
state oxygen level and a constant
temperature. Again the bubbling
rate should be carefully regulated
(3 - 6 bubbles per second) so that
both calibrating liquids are at the
same temperature.
Calibrating standards and samples
must be at the same temperature for
accurate Oxygen measurements.
-
Immerse the tip of the electrode
into the 0% standard and adjust
the zero of the meter after a
stable reading is obtained.
-
Remove the electrode from the
first standard and place it into
the second standard. Adjust the
calibration control to the value
of the second standard (ex: 21%)
Alternate between the two
standards until you become
confident of stability and
reproducibility. The electrode
is now ready to use.
Handling
When
necessary, the membrane of the
electrode can be replaced by
following the assembly procedure
above. When removing and replacing
a membrane as well as when
calibrating or making measurements,
be careful not to apply pressure
against the internal electrode. Any
excessive pressure against the
internal electrode can cause the
electrode to crack rendering it
useless and unrepairable.
Cleaning
When using the electrode in
solutions containing protein, the
electrode should be soaked in an
enzyme cleaning solution such as
Terg-a-zyme
(Alconox,
Inc.) after each use for
a couple of minutes to remove the
protein from the membrane surface.
This will prolong the useful life of
the membrane.
Storage
Always clean and rinse the electrode
before storing:
Long-term (over 2 month):
Remove the membrane housing from the
electrode. Rinse the internal
electrode with distilled water and
pat dry. Place a new, unfilled
membrane housing over the internal
electrode and attach loosely (Do not
seat completely). This membrane
will serve to keep the dust off of
the electrode tip.
Short-term: The
electrode can be left in room air
with membrane housing still
attached.
Output Conversion
Formula
for conversion of % oxygen to
solubility in moles/liter:
S = (a/22.414) x (760-p)/760) x
(r%/100)
S = solubility of gas in moles per
liter
a = absorption coefficient of gas at
temperature
P = vapor pressure of water at
temperature
r% = actual reading in percent
Oxygen
Temperature (T) vs.
absorption coefficient (a) for
oxygen in water:
Degrees
Celsius |
Absorption
Coefficient |
Degrees
Celsius |
Absorption
Coefficient |
|
5
|
0.04287
|
19
|
0.03161
|
|
6
|
0.04180
|
20
|
0.03102
|
|
7
|
0.04080
|
21
|
0.03044
|
|
8
|
0.03983
|
22
|
0.02988
|
|
9
|
0.03891
|
23
|
0.02934
|
|
10
|
0.03802
|
24
|
0.02881
|
|
11
|
0.03718
|
25
|
0.02831
|
|
12
|
0.03637
|
26
|
0.02783
|
|
13
|
0.03559
|
27
|
0.02736
|
|
14
|
0.03486
|
28
|
0.02691
|
|
15
|
0.03415
|
29
|
0.02649
|
|
16
|
0.03348
|
30
|
0.02608
|
|
17
|
0.03283
|
35
|
0.02440
|
|
18
|
0.03220
|
40
|
0.02306
|
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