Instructions

accumet® combination MicroProbe® electrodes with Calomel Reference

Catalog No.

Description

13-620-95

13-620-96

Micro pH electrode, 6” stem (254mm) x 3 mm diameter, Calomel reference

Connector Refilling Solution

BNC

Micro pH electrode, 1.5” stem (127mm) x 3 mm diameter, Calomel reference BNC

SP138-500

SP138-500

Performance Specifications pH Range

Temperature Range

Slope (out of box)

Zero Point

Offset (assymetry potential)

Response Time

Stability

Glass Membrane Impedance

Reference Junction Impedance

Body Material 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 proteins.

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.

GETTING STARTED

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.

1 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 position.

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.

ELECTRODE OPERATION

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”.

CALIBRATION/STANDARDIZATION

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.

STORAGE

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.

2 Manual revision date: November 2004

TROUBLESHOOTING

SYMPTOM / CAUSE (REMEDY)

· 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) .

REPLACEMENTS & ACCESSORIES

Catalog No.

Description

SB105 Fisher Buffer-Pac (500 mL each of pH 4, 7, and 10 buffers)

13-300-147 Single use assortment packets (five each of pH 4, 7, 10, and rinse)

SB101-500 pH 4.00, 500 mL

13-300-150 pH 4.00, single use packets 20/box

SB107-500 pH 7.00, 500 mL

13-300-149 pH 7.00, single use packets 20/box

SB115-500 pH 10.00, 500 mL

13-300-148 pH 10.00, single use packets 20/box

13-300-180 Rinse water, single use packets 20/box

SE40-1 Electrode storage solution, 1 L

13-300-178 Electrode storage solution, 500 mL

13-300-179 Electrode cleaning solution, 500 mL

13-620-499 Electrode storage bottle

SP138-500 Refill solution for calomel and double-junction (Accumet purple band) electrodes, Saturated KCl, 500 mL

13-620-19 Automatic Temperature Compensation (ATC) Probe for accumet AB, AR, XL benchtop series models,

Mini-Phone Plug

15-094-28 NIST traceable calibration certificate for pH meters

WARRANTY accumet electrodes are warranted to be free from defects in material and workmanship for a period of (12) months from date of purchase.

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: www.fishersci.com

For electrochemistry technical support, call 1-888-358-4706, fax 847-327-2987, or email [email protected]

.

3 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.

4 Manual revision date: November 2004