This combination pH electrode comes in many styles and is designed for maximum reliability, accuracy, and ease of use.  The outer body can be glass, epoxy, or other plastic materials.  The plastic body electrode is available with a permanent non-removable bulb guard or a removable guard which is shipped attached to the cable.  The reference half-cell can be refillable or permanently sealed at the factory and non-refillable.  The refillable electrode will have one or two fill holes located underneath the cap at the top of the electrode.  Some models are constructed with a built-in temperature sensor(ATC).   The electrode is shipped with a protective boot filled with a membrane/junction wetting agent (1:1 pH4 buffer/KCl).  Crystals which may form around the protective boot in no way affect electrode performance.

PREPARATION

1.        Remove the pH bulb protector boot covering the pH bulb and rinse the bulb area with deionized water or pH buffer.  Save the boot if the electrode will be stored.  It is possible that air bubbles may have migrated into the pH sensitive bulb during shipment.  Since the electrode is not able to function with air behind the pH bulb, gently shake the electrode downward in the same manner as a clinical thermometer to remove any trapped air bubbles.

2.        Sleeve junction electrode: Remove parafilm from underneath sleeve and slide teflon or glass sleeve firmly into position on tip of electrode.  Measurements should be made with only the lower part of sleeve immersed.  For sleeve junction electrodes, when the liquid junction becomes clogged, the electrode may be flushed after loosening the sleeve.  If the sleeve freezes in place, soak it in warm water to loosen it.  After the sleeve is free, replenish the filling solution.

3.        Reference electrodes that are refillable: For electrodes shipped with fill-hole plugs, remove the shipping tape covering the rubber fill-hole plug and withdraw the plug to expose the fill-hole.  For electrodes shipped with a sleeve over the fill-hole(s), slide the rubber sleeve down and remove the shipping tape to expose the fill-hole.  Fill the refillable electrodes with any fill solution(s) shipped with the electrode to a level just below the fill-hole(s).  The fill hole should be open whenever  the electrode is in solution.

4.        Attach the removable bulb guard, if provided, to the epoxy electrode by sliding guard over the end of the electrode.

5.        Prior to first usage, or after long-term storage, immerse the pH bulb in pH buffer for thirty minutes.  This hydrates the pH bulb and wets the reference junction for optimum performance.  The electrode is now ready for use.

REQUIRED MATERIALS

Meter: This electrode will work with any pH and/or mV meter commercially available.  Consult the meter instruction manual for specific details on connecting the pH electrode to the meter or operating the meter.  Some electrodes may require adaptor cables or detachable lead cables for connection to the pH and/or mV meter.

Buffers:  For precise electrode standardization, two buffers are required, of which one should be close to the desired sample pH.  pH 7.00 (at 25°C) buffer is recommended for initial standardization followed by pH  4.01 ( at 25°C) or pH 10.01 (at 25°C) buffer to span(slope) the electrode.

ELECTRODE STANDARDIZATION

1.        Place the electrode in fresh pH 7.00  buffer and stir.  Adjust the meter to read the buffer value according to the meter instruction manual.  If impossible, see cleaning procedures.

2.        Rinse the electrode in distilled water and place the electrode in either fresh pH 4.01 buffer or fresh pH 10.01 buffer depending on whether the sample is acidic or basic.  Stir and allow meter reading to stabilize for 30 seconds to one minute.  Adjust the meter reading to the buffer value according to the meter instruction manual.  If impossible, see cleaning procedure.

3.        Rinse the electrode with distilled water.  Place in sample and stir.  Allow meter reading to stabilize for 30 seconds to one minute.  Record reading.  For best accuracy, the temperature of the buffers and samples should be identical and at room temperature.

ELECTRODE STORAGE

For best results, always keep the pH bulb wet, preferably in pH 4.01 buffer with 1/100 part of saturated KCl added.  Other pH buffers or tap water are acceptable storage media, but avoid storage in distilled water.  The protective boot filled with buffer will provide an ideal storage chamber for long periods.  NOTE: Electrodes  should not be stored for a period longer than 6 months for best results.  Electrode stock should be rotated accordingly.

TROUBLESHOOTING HINTS

Symptom                          Possible Causes                Next Step

Out of Range Reading             defective meter                         check meter with shorting plug                                                           defective electrode                check electrode operation

electrode wired incorrectly     check wiring connections                                                                air bubble on pH bulb             remove electrode and reattach

Noisy or Unstable Display      defective meter                         check meter with shorting plug

solution not grounded             ground meter and electrode

air bubble on pH bulb             remove electrode and reattach

Drift (reading                           pH bulb contaminated             see CLEANING hints

slowly changing                       reference clogged                     see CLEANING hints     

in one direction)