Thermo Electron 96-09 User manual

F
Orion 94-09, 96-09
Orion ionplus
Fluoride Electrode
INSTRUCTION MANUAL
-
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TABLE OF CONTENTS
General Information 1
Introduction 1
Required Equipment 2
Required Solutions 3
Using The Electrode 5
Electrode Preparation 5
Filling Instructions 5
Checking Electrode Operation (Slope) 6
Before Analysis 7
Units of Measurement 7
Sample Requirements 7
Measuring Hints 8
Analytical Procedures 9
Analytical Techniques 9
Direct Calibration 11
Low-Level Measurement 14
Known Addition 16
Titrations 22
Fluoride in Acid Solutions 24
Fluoride in Alkaline Solutions 25
Electrode Storage 26
Troubleshooting 28
Troubleshooting Checklist 28
Troubleshooting Guide 30
Assistance 32
Electrode Characteristics 33
Electrode Response 33
Reproducibility 33
Limits of Detection 34
Temperature Effects 34
Interferences 35
pH Effects 35
Complexation 37
Electrode Life 37
Theory of Operation 38
Warranty 41
Ordering Information 45
Specifications 46

1
GENERAL INFORMATION
Introduction
The Orion 94-09 Half-Cell Fluoride and Orion 96-09 Combination
Fluoride Electrodes measure free fluoride ions in aqueous
solutions quickly, simply, accurately, and economically. General
analytical procedures, required solutions, electrode
characteristics, and electrode theory are discussed in this
manual. Operator instructions for Orion meters are outlined in
the individual meter instruction manuals.
The measurement of fluoride in drinking water is an approved
ASTM method: Approval number ASTM D 1179.
Thermo Electron Corporation Technical Service Chemists can be
consulted for assistance and troubleshooting advice. Please
refer to TROUBLESHOOTING for information before contacting
Thermo.

Required Equipment
Meter
The easiest instruments to use are direct concentration readout
specific ion meters, such as Orion’s EA 940, 920A, 920Aplus,
720A, 720Aplus, 710A, 710Aplus, 290A or 290Aplus. If
unavailable, use a pH/mV meter with readability to 0.1 mV, such
as Orion’s 420A, 420Aplus, 520A, 520Aplus, 525A or 525Aplus.
Reference Electrode
For Orion 94-09: Use with Orion 90-01
Single Junction Reference Electrode.
For Orion 96-09: None required.
Stirring Accessories
Magnetic stirrer or stir bars are highly recommended
for laboratory measurements.
Graph Paper
4-cycle semilogarithmic paper for preparing calibration
curves (for use with digital pH/mV laboratory meters).
Plastic Labware
Plastic beakers are highly recommended for
fluoride measurements.
2

Required Solutions
Distilled or Deionized Water
To prepare all solutions and standards.
Standard Solutions
Select the appropriate Thermo Electron Corporation standard(s)
from the list below.
Standard Solutions Orion No.
0.1 M Sodium Fluoride Standard 940906
100 ppm Fluoride Standard 940907
1 ppm Fluoride Standard with TISAB 040906
2 ppm Fluoride Standard with TISAB 040907
10 ppm Fluoride Standard with TISAB 040908
Electrode Filling Solutions
Inner Chamber Filling Solution 900001
(Orion 90-01 Single Junction Reference)
Optimum ResultsTM A900061
(Orion 96-09 Combination Electrode)
Total Ionic Strength Adjustor (TISAB)
To provide constant background ionic strength, decomplex
fluoride and adjust solution pH
TISAB II: (50 mL TISAB II to 940909
each 50 mL sample or standard)
TISAB III: (5 mL TISAB III to 940911
each 50 mL sample or standard)
3

4

USING THE ELECTRODE
Electrode Preparation
Orion 94-09
1. Remove the rubber cap covering the electrode tip.
Orion 90-01
1. Remove the rubber cap covering the electrode tip.
2. Fill reference electrode with Orion No. 900001.
Orion 96-09
1. Remove the rubber cap covering the electrode tip.
2. Fill outer chamber with Orion No. 900061.
NOTE: The Optimum ResultTM A filling solution
(Orion No. 900061) supplied with Orion 96-09 electrode
is designed to minimize junction potentials and fluoride
ion contamination of the sample, and can be used for all
fluoride measurements. Use of any other filling solutions
will void the warranty on the electrode.
Filling Instructions
The electrode is shipped without filling solution in the reference
chamber. To fill from the flip-spout bottle:
1. Lift the spout to a vertical position.
2. Insert the spout into the filling hole in the outer sleeve and
add a small amount of filling solution to the chamber. Tip
the electrode to moisten the 0-ring at the top and return
electrode to a vertical position.
3. Holding the electrode by the barrel with one hand, use the
thumb to push down on the electrode cap, allowing a few
drops of filling solution to drain to wet the inner cone.
4. Release sleeve. If sleeve does not return to its original
position immediately, check to see if the 0-ring is moist
enough and repeat steps 2-4 until the sleeve has returned to
original position. Add filling solution up to the filling hole.
NOTE: Add filling solution each day before using
electrode. The filling solution level should be at least one
inch above the level of sample in the beaker to ensure a
proper flow rate. If the filling solution is less than one
inch above the sample solution level, electrode potentials
may be erratic. Do not seal the filling hole when
making measurements.
5

Checking Electrode Operation (Slope)
These are general instructions, which can be used with most
meters to check electrode operation. See individual meter
instruction manuals for more specific information.
This procedure measures electrode slope. Slope is defined 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 electrodes have been stored dry, prepare the electrodes as
described under Electrode Preparation.
2. Connect electrodes to meter.
For electrode with U.S. Standard Connector: Insert reference
pin-tip and the sensing electrode connector into appropriate
jacks on the meter.
For electrode with BNC Connector: Screw the connector into
the appropriate jacks on the meter,
NOTE: Non-Orion meters may require special adapters.
Consult your meter instruction manual.
3. Place 50 mL distilled water and 50 mL of TISAB II,
or 90 mL of distilled water and 10 mL of TISAB III into
a 150 mL beaker.
4. Rinse electrodes with distilled water and place in the solution
prepared in step 3 above.
5. Select either 0.1 M Fluoride or 100 ppm Fluoride. Pipet 1 mL
of the selected standard into the beaker. Stir thoroughly.
When a stable reading is displayed, record the electrode
potential in millivolts.
6. Pipet 10 mL of the same standard into the same beaker. Stir
thoroughly. When a stable reading is displayed, record the
electrode potential in millivolts.
7. The difference between the first and second potential
readings is the slope of the electrode. The difference should
be in the range of 54-60 mV/decade when the solution
temperature is 25 °C. If the difference in potential is not
within this range, refer to TROUBLESHOOTING.
6

Before Analysis
Units of Measurement
Fluoride concentration can be measured in units of moles per
liter, parts per million, or any convenient concentration unit
(see Table 1).
Table 1
Concentration Unit Conversion Factors
Moles/Liter ppm F-
10-1 1900
10-2 190
10-3 19
10-4 1.9
Sample Requirements
The epoxy electrode body Orion 94-09 and Orion 96-09 are
resistant to attack by inorganic solutions. The electrode may be
used intermittently in solutions containing methanol benzene or
acetone. Consult Thermo’s Technical Service Chemists for
information on using the electrode in specific applications.
Samples and standards should be at the same temperature.
Temperature must be less than 100 °C.
7

Measuring Hints
•Pipet 50 mL of TISAB II per 50 mL standard or sample,
or 10 mL of TISAB III per 90 mL standard or sample.
•Stir all standards and samples at a uniform rate during
measurement. Magnetic stirrers may generate sufficient heat
to change solution temperature. Place a piece of insulating
material such as cork, cardboard, or styrofoam between the
stirrer and beaker.
•Verify calibration every two hours by placing electrodes in a
fresh aliquot of the first standard solution used for
calibration. If the value has changed, recalibrate.
•Always use fresh standards for calibration.
•Always rinse electrodes with deionized water between
measurements (see Electrode Preparation). Shake after
rinsing to prevent solution carry-over. Do not wipe or rub
the sensing element.
•Allow all standards and samples to come to the same
temperature for precise measurement.
•After immersion in solution, check electrode for any air
bubbles on element surface and remove by redipping
electrode into solution.
•For high ionic strength samples, prepare standards with
composition similar to that of sample.
•Highly acidic or highly basic solutions should be adjusted to
pH 5-6 before addition of TISAB.
8

Analytical Procedures
A variety of analytical techniques are available to the analyst.
The following is a description of these techniques.
Direct Calibration
This simple procedure is for measuring a large number of
samples. Only one meter reading is required for each sample.
Calibration is performed in a series of standards. The
concentration of the samples is determined by comparison to
the standards. ISA is added to all solutions to ensure that
samples and standards have similar ionic strength.
Incremental Techniques
This is a useful method for measuring samples with no
calibration requirements. As in direct calibration, any
convenient concentration unit can be used. The different
incremental techniques are described below. They can be used
to measure the total concentration of a specific ion in the
presence of a large (50-100 times) excess of complexing agent.
•Known Addition is an alternate method useful for measuring
dilute samples, checking the results of direct calibration
(when no complexing agents are present), or measuring the
total concentration of an ion in the presence of an excess
complexing agent. The electrodes are immersed in the
sample solution and an aliquot of a standard solution
containing the measured species is added to the sample
solution. The original sample concentration is determined
from the change in potential before and after the addition.
•Known Subtraction is useful as a quick version of a titration,
or for measuring species for which stable standards do not
exist. It is necessary to know the stoichiometric ratio
between standard and sample. For known subtraction, an
electrode sensing the sample species is used. Stable
standards of a species reacting completely with the sample in
a reaction of known stoichiometry are necessary.
9

•Analate Addition is often used to measure soluble solid
samples, viscous samples, small or very concentrated
samples, or to diminish the effects of varying sample
temperatures. This method is not suitable for dilute or low
concentration samples. Total concentration is measured
even in the presence of complexing agents. The electrodes
are immersed in a standard solution containing the ion to be
measured, and an aliquot of the sample is added to the
standard. The original sample concentration is determined
from the change in potential before and after the addition.
•Analate Subtraction is used in the measurement of ions for
which no ion-selective electrode exists. The electrodes are
immersed in a reagent solution, which contains a species
that the electrode senses, and that reacts with the sample.
It is useful when sample size is small, or samples for which a
stable standard is difficult to prepare, and for viscous or very
concentrated samples. The method is not suited for very
dilute samples. It is also necessary to know the
stoichiometric ratio between standard and sample.
Specific instructions for known addition, known subtraction,
analate addition, and analate subtraction can be found in
Thermo Meter Instruction Manual Orion 960.
Titrations
Titrations are quantitative analytical techniques for measuring
the concentration of a species by incremental additions of a
reagent (titrant) that reacts with the sample species. Sensing
electrodes can be used for determination of the titration
endpoint. Ion-selective electrodes are useful as endpoint
detectors, because they are unaffected by sample color
or turbidity. Titrations are approximately 10 times more
precise than direct calibration, but are more time-consuming.
Orion 960 is an excellent source of automated titration
instrument.
10

Direct Calibration
Setup
1. Remove the rubber cap covering the electrode(s) tip.
2. If using Orion 94-09 electrode with Orion 90-01 Reference
Electrode, fill the reference electrode chamber with
Orion No. 900001. If using Orion 96-09, fill the chamber
of the electrode with Orion No. 900061.
3. Connect electrode(s) to meter.
4. Prepare two standards that bracket the expected sample
range and differ in concentration by a factor of ten.
Standards can be prepared in any concentration unit to suit
the particular analysis requirement. All standards should be
at the same temperature as the samples (for details on
temperature effects on electrode performance, refer to
Temperature Effects).
Using a meter with direct concentration readout capability
See individual meter instruction manuals for more
specific information.
1. Measure 50 mL of the more dilute standard and 50 mL of
TISAB II or 5 mL of TISAB III into a 150 mL beaker.
Stir thoroughly.
2. Rinse electrode(s) with deionized water, blot dry and place
into the beaker. Wait for a stable reading. Then calibrate the
meter to display the value of the standard as described in the
Meter Instruction Manual.
3. Measure 50 mL of the more concentrated standard and
50 mL of TISAB II or 5 mL TISAB III into a 150 mL beaker.
Stir thoroughly.
4. Rinse electrode(s) with distilled water, blot dry, and place
into the beaker with the more concentrated standard. Wait
for a stable reading then adjust the meter to display the value
of the second standard as described in the Meter
Instruction Manual.
5. Measure 50 mL of the sample and 50 mL of TISAB II or
5 mL of TISAB III into a 150 mL beaker. Stir thoroughly.
6. Rinse electrode(s) with deionized water, blot dry and
place into sample. The concentration will be displayed
on the meter.
11

Figure 1
Typical Calibration Curve
In the direct measurement procedure using a pH/mV meter, a
calibration curve is constructed on semilogarithmic paper.
Electrode potentials of standard solutions are measured and
plotted on the linear axis against their concentrations on the log
axis. In the linear regions of the curve, at least three standards
are needed to determine a calibration curve. In the non-linear
regions, more points must be taken. The direct measurement
procedures in this manual are given for concentrations in the
region of linear electrode response. Low-level measurement
procedures are given for measurements in the non-linear region.
12
10 - 5
0.1
180
160
140
120
100
80
60
40
20
0
-20
-40
-60
1 10 100 1000
10 - 410 - 310 - 210 - 1
molarity
ppm fluoride as F-
10-fold change
electrode
potential
(mV)
~ 56 mV

Using a meter with millivolt readout only
1. Adjust the meter to measure mV.
2. Measure 50 mL of the more dilute standard with 50 mL of
TISAB II or with 5 mL of TISAB III into a 150 mL beaker.
Stir thoroughly.
3. Rinse electrode(s) with deionized water, blot dry and place
into the beaker. When a stable reading is displayed, record
the mV value and corresponding standard concentration,
4. Measure 50 mL of the more concentrated standard with
50 mL of TISAB II or with 5 mL of TISAB III into a 150 mL
beaker. Stir thoroughly.
5. Rinse electrode(s) with deionized water, blot dry and
place into the second beaker. When a stable reading is
displayed, record the mV value and corresponding
standard concentration.
6. Using a semilogarithmic graph paper, prepare a calibration
curve by plotting the mV values on the linear axis, and the
standard concentration values on the logarithmic axis.
See Figure 1.
7. Measure 50 mL of sample with 50 mL of TISAB II or with
5 mL of TISAB III into a 150 mL beaker. Stir thoroughly.
8. Rinse electrodes with deionized water, blot dry, and place
into the beaker. When a stable reading is displayed, record
the mV value.
9. Using the calibration curve prepared from step 6, determine
the unknown concentration.
13

Low-Level Measurement
These procedures are for low ionic strength solutions with a
fluoride concentration of less than 2x10-5M (or 0.38 ppm) and
containing no fluoride complexing agents. For solutions low in
fluoride but high in total ionic strength, perform the same
procedure by preparing a calibrating solution with a composition
similar to the sample. Accurate measurement requires that the
following conditions be met:
•Adequate time must be allowed for electrode
stabilization. Longer response time will be needed at
low-level measurements.
•Stir all standards and samples at a uniform rate.
•Always use low level TISAB for standards and samples.
For meters with only a millivolt scale, without special low level
procedures, or without blank correction, prepare a calibration
curve as follows:
Setup
1. Remove the plastic cap covering the electrode(s) tip.
2. If using Orion 94-09 Fluoride Half Cell, fill the Orion 90-01
Single Junction Reference Electrode with Orion No. 900001.
If using Orion 96-09 Fluoride Combination Electrode, fill the
electrode chamber with Orion No. 900061.
3. Connect the electrodes to the meter. Set the meter
to read mV.
4. Prepare 100 mL of standard solution. Either dilute the
100 ppm NaF (Orion No. 940907) to 10 ppm or dilute the
0.1 M NaF (Orion No. 940906) to 10-3 M. Add 100mL of
low-level TISAB to 100 mL standard.
5. Prepare low-level TISAB. Use low-level TISAB for low-level
measurements only.
14

Making Measurements
1. Measure 50 mL deionized water and 50 mL low-level TISAB
into a 150 mL beaker.
2. Rinse the electrode(s) with deionized water and place into
beaker. Stir thoroughly.
3. Add increments of 19 ppm or 10-3 M, which has been diluted
with low-level TISAB standard, to the beaker using steps
outlined in Table 2. Record stable millivolt reading after each
increment. On semi logarithmic paper, plot the concentration
(log axis) against the millivolt potential (linear axis). Prepare
a new calibration curve with fresh standards each day.
4. Measure 50 mL of sample diluted with 50 mL of low-level
TISAB from a beaker. Rinse the electrode(s) with distilled
water, blot dry, and place into sample.
5. Stir thoroughly. When a stable reading is displayed, record
the mV value.
6. Determine the sample concentration corresponding to the
measured potential from the low-level calibration curve.
Table 2
Calibration Curve For Low-Level Measurements
Additions of standard (with added TISAB) to 50 mL distilled
water and 50 mL low-level TISAB.
Pipet Added Concentration
Step Size Volume ppm Molarity
11mL 0.1 mL 0.01 1 x 1 0-6
21mL 0 1 mL 0.02 2 x 1 0-6
31mL 0.2 mL 0.04 4 x 10-1
41mL 0.2 mL 0.06 6 x 10-6
51mL 0.4 mL 0.10 1 x 10-5
62mL 2.0 mL 0.29 2.9 x 10-5
72mL 2.0 mL 0.48 4.8 x 10-5
15

Known Addition
Known addition is a convenient technique for measuring
samples because no calibration curve is required. It can be
used to verify the results of a direct calibration or to measure
the total concentration of an ion in the presence of a large
excess of a complexing agent. The sample potential is
measured before and after addition of a standard solution.
Accurate measurement requires that the following conditions
be met:
•Concentration should approximately double as a result of
the addition.
•Sample concentration should be known to within a factor
of three.
•In general, either no complexing agent or a large excess of
the complexing agent may be present.
•The ratio of the uncomplexed ion to complexed ion must not
be changed by addition of the standard.
•All samples and standards should be at the
same temperature.
16

Setup
1. Remove the plastic cap covering the electrode(s) tip.
2. If using Orion 94-09 Fluoride Half Cell, fill the Orion 90-01
Single Junction Reference Electrode with Orion No. 900001.
If using Orion 96-09 Fluoride Combination Electrode, fill the
electrode chamber with Orion No. 900061.
3. Connect the electrode(s) to the meter.
4. Prepare a standard solution, which upon addition to the
sample will cause the concentration of the fluoride ion to
double. Refer to Table 3 as a guideline.
5. Determine the slope of the electrode(s) by performing the
procedure under Checking Electrode Operation (Slope).
6. Rinse electrode(s) between solutions with deionized water.
Table 3
Guideline For Known Addition
Volume of Addition Concentration of Standard
1 mL 100 x sample concentration
5 mL 20 x sample concentration
10 mL* 10 x sample concentration
*Most convenient volume to use
Using a meter with direct known addition readout capability
See individual meter instruction manuals for more
specific information.
1. Set up the meter to measure in the known addition mode.
2. Measure 50 mL of the sample and 50 mL of TISAB II or
5 mL of TISAB III in a beaker. Rinse electrode(s) with
distilled water and place in sample solution. Stir thoroughly.
3. When a stable reading is displayed, calibrate the meter as
described in the meter instruction manual.
4. Pipet the appropriate amount of the standard solution into
the beaker. Stir thoroughly.
5. When a stable reading is displayed, record the
sample concentration.
17