Thermo Scientific 9609BNWP Instruction Manual

User Guide

Fluoride Ion
Selective
Electrode

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This publication supersedes all previous publications on this
subject.

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Required Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Electrode Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Electrode Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Checking Electrode Operation (Slope) . . . . . . . . . . . . . . . . . . . . . 6

Measurement Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Sample Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Measuring Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Electrode Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Electrode Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Analytical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Direct Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Low-Level Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Single Known Addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Titrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Fluoride in Acid Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Fluoride in Alkaline Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Electrode Characteristics . . . . . . . . . . . . . . . . . . . . . . . . .33

Electrode Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Reproducibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Limits of Detection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Temperature Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

pH Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Complexation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Warranty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Troubleshooting Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

Specifi cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

Introduction

This user guide contains information on the preparation,
operation and maintenance for the fl uoride ion selective
electrode (ISE). General analytical procedures, electrode
characteristics and electrode theory are also included in this
user guide. Fluoride electrodes measure free fl uoride ions in
aqueous solutions quickly, simply, accurately and economically.

The measurement of fl uoride in drinking water and wastewater
using an ion selective electrode is an EPA approved test
procedure. EPA-approved ISE test procedures for fl uoride in
drinking water are ASTM D1179-04 (B) and Standard Methods
4500-F- C (21st edition). EPA-approved ISE test procedures for
fl uoride in wastewater are ASTM D1179-93, 99 (B) and Standard
Methods 4500-F- C-97 (online) or 4500-F- B (18, 19, 20th
editions). Approved test method lists are updated periodically.
Check with your regulatory agency for latest approve method
revisions.

Technical Support Chemists can be consulted for assistance
and troubleshooting advice. Within the United States call

1.800.225.1480 and outside the United States call 978.232.6000
or fax [phone]. In Europe, the Middle East and Africa,
contact your local authorized dealer. For the most current
contact information, visit www.thermoscientifi c.com/water.

Fluoride ionplus® Sure-Flow® Solid State Combination ISE

The reference and sensing electrodes are built into one
electrode, which decreases the amount of required solution
and reduces waste. The built-in Sure-Flow reference junction
prevents electrode clogging and provides fast and stabile
readings. The fl uoride ionplus combination ISE is available with
a waterproof BNC connector, Cat. No. 9609BNWP. Electrodes
with a waterproof BNC connector can be used on any ISE meter
with a BNC connection.

Fluoride Solid State Half-Cell ISE

The fl uoride half-cell electrode must be used with the single
junction reference electrode, Cat. No. 900100. The fl uoride
half-cell is available with a BNC connector, Cat. No. 9409BN;
and a screw cap connector, Cat. No. 9409SC. Electrodes with a
screw cap connector require a separate cable.

1Fluoride Ion Selective Electrode User Guide

inner

body

filling solution

chamber

outer body

reference

element

cap

spring

cable

O-ring

filling hole

inner cone

sensing crystal

Figure 1
9609BNWP Fluoride Combination Electrode

2 Fluoride Ion Selective Electrode User Guide

Required Equipment

1. Thermo Scientifi c Orion ISE meter, such as the Orion 4-Star
pH/ISE meter, Orion 5-Star pH/ISE/DO/conductivity meter
or Orion DUAL STAR meter.

Fluoride electrodes can be used on any ISE 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.thermoscientifi c.com/water for details.

2. Thermo Scientifi c Orion fl uoride ion selective electrode.

The 9409BN and 9409SC fl uoride half-cell electrodes

require a separate reference electrode,
Cat. No. 900100.

3. Magnetic stirrer or Orion stirrer probe, Cat. No. 096019.
The Orion stirrer probe can be used with 3-Star, 4-Star, 5­Star benchtop meters, and Dual Star meter.

4. Volumetric fl asks, graduated cylinders and beakers.
Plastic labware is highly recommended for fl uoride analysis.

5. Distilled or deionized water.

6. Fluoride electrode fi lling solution.

Use Optimum Results A fi lling solution, Cat. No. 900061,

for the 9609BNWP fl uoride electrodes.

Use single junction reference electrode fi lling solution,

Cat. No. 900001, for the reference electrode used with the
9409BN and 9409SC fl uoride electrodes.

7. Fluoride calibration standards.

Cat. No. Description

940906 0.1 M NaF, 475 mL bottle

940907 100 ppm F¯, 475 mL bottle

040908 10 ppm F¯ with TISAB II, 475 mL bottle

040907 2 ppm F¯ with TISAB II, 475 mL bottle

040906 1 ppm F¯ with TISAB II, 475 mL bottle

3Fluoride Ion Selective Electrode User Guide

8. Total Ionic Strength Adjustment Buffer (TISAB),
which provides a constant background ionic strength,
decomplexes fl uoride ions and adjusts the solution pH.

Cat. No. Description

940909 TISAB II, 3.8 L bottle

940999 TISAB II, 4 x 3.8 L bottle

940911 TISAB III concentrate, 475 mL bottle

Low-Level TISAB

For use when measuring in samples containing less than 0.4
ppm (2 x 10
as iron or aluminum are present.

To prepare low level TISAB: Place 500 mL of distilled water in
a 1 liter beaker. Add 57 mL of glacial acetic acid and 58 g of
reagent grade sodium chloride to the beaker. Place the beaker
in a water bath for cooling. Immerse a calibrated pH electrode
into the solution and slowly add 5 M NaOH until the pH is
between 5.0 and 5.5. Cool the solution to room temperature.
Pour the solution into a 1 liter volumetric fl ask and dilute to the
fl ask mark with distilled water. All reagents must be as pure as
possible to keep the fl uoride level low in the buffer.

Use as directed for TISAB II; combine equal volumes of low level
TISAB and sample or standard before taking any measurements.

-5

M) fl uoride and no fl uoride complexing agents such

TISAB IV

TISAB IV will complex more than 100 ppm of iron or aluminum
in the presence of 1 ppm fl uoride. A measurement of 1 ppm
fl uoride will be in error by 5% in the presence of 200 ppm iron
or aluminum.

To prepare TISAB IV: Place 500 mL of distilled water in a 1 liter
volumetric fl ask. Add 84 mL of concentrated HCl (36 to 38 %),
242 g TRIS (hydroxymethyl) aminomethane and 230 g sodium
tartrate (Na
and cool the solution to room temperature. Dilute to the fl ask
mark with distilled water.

-2H2O) to the fl ask. Stir to dissolve the solids

2C4H406

Use as directed for TISAB II; combine equal volumes of TISAB IV
and sample or standard before measurements.

4 Fluoride Ion Selective Electrode User Guide

Electrode Setup

Electrode Preparation

9409BN and 9409SC Fluoride Half-Cell Electrode– Remove the
protective shipping cap from the sensing element and save the
cap for storage.

900100 Single Junction Reference Electrode– Prepare the
reference electrode according to the reference electrode user
guide. Fill the reference electrode with single junction reference
fi lling solution, Cat. No. 900001.

9609BNWP Fluoride Combination Electrode– Remove the
protective shipping cap from the sensing element and save
the cap for storage. Fill the electrode with Optimum Results A
fi lling solution, Cat. No. 900061.

Note: Optimum Results A fi lling solution minimizes junction
potential issues and fl uoride contamination in the sample. The
use of any other fi lling solution will void the electrode warranty.

Electrode Filling Instructions

1. Lift the fl ip spout on the fi lling solution bottle to a vertical
position.

2. Insert the spout into the fi lling hole on the outer body of the
electrode and add a small amount of fi lling solution to the
reference chamber. Invert the electrode to moisten the top
O-ring and then return the electrode to the upright position.

3. Hold the electrode body with one hand and use your thumb
to push down on the electrode cap to allow a few drops of
fi lling solution to drain out of the electrode.

4. Release the electrode cap. If the sleeve does not return to
its original position, check if the O-ring is moist and repeat
steps 2-4 until the sleeve returns to the original position.

5. Add fi lling solution to the electrode up to the fi lling hole.

Note: Add fi lling solution each day before using the electrode.
The fi lling solution level should be at least one inch above the
level of sample in the beaker to ensure a proper fl ow rate. The
fi ll hole should always be open when taking measurements.

5Fluoride Ion Selective Electrode User Guide

Checking Electrode Operation (Slope)

These are general instructions that can be used with most
meters to check the electrode operation. Refer to the meter
user guide for more specifi c information.

This procedure measures electrode slope. Slope is defi ned
as the change in millivolts observed with every tenfold change
in concentration. Obtaining the slope value provides the best
means for checking electrode operation.

1. If the electrode has been stored dry, prepare the electrode
as described in the Electrode Preparation section.

2. Connect the electrode to the meter. Set the meter to the
mV mode.

3. Place 50 mL of distilled water and 50 mL of TISAB II (Low­level TISAB or TISAB IV) into a 150 mL beaker. Stir the
solution thoroughly.

If using TISAB III, place 90 mL of distilled water and

10 mL of TISAB III into a 150 mL beaker. Stir the solution
thoroughly.

4. Rinse the electrode with distilled water and place the
electrode into the solution prepared in step 3.

5. Select either a 0.1 M sodium fl uoride or 100 ppm fl uoride
standard. Pipette 1 mL of the standard into the beaker and
stir thoroughly. When a stable reading is displayed, record
the electrode potential in millivolts.

6. Pipette 10 mL of the same standard into the same beaker
and stir thoroughly. When a stable reading is displayed,
record the electrode potential in millivolts.

7. There should be a 54 to 60 mV difference between the
two millivolt readings when the solution temperature is
between 20 to 25 ˚C. If the millivolt potential is not within
this range, refer to the Troubleshooting section.

6 Fluoride Ion Selective Electrode User Guide

Measurement Units

Fluoride concentration can be measured in moles per liter (M),
parts per million (ppm) or any convenient concentration unit.

Table 1
Concentration Unit Conversion Factors

Moles/Liter (M) ppm

1.0 19000

-1

10

-2

10

-3

10

-4

10

1900

190

19

1. 9

Sample Requirements

The epoxy body of the fl uoride electrode is resistant to damage
by inorganic solutions. The electrode may be used intermittently
in solutions that contain methanol or acetone. Contact Technical
Support for information on using the electrode for specifi c
applications.

Samples and standards should be at the same temperature.
The solution temperature must be less than 100 °C.

In all analytical procedures, TISAB must be added to all samples
and standards before measurements are taken.

7Fluoride Ion Selective Electrode User Guide

Measuring Hints

• Add 50 mL of TISAB II (Low-level TISAB or TISAB IV) to
every 50 mL of standard or sample. Add 10 mL of TISAB III
to every 90 mL standard or sample. Once TISAB II (Low­level TISAB or TISAB IV) or TISAB III is selected, it should be
added to all samples and standards so the dilution ratio of
TISAB to solution remains the same.

• Stir all standards and samples at a uniform rate.

• Always use fresh standards for calibration.

• Always rinse the electrode with deionized water between
measurements and shake the electrode to remove the
water and prevent sample carryover. Do not wipe or rub
the electrode sensing element.

• Allow all standards and samples to come to the same
temperature for precise measurements.

• 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.

• Verify the electrode calibration every two hours by placing
the electrode in a fresh aliquot of the least concentrated
standard used for calibration. If using more than 2
standards, use a mid-level standard. If the value has
changed by more than 2%, recalibrate the electrode.

• After immersing the electrode in a solution, check the
electrode sensing surface for air bubbles and remove air
bubbles by reimmersing the electrode in the solution.

• For high ionic strength samples, prepare standards with
a background composition similar to the sample or use
manual known addition procedure or a Dual Star meter.

• Adjust highly acidic or highly basic solutions to pH 5 - 6
before adding TISAB.

• Remove the fi lling hole cover during measurements to
ensure a uniform fl ow of fi lling solution.

• If the electrode is used in dirty or viscous samples or the
electrode response becomes sluggish, empty the electrode
completely, hold the junction open and fl ush the junction
with deionized water. Empty any water from the electrode
and refi ll it with fresh fi lling solution. Press down on the
electrode cap to let a few drops of the fi lling solution fl ow
out of the electrode and then replenish any lost solution.

8 Fluoride Ion Selective Electrode User Guide

Electrode Storage

9409BN and 9409SC Fluoride Half-Cell Electrode

The fl uoride half-cell electrodes should be rinsed thoroughly
with distilled water and stored dry in the air at all times. When
storing the electrode for long periods of time, cover the sensing
element with the protective shipping cap.

900100 Single Junction Reference Electrode

The single junction reference electrode may be stored in the
single junction electrode fi lling solution, Cat. No. 900001,
between sample measurements and up to one week. A 0.01 M
or 100 ppm fl uoride standard is also an acceptable storage
solution. The fi lling solution inside the electrode should not be
allowed to evaporate, as crystallization will result.

For storage longer than one week, drain the reference electrode,
fl ush the inside with distilled water and store the electrode dry.

9609BNWP Fluoride Combination Electrode

For storage between measurements and up to one week, store
the electrode in electrode fi ll solution, Cat. No. 900061, with
fl uoride added. The fl uoride concentration of the storage solution
should be close to least concentrated fl uoride calibration
standard. Do not add TISAB to the storage solution. The fi lling
solution should not be allowed to evaporate, as crystallization
will result. If fi ll solution is unavailable, store in 2 M potassium
nitrate with fl uoride added.

For storage longer than one week, drain the electrode. Flush
the chamber with distilled water. Disassemble the electrode as
described in the electrode maintenance section. Rinse the inner
sleeve with distilled water and blot dry with a Kimwipe. Do not
touch the reference element other than to blot dry. Let air dry
and then reassemble for storage. Use the protective shipping
cap to cover the sensing element.

9Fluoride Ion Selective Electrode User Guide

Electrode Maintenance

Polishing the Sensing Surface of the Fluoride Combination
Electrodes and Fluoride Half-Cell Electrodes

The sensing surface of the fl uoride electrode might need
restoration over time as deposits coat the sensing surface. The
sensing crystal can be restored using the following procedure.
Toothpaste that contains fl uoride will be needed for this
procedure.

1. Dispense a small amount of fl uoridated toothpaste on
a kimwipe. Add a few drops of deionized water. A soft
toothbrush can also be used in placed of a kimwipe.

2. Rub the toothpaste on the sensing element on the bottom
of the electrode in a circular motion for around one minute.

3. Rinse the electrode thoroughly with DI water, fl ush the
electrode fi ll solution out (if using a combination fl uoride
electrode) by pressing on the cap of the electrode) then
refi ll with fresh fi ll solution.

4. Soak the electrode in 100 ppm fl uoride standard for 2 hours.

Flushing the 9609BNWP and 900100 Single Junction
Reference Electrode

If the area between the electrode sleeve and inner cone
becomes clogged with sample or precipitate, fl ush the area with
fi lling 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 fi lling 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 fi lling solution up to the fi ll
hole. Push down on the cap to allow a few drops of fi lling
solution to drain out of the electrode and then refi ll any lost
fi lling solution.

10 Fluoride Ion Selective Electrode User Guide

Disassembling the Fluoride Combination Electrodes and
Single Junction Reference Electrode

Note: Disassembly is usually not required and should not be
done unless a thorough cleaning is required.

1. Tip the electrode so the fi lling 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 fi rmly push down
on the threaded portion with the thumb and forefi nger 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 reference electrode element (coiled wire
in combination electrode, pellet in single junction reference)
above the cone, it will damage to the reference element.
Rinse the outside of the electrode body and the entire
sleeve with distilled water. Blot dry with a Kimwipe and
allow to air dry if needed.

Reassembling the Fluoride Combination Electrodes and
Single Junction Reference Electrode

1. Moisten the O-ring on the electrode body with a drop of
fi lling 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 fl ush
with the tapered end of the sleeve.

3. Place the spring onto the electrode body and screw on the
cap. Refi ll the electrode with fi lling solution.

11Fluoride Ion Selective Electrode User Guide