Page 1
User Guide
AquaPro and
Double Junction
pH Electrodes
Page 2
ROSS and the COIL trade dress are trademarks of Thermo Fisher Scientific Inc.
AQUAfast, Cahn, ionplus, KNIpHE, No Cal, ORION, perpHect, PerpHecT, PerpHecTion,
pHISA, pHuture, Pure Water, Sage, Sensing the Future, SensorLink, ROSS, ROSS
Ultra, Sure-Flow, Titrator PLUS and TURBO2 are registered trademarks of
Thermo Fisher.
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DirectCal, DuraProbe, Environmental Product Authority, Extra Easy/Extra Value,
FAST QC, GAP, GLPcal, GLPcheck, GLPdoc, ISEasy, KAP, LabConnect, LogR, Low
Maintenance Triode, Minimum Stir Requirement, MSR, NISS, One-Touch, One-Touch
Calibration, One-Touch Measurement, Optimum Results, Orion Star, Pentrode,
pHuture MMS, pHuture Pentrode, pHuture Quatrode, pHuture Triode, Quatrode,
QuiKcheK, rf link, ROSS Resolution, SAOB, SMART AVERAGING, Smart CheK, SMART
STABILITY, Stacked, Star Navigator 21, Stat Face, The Enhanced Lab, ThermaSense,
Triode, TRIUMpH, Unbreakable pH, Universal Access are trademarks of
Thermo Fisher.
Guaranteed Success and The Technical Edge are service marks of Thermo Fisher.
PerpHecT meters are protected by U.S. patent 6,168,707.
PerpHecT ROSS are protected by U.S. patent 6,168,707.
ORION Series A meters and 900A printer are protected by U.S. patents 5,198,093,
D334,208 and D346,753.
ionplus electrodes and Optimum Results solutions are protected by
US Patent 5,830,338.
ROSS Ultra electrodes are protected by US patents 6,793,787.
Orion ORP Standard is protected by US Patent 6,350,367.
Orion NoCal electrodes are protected by US Patent 7,276,142.
© 2008 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the
property of Thermo Fisher Scientific Inc. and its subsidiaries.
The specifications, descriptions, drawings, ordering information and part numbers
within this document are subject to change without notice.
This publication supersedes all previous publications on this subject.
Page 3
Introduction
This user guide contains information on the preparation,
operation and maintenance of the Thermo Scientific Orion
AquaPro and double junction pH electrodes.
AquaPro Professional pH Electrodes
All AquaPro pH electrodes feature a patented double junction
reference design and are mercur y-free. These electrodes use
an isolated Ag/AgCl internal reference and a polymer external
reference with an open junction for fast, accurate readings
in complex sample matrices without the sample coming in
contact with silver ions. The AquaPro electrodes are easy to
use and require minimal electrode preparation due to the low
maintenance polymer gel reference.
Double Junction pH Electrodes
Double junction pH electrodes are for general purpose samples
and feature an isolated Ag/AgCl internal reference and an
external reference that is either refillable or gel-filled. These
electrodes offer a mercury-free alternative to hazardous calomel
pH electrodes.
KNIpHE® Double Junction pH Electrodes
The KNIpHE double junction pH electrode is designed for meat,
cheese and other solid or semi-solid food samples. The pH
electrode is surrounded by a stainless steel blade that protects
the electrode and cuts through solid or tough materials. This
electrode is mercury-free and environmentally safe.
1AquaPro and Double Junction pH Electrode User Guide
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Cat. No. Description
9102AP AquaPro combination pH electrode with
glass body and BNC connector
9103APWP AquaPro combination pH electrode with
glass body, semi-micro tip, and waterproof
BNC connector
9104APWP AquaPro combination pH electrode with
glass body, rugged bulb, and waterproof
BNC connector
9107APMD AquaPro pH/ATC Triode with epoxy body
and waterproof BNC and 8 pin MiniDIN
connectors
9115APWP AquaPro combination pH electrode with
epoxy body, semi-micro tip, and waterproof
BNC connector
9135APWP AquaPro combination pH electrode with
epoxy body, flat surface tip, and waterproof
BNC connector
9156APWP AquaPro combination pH electrode with
epoxy body and waterproof BNC connector
9102DJWP
9110DJWP Double junction refillable combination pH
9156DJWP Double junction gel-filled combination pH
9120APWP KNIpHE double junction refillable
Double junction refillable combination pH
electrode with glass body and waterproof
BNC connector
electrode with glass body, semi-micro tip,
and waterproof BNC connector
electrode with epoxy body and waterproof
BNC connector
combination pH electrode with stainless
steel cutting blade and waterproof BNC
connector
• All electrodes with a waterproof BNC and BNC connector
have one meter cable lengths.
• Electrodes with a waterproof BNC connector can be used
on any pH meter with a BNC connection.
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Required Equipment
1. Thermo Scientific Orion pH meter, such as the 3-Star pH
meter, 4-Star pH/ISE meter, 4-Star pH/DO meter, 4-Star pH/
conductivity meter or 5-Star pH/ISE/DO/conductivity meter.
AquaPro and double junction pH electrodes can be used
on any pH meter with a BNC connection. The electrodes
can also be used on meters with a variety of inputs when
an adapter cable is used. Visit www.thermo.com/water for
details.
The AquaPro Triode has a temperature connector that is
compatible with specific meters, refer to the list below.
2. Thermo Scientific Orion AquaPro or double junction pH
electrode.
• The 9107APMD pH/ATC Triode has a temperature
connector that is compatible with the Star Series
pH meters.
3. Electrode filling solution (for 9102DJWP, 9110DJWP and
9120APWP electrodes only), Cat. No. 910008.
4. pH electrode storage solution, Cat. No. 910001.
5. pH buffers, at least two pH buffers are recommended for
precise measurements. One buffer should be near pH 7
and buffers should be one to three pH units apart.
6. Beakers, plastic or glass.
7. Magnetic stirrer or Orion stirrer probe, Cat. No. 096019.
The stirrer probe can be used with 3-Star, 4-Star and 5-Star
benchtop meters.
8. Distilled or deionized water.
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Electrode Preparation
1. AquaPro electrodes ship in a storage bottle that contains
storage solution. Remove the electrode from the storage
bottle and save the storage bottle for later storage. Refer to
the figure below.
For double junction electrodes, carefully remove the
protective shipping cap from the sensing element and save
the cap for storage.
2. Clean any salt deposits from the exterior of the electrode by
rinsing with distilled water.
3. If using a refillable electrode, uncover the filling hole by
removing the tape and then add electrode filling solution,
Cat. No. 910008, to the electrode. To maintain an adequate
flow rate, the level of filling solution must always be above
the reference junction and at least one inch above the
sample level. The filling hole should be open whenever the
electrode is in use.
4. Soak electrode in pH electrode storage solution, Cat. No.
910001, for 30 to 60 minutes.
5. Connect the electrode to the meter.
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KNIpHE Electrode Preparation
1. Remove the protective shipping cap from the sensing
element and save the cap for storage.
2. Unscrew the electrode cap and remove the electrode from
the handle. Make sure that the O-ring on the electrode
does not fall off.
3. Clean any salt deposits from the exterior of the electrode by
rinsing with distilled water.
4. Uncover the filling hole and add electrode filling solution,
Cat. No. 910008, to the electrode. The level of filling
solution must be no less than 1 cm below the fill hole.
5. Reinsert the electrode into handle and screw the electrode
cap on.
6. Place the O-ring packaged with the blade over the electrode
bulb until it is seated under the threaded end of the handle
shaft.
7. Gently screw the blade onto the threads, covering the
O-ring.
8. Do not invert the electrode while in use or filling solution
will leak into the handle.
Cat. No. Compatible Electrodes
Replacement electrode for 9120APWP
9121APWP
712001
712002
KNIpHE electrode
Replacement blade for 9120APWP
KNIpHE electrode
Replacement sheath for 9120APWP
KNIpHE electrode
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Sample Requirements
Electrodes with an epoxy body should only be used in aqueous
solutions.
AquaPro pH electrodes contain a silver/silver chloride (Ag/AgCl)
internal reference and polymer external reference. Due to the
unique reference system, the sample does not come in contact
with silver ions. These electrodes can be used with samples
containing silver complexing or binding agents such as TRIS,
proteins and sulfides.
Double junction pH electrodes contain a silver/silver chloride
(Ag/AgCl) internal reference and refillable or gel external
reference. Due to the double junction design, the sample does
not come in contact with silver ions. These electrodes can
be used with samples containing silver complexing or binding
agents such as TRIS, proteins and sulfides.
All sample temperatures must be between 0 and 60 ˚C.
6 AquaPro and Double Junction pH Electrode User Guide
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Measuring Hints
• Always use fresh buffers for calibration. Choose buffers
that are one to three pH units apart.
• Check the electrode slope daily by performing a two buffer
calibration. The slope should be 92 to 102%.
• If using a refillable electrode, remove the filling hole cover
during measurements to ensure a uniform flow of filling
solution.
• Between measurements, rinse electrodes with distilled
water and then with the next solution to be measured.
• Stir all buffers and samples at a uniform rate.
• Place a piece of insulating material, such as Styrofoam or
cardboard, between the magnetic stirrer and beaker to
prevent measurement errors from the transfer of heat to
the sample.
• To reduce the chance of error due to polarization, avoid
rubbing or wiping the electrode bulb. Use a lint-free tissue
and gently blot the electrode bulb.
• Flat surface electrodes may be used on any moist surface
or in liquids.
• Buffers and samples should be at the same temperature. If
samples are at different temperatures, perform temperature
compensation as described in the meter user guide.
7AquaPro and Double Junction pH Electrode User Guide
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Electrode Calibration
General Calibration Procedure
For detailed instructions on pH calibration, manual pH calibration
and temperature compensation, consult your meter user guide.
One Buffer Calibration
1. Choose a buffer near expected sample pH.
2. The buffer should be at same temperature as the sample.
If the buffer and samples are at varying temperatures,
temperature compensation is recommended.
3. Prepare the meter according to the meter user guide.
4. Rinse the electrode first with distilled water and then with
the buffer being used for calibration.
5. Place the electrode into the buffer. When the reading is
stable, set the meter to the pH value of the buffer at the
measured temperature. Refer to the meter user guide for a
detailed procedure. Table 1 provides pH values at
various temperatures.
6. Proceed to the pH Measurement section.
Table 1 pH Values of Buffers at Various Temperatures
Nominal
Buffer Value
at 25°C
1.68 1.67 1.67 1.67 1.67 1.68
3.78 3.86 3.84 3.82 3.79 3.77
4.01 4.00 4.00 4.00 4.00 4.02
6.86 6.98 6.95 6.92 6.87 6.85
7.00 7.11 7.08 7.06 7.01 6.98
7.41 7.53 7.50 7.47 7.43 7.40
9.18 9.46 9.40 9.33 9.23 9.14
10.01 10.32 10.25 10.18 10.06 9.97
Temperature
0 °C 5 °C 10 °C 20 °C 30 °C
8 AquaPro and Double Junction pH Electrode User Guide
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Two Buffer Calibration
This procedure is recommended for precise measurements.
1. Select two buffers that bracket the expected sample pH.
The first buffer should be near the electrode isopotential
point (pH 7) and the second should be near the expected
sample pH (pH 4 or pH 10).
2. The buffers should be at same temperature as the sample.
If the buffers and samples are at var ying temperatures,
temperature compensation is recommended.
3. Rinse the electrode first with distilled water and then with
the first buffer.
4. Place the electrode into the first buffer. When the reading
is stable, set the meter to the pH value of the buffer at the
measured temperature. Refer to the meter user guide for
a detailed procedure. Table 1 provides pH values at
various temperatures.
5. Rinse the electrode first with distilled water and then with
the second buffer.
6. Place the electrode into the second buffer. When the
reading is stable, set the meter to the pH value of the
buffer at the measured temperature. Refer to the meter
user guide for a detailed procedure. Table 1 provides pH
values at various temperatures.
7. Proceed to the pH Measurement section.
Temperature
40 °C 50 °C 60 °C 70 °C 80 °C 90 °C
1.69 1.71 1.72 1.74 1.77 1.79
3.75 3.75
4.04 4.06 4.09 4.13 4.16 4.21
6.84 6.83 6.84 6.85 6.86 6.88
6.97 6.97 6.97 6.99 7.03 7.08
7.38 7.37
9.07 9.01 8.96 8.92 8.89 8.85
9.89 9.83
9AquaPro and Double Junction pH Electrode User Guide
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pH Measurement
1. Calibrate the electrode as described in the Electrode
Calibration section.
2. Rinse the electrode with distilled water and then with
the sample.
3. Place the electrode into the sample.
4. When the reading is stable, record the pH and temperature
of the sample.
Electrode Storage
To ensure a quick response and free-flowing junction, the
sensing element and reference junction must not dry out.
Short-term Storage (up to one week)
Soak the electrode in pH electrode storage solution, Cat. No.
910001. AquaPro electrodes should be stored in the storage
bottle shipped with the electrode. Securely store the electrode
so it will not tip over and the bulb stays in the storage solution.
Long-term Storage (more than one week)
AquaPro electrodes should be stored in the storage bottle
shipped with the electrode. Cover the sensing element and
reference junction of double junction electrodes with the
protective cap with a few drops of storage solution or a storage
bottle with enough storage solution to cover the electrode
reference junction. If using a refillable electrode, fill the
reference chamber and securely cover the filling hole. Securely
store the electrode so it will not tip over and the bulb stays in
the storage solution.
Storage Bottle Compatible Electrodes
9102AP, 9104APWP, 9107APMD, 9135APWP,
910003
910004 9115APWP
910006 9103APWP, 9110DJWP
9156APWP, 9102DJWP, 9156DJWP
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Electrode Maintenance
1. Inspect the electrode for scratches, cracks, salt crystal
buildup, or membrane/junction deposits.
2. Rinse off any salt buildup with distilled water. Remove any
membrane/junction deposits as directed in the General
Cleaning section.
3. If using a refillable electrode, drain the reference chamber,
flush it with fresh filling solution and refill the chamber with
fresh filling solution.
Electrode Cleaning Procedures
General Cleaning
1. Soak the electrode in 0.1 M HCl or HNO3 for half an hour.
The electrode can also be soaked for 15 minutes in a 1:10
dilution of household laundry bleach or a 0.1 to 0.5% liquid
detergent solution mixed with hot water. The solution
should be stirred at a moderate to fast rate.
2. If using a refillable electrode, drain the reference chamber
and refill it with fresh filling solution.
3. Soak the electrode in pH electrode storage solution for at
least one hour.
Cleaning Solutions
Cat. No. 900021– pH cleaning solution A for removing protein
contaminants.
Cat. No. 900022– pH cleaning solution B for removing bacterial
contaminants.
Cat. No. 900023– pH cleaning solution C for general cleaning.
Cat. No. 900024– pH cleaning solution D for removing oil and
grease contaminants.
Cat. No. 900020– pH cleaning solution kit, includes cleaning
solutions A, B, C and D.
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Electrode Characteristics
Temperature Effects
The most common cause of error in pH measurements is
temperature. There are at least five ways that temperature
variations can affect pH: electrode slope, buffers, samples,
reference element drift and temperature sensor errors.
Electrode Slope Changes
The electrode slope will change with variations in temperature.
Slope changes may be compensated manually or automatically
with an automatic temperature compensation (ATC) probe.
Thermo Scientific Orion pH meters calculate the slope based
on the measured temperature and automatically adjust the pH
value based on the temperature.
Buffer and Sample pH Changes
Buffer and sample pH values change with temperature because
of their temperature dependent chemical equilibria. The pH
electrode should be calibrated with buffers that have known
pH values at different temperatures. Buffer values at different
temperatures are given in Table 1. Thermo Scientific Orion
pH meters automatically calibrate with the correct pH buffer
values based on the measured temperature. All pH meters are
unable to correct pH values back to a reference temperature
because ever y sample has a unique pH value vs. temperature
relationship. Therefore, calibration and measurements should
be performed at the same temperature and pH values should be
reported with temperature.
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Reference Element Drift
Drift can occur when the internal reference elements inside the
pH and reference portions of the electrode are reaching thermal
equilibrium after a temperature change. Long-term drift or slow
response can last until the sample and electrode are at the
same temperature.
Temperature Sensor Errors
When a pH and temperature probe are placed into a sample
that varies significantly in temperature, the readings can
drift for two reasons. First, the temperature response of the
electrode and temperature probe may not be similar, which
prolongs equilibration and drift. Second, a sample may not
have a uniform temperature. Therefore, the pH electrode and
temperature probe are responding to different environments.
13AquaPro and Double Junction pH Electrode User Guide
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Troubleshooting
Follow a systematic procedure to isolate the problem. The pH
measuring system can be divided into four components for ease
in troubleshooting: pH meter, electrode, sample/application
and technique.
pH Meter
The meter is the easiest component to eliminate as a possible
cause of error. Thermo Scientific Orion pH meters include
an instrument checkout procedure and shorting cap for
convenience in troubleshooting. Consult the pH meter user
guide for directions.
Electrode
To test electrode operation:
1. Connect the electrode to a working meter that has a mV
measuring mode.
2. Set the meter to the mV measuring mode.
3. Rinse the electrode with distilled water and then insert the
electrode into fresh pH 7 buffer.
4. When the reading is stable, record the mV value of the
pH 7 buffer. The mV value should be -30 to +30 mV.
5. Rinse the electrode with distilled water and then insert the
electrode into fresh pH 4 buffer.
6. When the reading is stable, record the mV value of the
pH 4 buffer. The mV value should be +150 to +210 mV.
7. Calculate the absolute mV difference between the two
buffers. The mV difference should be 160 to 180 mV. The
actual mV values will change as the electrode ages, but the
mV difference between the two buffers should always be
160 to 180 mV.
If the electrode fails this procedure, clean the electrode
thoroughly as directed in the Electrode Maintenance section.
If the electrode response is slow or drifting and the electrode
is refillable, drain and refill the electrode with fresh filling
solution, Cat. No. 910008. Replace the electrode if cleaning and
maintenance fail to rejuvenate it.
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Sample/Application
The electrode and meter may operate with buffers, but not with
the sample. In this case, check the sample composition for
interferences, incompatibilities or temperature effects.
Technique
If trouble persists, review operating procedures. Review
calibration and measurement sections to be sure proper
technique has been followed.
Assistance
After troubleshooting all components of your measurement
system, contact Technical Support. Within the United States call
1.800.225.1480 and outside the United States call 978.232.6000
or fax 978.232.6031. In Europe, the Middle East and Africa,
contact your local authorized dealer. For the most current
contact information, visit www.thermo.com/water.
Warranty
For the most current warranty information,
visit www.thermo.com/water.
15AquaPro and Double Junction pH Electrode User Guide
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Ordering Information
Electrodes
Refer to the Introduction section for a complete list of AquaPro
and double junction pH electrodes.
Accessories
Cat. No. Description
910008 Double junction filling solution, 5 x 60 mL bottles
910001 pH electrode storage solution, 475 mL bottle
910003 Storage bottle for 12 mm electrodes, 3 pack
910004 Storage bottle for 8 mm electrodes, 3 pack
910006 Storage bottle for 6 mm electrodes, 3 pack
900020 pH cleaning solution kit, includes 1 x 15 mL
bottle each of cleaning solutions A, B, C and D;
pipette and beaker
900021 pH cleaning solution A, includes 4 x 15 mL
bottles, pipette and beaker
900022 pH cleaning solution B, includes 4 x 15 mL
bottles, pipette and beaker
900023 pH cleaning solution C, includes 4 x 15 mL
bottles, pipette and beaker
900024 pH cleaning solution D, includes 4 x 15 mL
bottles, pipette and beaker
910199 All-in-One pH buffer kit, includes 475 mL bottle
each of pH 4.01, 7.00, and 10.01 buffers and
storage solution, and storage bottle (12 mm)
910168 pH 1.68 buffer, 475 mL bottle
910104 pH 4.01 buffer, 475 mL bottle
910105 pH 5.00 buffer, 475 mL bottle
910686 pH 6.86 buffer, 475 mL bottle
910107 pH 7.00 buffer, 475 mL bottle
910918 pH 9.18 buffer, 475 mL bottle
910110 pH 10.01 buffer, 475 mL bottle
910112 pH 12.46 buffer, 475 mL bottle
Visit www.thermo.com/water for additional buffers and buffer sizes.
16 AquaPro and Double Junction pH Electrode User Guide
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Thermo Fisher Scientific
Environmental Instruments
Water Analysis Instruments
166 Cummings Center
Beverly, MA 01915 USA
Tel: 978-232-6000
Toll Free: 800-225-1480
Dom. Fax: 978-232-6015
Int’l. Fax: 978-232-6031
254795-001 Rev.A
www.thermo.com/water
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