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Fluoride Ion Selective Electrode User Guide

Fluoride in Acid Solutions

In solutions with a pH below 5, hydrogen ions complex a
portion of the ﬂ uoride ions, forming HF or HF

2

¯, which cannot

be detected by the ﬂ uoride electrode. To free the complexed
ﬂ uoride, the pH of the solution must be adjusted to the weakly
acidic to weakly basic region before making measurements.
A strong base, such as sodium hydroxide, should not be
used for pH adjustment, since the total ionic strength of the
adjusted samples and standards will vary according to the
original solution pH and the amount of sodium hydroxide
added. Variations in total ionic strength affect the accuracy
of concentration measurements. Dilution of samples and
standards with a large excess of sodium acetate, on the other
hand, will buffer the pH to above 5 and help adjust the total ionic
strength of samples and standards to the same level.

Procedure

1. Prepare a 15% sodium acetate solution. Dissolve reagent-

grade sodium acetate (CH

3

COONa) in distilled water.

Prepare a large enough quantity of 15% sodium acetate
solution to dilute all samples and standards.

2. Prepare a background solution that contains all sample

components except ﬂ uoride. Use this solution to prepare
the standards.

3. Prepare standards in the concentration range of the

unknown samples by adding ﬂ uoride to the background
solution. Dilute each standard 10:1 with the sodium acetate
solution (9 parts sodium acetate and 1 part standard).
Prepare fresh standards every two weeks if the standard
contains less than 10 ppm ﬂ uoride. If an ISE (concentration)
meter is used, prepare at least two standards. If a meter
with a mV mode is used, prepare at least three standards.

4. Calibrate the electrode using the instructions in the

Checking Electrode Operation (Slope)

section.

5. Measure the unknown samples: Dilute each unknown

sample 10:1 with sodium acetate before performing taking
measurements (9 parts sodium acetate and 1 part unknown
sample).

Note:

In many cases, standards do not need to be prepared

using background solutions. If a standard prepared from the
background solution gives the same reading (after dilution with
sodium acetate) as a standard prepared from pure sodium
ﬂ uoride, then the background solution is unnecessary.

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Содержание 9609BNWP

Страница 1: ...User Guide Fluoride Ion Selective Electrode ...

Страница 2: ... Triode Minimum Stir Requirement MSR NISS Optimum Results Orion Dual Star Orion Star SAOB SMART AVERAGING SMART STABILITY Star LogR Star Navigator 21 Stat Face Triode are trademarks of Thermo Fisher Scientiﬁc Inc and its subsidiaries Guaranteed Success and The Technical Edge are service marks of Thermo Fisher Scientiﬁc Inc and its subsidiaries 2011 Thermo Fisher Scientiﬁc Inc All rights reserved A...

Страница 3: ...ues 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 Troubleshoo...

Страница 4: ......

Страница 5: ...nical 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 978 232 6031 In Europe the Middle East and Africa contact your local authorized dealer For the most current contact information visit www thermoscientiﬁc com water Fluoride ionplus Sure Flow Solid State Combination ISE...

Страница 6: ... Ion Selective Electrode User Guide cap cable spring O ring ﬁlling hole inner cone sensing crystal reference element ﬁlling solution chamber outer body inner body Figure 1 9609BNWP Fluoride Combination Electrode ...

Страница 7: ...rrer or Orion stirrer probe Cat No 096019 The Orion stirrer probe can be used with 3 Star 4 Star 5 Star benchtop meters and Dual Star meter 4 Volumetric ﬂasks graduated cylinders and beakers Plastic labware is highly recommended for ﬂuoride analysis 5 Distilled or deionized water 6 Fluoride electrode ﬁlling solution Use Optimum Results A ﬁlling solution Cat No 900061 for the 9609BNWP ﬂuoride elect...

Страница 8: ... between 5 0 and 5 5 Cool the solution to room temperature Pour the solution into a 1 liter volumetric ﬂask and dilute to the ﬂask mark with distilled water All reagents must be as pure as possible to keep the ﬂuoride 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 TISAB IV TISAB IV will complex mor...

Страница 9: ...de warranty Electrode Filling Instructions 1 Lift the ﬂip spout on the ﬁlling solution bottle to a vertical position 2 Insert the spout into the ﬁlling hole on the outer body of the electrode and add a small amount of ﬁlling 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 ...

Страница 10: ...ow level 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 ﬂuoride or 100 ppm ﬂuoride standard Pipette 1 mL of the standard ...

Страница 11: ...Sample Requirements The epoxy body of the ﬂuoride 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 speciﬁc applications Samples and standards should be at the same temperature The solution temperature must be less than 100 C In all analy...

Страница 12: ...de 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...

Страница 13: ...erence electrode ﬂush 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 ﬁll solution Cat No 900061 with ﬂuoride added The ﬂuoride concentration of the storage solution should be close to least concentrated ﬂuoride calibration standard Do not add TISAB to the storag...

Страница 14: ...ush the electrode ﬁll solution out if using a combination ﬂuoride electrode by pressing on the cap of the electrode then reﬁll with fresh ﬁll solution 4 Soak the electrode in 100 ppm ﬂuoride 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 ﬂush the area with ﬁ...

Страница 15: ...an 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 ...

Страница 16: ...12 Fluoride Ion Selective Electrode User Guide ...

Страница 17: ...ectrode is immersed in the sample solution and an aliquot of a standard solution containing the measured species is added to the sample when performing single known addition From the change in potential before and after the addition the original sample concentration is determined Double known addition is recommended for complex sample matrices Known Subtraction is useful as a quick version of a ti...

Страница 18: ...ed samples The method is not suited for very dilute samples It is also necessary to know the stoichiometric ratio between standard and sample Titrations are quantitative analytical techniques for measuring the concentration of a species by incremental addition of a reagent titrant that reacts with the sample species Sensing electrodes can be used for determination of the titration end point Ion se...

Страница 19: ...ir concentrations on the log axis In the linear regions of the curves only two standards are needed to determine a calibration curve In non linear regions more points must be taken These direct calibration procedures are given for concentrations in the region of linear electrode response Low level measurement procedures are given in the next section for measurements in the non linear region 10 5 0...

Страница 20: ...n electrode performance refer to the Temperature Effects section Serial Dilutions Serial dilution is the best method for the preparation of standards Serial dilution means that an initial standard is diluted using volumetric glassware to prepare a second standard solution The second standard is similarly diluted to prepare a third standard and so on until the desired range of standards has been pr...

Страница 21: ...00 mL 100 ppm V1 1 ppm 100 mL V1 1 ppm 100 mL 100 ppm 1 mL To make the 1 ppm ﬂuoride standard pipette 1 mL of the 100 ppm ﬂuoride standard into a 100 mL volumetric ﬂask Dilute to the mark with deionized water and mix well Fluoride Standards withTISAB II The 10 ppm ﬂuoride with TISAB II standard Cat No 040908 2 ppm ﬂuoride with TISAB II standard Cat No 040907 and 1 ppm ﬂuoride with TISAB II standar...

Страница 22: ...trode with deionized water blot dry and place into the beaker with the more concentrated standard Wait for a stable reading and then adjust the meter to display the value of the second standard as described in the meter user guide 5 Record the resulting slope value The slope should be between 54 to 60 mV when the standards are between 20 25 C When using a Thermo Scientiﬁc meter with the Autoblank ...

Страница 23: ...ughly 5 Rinse the electrode with deionized water blot dry and place into the beaker with the more concentrated standard When a stable reading is displayed record the mV value and corresponding standard concentration 6 Using a calculator or electronic spreadsheet prepare a calibration curve by graphing the log of the ﬂuoride concentration against the millivolt value readings 7 Measure 50 mL of the ...

Страница 24: ...e Electrode Preparation section 2 Connect the electrode to the meter Set the meter to read mV 3 Prepare the low level TISAB Refer to the Required Equipment section for instructions Use low level TISAB for low level measurements only 4 Prepare 100 mL of standard solution Dilute the 100 ppm ﬂuoride standard Cat No 940907 to 10 ppm or dilute the 0 1 M NaF standard Cat No 940906 to 10 3 M 5 Add 100 mL...

Страница 25: ...n select the meter calibration mode and wait for a stable reading Adjust the meter to display the value of the standard as described in the meter user guide 6 Repeat step 5 for the second and third standards and complete the calibration as described in the meter user guide 7 Record the resulting slope value The absolute value of millivolt difference should be greater than 54 mV 8 Measure equal amo...

Страница 26: ...t value readings Prepare a new calibration curve with fresh standards each day 5 Measure 50 mL of sample and 50 mL of low level TISAB and add to a clean 150 mL beaker Rinse the electrode with deionized water blot dry and place into the sample 6 Stir the solution thoroughly When a stable reading is displayed record the mV value 7 Determine the sample concentration corresponding to the measured pote...

Страница 27: ... 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 Either no complexing agent or a large excess of the complexing agent may be present The ratio of the uncomple...

Страница 28: ...f the sample to double when added to the sample solution Refer to Table 3 for guidelines 4 Determine the electrode slope by performing the procedure in the Checking Electrode Operation Slope section 5 Rinse the electrode with deionized water Table 3 Guideline For Known Addition Volume of Addition Concentration of Standard 1 mL 100 times sample concentration 5 mL 20 times sample concentration 10 mL...

Страница 29: ...e sample concentration Single Known Addition Using a Meter with a Millivolt Mode 1 Set the meter to relative millivolt mode If a relative millivolt mode is not available use the millivolt mode 2 Measure 50 mL of sample and 50 mL of TISAB II or 5 mL of TISAB III and add to a 150 mL beaker Stir the solution thoroughly 3 Rinse the electrode with deionized water blot dry and place into the beaker When...

Страница 30: ...sample Q Cstandard where Cstandard standard concentration Csample sample concentration Q value from Table 4 The table of Q values is calculated for a 10 volume change The equation for the calculation of Q for different slopes and volume changes is given below Q p r 1 p 10 ΔE S 1 where Q value from Table 4 ΔE E2 E1 S slope of the electrode p volume of standard volume of sample and ISA r volume of s...

Страница 31: ...0 1771 9 4 0 1649 0 1677 0 1706 0 1734 9 6 0 1614 0 1642 0 1671 0 1698 9 8 0 1581 0 1609 0 1636 0 1664 10 0 0 1548 0 1576 0 1603 0 1631 10 2 0 1517 0 1544 0 1571 0 1598 10 4 0 1487 0 1514 0 1540 0 1567 10 6 0 1458 0 1484 0 1510 0 1537 10 8 0 1429 0 1455 0 1481 0 1507 11 0 0 1402 0 1427 0 1453 0 1479 11 2 0 1375 0 1400 0 1426 0 1451 11 4 0 1349 0 1374 0 1399 0 1424 11 6 0 1324 0 1349 0 1373 0 1398 ...

Страница 32: ... 0405 0 0416 0 0427 29 5 0 0383 0 0394 0 0405 0 0416 30 0 0 0373 0 0383 0 0394 0 0405 31 0 0 0353 0 0363 0 0373 0 0384 32 0 0 0334 0 0344 0 0354 0 0364 33 0 0 0317 0 0326 0 0336 0 0346 34 0 0 0300 0 0310 0 0319 0 0328 35 0 0 0285 0 0294 0 0303 0 0312 36 0 0 0271 0 0280 0 0288 0 0297 37 0 0 0257 0 0266 0 0274 0 0283 38 0 0 0245 0 0253 0 0261 0 0269 39 0 0 0233 0 0241 0 0249 0 0257 40 0 0 0222 0 022...

Страница 33: ...num nitrate solution by dissolving 43 3 g of reagent grade La NO3 3 6H20 in a 1 liter volumetric ﬂask that contains approximately 700 mL of distilled water Once the solids are dissolved ﬁll the ﬂask to the mark with distilled water 2 Standardize the lanthanum nitrate solution by titrating against a 0 1 M ﬂuoride standard Pipette exactly 25 mL of ﬂuoride standard into a 250 mL plastic beaker and ad...

Страница 34: ...1 M Vtx volume of titrant added in unknown sample titration at endpoint Vto volume of titrant added in standardization titration at endpoint Vfx volume of sample used in sample titration 25 mL Vfo volume of standard used in standardization titration 25 mL 100 50 0 50 100 5 10 15 20 25 titrant volume mL electrode potential mV Figure 3 Titration of 0 114 M F with 0 1 M La NO3 3 ...

Страница 35: ... a large enough quantity of 15 sodium acetate solution to dilute all samples and standards 2 Prepare a background solution that contains all sample components except ﬂuoride Use this solution to prepare the standards 3 Prepare standards in the concentration range of the unknown samples by adding ﬂuoride to the background solution Dilute each standard 10 1 with the sodium acetate solution 9 parts s...

Страница 36: ...surrounding the reaction with a water bath Add 50 KOH solution to the acetic acid slowly stirring constantly until a pH of 5 is reached Prepare a large enough quantity of the potassium acetate solution to dilute all samples and standards 2 If required prepare a background solution that contains all sample components except ﬂuoride Use this solution to prepare the standards 3 Prepare standards in t...

Страница 37: ...me minutes 1 160 120 80 40 0 40 80 2 3 4 10 3 M to 10 6 M 10 3 M to 10 5 M 10 3 M to 10 4 M 10 3 M to 10 2 M electrode potential mV Figure 4 Typical Electrode ResponseTo Step Changes in NaF Concentration Reproducibility Reproducibility is limited by factors such as temperature ﬂuctuations drift and noise Within the operating range of the electrode reproducibility is independent of concentration Wi...

Страница 38: ...Values Temperature C Slope mV 0 54 2 10 56 2 20 58 2 25 59 2 30 60 1 40 62 1 50 64 1 The electrode can be used at temperatures from 0 to 100 C provided that temperature equilibrium has occurred For use at temperatures substantially different from room temperature equilibrium times of up to one hour are recommended The electrode must be used only intermittently at solution temperatures above 80 C I...

Страница 39: ...10 7 M or less there is no hydroxide interference with ﬂuoride measurements At pH 10 where the hydroxide concentration is 10 4 M there is no error at 10 2 M ﬂuoride about a 10 error at 10 4 M ﬂuoride and considerable error at 10 5 M ﬂuoride See Figure 6 Addition of TISAB II or III to ﬂuoride standards and samples will buffer the pH between 5 0 and 5 5 to avoid hydroxide interferences or the format...

Страница 40: ...on of complexing agent the total ﬂuoride concentration and pH of the solution and the total ionic strength of the solution TISAB II and III contain a reagent CDTA that preferentially complexes aluminum or iron in the sample In a 1 ppm ﬂuoride sample TISAB II or III complexes about 5 ppm aluminum or iron Higher levels of aluminum or iron can be complexed by using TISAB IV solution pH 7 100 75 50 25...

Страница 41: ...here E measured electrode potential Eo reference potential a constant A ﬂuoride ion activity level in solution S electrode slope about 57 mV per decade The level of ﬂuoride ion A is the activity or effective concentration of free ﬂuoride ion in solution The ﬂuoride ion activity is related to free ﬂuoride ion concentration Cf by the activity coefﬁcient yi A yi Cf Ionic activity coefﬁcients are vari...

Страница 42: ...r control is the composition of the liquid junction ﬁlling solution The ﬁlling solution should be equitransferent That is the speed with which the positive and negative ions in the ﬁlling solution diffuse into the sample should be nearly as equal as possible If the rate at which positive and negative charge is carried into the sample solution is equal then no junction potential can result However ...

Страница 43: ...ean the electrode thoroughly as directed in the Electrode Maintenance section Drain and reﬁll the electrode with fresh ﬁlling solution 4 Repeat the procedure in the Checking Electrode Operation Slope section 5 It the electrode fails this procedure again and the half cell ﬂuoride electrode is being used determine whether the ﬂuoride or reference electrode is at fault To do this substitute a known w...

Страница 44: ...edures Review calibration and measurement sections to be sure proper technique has been followed Verify that the expected concentration of the ion of interest is within the limit of detection of the electrode Check the method of analysis for compatibility with your sample Direct measurement may not always be the method of choice If a large amount of complexing agents are present known addition may...

Страница 45: ... cleaning instructions Standards are contaminated or made incorrectly Prepare fresh standards Refer to the Measurement Hints and AnalyticalTechniques sections TISAB not used or incorrect TISAB used TISAB must be added to all standards and samples Refer to the Required Equipment section for information on TISAB solutions Samples and standards at different temperatures Allow solutions to reach the s...

Страница 46: ...rate reference electrode 900100 Single junction reference electrode pin tip connector 900061 Optimum Results A electrode ﬁlling solution 5 x 60 mL bottles 900001 Single junction reference electrode ﬁlling solution 5 x 60 mL bottles 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...

Страница 47: ...e 0 to 80 C continuous use 80 to 100 C intermittent use Electrode Resistance 150 to 200 kilohms Reproducibility 2 Minimum Sample Size 5 mL in a 50 mL beaker Size 9609BNWP Body Diameter 13 mm Cap Diameter 16 mm Cable Length 1 meter Size 9409BN and 9409SC Body Diameter 12 mm Cap Diameter 16 mm Cable Length 1 meter Speciﬁcations are subject to change without notice ...

Страница 48: ...tiﬁc 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 www thermo com water 267081 001 Rev A ...

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