ISO2 Oxygen Meter - World Precision Instruments

ISO2 Oxygen Meter - World Precision Instruments
WORLD
PRECISION
INSTRUMENTS
Instrumenting scientific ideas
INSTRUCTION MANUAL
ISO2
Isolated dissolved oxygen meter and oxygen electrode
Serial No._____________________
www.wpiinc.com
030416
ISO2
CONTENTS
ABOUT THIS MANUAL.................................................................................................................... 1
INTRODUCTION............................................................................................................................... 1
Parts List....................................................................................................................................... 2
Unpacking.................................................................................................................................... 2
INSTRUMENT DESCRIPTION......................................................................................................... 3
Sensor Structure and Assembly............................................................................................. 3
Recorder Output........................................................................................................................ 3
OPERATING INSTRUCTIONS.......................................................................................................... 4
Calibration................................................................................................................................... 4
Polarization............................................................................................................................ 4
Zero (Oxygen) Point Calibration....................................................................................... 5
Scale Factor Adjustment..................................................................................................... 6
Calibration for O2 in Living Tissue/Blood.............................................................................. 8
MAINTENANCE................................................................................................................................. 9
Durability and Handling............................................................................................................ 9
Storing the Sensor..................................................................................................................... 9
Cleaning the Membrane........................................................................................................10
Sterilizing the Membrane.......................................................................................................10
Replacing the Membrane Sleeve.........................................................................................10
Cleaning the Electrode Surface............................................................................................12
Batteries.....................................................................................................................................12
ACCESSORIES.................................................................................................................................12
TROUBLESHOOTING....................................................................................................................13
Dry Sensor Test........................................................................................................................13
APPENDIX........................................................................................................................................15
DECLARATION OF CONFORMITY
...........................................................................................................................................................18
WARRANTY......................................................................................................................................19
Claims and Returns.................................................................................................................19
Repairs........................................................................................................................................19
Copyright © 2016 by World Precision Instruments, Inc. All rights reserved. No part of this publication
may be reproduced or translated into any language, in any form, without prior written permission of
World Precision Instruments, Inc.
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ISO2
ABOUT THIS MANUAL
The following symbols are used in this guide:
This symbol indicates a CAUTION. Cautions warn against actions that can cause
damage to equipment. Please read these carefully.
This symbol indicates a WARNING. Warnings alert you to actions that can cause
personal injury or pose a physical threat. Please read these carefully.
NOTES and TIPS contain helpful information.
Fig. 1—The ISO2 meter works with the OXELP oxygen sensor.
IMPORTANT NOTE: Before using the ISO2 dissolved oxygen meter for the first time,
connect the sensor and apply power to the instrument overnight.
IMPORTANT NOTE: The OXELP oxygen sensor is specifically designed to be used
with WPI’s ISO2 dissolved oxygen meter. To use the OXELP with other instruments,
see Fig. 2 on page 3 for plug information.
INTRODUCTION
ISO2 and its associated OXELP sensor provide accurate, stable and electrically isolated
oxygen measurements. The recorder output is not electrically connected to the
OXELP sensor circuitry. This offers the important advantage that other sensors may
be used in the same sample as the OXELP without interfering with one another, and
background noise is greatly reduced. With a sensor tip diameter of just 2mm and low
oxygen consumption, ISO2 and its associated sensor excel in making measurements
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in small sample volumes. Other features include a fast response time and a sturdy
stainless steel sensor body.
The instrument amperometrically measures the concentration of oxygen in aqueous
solutions and gas mixtures. Measurements can be displayed either as a percentage of
atmospheric pressure, parts per million (ppm), or as a redox current in nanoamperes
(nA). The oxygen sensor houses a platinum working electrode and a silver counter/
reference sensor inside a stainless steel sleeve. A gas permeable polymer membrane
fits over the end of the sleeve which allows oxygen to pass while blocking liquids, ions
and particulate matter. Oxygen diffuses through the membrane and is reduced at the
platinum cathode which is held at –0.7V when the instrument is on. This results in an
electrical current being generated, the magnitude of which is determined by the rate of
diffusion to the sensor which is proportional to the partial pressure of oxygen outside
the membrane. The current serves as a measure of the partial pressure of oxygen.
ISO2 comes ready to use. Just attach the OXELP sensor to the meter, turn the power
on and wait for the current to decay to a stable value. This usually takes a couple of
hours. The current can be monitored by setting the ISO2 to the nA setting. Once the
current stabilizes you may then calibrate the instrument.
Parts List
After unpacking, verify that there is no visible damage to the sensor. Verify that all
items are included:
(1) 5377 OXELP Startup kit, including:
(2) 2mm OXELP sleeves
(1) 3563 1CC syringe without needle
(1) 5379Filler bottle
(1) 7326 Bottle of filling solution, 10mL
(1) MF28G67 Microfil, 28 gauge
(1) ISO2 Dissolved oxygen meter
(1) OXELP Oxygen electrode probe
(1) Instruction Manual
Unpacking
Upon receipt of this instrument, make a thorough inspection of the contents and
check for possible damage. Missing cartons or obvious damage to cartons should be
noted on the delivery receipt before signing. Concealed damage should be reported
at once to the carrier and an inspection requested. Please read the section entitled
“Claims and Returns” on page 19 of this manual. Please contact WPI Customer
Service if any parts are missing at 941-301-1003 or customerservice@wpiinc.com.
Returns: Do not return any goods to WPI without obtaining prior approval (RMA
# required) and instructions from WPI’s Returns Department. Goods returned
(unauthorized) by collect freight may be refused. If a return shipment is necessary,
use the original container, if possible. If the original container is not available, use a
suitable substitute that is rigid and of adequate size. Wrap the instrument in paper or
plastic surrounded with at least 100mm (four inches) of shock absorbing material. For
further details, please read the section entitled “Claims and Returns” on page 19 of
this manual.
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INSTRUMENT DESCRIPTION
Sensor Structure and Assembly
The basic structure of the OXELP sensor is shown below (Fig. 2).
Membrane
Sleeve
Locking Cap
Probe Handle
Electrodes
Male BNC
Connector
Fig. 2—OXELP Sensor assembly
Membrane–Gas permeable, polymeric membrane covering the end of the stainless
sleeve to separate it from the external environment
Sleeve–Disposable, protective stainless steel sleeve (WPI#5378) that houses the
sensitive electrode pair. The sleeve is flanged to properly connect with the locking
cap. It must contain fresh electrolyte (WPI#7326).
Electrode–Internal O2-sensing pair of working and counter (reference) electrodes
Probe Handle
Locking Cap–Attaches the sleeve to the probe handle
When the sensor is fully assembled (with locking cap and sleeve in place) the internal
electrode should press gently against the polymeric membrane, which will be slightly
stretched. This ensures that the electrolyte diffusion is as thin as possible, minimizing
sensor response time.
NOTE: Once a membrane is stretched it is permanently
deformed and should not be reused if the sleeve is removed
from the electrode.
Additional membrane sleeves are available in packages of 4
with electrolyte filling solution (WPI #5378). The start-up kit
(WPI #5377) also includes replacement membrane sleeves,
along with all the accessories to fill them properly with
electrolyte solution.
Fig. 3—(Right) The 5377 ISO2 startup kit includes a calibration
bottle, filling solution, syringe, MicroFil and two membrane sleeves.
Recorder Output
The recorder output terminal is electrically isolated. This offers an important recording
advantage because other sensors in the same test medium will not interact adversely
with OXELP. The output signal from the Recorder connector is 1mV/nA of sensor
current regardless of whether the selector switch is in the %, ppm or nA range.
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OPERATING INSTRUCTIONS
Calibration
For accurate results the sensor should be calibrated as closely as possible to the
temperature and medium at which the measurement is to be made (if measurements
are in gas, calibrate in gas).
To calibrate the sensor:
1. Turn on the ISO2, and polarize the sensor (“Polarization” on page 4).
2. Zero the sensor (“Zero (Oxygen) Point Calibration” on page 5).
3. Adjust the scale factor (“Scale Factor Adjustment” on page 6).
NOTE: The O2 solubility ppm tables are located in the Appendix.
NOTE: With an external data recorder, a three-point calibration can be used. Refer to
the ISO-OXY-2/OXELP manual available from www.wpiinc.com/manuals.
Polarization
The OXELP sensor should always remain connected to the ISO2. When the ISO2 is
turned off a potential of –0.2V is applied to the platinum working electrode. This is
done to minimize the time required for the current to decay when the instrument is
turned on and a potential of –0.7V is applied to the working electrode.
The ISO2 meter will keep the OXELP sensor polarized if it is left connected to the
meter, even when the meter is switched off. For best results, polarization of a new
sensor should be performed over a 24-hour period. However, a 2-hour period will
polarize the sensor enough for 95% accuracy.
TIP: You can determine whether or not the correct potential is being applied to the
working electrode when the instrument is on by placing the instrument in the Vw
setting. The LCD display shows the potential being applied. If the potential is not –0.7V,
then change the potential to the correct value by using a small screw driver to adjust
the Vw ADJ screw on the front panel of the instrument.
To polarize the sensor:
1. Place the sensor in 0.1M PBS solution or water.
2. Connect the sensor to the ISO2. Position the BNC connector, push it into place
and turn the locking nut clockwise to securely connect it.
3. Turn on the ISO2 and switch the meter to the nA mode.
4. The sensor current initially will be high, but it will fall and settle to a stable value
usually after about two hours. The sensor should be allowed at least one hour to
reach a stable baseline current of 16–80nA before it is used for measurement.
Once the current stabilizes, calibrate the instrument.
5. If the stabilized baseline value exceeds 80nA, see “Replacing the Membrane
Sleeve” on page 10.
NOTE: This polarization procedure assumes the temperature is 25ºC. At 37ºC the
baseline current is higher.
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Zero (Oxygen) Point Calibration
The true electronic zero reading can be obtained by removing the sensor from the
ISO2 meter. At that point, the meter has no current running through it and is at the
electronic zero. The meter should read zero. As soon as you connect the sensor to the
meter, you can have a small current leakage, called the baseline current. We calibrate
an instrument to correct for the baseline current. To ensure that the sensor is
registering only the baseline current, ALL oxygen must be purged from the calibration
medium.
Sensor
There are several methods for calibrating the sensor:
• In liquid (water or PBS) bubbled with N2 gas to
purge any intrinsically dissolved O2
• In liquid saturated with sodium hydrosulfide
(Na-Dithionite Na2SO4) to inhibit any intrinsically
dissolved O2
• In a pure N2 gas environment
Bottle Cap
1/8˝
Tubing
Choose the calibration method that most closely
approximates the conditions of the experiment to be
run. For example, if you are measuring oxygen in a PBS
solution, use the liquid calibration method.
Fig. 4—(Right) The calibration bottle is included with the ISO2 system.
Liquid Calibration
The OXELP sensor is designed for measurement of oxygen in liquids. For short
periods of time, it can be used in a gas environment. If the sensor will be used in a gas
environment, use the gas calibration method (page 6).
1. Polarize the sensor. See “Polarization” on page 4. Leave the polarized sensor
immersed in PBS and plugged into the ISO2 meter until you are ready to calibrate it.
2. Fill the supplied plastic calibration bottle (Fig. 4) about 2/3 full of distilled water.
Screw the bottle cap on the bottle.
TIP: If your experiment uses PBS solution, use PBS to calibrate the sensor and
purge the oxygen by bubbling nitrogen in the mixture (Step 3).
3. To purge the oxygen from the liquid, connect 1/8˝ ID plastic tubing (not supplied)
to the port on the side of the bottle. Connect the other end of the tubing to a
pure nitrogen gas source at a low pressure (less than 5 PSI). Bubble nitrogen into
the calibration medium for at least 10 minutes.
TIP: If you prefer, you may use an oxygen scavenger like Na2S2O4 (Sigma-Aldrich
#157953) or Na2SO3 (Sigma-Aldrich #71988) to inhibit the oxygen action in
the distilled water. Be aware that temperature and salinity changes affect the
concentration of the solute needed to purge the oxygen. Solubility tables can be
found in the “Appendix” on page 15. Be sure to use enough of your oxygen
scavenger to completely eliminate the oxygen in the bottle for the duration of the
calibration procedure.
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CAUTION: Wear nitrile gloves when handling sodium sulfite (Na2SO3).
4. Carefully slide the tip of the OXELP sensor through the hole in the top of the
bottle cap. Position the sensor so that the probe handle rests against the bottle
cap. If the bottle is top heavy, you may need to support the sensor. The current
should drop rapidly (after a few seconds) to a value of 0nA.
5. If the current value is not zero, use the Zero ADJ knob to get a zero reading. Use
this procedure to obtain a zero reading on any scale setting (nA, ppm, %). Do not
rotate the zero adjust knob after the zero calibration is complete.
NOTE: If you move the sensor to a liquid that has a change in salinity, it may take a
few minutes for the sensor current to re-stabilize.
Gas Calibration
The OXELP sensor is not designed for long-term use in a gas environment, but may
be used for short experiments.
1. Polarize the sensor. See “Polarization” on page 4. Leave the polarized sensor
immersed in PBS and plugged into the ISO2 meter until you are ready to calibrate it.
2. Screw the bottle cap on the plastic calibration bottle. Connect 1/8˝ ID plastic
tubing (not supplied) to the port on the side of the bottle. Connect the other end
of the tubing to a pure nitrogen gas source at a low pressure (less than 5 PSI). Fill
the supplied plastic calibration bottle with pure nitrogen gas for 10 minutes.
3. Carefully slide the tip of the OXELP sensor through the hole in the top of the
bottle cap. Position the sensor so that the probe handle rests against the bottle
cap. If the bottle is top heavy, you may need to support the sensor. The current
should drop rapidly (after a few seconds) to a value of 0nA.
4. If the current value is not zero, use the Zero ADJ knob to get a zero reading. Use
this procedure to obtain a zero reading on any scale setting (nA, ppm, %). Do not
rotate the zero adjust knob after the zero calibration is complete.
Scale Factor Adjustment
After the instrument has been zeroed, you must adjust the scale factor according
to whether or not the intended measurements are to be made in the gas phase or
aqueous medium.
Gas Phase Measurements
Sensor calibration for gas phase measurements can be accomplished using the
calibration bottle, as described above for zeroing the instrument with nitrogen.
Further calibration can be performed using a tank of known oxygen concentration (for
example, 100% O2 or carbogen–95% O2).
1. Turn the Select knob to %.
2. When the bottle is purged with nitrogen as described in “Gas Calibration” on page
6, the display should read 0.
3. Use the same method to purge the bottle with a known concentration of oxygen.
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If you use pure oxygen, the display should read 100. If the display does not show
the correct value, use a small screwdriver to adjust the % adjustment screw so
that the meter reads 100%.
TIP: Air can also be used as a calibration standard, but since water vapor affects
the sensor reading it is best to use dry air unless the ambient humidity is
accurately known. Dry air can be obtained by passing room air through a column
containing a solid drying agent such as silica gel or calcium chloride and then into
the calibration bottle for calibration. To do this, turn the Select knob to %. The
display should read 21. If not, use a small screwdriver to adjust the % adjustment
screw so that the meter reads 21. If ambient air is used to calibrate at 21%,
ambient humidity may cause a calibration error of as much as 1% O2.
In the % mode, the ISO2 meter displays the percentage of atmospheric pressure that
the oxygen present exerts. For example:
•
In a 100% oxygen environment, the display will read 100 which means that
the partial pressure of oxygen is 1atm (760mmHg).
•
If the display reads 21, then the partial pressure of oxygen is 0.21atm
(160mmHg).
Aqueous Measurements
1. For aqueous calibration, fill the calibration bottle about 2/3 full with distilled water
or PBS.
2. Carefully slide the tip of the OXELP sensor through the hole in the top of the
bottle cap and immerse the sensor tip in the water.
3. Aerate the solution, for a few minutes, by bubbling air through the side arm of the
bottle at a low pressure using a simple aquarium aeration pump.
4. Turn the Select knob to %. The scale reading should be allowed to settle to a
stable reading.
5. Dissolved oxygen calibration is corrected for the effect of water vapor by the
following equations:
(1) pO = 21% × (1 - pH O)
or
(2) pO = 21% × (1 -p’H O/760)
2
2
2
2
where pH O and p’H O are the partial pressure of water vapor at standard
atmospheric pressure in atmospheres and in mmHg, respectively.
For example, the pH O in water-saturated air at 24º is 22mmHg. Therefore, the pO
= 21% × (1 - 22/760) = 20.4%. Note that for purposes of oxygen measurements,
liquid water is considered to be “water-saturated air.” The display should read
20.4%. If it does not, use a screwdriver to adjust the % adjustment screw so that
the meter reads the correct calibration value. The values of water vapor pressures
at different temperatures are listed in the Appendix, Table 3, page 17.
2
2
2
2
6. To measure dissolved oxygen in parts per million (ppm), switch the Select knob
to ppm. See Appendix, Table 1a, page 15. This table gives the solubility of
oxygen in water at different temperatures at an ambient pressure of 1 atm. If
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the solution temperature is 25°C, for example, the proper oxygen reading when
the sensor is in fresh water should be 8.4 ppm. If the display does not show this
value, adjust the ppm screw with a screwdriver so that the meter displays the
correct value. You do not need to correct for the water-vapor effect for a ppm
calibration since the values in Table 1a are obtained in “water-saturated air” at an
atmospheric pressure of 760mmHg.
Parts Per Million
The unit ppm is equivalent to mg/L. The solubility of oxygen in water at 0ºC according
to the Merck index is 4.889mL/100mL. Using the ideal gas law, we can calculate the
number of moles of oxygen present in 100mL:
PV = nRT
n = P × V/R*T
n = (0.21) × (4.889x10-3) / (0.08206) × (273)
n = 45.8 × 10-6 moles
Where P is the partial pressure of oxygen, V is the volume of oxygen, n is the number
of moles of oxygen, R is the universal gas constant, and T is the absolute temperature.
From the number of moles of oxygen we can calculate the number of grams of
oxygen: 45.8 × 10-6 mol × 32g/mol = 1.46 × 10-3g
There is (1.46 x 10-3g/0.1L) 14.6mg of oxygen per liter.
Since 1L of water has a mass of 1000g, and there are 1,000,000mg in 1000g, the
concentration in ppm is: (14.6 × 10-3g/L) / (1000g/L) = 14.6 ppm
This value corresponds to that given in Table 1a.
For accurate results, the temperature of the water sample and the fluid being tested
should be identical. They should be continuously stirred using a magnetic stirrer.
Redox current can be measured by switching the Select switch to nA.
When measuring fluid samples for dissolved oxygen, periodically rinse the exterior
of the sensor with distilled water, blot the membrane dry and recheck the sensor’s
calibration as described above.
Calibration for O2 in Living Tissue/Blood
The ISO2 meter and OXELP sensor may be used in applications involving O2
measurements in vitro or in vivo in living tissue or fluids such as blood. You may
still use the calibration procedure in this manual for these measurements since a
membrane-covered amperometric oxygen sensor always measures oxygen activity,
not concentration. Although it is normal to think in terms of dissolved oxygen
concentration, it is actually more appropriate to define oxygen in solution in terms of
activity, since this is the “effective concentration.” For example, in distilled water the
activity coefficient, gc, is close to unity, but in solutions with high salt concentration the
activity coefficient is different from unity and concentration and activity of dissolved
oxygen are no longer equal. The concentration falls while activity remains constant.
For a membrane-covered oxygen sensor, this is an important effect, since an oxygen
detector only responds to the difference in activity across the membrane rather than
the concentration difference. In samples containing an electrolyte, while the oxygen
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concentration falls with increasing salt concentration, the sensor current remains
constant.
If it is necessary to have a measure of dissolved oxygen in terms of concentration,
then the calibration is somewhat more complicated since the relationship between
activity and concentration may change with the change of salt concentration in the
samples. The activity coefficient, a ratio of the activity to the concentration, generally
cannot be predicted and we rely on empirical determinations since the compositions
of living fluids such as blood are extremely complicated. Use the fluid to be tested as
a “solvent” to prepare a calibration standard. Alternatively, use the Bunsen absorption
coefficient, a, to calculate the oxygen concentration in blood in terms of the results
with the oxygen sensor. The equation is:
C=
α
× (pt-pH2O) × pO2
where K is a conversion factor depending on the unit of pressure chosen (1 for atm), pt
and pH O are the total pressure of gas and the partial pressures of water, respectively.
2
pO is the partial pressure of oxygen in blood obtained from the measurements with the
2
oxygen sensor. Bunsen Coefficients for solubility of oxygen in plasma and blood can be
found in the Appendix, Table 4 on page 17. It is very important to calibrate at
the same temperature as that of the measurement site.
molar volume × K
MAINTENANCE
Durability and Handling
The OXELP sensor is designed to be used in buffered aqueous solutions and in gases
at ambient pressure. The use of the sensor in other fluids or pressures may damage
the membrane. Organic solvents must not be used. If you have a particular solution
that may be in question, please contact WPI for information.
The sensor is relatively durable, except for the membrane sleeve. Exercise caution
when handling any sensor to avoid actions that could damage the sensor tip. Pay
particular attention to the sensor membrane, because the membrane is extremely
delicate and improper handling will lead to damage. Refer to the Sensor Unpacking
Instructions that came with your sensor for handling instructions.
CAUTION: Do NOT scratch the sensor membrane sleeve. Do NOT wipe the
sensor membrane with anything, even Kimwipes. If necessary, squirt it with
distilled water or compressed air. The sensor membrane is easily punctured if it
comes into contact with sharp objects. Do NOT let a stir bar come into contact with
the sensor membrane.
Storing the Sensor
With proper care and by following the instructions below a membrane sleeve should
last for one month. Use the following guidelines to maximize the life of the sensor:
STANDBY: If the oxygen sensor is being used on a daily basis, leave the monitoring
device ON continuously with the sensor plugged in and its tip suspended in distilled
water to maintain polarization.
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SHORT-TERM: The reduction of oxygen and other trace impurities on the electrode
surface causes a decrease in the surface activity of the working electrode. This
phenomenon is referred to as “poisoning,” and over time has the effect of gradually
reducing the electrode’s capability to generate a sufficient redox current. If the
sensor is not to be used for a period of more than 2-3 days, disconnect it from the
monitoring device, and store it with the tip immersed in distilled water. This practice
reduces the possibility of a gradual reduction of the electrode surface activity under
long-term polarization.
CAUTION: Storing the sensor short-term in this condition can cause the inner
filling solution to dry out as the solution evaporates out of the top of
membrane sleeve. The membrane itself is water impermeable. Crystallization
of the filling solution inside a sleeve can cause damage to the electrode when the
sleeve is removed. (An electrode with crystallized particles on the tip gives high
readings on the meter.)
LONG-TERM: For long-term storage of more than one week, remove the membrane
sleeve, clean the sensor tip with deionized water and dry it carefully. Protect the tip
and store the sensor with the membrane sleeve removed in a dry, cool environment.
See “Replacing the Membrane Sleeve” on page 10.
TIP: Used membrane sleeves (with or without the membrane) make an ideal cover for
protecting a dry sensor in long-term storage.
Cleaning the Membrane
The membrane sleeve itself requires very little maintenance. The primary concern is
to avoid damage to the membrane and to keep it as clean as possible. After each use
the membrane should be cleaned by suspending the tip in distilled water for 20–30
minutes to dissolve salts and remove particles which may have accumulated on it.
If the probe was used in a protein-rich solution, the tip should first be soaked in a
protease solution for several minutes to remove protein build-up, and then in distilled
water. Enzymatic detergent (for example, Enzol, WPI#7363) can also be used.
Accumulated organic matter can be removed by briefly immersing the tip in a 0.1M
HCl or 0.1M NaOH (at times both may be necessary) for 10 seconds.
A good indication of a dirty membrane sleeve is a sluggish response or an unusually
low sensitivity. If these problems are not rectified by cleaning, then the membrane
sleeve should be replaced.
Sterilizing the Membrane
The membrane sleeves can be sterilized chemically using an appropriate disinfectant
(for example, Cidex, WPI#7364).
CAUTION: Do not use alcohol on the sensors, and do NOT expose them to
organic solvents
Replacing the Membrane Sleeve
Even with the best of care and proper maintenance, the membrane sleeve will
eventually need to be replaced.
1. Unscrew the locking cap from the handle.
2. Hold the stainless steel sleeve and the locking cap and pull them away from
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3. 4. 5. 6. the internal electrode assembly. Be careful not to bend the internal electrode
assembly.
Rinse the internal electrode with distilled water (particularly the tip) and let it soak
for at least 15 minutes. Be careful not to let water get up into the handle.
Gently dry the sensor with a soft tissue (Kimwipes). Be sure to dry thoroughly the
flat surface at the tip of the electrode. After drying the current should stabilize
fairly quickly to a low value (for example, 0-20pA). If this occurs, it is a good
indication that the electrode is functioning properly.
If the electrode is not clean, repeat steps 3 and 4.
Slide the locking cap from the old, used sleeve, and gently slide it onto the new
replacement sleeve. Additional membrane kits with sleeves and filling solution
(WPI#5378) may be purchased separately.
Fig. 5—(Right) Membrane placement. The
internal electrode tip should protrude slightly
out into the membrane.
7. Dip the internal electrode 1–2cm into
The internal electrode tip
the ISO2 Filling Solution (WPI #7326) included
should protrude slightly
in the start-up kit (WPI #5377). In the 100nA
out into the membrane.
range, the current rises rapidly (for example,
60–300nA). Then, the current value will beging
to fall. Using the MicroFil™ nonmetallic syringe needle (WPI #MF28G67-5) and
1mL plastic syringe (included in the start-up kit) inject approximately 100µL
of electrolyte directly into the new sleeve. Insert the MicroFil in as far as it will
go, and slowly draw the MicroFil out of the sleeve as it fills. The filling process
should be performed slowly enough so as not to create turbulence, which could
introduce air bubbles into the electrolyte. The MicroFil (#MF28G67) included in
the startup kit is less than the length of the sleeve, so that it will not puncture the
delicate membrane at the tip of the sleeve during injection.
TIP: If air bubbles form in the electrolyte, gently flick or tap the side of the sleeve
to remove the bubbles.
8. Slowly and smoothly insert the electrode into the sleeve, and screw the locking
cap into the handle. The locking cap screws into the probe handle. Tighten it just
enough for the membrane to touch the electrode. DO NOT OVER-TIGHTEN. The
electrode should be observed to press gently against the membrane (Fig. 5).
9. The current displayed on the meter at this time will be high or offscale.
10. Suspend the tip of the newly assembled probe in 0.1M PBS buffer solution.
11. After 10-15 minutes the current should no longer be offscale and will gradually
decrease with time. It may take up to one hour for the sensor current to reach a
low stable value, at which time it will be ready for use.
TIP: The integrity of the new membrane can be determined by immersing the
probe tip into a strong saline solution (1M). If the current increases dramatically
or is offscale, then the membrane integrity is not good and a new membrane will
have to be fitted. Additional membranes (packages of 4) with filling solution are
available from WPI (#5378).
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Cleaning the Electrode Surface
The reduction of oxygen causes a decrease in the surface activity of the working
electrode which gradually “poisons” it. This poisoning reduces the redox current from
the reduction of oxygen. In order for the ISO2 to function properly, the minimum
current required at room temperature and 21% oxygen (air) is 15nA. If the reduction
current drop below this value, then the instrument no longer functions properly.
Once the reduction current does drop below 15nA, there is a CLEAN function which
may be used to reverse some of the damage and restore activity so that the sensor
can continue to be used. This function can be used every two months or so when the
sensitivity of the sensor drops to 25% of its original sensitivity.
1. Switch the power knob to the CLEAN setting. When this is done the potential
applied to the platinum electrode changes to +0.9V. This causes a change of
polarity on the surface of the electrode to reverse some of the oxidation that has
taken place on the tip of the electrode. This helps to restore the electrode activity.
2. Leave the instrument on this setting for a period of 30 minutes. The LCD display
output in this setting is meaningless and should be ignored.
3. After the 30 minutes, turn the instrument off and leave it off for at least one hour
before using the sensor. It may be necessary to experiment with the timing of the
cleaning process, since each sensor is unique.
The cleaning process will not indefinitely extend the life of an electrode. Eventually, the
electrode must be replaced, but if it is well cared for, an electrode can last a long time.
Batteries
The battery operated ISO2 should work for hundreds of hours before its two 9V
batteries require replacement. A low battery indicator on the panel LCD appears if the
batteries are low. To replace the batteries, first turn the power off. Remove the four
screws on the bottom of the instrument case and then remove the entire front panel
assembly. Replace the batteries and then reassemble the case.
Remember to turn the instrument power off when it is not in use.
ACCESSORIES
OXELP
5378 7326
5377
5399
5381
12
Oxygen electrode in sealed bottle
Package of 4 replacement sleeves with membranes
ISO2 filling solution (10mL)
Replacement Startup kit includes a Calibration Bottle, 10mL Filling Solution,
1cc Syringe, 2 Replacement Membranes Sleeves, MicroFil (28 ga.)
T-Adaptor Flow-Through Kit includes: 2 female luer T’s, 3 luer lock fittings, 3
2mm gaskets, and 6 male luer to 1/8 inch tubing
Rack Mount Kit
World Precision Instruments
ISO2
TROUBLESHOOTING
Sensor is not responding to O2 or Unstable
is showing a longer response time readings
Meter
reads –1
Issue
Possible Cause
Solution
Sensor is shorted
Test the sensor with the dry sensor test.
See “Dry Sensor Test” on page <OV>.
Sensor surfaces may be coated
Try the clean function and retest. See
“Cleaning the Electrode Surface” on page
12.
Sensor has aged
Try the dry sensor test and compare the
wet test current consumption results
after a 2 hour polarization to the proof
of performance sheet. If the current is
outside the upper ranges of 30–50nA and
the sensor detects O2 and is still linear,
but sluggish, then one of the electrodes
may be compromised. This sensor should
be replaced soon.
The membrane is clogged
Replace the membrane sleeve. See “Replacing the Membrane Sleeve” on page
10.
ISO2 meter tests
Remove the electrode from the BNC.
Zero the meter and place a 1MΩ resistor
across the input BNC. At 700mV the
display should read 700nA. The ISO2 can
measure up to ±2000nA.
Dry Sensor Test
Liquid sensors that are stored assembled for more than 45 to 60 days may dry out
internally and may no longer be functional or recoverable. To determine if the sensor
itself is defective or has a short, you may perform a dry sensor test on a sensor
without a sleeve.
1. Carefully remove the membrane sleeve. See “Replacing the Membrane Sleeve” on
page 10.
NOTE: If the sensor has not been used for several months, the electrolyte
solution may have dried out. If this is the case, the membrane sleeve is more
difficult to remove, because it tends to stick to the sensor. Soak the assembly in
distilled water for 2 hours and gently remove the sleeve to avoid damaging the
delicate sensor tip.
World Precision Instruments
13
2. Remove any crystals and lightly wash the sensor with distilled water.
3. Allow sensor to air dry.
4. Without the sensor connected to the meter, turn on the ISO2 meter and zero the
instrument to 0nA. Do not move the zero set control from this point.
5. DRY TEST: Connect the dry electrode and observe the display. You should see
a near zero reading (~0nA). If the reading is higher, the sensor is defective and
needs to be replaced.
6. WET TEST: If the sensor passed the test in step 5, insert the sensor into a vIal with
filling solution. The ISO2 should display a reading between 50–3000nA and then
slowly decrease over the next few minutes. If the value does not fall below 10nA,
then this sensor is damaged and should be replaced. Try cleaning the sensor. See
“Cleaning the Electrode Surface” on page 12.
7. If the sensor passed the tests in steps 5 and 6, the sensor itself is probably
working properly. Install a new membrane sleeve and calibrate it in normal test
solutions to determine the new sensitivity slope of the electrode. See “Replacing
the Membrane Sleeve” on page 10.
NOTE: If the sensor does not read a high nA value on refilling the membrane sleeve,
then an air pocket may be trapped in the bottom of the sleeve. Use care in the refilling
process with the correct length of Microfil (WPI #MF28G67-5) and gently tap the
sensor to dislodge these air pockets.
TIP: Do not reuse an old membrane, because the membrane itself is stretched
once it is used. After it is removed, it maintains the surface deformity and system
performance may diminish.
NOTE: If you have a problem/issue that falls outside the definitions of this
troubleshooting section, contact the WPI Technical Support team at 941-301-1003 or
technicalsupport@wpiinc.com.
14
World Precision Instruments
ISO2
SPECIFICATIONS
This unit conforms to the following specifications:
Modes...............................................................% O2: 0–100%, ppm: 0–20, Current: 0–199.9nA
Resolution...............................................................................................................................0.1 ppm
Accuracy...................................................................................................................................... ±1.5%
Output Resistance...................................................................................................................1000Ω
Display.............................................................................................................................3.5-digit LCD
Recorder Output...................................... 1mv = 1nA (i.e., 10mV = 10% O2 = 10ppm = 10nA)
Power........................................ Two 9V alkaline batteries (included) NEDA: MN1604, 6LR61
Battery Life..................................................................................................... 1000 hours (approx.)
Dimensions...............................................................................20.3 x 10.2 x 5.1cm (8 x 4 x 2 in.)
Weight/ Shipping Weight..........................................................................2 lb (0.9kg)/5 lb (2.3kg)
OXELP
Tip Length.................................................................................................................................. 76mm
Overall Length........................................................................................................................137mm
Tip Diameter................................................................................................................................2mm
Cable Length.....................................................................22cm (4 ft), including BNC connector
Response Time........................................ 10 seconds, 90% response in well-stirred solution
Drift.......................................................................................................................................< 1%/min.
APPENDIX
Table 1a: Solubility of Oxygen in Fresh Water
°F
°C
ppm
°F
°C
ppm
32
0
14.6
66
19
9.4
34
1
14.2
68
20
9.2
35
2
13.8
70
21
9.0
37
3
13.5
72
22
8.8
39
4
13.1
73
23
8.7
41
5
12.8
75
24
8.5
43
6
12.5
77
25
8.4
45
7
12.2
79
26
8.2
46
8
11.9
81
27
8.1
48
9
11.6
82
28
7.9
50
10
11.3
84
29
7.8
52
11
11.1
86
30
7.6
54
12
10.8
88
31
7.5
55
13
10.6
90
32
7.4
57
14
10.4
91
33
7.3
59
15
10.2
93
34
7.2
61
16
10.0
95
35
7.1
63
17
9.7
97
36
7.0
64
18
9.5
99
37
6.9
Solubility of oxygen in parts per million (ppm) in fresh water at different temperatures, in equilibrium
with air at barometric pressure of 760mmHg (101.3 kPa) and oxygen partial pressure of 159mmHg
(21.1 kPa).
World Precision Instruments
15
Table 1b: Solubility of Oxygen in Seawater
°C
5 g/L
10 g/L
15 g/L
20 g/L
0
13.8
13.0
12.1
11.3
1
13.4
12.6
11.8
11.0
2
13.1
12.3
11.5
10.8
3
12.7
12.0
11.2
10.5
4
12.4
11.7
11.0
10.3
5
12.1
11.4
10.7
10.0
6
11.8
11.1
10.5
9.8
7
11.5
10.9
10.2
9.6
8
11.2
10.6
10.0
9.4
9
11.0
10.4
9.8
9.2
10
10.7
10.1
9.6
9.0
11
10.5
9.9
9.4
8.8
12
10.3
9.7
9.2
8.6
13
10.1
9.5
9.0
8.5
14
9.9
9.3
8.8
8.3
15
9.7
9.1
8.6
8.1
16
9.5
9.0
8.5
8.0
17
9.3
8.8
8.3
7.8
18
9.1
8.6
8.2
7.7
20
8.7
8.3
7.9
7.4
21
8.6
8.1
7.7
7.3
22
8.4
8.0
7.6
7.1
23
8.3
7.9
7.4
7.0
24
8.1
7.7
7.3
6.9
25
8.0
7.6
7.2
6.7
26
7.8
7.4
7.2
6.7
27
7.7
7.3
6.9
6.5
28
7.5
7.1
6.8
6.4
30
7.3
6.9
6.5
6.1
Solubility of oxygen (milligrams/liter) in seawater of different salinities, in equilibrium with air at
barometric pressure of 760mmHg (101.3kPa) and oxygen partial pressure of 159mmHg (21.2kPa).
Table 2: Oxygen Solubility vs. Altitude
Altitude (ft)
-540
Sea Level
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
Pressure (mmHg)
775
760
746
732
720
707
694
681
668
656
644
632
621
609
Solubility Correction Factor
1.02
1.00
0.98
0.96
0.95
0.93
0.91
0.90
0.88
0.86
0.85
0.83
0.82
0.80
Oxygen solubility obtained from Table 1a or Table 1b should be corrected if barometric pressure is
different than 760mmHg or at altitudes other than sea level.
16
World Precision Instruments
ISO2
Table 3: Water-vapor Partial Pressure
Temp.
°C
0
2
4
6
8
10
12
14
16
18
Pv
mmHg
5
5
6
7
8
9
11
12
14
16
Temp.
°C
20
22
24
26
28
30
32
34
36
38
40
Pv
mmHg
18
20
22
25
28
32
36
40
45
50
55
Table 4: Bunsen Coefficients (a) for Solubility of Oxygen in Plasma and Blood
Temp °C
15
20
25
28
30
35
37
40
Plasma
0.0302
0.0277
0.0257
0.0246
0.0238
0.0220
0.0214
0.0208
5g
0.0310
0.0282
0.0261
0.0249
0.0241
0.0226
0.0220
0.0221
World Precision Instruments
Blood Hb g/100 mL
10 g
15 g
0.0312
0.0316
0.0284
0.0287
0.0263
0.0265
0.0251
0.0253
0.0243
0.0245
0.0227
0.0229
0.0221
0.0223
0.0212
0.0214
20 g
0.0323
0.0293
0.0271
0.0259
0.0251
0.0234
0.0228
0.0219
17
DECLARATION OF CONFORMITY
18
World Precision Instruments
ISO2
WARRANTY
WPI (World Precision Instruments, Inc.) warrants to the original purchaser that this equipment, including
its components and parts, shall be free from defects in material and workmanship for a period of
30 days* from the date of receipt. WPI’s obligation under this warranty shall be limited to repair or
replacement, at WPI’s option, of the equipment or defective components or parts upon receipt thereof
f.o.b. WPI, Sarasota, Florida U.S.A. Return of a repaired instrument shall be f.o.b. Sarasota.
The above warranty is contingent upon normal usage and does not cover products which have been
modified without WPI’s approval or which have been subjected to unusual physical or electrical stress
or on which the original identification marks have been removed or altered. The above warranty will not
apply if adjustment, repair or parts replacement is required because of accident, neglect, misuse, failure
of electric power, air conditioning, humidity control, or causes other than normal and ordinary usage.
To the extent that any of its equipment is furnished by a manufacturer other than WPI, the foregoing
warranty shall be applicable only to the extent of the warranty furnished by such other manufacturer.
This warranty will not apply to appearance terms, such as knobs, handles, dials or the like.
WPI makes no warranty of any kind, express or implied or statutory, including without limitation any
warranties of merchantability and/or fitness for a particular purpose. WPI shall not be liable for any
damages, whether direct, indirect, special or consequential arising from a failure of this product to
operate in the manner desired by the user. WPI shall not be liable for any damage to data or property
that may be caused directly or indirectly by use of this product.
Claims and Returns
Inspect all shipments upon receipt. Missing cartons or obvious damage to cartons should be noted on
the delivery receipt before signing. Concealed loss or damage should be reported at once to the carrier
and an inspection requested. All claims for shortage or damage must be made within ten (10) days
after receipt of shipment. Claims for lost shipments must be made within thirty (30) days of receipt of
invoice or other notification of shipment. Please save damaged or pilfered cartons until claim is settled.
In some instances, photographic documentation may be required. Some items are time-sensitive; WPI
assumes no extended warranty or any liability for use beyond the date specified on the container
Do not return any goods to us without obtaining prior approval and instructions from our Returns
Department. Goods returned (unauthorized) by collect freight may be refused. Goods accepted for
restocking will be exchanged or credited to your WPI account. Goods returned which were ordered
by customers in error are subject to a 25% restocking charge. Equipment which was built as a special
order cannot be returned.
Repairs
Contact our Customer Service Department for assistance in the repair of apparatus. Do not return
goods until instructions have been received. Returned items must be securely packed to prevent
further damage in transit. The Customer is responsible for paying shipping expenses, including
adequate insurance on all items returned for repairs. Identification of the item(s) by model number,
name, as well as complete description of the difficulties experienced should be written on the repair
purchase order and on a tag attached to the item.
* Electrodes, batteries and other consumable parts are warranted for 30 days only from the date on which
the customer receives these items.
World Precision Instruments
19
USA
International Trade Center, 175 Sarasota Center Blvd., Sarasota FL 34240-9258
Tel: 941-371-1003 • Fax: 941-377-5428 • E-mail: sales@wpiinc.com
UK
1 Hunting Gate, Hitchin, Hertfordshire SG4 0TJ
Tel: 44 (0)1462 424700 • Fax: 44 (0)1462 424701 • E-mail: wpiuk@wpi-europe.com
Germany
Zossener Str. 55, 10961 Berlin
Tel: 030-6188845 • Fax: 030-6188670 • E-mail: wpide@wpi-europe.com
China & Hong Kong
WPI Shanghai Trading Co., Ltd.
Rm 29a, No8 Dongfang Rd., Pudong District, Shanghai, 200120 PR China
Tel: +86 21 6888 5517 • E-mail:chinasales@china.wpiinc.com
Brazil
Av. Conselheiro Nébias, 756 sala 2611, Santos-CEP: 11045-002, São Paulo Brazil •
Tel: (013) 406-29703 • E-mail: info@brazil.wpiinc.com
Internet
www.wpiinc.com • www.wpi-europe.com • www.wpiinc.cn
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