Thermo Scientific REDOX/ORP 9678BNWP User manual

Thermo Fisher Scientific
Environmental Instruments
Water Analysis Instruments
166 Cummings Center
Beverly, MA 01915 USA
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www.thermo.com/water
User Guide
Redox/ORP
Electrodes

1Redox/ORP Electrode User Guide
Introduction
This user guide contains information on the preparation,
operation and maintenance of the Thermo Scientific Orion ORP
electrodes. These ORP electrodes combine a platinum redox
sensing electrode and a silver/silver chloride reference electrode
in one body.
The redox/ORP electrodes can be used to make direct
measurements of redox potentials or perform potentiometric
titrations. The ORP Triode electrodes have a built-in thermistor
for measuring temperature.
Epoxy Sure-Flow Combination Redox/ORP Electrodes,
Cat. No. 9678BNWP and 967800
The Sure-Flow junction prevents the electrode from clogging in
dirty, viscous or wastewater samples. The epoxy body is break-
resistant for rugged environments.
Glass Combination Redox/ORP Electrodes,
Cat. No. 9778BNWP and 9778SC
The glass body enables the electrode to be used in solutions
that contain organic solvents. Use the electrode in water,
wastewater, metal plating and organic solvent samples.
Epoxy Refillable ORP/ATCTriode,
Cat. No. 9180BNMD and 9180BN
The electrode includes a built-in temperature probe for
measuring ORP and temperature with one electrode. The
refillable design allows the electrode filling solution to be
changed in case of contamination or clogging.
Epoxy Low Maintenance ORP/ATCTriode,
Cat. No. 9179BNMD and 9179BN
The electrodes include a built-in temperature probe for
measuring ORP and temperature with one electrode. The
electrodes contain a gel reference solution, so no filling solution
is required.
Note: Redox/ORP electrodes are not designed for constant
current or amperometric titrations, such as Karl Fischer
moisture analysis.

2Redox/ORP Electrode User Guide
Required Equipment
1. Thermo Scientific Orion pH/mV 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.
ORP electrodes can be used on any pH/mV meter with a
BNC or U.S. standard 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.
Refillable ORP Triodes have temperature connectors that
are compatible with specific meters, refer to the list below.
2. Thermo Scientific Orion ORP electrode.
• The 9180BNMD and 9179BNMD ORP/ATC Triode
electrodes have a temperature connector that is
compatible with the Star Series meters.
• The 9180BN and 9179BN ORP/ATC Triode electrode
have a temperature connector that is compatible with
the A+ Series meters.
3. ORP electrode filling solution. Use Cat. No. 900011
filling solution for samples that have a total ionic strength
greater than 0.2 M. Use Cat. No. 900001 filling solution for
samples that have a total ionic strength less than 0.2 M.
ORP electrode filling solution is not required if using a
9179BNMD or 9179BN low maintenance ORP/ATC Triode
4. ORP standard, Cat. No. 967901 or 967961.
ORP standard is highly recommended to ensure accurate
ORP measurements.
5. Beakers, plastic or glass.
6. 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.
7. Distilled or deionized water.

3Redox/ORP Electrode User Guide
Sample Requirements
Electrodes with an epoxy body should only be used in aqueous
solutions.
Electrodes with a glass body may be used in non-aqueous
solutions and solutions that contain organic solvents.
The ORP electrodes contain a silver/silver chloride (Ag/AgCl)
reference that may become clogged in solutions that contain
silver complexing or binding agents such as TRIS, proteins and
sulfides. Frequent cleaning may be required when measuring
solutions that contain these agents. Proteins cause the
additional problem of coating the electrode, so extra care should
be taken to keep the electrode clean while measuring samples
that contain proteins.

4Redox/ORP Electrode User Guide
Electrode Preparation
Electrode Preparation for Refillable Electrodes
1. 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. Uncover the filling hole by removing the tape and then add
electrode filling solution, Cat. No. 900011, 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. For Sure-Flow electrode only, wet the junction by pressing
down on the electrode cap to let a few drops of the filling
solution flow out of the electrode and then replenish any
lost solution.
5. Shake the electrode downward (similar to a clinical
thermometer) to remove air bubbles.
6. Connect the electrode to the meter.
Note: The fill hole must be open when the electrode is in use.
Electrode Preparation for Gel-Filled Electrodes
1. 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. Shake the electrode downward (similar to a clinical
thermometer) to remove air bubbles.
4. Connect the electrode to the meter.

5Redox/ORP Electrode User Guide
filling hole
Ag/AgCl
internal
reference
filling
solution
chamber
ceramic
reference
junction
sensing
element
fill hole
AgAgCl
internal
reference
reference
filling solution
chamber
Sure-Flow
junction
sensing
element
Figure 1– Refillable ORP Electrode
filling hole
Ag/AgCl
internal
reference
filling
solution
chamber
ceramic
reference
junction
sensing
element
fill hole
AgAgCl
internal
reference
reference
filling solution
chamber
Sure-Flow
junction
sensing
element
Figure 2– Sure-Flow Refillable ORP Electrode

6Redox/ORP Electrode User Guide
Electrode Calibration
ORP readings can be reported using the absolute mV values
or the EHmV values. EHmV values give the corresponding
mV values that would be obtained using a Standard Hydrogen
Electrode (SHE), also known as the Normal Hydrogen Electrode
(NHE). Orion ORP standard, Cat. No. 967901 or 967961, allows
operators to correlate measurements to the EHmV value with
an Orion ORP electrode.
The relative mV mode can be used to calibrate the ORP
electrode so the electrode reads the EHmV values in samples.
When an ORP electrode is calibrated to read EHmV values, the
resulting sample readings can be compared among multiple
meter and electrode systems.
Note: If the meter can perform an automatic ORP calibration
using an EHmode, refer to the meter user guide for detailed
instructions on the meter calibration procedure.
1. Set the meter to the relative millivolt mode. Refer to the
meter user guide for detailed instructions.
2. Place the ORP electrode in ORP standard, Cat. No. 967901
or 967961.
3. Set the meter to the EHmV value of the ORP standard at
the measured temperature using the information in Table 1.
Table 1– ORP Standard Values
Absolute mV values may vary by ± 60 mV
Temperature
(°C)
EHValue
(mV)
Absolute Value
with Cat. No.
900011 Filling
Solution (mV)
Absolute Value
with Cat. No.
900001 Filling
Solution (mV)
0 438 218 176
1 437 218 176
2 437 218 176
3 436 218 176
4 435 218 176
5 435 218 176
6 434 218 176
7 433 218 176
8 433 218 175
9 432 219 175

7Redox/ORP Electrode User Guide
Temperature
(°C)
EHValue
(mV)
Absolute Value
with Cat. No.
900011 Filling
Solution (mV)
Absolute Value
with Cat. No.
900001 Filling
Solution (mV)
10 431 219 175
11 430 219 175
12 430 219 175
13 429 219 175
14 428 219 175
15 428 219 175
16 427 219 174
17 426 219 174
18 425 219 174
19 424 219 174
20 424 219 174
21 423 219 174
22 422 219 174
23 421 219 173
24 420 220 173
25 420 220 173
26 419 220 173
27 418 220 173
28 417 220 172
29 416 220 172
30 415 220 172
31 414 220 172
32 413 220 172
33 412 220 171
34 412 220 171
35 411 220 171
36 410 220 171
37 409 220 171
38 408 220 170
39 407 220 170
40 406 220 170
41 405 220 170
42 404 220 169
43 403 220 169
44 402 220 169
45 401 220 169
46 400 220 168
47 399 220 168
48 398 220 168
49 397 220 168
50 396 220 167

8Redox/ORP Electrode User Guide
Measurement Techniques
• Always use fresh ORP standard for calibration.
• If the electrode is refillable, remove the filling hole cover
during measurements to ensure a uniform flow of filling
solution.
• Between measurements, thoroughly rinse the electrode
with distilled water. Gently shake the electrode after rinsing
to prevent solution carryover and then blot the electrode
dry with a lint-free tissue.
• Stir all standards 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.
• Allow all standards and samples to come to room
temperature for precise measurements.
• If the electrode is used in dirty or viscous samples or the
electrode response becomes sluggish, empty the electrode
completely and hold the junction under running water.
Empty any water from the electrode and refill it with fresh
electrode filling solution.
• If a Sure-Flow electrode is used in dirty or viscous samples
or the electrode response becomes sluggish, empty the
electrode completely and hold the junction open under
running water. Empty any water from the electrode and
refill it with fresh electrode filling solution. Press down on
the electrode cap to let a few drops of the filling solution
flow out of the electrode and then replenish any lost
solution.
• Make sure the electrode filling solution is appropriate
for the sample. Use Cat. No. 900011 filling solution for
samples that have a total ionic strength greater than 0.2 M.
Use Cat. No. 900001 filling solution for samples that have a
total ionic strength less than 0.2 M.

9Redox/ORP Electrode User Guide
Electrode Measurements
Direct Measurements
Direct oxidation-reduction potential (ORP) measurements
can be used to determine the oxidizing or reducing capability
of a solution and are commonly made in polluted streams,
chlorinated waters, industrial wastewaters and other water
samples.
1. Prepare the electrode according to the Electrode
Preparation section.
2. Set the meter to the millivolt, relative millivolt or EH
measurement mode.
3. Place the electrode into the sample solution.
4. When the reading stabilizes, record the displayed mV
potential and temperature.
Note: Platinum redox electrodes may give unstable readings in
solutions that contain chromous, vanadous and titanous ions or
other ions that are stronger reducing agents than hydrogen or
platinum.

10 Redox/ORP Electrode User Guide
Oxidation-Reduction Titrations
Oxidation-reduction or redox titrations provide a simple,
reliable method for determining many substances in solution.
A redox titration consists of adding to an unknown sample
small increments of a titrant that converts the unknown to
a different oxidation state. After each addition of titrant, the
platinum redox electrode develops a potential proportional to
the logarithm of the ratio of the activities of the two oxidation
states. At the inflection point, or endpoint, the titrant has
completely oxidized or reduced the unknown, causing a sharp
change in the logarithm of the ratio of the activities of the two
oxidation states. A corresponding sharp change in the potential
is developed by the platinum electrode. Often several oxidizing
or reducing species can be precisely determined in the same
solution by a single titration with several inflection points.
Table 2 lists suitable titrants for different unknowns, the
equation for the titration reaction, interferences, and a reference
where information about preparing the sample and running the
titration can be found. For similar information about unknowns
not listed in the table, consult the standard texts listed as
references.
The following is a general procedure for performing a redox
titration once the sample is prepared.
1. Fill a 10 mL buret with a standard titrant solution whose
normality is 5-10 times that of the sample.
2. Connect the electrode to the meter and set the meter to
the mV mode.
3. Pipet 50 mL of sample into a 150 mL beaker. Stir the
solution thoroughly throughout the titration.
4. At first, add titrant in 0.5 to 1 mL increments, recording the
potential after each addition. Near the endpoint, when large
potential changes appear, add increments of 0.1 to 0.2 mL.
Continue the titration 3 to 4 mL past the endpoint.
5. Plot the electrode potential versus volume of added titrant
on linear graph paper and draw a smooth curve through the
points. The endpoint is the point of inflection (the point of
greatest slope).

11Redox/ORP Electrode User Guide
6. Calculate the normality of the sample, Nx, in equivalents per
liter.
Nx= (Vt* Nt) / Vx
where:
Nt= normality of titrant (Eq/1)
Vt= volume of titrant at end point (mL)
Vx= volume of sample (mL)
Table 2 References:
1. Furman (ed.), Scott’s Standard Methods of Chemical
Analysis, 5th Ed., Van Nostrand, Princeton, N.J. 1938.
2. Hillebrand, Lundell, Bright, and Hoffman, Applied Inorganic
Analysis, 2nd Ed., Wiley, New York, 1953.
3. Kolthoff and Sandell, Testbook of Quantitative Inorganic
Analysis, 3rd. Ed., MacMillan, New York, 1952.
4. Oesper, Newer Methods of Volumetric Chemical Analysis,
Van Nostrand, Princeton, N.J., 1938.
5. Treadwell and Hall, “Analytical Chemistry,” vol. 2,
Quantitative Analysis, 8th Ed., Wiley, New York, 1935.

12 Redox/ORP Electrode User Guide
Table 2– Typical Redox Titration Methods
Unknown Interferences
antimony (Sb+3) As, Fe, SO2,V, and organic
substances
arsenic (As+3) other reducing agents
hydrogen peroxide
(H2O2)
preservatives present in commercial
H2O2may interfere
hypochlorite ion (ClO¯)
or chlorine (Cl2)
Br2and other oxidizing agents
interfere by liberating I2
iodine (I2) other reducing agents
iodine (I2) direct sunlight, high acidity, copper
salts and other catalysts promote air
oxidation and cause false high results
iron (as Fe+2, Fe+3
or in steel)
high levels of organic acids, such as
acetic, oxalic, tartaric, and alcohols;
F¯ if present in more than trace
amounts; Cl¯, PO4-3 (remove by
adding acid)
iron (as Fe+2, Fe+3
or in steel)
other reducing agents
manganese (as
permanganate Mn04¯)
other oxidizing agents
manganese (as Mn+2) other reducing agents
stannous tin (Sn+2) other reducing agents
sulfur (as sulfur
dioxide SO2)
S-2 and SO2-2 , remove by shaking
with CdCO3and filtering
thallium (Ti+) other reducing agents
thiosulfate ion
(S2O3 -2)
S-2 and SO2 -2 , remove by shaking
with CdCO3and filtering
uranium (as uranyl ion
UO+2)
other reducing agents
Zinc (Zn+2) other reducing agents

13Redox/ORP Electrode User Guide
Suitable Titrants Titration Reaction Ref
potassium permanganate
(KMnO4)
5Sb+3 + 2MnO4¯ + 16H+–›
5Sb+3 + 2Mn+2 + 8H2O
2
sodium bromate (NaBrO3) BrO3¯ + 3As+3 + 6H+ –›
Br¯ + 3As+5 + 3H2O
3
potassium permanganate
(KMnO4)
5H2O2+ 2MnO4¯ + 6H+–›
5O2+ 2Mn+2 + 8H2O
5
sodium iodide (NaI) in acid solution Cl2+2I¯ –› I2+
2Cl¯, In basic solution
2ClO¯ + 2I¯ –› I2+ 2Cl¯ + 2OH¯
1
sodium iodate ( NaIO3) 2I2+ IO3¯ + 5HCN + H+–›
5ICN + 3H2O
4
sodium thiosulfate
(Na2S2O3)
I2+ 2S2O3 -2 –› 2I¯ + S4O6 -2 3
ceric sulfate [Ce(SO4)2]
(not recommended for
samples containing Cl¯)
Fe+2 + Ce+4 –› Ce+3 + Fe+3 2
potassium dichromate
(K2Cr3O7), recommended
for samples containing Cl¯
Cr2O7 -2 + 6Fe+2 + 14H+–›
2Cr+3 + 6Fe+3 + 7H2O
3
ferrous sulfate (FeSO4) MnO4¯ + 5Fe+2 + 8H+–›
Mn+2 + 5Fe+3 + 4H2O
2
potassium permanganate
(KMnO4)
3Mn+2 + 2MnO4¯ + 7H2O –›
5MnO3+ H2O + 4H+
1
ceric sulfate [Ce(SO4)2] Sn+2 + 2Ce+4 –› Sn+4 + 2Ce+3 4
iodine (I2) SO2+ I2+ 2H2O –›
SO4-2 + 2I¯+ 4H+
1
sodium bromate (NaBrO3) BrO3¯ + 3Ti+6H+–›
Br¯ + Ti+3 + 3H2O
3
Iodine (I2) I2+ 2S2O3-2 –› 2I¯ + S4O63
potassium dichromate
(K2Cr2O7)
3UO+2 + Cr2O7-2 + 8H+–›
3UO2+2 + 2Cr+3 + 4H2O
3
sodium iodate (NaIO3) ZnHg(SCN)4+ 6IO3¯ + 6Cl¯ +
8H+–› Zn+2 + Hg+2 + 6ICl +
4HCN + 4SO4-2
2

14 Redox/ORP Electrode User Guide
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 the electrode is refillable, drain the reference chamber,
flush it with fresh filling solution and refill the chamber with
fresh filling solution.
4. If the electrode is refillable, make sure that the filling
solution does not crystallize or dry out. Remove any
crystals by rinsing the electrode with distilled water
or wiping with a damp, lint-free tissue. To prevent
crystallization of the filling solution, cover the fill hole
whenever the electrode is being stored and open the fill
hole when calibrating and measuring.

15Redox/ORP Electrode User Guide
Electrode Cleaning Procedures
General Cleaning
1. Soak the electrode in 0.1 M HCl or HNO3for 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 the electrode is refillable, drain the reference chamber
and refill it with fresh filling solution.
3. Thoroughly rinse the electrode with distilled water.
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.

16 Redox/ORP Electrode User Guide
Sure-Flow Electrode Cleaning
Cat. No. 9678BNWP and 967800
If the area between the electrode sleeve and inner cone
becomes clogged with sample or precipitate, flush the area with
filling solution or distilled water.
1. Hold the electrode body with one hand and use your thumb
to push down on the electrode cap to drain the chamber.
Push down on the cap until all the filling solution is drained
from the chamber.
2. Fill the electrode with distilled water and then push down
on the cap until all the water is drained from the chamber.
3. Fill the electrode with fresh filling solution up to the fill
hole. Push down on the cap to allow a few drops of filling
solution to drain out of the electrode and then refill any lost
filling solution.
Disassembling the Sure-Flow Electrode
Note: Disassembly is usually not required and should not be
done unless a thorough cleaning is required.
1. Tip the electrode so the filling solution moistens the O-ring
on the electrode body. Hold the electrode body with one
hand and use your thumb to push down on the electrode
cap to drain the chamber.
2. Unscrew the cap counter clock-wise and then slide the cap
and the spring up the cable.
3. Hold the outer sleeve with one hand and firmly push down
on the threaded portion with the thumb and forefinger to
separate the inner body from the sleeve.
4. Grasp the cone with a clean, lint-free tissue and withdraw
the body from the sleeve using a gentle twisting motion.
Do not touch the pellet above the cone, it will damage to
the pellet. Rinse the outside of the electrode body and the
entire sleeve with distilled water. Allow it to air dry.

17Redox/ORP Electrode User Guide
Reassembling the Sure-Flow Electrode
1. Moisten the O-ring on the electrode body with a drop of
filling solution. Insert the screw-thread end of the electrode
body into the tapered, ground end of the sleeve.
2. Push the body into the sleeve using a gentle twisting
motion until the bottom surface of the inner cone is flush
with the tapered end of the sleeve.
3. Place the spring onto the electrode body and screw on the
cap. Refill the electrode with filling solution.
Electrode Storage
Short-term Storage (up to one day)
To ensure a quick response and free-flowing junction, the
reference junction must not dry out. It is recommended that
the electrode be soaked in a 4 M potassium chloride (KCl)
solution. Electrodes may also be stored in water.
Long-term Storage (over one day)
For gel-filled electrodes– rinse the electrode with distilled
water, dry the electrode with a lint-free tissue and cover the
measuring surface with the protective cap.
For refillable electrodes– rinse the electrode with distilled
water, drain all of the filling solution from the electrode, flush
out the electrode with distilled water, cover the measuring
surface with the protective cap and store the electrode dry.

18 Redox/ORP Electrode User Guide
Troubleshooting
Follow a systematic procedure to isolate the problem. The
measuring system can be divided into four components for ease
in troubleshooting: meter, electrode, sample/application
and technique.
Meter
The meter is the easiest component to eliminate as a possible
cause of error. Thermo Scientific Orion meters include
an instrument checkout procedure and shorting cap for
convenience in troubleshooting. Consult the pH meter user
guide for directions.
Electrode
1. Thoroughly rinse the electrode with distilled water.
2. Place electrode in the Orion ORP standard and wait until
the reading stabilizes.
3. The mV potential should be 220 mV ± 60 mV. If the mV
reading is out of range, repeat the measurement with
fresh ORP standard. 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. Replace the electrode
if cleaning and maintenance fail to rejuvenate it.
Sample/Application
The electrode and meter may operate with standards, 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.