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Electrodes ▼ pH/ORP

Electrode

Selection Guide

The right electrode

While the basic principles of pH measurement are simple, getting

an accurate measurement can often be challenging. There are

hundreds of applications for pH measurement and each presents

different problems. Selecting the right electrode can make the

most difficult samples easy to accurately measure.

Gel-filled vs refillable electrodes

Gel-filled electrodes are convenient and easier to maintain

than refillable liquid-filled electrodes. However the liquid-filled

electrode will provide a faster response. In addition the user

can adjust the fill solution to optimize performance, for example

adding glycol for better performance at low temperatures.

Glass vs epoxy body electrodes

Glass body electrodes will typically be able to withstand higher,

temperatures (100°C as opposed to 80°C for epoxy). In addition,

the glass design offers better sealing, fusing glass to glass

instead of relying on adhesives. The epoxy body however is less

susceptible to breakage. Note: Even though the body of an epoxy

electrode is plastic, the measuring bulb will still be glass.

Body design

Oakton

offers electrodes in a variety of lengths and diameters.

Small diameter probes are ideal for measuring samples in test

tubes. Electrodes with wider barrels, greater weight, and longer

cable lengths are available for measurements in streams. lakes,

or ponds.

Bulb design

Oakton pH electrodes are handblown by experienced craftsmen.

The bulb shape can be modified to provide a semi-dome for

increased ruggedness, a spear tip for soft penetration applications,

or even a flat surface. In addition, the glass formulation can

provide increased range.

Reference design

To achieve accurate results, the reference electrode must allow

electrolyte solution (or ions, in the case of a gel-filled electrode)

to flow into the sample. Depending on the size and material of the

junction, this flow rate can be increased or kept to a minimum.

Faster flow produces stable readings faster but results in greater

service requirements or premature electrode failure.

Reference chemistry

The leading cause of electrode failure is reference contamination.

The most popular electrodes use a silver chloride (AgCl) reference

solution that can react with heavy metals, sulfides, and organics.

If your application has any of these contaminants present, be

sure to select either a double-junction or calomel electrode.

The double-junction electrode uses a second internal reference

junction, restricting the AgCl solution to the upper chamber where

it is isolated from the sample. The calomel electrode replaces the

AgCl with HgCl.

Double-junction, glass-body, refillable pH electrode 35805-04

Single-junction, epoxy-body, gel-filled pH electrode 35808-71

Submersible pH electrode 35805-24

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ph Electrode Anatomy

1) Cable

2) Cap

3) Fill hole

4) Body—glass

or epoxy

5) Outer reference

chamber filled with

internal fill solution

6) Ag/AgCI wire

7) Annular

reference

junction allows

reference

solution to leak

8) Inner reference

chamber

9) Outer reference

chamber

10) pH sensing bulb

10 10

http://www.novatech-usa.com/Products/Laboratory-Equipment-Supply-Products Tel: (281) 359-8538 Toll Free:(866) 433-6682

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