EUTECH INSTRUMENTS EC-FO-03, EC-SCS-FL1-BT, EC-SCS-FL2-BT, EC-SCS-FL3-BT, EC-ISA-FL1-BT Instruction Manual
...
Instruction Manual Fluoride Electrode
1
EUTECH INSTRUMENTS PTE LTD.
INSTRUCTION MANUAL
FLUORIDE ION ELECTRODE
Instruction Manual Fluoride Electrode
2
TABLE OF CONTENTS
GENERAL INSTRUCTIONS ..........................................................................................................3
Introduction................................................................................................................................................................... 3
Required Equipment ..................................................................................................................................................... 3
Required Solutions........................................................................................................................................................ 3
GENERAL PREPARATION............................................................................................................4
Electrode Preparation.................................................................................................................................................... 4
Electrode Slope Check (with pH/mV meter)................................................................................................................4
Electrode Slope Check (with ion meter).......................................................................................................................5
MEASUREMENT..............................................................................................................................5
Measuring Hints............................................................................................................................................................ 5
Sample Requirements ................................................................................................................................................... 6
Units of Measurement................................................................................................................................................... 6
MEASUREMENT PROCEDURE ...................................................................................................6
Direct Measurement...................................................................................................................................................... 6
Direct Measurement of Fluoride (using a pH/mV meter)............................................................................................. 6
Direct Measurement of Fluoride (using an ion meter).................................................................................................. 8
Direct Measurement of Fluoride in Water (ASTM D1179, METHOD B)...................................................................8
Direct Measurement of Fluoride in Acid Solutions...................................................................................................... 9
Direct Measurement of Fluoride in Alkaline Solutions................................................................................................ 9
Low Level Fluoride Measurements (using a pH/mV meter) ...................................................................................... 10
Low Level Fluoride Determination (using an ion meter) ........................................................................................... 11
Titration ......................................................................................................................................................................12
Titration Procedure for Fluoride Determination......................................................................................................... 12
ELECTRODE CHARACTERISTICS........................................................................................... 13
Reproducibility ........................................................................................................................................................... 13
Interference................................................................................................................................................................. 13
Complexation..............................................................................................................................................................14
Temperature Influences ..............................................................................................................................................14
Electrode Response.....................................................................................................................................................14
Limits of Detection..................................................................................................................................................... 15
pH Effects................................................................................................................................................................... 15
Electrode Life.............................................................................................................................................................. 16
Electrode Storage........................................................................................................................................................ 17
ELECTRODE THEORY................................................................................................................17
Electrode Operation.................................................................................................................................................... 17
TROUBLESHOOTING GUIDE....................................................................................................18
Meter........................................................................................................................................................................... 18
Plastic-ware................................................................................................................................................................. 18
Electrodes.................................................................................................................................................................... 18
Standards and Reagents .............................................................................................................................................. 19
Sample ........................................................................................................................................................................ 19
Technique.................................................................................................................................................................... 19
TROUBLESHOOTING HINTS.....................................................................................................20
SPECIFICATIONS..........................................................................................................................22
ORDERING INFORMATION.......................................................................................................22
Instruction Manual Fluoride Electrode
3
EUTECH INSTRUMENTS PTE LTD.
FLUORIDE ION ELECTRODE
INSTRUCTION MANUAL
GENERAL INSTRUCTIONS
Introduction
Eutech Instruments Fluoride Ion Electrode is used to measure fluoride ions in aqueous solutions
quickly, simply, accurately, and economically.
Required Equipment
1. A pH/mV meter or an ion meter, either line operated or portable.
2. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the
meter in the mV mode.
3. A magnetic stirrer.
4. Eutech Fluoride Ion Combination Epoxy-body Electrode, Code no. EC-FO-03.
5. Lab-ware made of plastic, not glass.
6. Polishing Paper, Code no. EC-MIS-PP, to polish dirty or etched electrode membranes.
Required Solutions
1. Deionized or distilled water for solution and standard preparation.
2. Eutech Fluoride Standard Solution, 0.1 M NaF, Code No. EC-SCS-FL1-BT. To prepare
this solution from your own laboratory stock, half fill a one liter volumetric flask with
distilled water and add 4.2 grams of reagent-grade sodium fluoride. Swirl the flask gently
to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several
times to mix the solution.
3. Eutech Fluoride Standard, 1,000 ppm F-1, Code No. EC-SCS-FL2-BT. To prepare this
solution from your own laboratory stock, half fill a one liter volumetric flask with distilled
water and add 2.21 grams of reagent-grade sodium fluoride. Swirl the flask gently to
dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several
times to mix the solution.
4. Eutech Fluoride Standard, 100 ppm F
-1
, Code No. EC-SCS-FL3-BT. To prepare this
solution from you own laboratory stock, half fill a one liter volumetric flask with distilled
water and add 0.22 grams of reagent-grade sodium fluoride. Swirl the flask gently to
dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several
times to mix the solution.
Instruction Manual Fluoride Electrode
4
5. Eutech Total Ionic Strength Adjuster Buffer (TISAB 1), Code No. EC-ISA-FL1-BT.
TISAB 1 is used to adjust the pH of the solution, de-complex fluoride and provide a
constant background ionic strength. To prepare this solution from your own laboratory
stock, half fill a four liter beaker with distilled water. Place the beaker on a magnetic
stirrer, add a large stirring bar, and begin stirring. Slowly add 230 ml of concentrated
acetic acid, 232 grams of reagent-grade sodium chloride, and 16 grams of reagent-grade
CDTA. After the solids have dissolved, allow the solution to cool to room temperature.
Slowly add 150 grams of reagent-grade sodium hydroxide. After the solids have dissolved,
allow the solution to cool to room temperature. Calibrate a pH electrode and adjust the pH
to 5.25 with small addition of 5 M NaOH. Fill to the mark with distilled water.
6. Eutech Low Level Total Ionic Strength Adjuster Buffer (TISAB 2), Code No. EC-ISAFL2-BT. Use when measuring in samples containing less than 2X10-5M (0.4 ppm) fluoride
and containing no fluoride complexing agents. To prepare this solution from your own
laboratory stock, place about 2'000 ml distilled water in a four liter beaker. Add 57 ml
glacial acetic acid and 58 grams sodium chloride. Place the beaker on a magnetic stirrer,
add a stirring bar and begin stirring. Immerse a calibrated pH electrode into the solution.
Slowly add 5 M NaOH until the pH is 5.25. Allow the solution to cool and fill to the mark
with distilled water.
GENERAL PREPARATION
Electrode Preparation
Remove the rubber caps covering the electrode tips and the rubber insert covering the filling hole of
the reference electrode. Fill the combination electrode or the reference electrode with the filling
solution shipped with the electrode to a level just below the fill hole. No preparation is required
with a sealed reference electrode. Connect the electrodes to the proper terminals of the meter as
recommended by the meter manufacturer.
Electrode Slope Check (with pH/mV meter)
(Check electrodes each day)
1. To a 150 ml plastic beaker, add 50 ml of distilled water and 50 ml of TISAB. Place the
beaker on a magnetic stirrer and begin stirring at a constant rate. After assuring that the
meter is in the millivolt mode, lower the electrode tips into the solution.
2. Using a pipet, add 1 ml of 0.1M, 1,000 ppm, or 100 ppm fluoride standard to the beaker.
When the reading has stabilized, record the mV reading.
3. Using a pipet, add 10 ml of the same fluoride standard used above to the beaker. When the
reading has stabilized, record the mV reading.
4. Determine the difference between the two readings. The electrode is operating correctly if
the millivolt potential has changed by 57±2 mV, assuming the solution temperature is
between 20o and 25oC. See the TROUBLESHOOTING section if the potential change is not
within this range.
Instruction Manual Fluoride Electrode
5
Slope is defined as the change in potential observed when the concentration changes by a factor of
10.
Electrode Slope Check (with ion meter)
(Check electrodes each day)
1. Prepare standard fluoride solutions whose concentrations vary by tenfold. Use either the
0.1M, 1,000 ppm, or 100 ppm fluoride standard. Use the serial dilution method for this
preparation.
2. To a 150 ml beaker, add 50 ml of the lower value standard and 50 ml of TISAB. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips
into the solution. Assure that the meter is in the concentration mode.
3. Adjust the meter to the concentration of the standard and fix the value in the memory
according to the meter manufacturer's instructions.
4. Rinse the electrodes with distilled water and blot dry.
5. To another 150 ml beaker, add 50 ml of the higher value standard and 50 ml of TISAB.
Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the
electrode tips into the solution.
6. Adjust the meter to the concentration of the standard and fix the value in the memory.
7. Read the electrode slope according to the meter instructions. Correct electrode operation is
indicated by a slope of 90-100%. See the TROUBLESHOOTING section if the slope is not
within this range.
MEASUREMENT
Measuring Hints
All samples and standards should be at the same temperature for precise measurement. A difference
of 1
o
C in temperature will result in a 2% measurement error.
Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can
generate sufficient heat to change the solution temperature. To counteract this effect, place a piece
of insulating material, such as a styrofoam sheet, between the stirrer and the beaker.
Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross-contamination.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Always check to see that the membrane is free from air bubbles after immersion into standard or
sample.
Instruction Manual Fluoride Electrode
6
Sample Requirements
All samples must be aqueous and not contain organics which can dissolve the epoxy electrode body
and/or the cement bonding the sensing crystal to the electrode body. Inorganic solutions will not
affect the electrode. Infrequent measurements in solutions containing methanol, acetone, or dioxane
are permitted. Highly polar solvents, such as CHCl
3
or DMF, should not be contained in the
samples. Please check with Eutech Instruments Pte Ltd. before using the electrode in other organic
solvents.
The addition of TISAB to samples and standards will adjust the pH to 5.0-5.5. Samples must be
above pH 5 to avoid forming complexes with hydrogen ions and below pH 7 to avoid interference
by hydroxide ions.
The temperature of the standard solutions and of the sample solutions should be the same and below
80
o
C. The use of TISAB 1 also preferentially forms complexes with aluminum and with iron,
breaking the complexes that fluoride forms with these ions. With 1 ppm fluoride present, up to 3-5
ppm aluminum or iron is complexed. If higher levels of aluminum or iron are present, use TISAB 3.
Units of Measurement
Fluoride concentrations are measured in units of ppm as fluoride, moles per liter, or any other
convenient concentration unit. Table 1 indicates some concentration units and conversion factors.
TABLE 1: Concentration Unit Conversion Factors
ppm F-1 moles/liter
190.0 1.0X10-2M
19.0 1.0X10-3M
1.9 1.0X10-4M
MEASUREMENT PROCEDURE
Direct Measurement
Direct measurement is a simple procedure for measuring a large number of samples. A single meter
reading is all that is required for each sample. The ionic strength of samples and standards should
be made the same by adjustment with TISAB for all fluoride solutions. The temperature of both
sample solution and standard solution should be made the same.
Direct Measurement of Fluoride (using a pH/mV meter)
1. By serial dilution, prepare three standard solutions from the 0.1M, 1,000 ppm, or the 100
ppm stock standard. The resultant concentrations should be 10
-2
M, 10-3M, and 10-4M or
100, 10, and 1 ppm. Add 50 ml of TISAB 1 or TISAB 2 to each 50 ml of standard. When
calibrating, assume that the added TISAB has no effect on the standard concentration.
2. Place the most dilute solution on the magnetic stirrer and begin stirring at a constant rate.
After assuring that the meter is in the mV mode, lower the electrode tips into the solution.
After the reading has stabilized, record the mV reading.
Instruction Manual Fluoride Electrode
7
3. Place the mid-range solution on the magnetic stirrer and begin stirring. After rinsing the
electrodes with distilled water, blot dry, and immerse the electrodes in the solution. When
the reading has stabilized, record the mV value.
4. Place the most concentrated solution on the magnetic stirrer and begin stirring. After
rinsing the electrodes with distilled water, blot dry, and immerse the electrodes in the
solution. When the mV reading has stabilized, record the mV value.
5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the
concentration (log axis). Extrapolate the curve down to about 1.0X10-5M. A typical
calibration curve can be found in Figure 1.
A calibration curve is constructed on semi-logarithmic paper when using the pH/mV
meter in the millivolt mode. The measured electrode potential in mV (linear axis) is
plotted against the standard concentration (log axis). In the linear region of the
curve, only three standards are necessary to determine a calibration curve. In the
non-linear region, additional points must be measured. The direct measurement
procedures given are for the linear portion of the curve. The non-linear portion of the
curve requires the use of low level procedures.
6. To a clean, dry, 150 ml plastic beaker, add 50 ml of sample and 50 ml of TISAB 1 or
TISAB 2. Place the beaker on the magnetic stirrer and begin stirring. Rinse the electrodes
with distilled water, blot dry, and lower the electrode tips into the solution. When the
reading has stabilized, record the mV reading. Using the calibration curve, determine the
sample concentration.
7. The calibration should be checked every 1-2 hours. Assuming no change in ambient
temperature, place the electrode tips in the mid-range standard. After the reading has
stabilized, compare it to the original reading recorded in Step 3 above. A reading differing
by more than 0.5 mV or a change in the ambient temperature will necessitate the repetition
of Steps 2-5 above. A new calibration curve should be prepared daily.
Loading...