Thermo Scientific ISE User Manual
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Thermo Scientific ISE User Manual

Thermo Scientific ISE User Manual

Fluoride ion selective electrode
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User Guide
Fluoride Ion
Selective
Electrode

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Summary of Contents for Thermo Scientific ISE

  • Page 1 User Guide Fluoride Ion Selective Electrode...
  • Page 2 Ross and the COIL trade dress are trademarks of Thermo Fisher Scientifi c, Inc. and its subsidiaries. AQUAfast, AQUASensors, BOD AutoEZ, ionplus, KNIpHE, LogR, No Cal, ORION, perpHect, PerpHecT, pHISA, pHuture, Pure Water, ROSS, ROSS Ultra, Sage, Sure-Flow, Titrator PLUS, and TURBO2 are registered trademarks of Thermo Fisher Scientifi...

  • Page 3: Table Of Contents

    Table of Contents Introduction ........1 Required Equipment .

  • Page 5: Introduction

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

  • Page 7: Required Equipment

    Required Equipment 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.
  • Page 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...

  • Page 9: Electrode Setup

    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.

  • Page 10: Checking Electrode Operation (Slope)

    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.

  • Page 11: Measurement Units

    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) 19000 1900 Sample Requirements The epoxy body of the fl uoride electrode is resistant to damage by inorganic solutions.

  • Page 12: Measuring Hints

    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 (Low- level 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.

  • Page 13: Electrode Storage

    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.

  • Page 14: Electrode Maintenance

    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...
  • Page 15 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. 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.
  • Page 16 Fluoride Ion Selective Electrode User Guide...

  • Page 17: Analytical Techniques

    Analytical Techniques A variety of analytical techniques are available to the analyst. The following is a description of these techniques. Direct Calibration is a simple procedure for measuring a large number of samples. Only one meter reading is required for each sample. Calibration is performed using a series of standards.
  • Page 18 • Analate Subtraction is used in the measurement of ions for which no ion-selective electrode exists. The electrode is immersed in a reagent solution that 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 diffi...
  • Page 19 Typical Calibration Curve In the direct calibration procedure, a calibration curve is constructed either in the meter memory or in an electronic spreadsheet and graphing the log of the fl uoride concentration against the millivolt value readings. Electrode potentials of standard solutions are measured and plotted on the linear axis against their concentrations on the log axis.

  • Page 20: Direct Calibration

    Direct Calibration Setup Prepare the electrode as described in the Electrode Preparation section. If using the 9409BN or 9409SC half- cell fl uoride electrode with the 900100 reference electrode, fi ll the reference electrode with Cat. No. 900001. If using the 9609BNWP combination fl...
  • Page 21 To prepare standards with a different concentration use the following formula: where = concentration of original standard = volume of original standard = concentration of standard after dilution = volume of standard after dilution For example, to prepare 100 mL of a 1 ppm fl uoride standard from a 100 ppm fl...
  • Page 22 Direct Calibration Using a Meter with an ISE Mode Note: See the meter user guide for more specifi c information. Measure 50 mL of the less concentrated standard and 50 mL of TISAB II and pour into a 150 mL beaker. Stir the solution thoroughly.
  • Page 23 Direct Calibration Using a Meter with a Millivolt Mode Adjust the meter to measure mV. Measure 50 mL of the less concentrated standard and 50 mL of TISAB II and add the standard and TISAB II to a 150 mL beaker. Stir the solution thoroughly. Rinse the electrode with deionized water, blot dry and place into the beaker with the less concentrated standard.

  • Page 24: Low-Level Measurements

    Low-Level Calibration and Measurement Using a Thermo Scientifi c Orion ISE Meter with Autoblank Capability When using a Thermo Scientifi c Orion ISE meter in ISE mode with Autoblank mode enabled, a three point calibration is usually suffi cient to prepare an accurate calibration curve at low levels.
  • Page 25 Prepare the standards as described in the Direct Calibration section of this user guide. Prepare calibration standards for testing by mixing a portion of the standard with an equal portion of low level TISAB in a non-glass beaker. Stir the solution.
  • Page 26 Low-Level Calibration and Measurement When Using a Meter with Millivolt Mode Measure 50 mL of deionized water and 50 mL of low-level TISAB and add to a 150 mL beaker. Rinse the electrode with deionized water and place into beaker. Stir the solution thoroughly. Add increments of the 10 ppm or 10 M fl...

  • Page 27: Single Known Addition

    Single 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.
  • Page 28 Single Known Addition Setup Prepare the electrode as described in the Electrode Preparation section. Connect the electrode to the meter. Prepare a standard solution that will cause the fl uoride concentration of the sample to double when added to the sample solution.
  • Page 29 Single Known Addition Using a Meter with a Known Addition Mode Note: See the meter user guide for more specifi c information. Set up the meter to measure in the known addition mode. Measure 50 mL of the sample and 50 mL of TISAB II or 5 mL of TISAB III and add to a beaker.
  • Page 30 Use Table 4 to fi nd the Q value that corresponds to the change in potential, ΔE. To determine the original sample concentration, multiply Q by the concentration of the added standard: = Q * C sample standard where = standard concentration standard = sample concentration sample...
  • Page 31 Table 4 Q Values for a 10% Volume Change Slopes (in column heading) are in units of mV/decade. ΔE Q Concentration Ratio Monovalent 57.2 58.2 59.2 60.1 0.2894 0.2933 0.2972 0.3011 0.2806 0.2844 0.2883 0.2921 0.2722 0.2760 0.2798 0.2835 0.2642 0.2680 0.2717 0.2754...
  • Page 32 ΔE Q Concentration Ratio Monovalent 57.2 58.2 59.2 60.1 17.5 0.0815 0.0833 0.0852 0.0870 18.0 0.0786 0.0804 0.0822 0.0839 18.5 0.0759 0.0776 0.0793 0.0810 19.0 0.0733 0.0749 0.0766 0.0783 19.5 0.0708 0.0724 0.0740 0.0757 20.0 0.0684 0.0700 0.0716 0.0732 20.5 0.0661 0.0677 0.0693...

  • Page 33: Titrations

    Titrations The electrode makes a highly sensitive endpoint detector for titrations of a fl uoride-containing sample using lanthanum nitrate as the titrant. Titrations are more time-consuming than direct electrode measurements, but results are more accurate and reproducible. With careful technique, titrations can be performed that are accurate to ±...
  • Page 34 Calculate sample concentration, C x = [(V x * V o) / (V o)] * C where x = sample concentration o = fl uoride standard concentration (0.1 M) x = volume of titrant added in unknown sample titration at endpoint o = volume of titrant added in standardization titration at endpoint x = volume of sample used in sample titration (25 mL)

  • Page 35: Fluoride In Acid Solutions

    (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.

  • Page 36: Fluoride In Alkaline Solutions

    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.

  • Page 37: Electrode Characteristics

    Electrode Characteristics Electrode Response The electrode potentials when using a calibration curve by graphing the log of the fl uoride concentration against the millivolt values will result in a straight line with a slope of about 54 to 60 mV per decade change in concentration. See Figure 2. The time response of the electrode, the time required to reach 99% of the stable potential reading, varies from several seconds in concentrated solutions to several minutes near the limit of...

  • Page 38: Temperature Effects

    Temperature Effects Since electrode potentials are affected by changes in temperature, samples and standard solutions should be within ± 1 °C (± 2 °F) of each other. At the 10 M fl uoride level, a 1 °C difference in temperature results in a 2% error. The absolute potential of the reference electrode changes slowly with temperature because of the solubility equilibria on which the electrode depends.

  • Page 39: Ph Effects

    pH Effects In acid solutions with a pH below 5, hydrogen complexes a portion of fl uoride in solution, forming the undissociated acid HF and the ion HF¯ . Figure 5 shows the proportion of free fl uoride ion in acid solutions. Hydroxide ion interferes with the electrode response to fl...

  • Page 40: Complexation

    electrode potential (mV) solution pH Figure 6 Electrode Response in Alkaline Solutions Complexation Fluoride ions complex with aluminum, silicon, iron (+3), and other polyvalent cations as well as hydrogen. The extent of complexation depends on the concentration of complexing agent, the total fl uoride concentration and pH of the solution, and the total ionic strength of the solution.

  • Page 41: Theory Of Operation

    fl uoride ion in solution, is measured against a constant reference potential with a digital pH/mV meter or ISE (concentration) meter. The measured potential corresponding to the level of fl uoride ion in solution is described by the Nernst equation.
  • Page 42 Total ionic strength adjustor buffer (TISAB) is added to all fl uoride standards and samples so that the background ionic strength is high, fl uoride is decomplexed and the pH of the solution is correct. Reference electrode conditions must also be considered. Liquid junction potentials arise any time when two solutions of different composition are brought into contact.

  • Page 43: Troubleshooting

    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 Scientifi c Orion meters include an instrument checkout procedure and shorting cap for convenience in troubleshooting.

  • Page 44: Assistance

    Sample/Application The quality of results depends greatly upon the quality of the standards. Always prepare fresh standards when problems arise, it could save hours of frustrating troubleshooting! Errors may result from contamination of prepared standards, accuracy of dilution, quality of distilled water, or a mathematical error in calculating the concentrations.

  • Page 45: Troubleshooting Checklist

    Troubleshooting Checklist • No electrode fi lling solution added – Fill the electrode with fi lling solution up to the fi ll hole. Refer to the Electrode Preparation section for details. • Incorrect electrode fi lling solution used – Refer to the Electrode Preparation section to verify the correct electrode fi...

  • Page 46: Ordering Information

    Ordering Information Cat. No. Description 9609BNWP Fluoride ionplus Sure-Flow combination electrode, waterproof BNC connector 9409BN Fluoride half-cell electrode, BNC connector (requires separate reference electrode) 9409SC Fluoride half-cell electrode, screw cap connector (requires separate reference electrode) 900100 Single junction reference electrode, pin tip connector 900061 Optimum Results A electrode fi...

  • Page 47: Specifi Cations

    Specifi cations Concentration Range M (0.02 ppm) to saturated pH Range pH 5-7 at 10 M (0.02 ppm F¯) Temperature Range 0 to 80 °C continuous use, 80 to 100 °C intermittent use Electrode Resistance 150 to 200 kilohms Reproducibility ±...
  • Page 48 Thermo Fisher Scientifi c 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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