Catálogo Hanna Instruments V31

pH Measuring System

pH Electrode

The sensor half-cell of an electrochemical cell that is typically

composed of a special glass membrane that responds to hydrogen ion

concentration.

Reference Electrode

The half-cell of an electrochemical cell that supplies a stable

voltage that is known, constant, and completely insensitive to the

measurement solution. Changes in voltages generated from the pH

sensor are measured versus this electrode’s voltage.

High Input Impedance Meter

The measurement device that processes the voltage from the

electrochemical cell and converts it into a meaningful measurement

unit (pH). The measurement is done with virtually zero current flow

to prevent polarization of the electrodes. Modern pH meters also may

provide sensor diagnostics, automatic buffer recognition, calibration

reminders and user prompts.

Chemical pH Buffers

Stable, well-characterized standards used for calibration. Two or more

pH buffers that bracket the sample pH range are suggested for the

most accurate results.

Thermometer or Temperature Probe

A temperature measurement is desired during calibration and

measurement to make adjustments to the Nernst slope factor. An

auxiliary or built-in temperature probe ensures both calibration and

measurement are automatically temperature compensated, thus

eliminating error.

Magnetic Stirrer

Used in a laboratory setting, amagnetic stirrer together withmagnetic

stir bars continually agitate the buffer and/or samples to keep them

homogenous, eliminating temperature or sample gradients.

Electrode Design

Ag/AgCl Internal

Wire

Buffered KCl

Solution

pH Sensitive

Glass

Internal Reference

Wire

High Concentration

Electrolyte Solution

(i.e. 3.5M KCl and

AgCl Electrolyte)

Salt Bridge Junction

Connecting the

Reference to the

External Solution

pH Half-cell

Reference

Half-cell

Ag/AgCl

Reference Wire

Ceramic Junction

Combination pH

Electrode

Inner Tube Housing

the Membrane Sensing

Wire

Electrolyte

Containing Silver

Half-cells vs. Combination pH electrodes

Until the 1970s, it was a common practice to offer two half cells

separately, aglass pHsensor anda referenceelectrode. Today it ismore

common to use a single combined electrode that has both sensing and

reference components. Reference electrodes still enjoy use in other

electrochemical techniques and their use is often preferred with ion

selective electrodes (ISE) half-cells.

pH Electrodes

Designed and Manufactured by Hanna

2.100

www.hannainst.com

electrodes