accumet® combination MicroProbe® electrodes with Calomel Reference
Catalog No.
Micro pH electrode, 6” stem (254mm) x 3 mm diameter, Calomel reference BNC
Micro pH electrode, 1.5” stem (127mm) x 3 mm diameter, Calomel reference BNC
Performance Specifications
pH Range
Temperature Range
Slope (out of box)
Zero Point
Offset (assymetry potential)
Response Time
Glass Membrane Impedance
Reference Junction Impedance
Body Material
Refilling Solution
pH 0 to 14 (Na+ < 0.1N)
-5 to +80°C (23 to 176°F)
59 ± 3 mV/pH unit at 25 °C ( 95 to 105% slope)
pH 7
0 mV ± 25 mV
< 10 sec (95% response) from pH 7.00 to pH 4.01
< 3 mV drift / 24 hours in pH 7.00 buffer
< 300 Mohm at 25 °C
< 50 Kohm at 25 °C
Glass body, Teflon tubing (flexible stem)
accumet combination electrodes offer the convenience of having the reference and measuring/indicating electrodes combined
in a single housing. They are offered in a variety of configurations to meet most application needs. When immersed in a
solution, the reference electrode makes contact with the sample through the junction, thus completing electrical contact
between the reference electrode, sample, and pH indicating electrode. accumet combination electrodes use FS-5 universal
glass, which offers high chemical resistance and low sodium error, responsive throughout the 0-14 pH range.
accumet refillable electrodes utilize a patented easy-to-use fill hole design (US Patent 4,770,762). Electrodes are color
coded for easy classification. A purple fill hole band signifies an electrode that is Tris compatible-typically using a doublejunction or calomel reference-and are less prone to clogging by sulfides, heavy metals, or proteins. A blue fill hole band
indicates a single-junction electrode designed for general purpose use for samples without sulfides, heavy metals, or
accumet calomel electrodes use a mercury/mercurous chloride reference design. The filling solution is saturated potassium
chloride (SP138), and contains no silver ions. Therefore the electrode is compatible with silver sensitive samples.
accumet MicroProbe electrodes are convenient for measurement of small volumes or small diameter containers or vessels.
The 6" stem is flexible, while retaining the ability to respond within the full pH range. For deep or difficult to reach sample
measurement, the 6" stem probe is recommended. For shallow, small diameter spaces, the 1.5" stem probe is
recommended for more controlled handling.
While the flexibility of the longer stem permits it to be less fragile, the bulb is still sensitive to scratching, as is any pH
sensitive bulb, and must be handled with care to avoid damage. To prevent damage to the flexible stem, avoid excessive
bending/flexing of the stem. Store the electrode in a manner which keeps the stem in a straight position.
Each accumet electrode has a unique serial number identified on its label and is quality checked before it leaves the factory. A
factory label with data is included with each electrode.
Your Microprobe electrode is shipped with a small rubber cap protecting the electrode tip which should be removed during use.
Occasionally some of the storage solution will creep out and appear as dry white crystal residue on the electrode. This will have
no long-term effect on the electrode and can be simply be rinsed off with clean water.
Manual revision date: November 2004
Your MicroProbe electrode is shipped with a bottle of SP138 electrode filling solution (electrolyte) appropriate for your electrode
along with a separate spout cap. New electrodes are shipped filled and with the filling hole closed. Adding fill solution to new
electrodes should not be required. To add electrolyte to the electrode it is necessary to replace the cap on the electrolyte bottle
with the spout cap.
The fill hole should be in the open position when in use. If necessary, rotate the hole in the cap ring from the closed to the open
If the electrolyte level in the reference cavity (outer annular space) is lower than ¼ inch or so below the cap, add SP138 using the
spout cap on the refilling bottle. If the electrolyte level is not visible, the electrode may be filled to capacity just beneath the hole.
Extend the spout from the cap of the electrolyte bottle and firmly press it into the fill hole to make an airtight seal. While
maintaining the seal, gently squeeze the filling bottle so that the electrode becomes pressurized.
Mount the electrode onto a suitable electrode holder and connect the electrode to the meter.
Immerse the electrode in pH 4 or pH 7 buffer for 5 to 10 minutes to condition the glass pH bulb.
1) The level of electrolyte in the outer cavity should be kept above the level of the solution being measured to prevent
reverse electrolyte flow. The electrode need only be immersed far enough to cover both the glass pH sensing bulb and
reference junction to obtain accurate readings.
2) If the electrode has not been hydrated (placed in solution for more than one hour) , allow the electrode to soak in a buffer
(preferably pH 4) as needed prior to standardization or measurement. This will help to optimize and re-establish the thin
hydration layer on the sensing bulb that is critical to pH measurement.
3) Rinse the electrode with deionized or distilled water between samples. Note: wiping the sensing bulb is not recommended as
the thin hydration layer of the sensing bulb could be effected and electrical charges may be produced.
4) Moving or touching the electrode cable may result in unstable readings due to the high impedance (resistance) of the pH
glass membrane.
5) To eliminate temperature errors associated with the electrode, manual or automatic temperature compensation (ATC)
should be used for best accuracy. Since temperature changes pH, the sample temperature should always be noted with
pH readings. i.e.) “pH 8.43 @ 23.2 °C”, not “pH 8.43”.
New accumet pH electrodes are factory-tested to have an efficiency or “slope” of > 95%. The theoretical pH response is
100% (59.16 mV/pH unit), so the millivolt difference between pH 4.00 and pH 7.00 certified calibration standards at 25ºC
should then be 177.48 mV. A 95% slope means that a new accumet electrode will have a response of at least 168.61 mV
between these values. As electrodes naturally age this efficiency deteriorates. Periodic calibration against known standards
is necessary to ensure the electrode efficiency. Most pH meters have features to display the current electrode slope and
protection that warn users of a low slope (usually 90%) or prevent erroneous calibrations.
After following the calibration procedure of your meter, compare the measured pH reading of each calibration buffer to the pH
value indicated for each buffer at the actual temperature. A chart with pH at various temperatures is usually found on the
calibration standard packaging or label. Using a one-point standardization, proper response is indicated if the reading is
within ± 0.05 pH units from the standardization point within 30 seconds when using certified pH buffers . Multiple-point
standardization is recommended for more precise measurements. To provide a linear response in the area of interest, use
one calibration standard above and one below the expected sample pH.
The electrolyte level in the outer cavity should be kept above the level of the solution being measured. Storing electrodes in
distilled or deionized water is NOT recommended as it will deplete the hydration layer of refillable electrodes, and decrease
the life of non-refillable electrodes. The electrode storage bottle can be used for short or long term storage. Store in electrode
storage solution (or a 50:50 mixture of 4 M potassium chloride and pH 4 standard buffer) and close the fill hole.
Manual revision date: November 2004
Erratic / unstable reading - typically with new or previously idle electrodes or after recent addition of filling
solution / Air bubbles trapped within stem are disrupting the electrical signal between the reference electrode, sample,
and pH indicating electrode. (Disconnect the electrode from the meter, slide the fill hole open, in an open area firmly
hold the cable approximately 12” from the cap of the electrode, allow the electrode to hang freely, while exercising
caution not to strike the electrode, swing the electrode continuously in a circular motion for 5-10 seconds. The
centrifugal force generated by this action will remove air bubbles trapped within the stem and force the electrolyte to the
bottom of the electrode. The electrode should produce a much more stable response if successful.
No response, all buffers or samples read the same pH—usually pH 7.00 or 0 mV / Broken sensing bulb or wiring
problem (replace electrode), probe not connected to input (verify correct channel selection when using multiple-channel
meters), probe is not in contact with sample (remove electrode storage bottle or rubber bulb guard), meter automatically
has frozen reading (verify that the hold feature or auto read feature is set to off when using meters with this feature)
Slow response with excessive crystallization inside probe / electrolyte flow clogged from supersaturated
electrolyte (“flush & fill” by remove the filling solution through the fill hole with a syringe or by shaking it upside down.
Repeatedly flush and rinse the reference cavity with clean, 60-80°C water to dissolve crystals until removed. Replace
filling solution and apply gentle pressure to filling hole. Re-hydrate electrode in storage solution or pH 4 buffer), (ensure fill
hole is in open position). To prevent this in the future, ensure that the re-fill hole is closed when electrode is not in use.
Slow response due to clogged junction-usually with single-junction electrodes / reaction with silver such as
silver sulfide formation or protein deposits which causes a dark spot on the ceramic reference junction (For protein
layers-prepare a 1% pepsin solution in 0.1 M of HCl and soak the reference junction for one hour in this solution. Rinse
the electrode with distilled water. Alternatively, heat a diluted KCl solution to 60 to 80 °C. Place the sensing part of the
electrode into the heated solution for about 10 minutes. Allow the electrode to cool in some unheated KCl solution.
Dried salt deposits present / electrolyte residue deposited on electrode surface –often with new electrodes or periods
of non-use. (simply dissolve the deposits in warm tap water followed by a brief soak in pH 4 buffer).
Slow Response, Noisy, unstable, or erratic readings / sensing bulb dry or dirty (clean electrode with mild detergent
& warm water and re-hydrate electrode) , temperature may be changing rapidly or electrode may be thermally shocked
(allow electrode to reach sample temperature), sample may be non-aqueous (take 30 second readings and soak in pH
buffer for one minute between measurements).
Catalog No. Description
Fisher Buffer-Pac (500 mL each of pH 4, 7, and 10 buffers)
Single use assortment packets (five each of pH 4, 7, 10, and rinse)
pH 4.00, 500 mL
pH 4.00, single use packets 20/box
pH 7.00, 500 mL
pH 7.00, single use packets 20/box
pH 10.00, 500 mL
pH 10.00, single use packets 20/box
Rinse water, single use packets 20/box
Electrode storage solution, 1 L
Electrode storage solution, 500 mL
Electrode cleaning solution, 500 mL
Electrode storage bottle
Refill solution for calomel and double-junction (Accumet purple band) electrodes, Saturated KCl, 500 mL
Automatic Temperature Compensation (ATC) Probe for accumet AB, AR, XL benchtop series models,
Mini-Phone Plug
NIST traceable calibration certificate for pH meters
accumet electrodes are warranted to be free from defects in material and workmanship for a period of (12) months from date of
To place an order or for customer service, call 1-800-766-7000
To fax an order, use 1-800-926-1166
To order online:
For electrochemistry technical support, call 1-888-358-4706, fax 847-327-2987, or email
Manual revision date: November 2004
For a complete selection of electrodes and accessories, please refer to the Fisher General Catalog, website, or contact your
Fisher Scientific sales representative.
We reserve the right to make changes, improvements, and modifications to these products.
accumet® is a registered trademark of Fisher Scientific.
Manual revision date: November 2004
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