MIDTERM LEC 2

The measurement of current or voltage generated by the activity of a specific ion

It measures blood pH and gases, electrolytes in blood and sweat samples, toxins, glucose, and urea.

It measures the voltage (electrical potential) caused by free ions in a solution

A change in voltage tells us how active each substance (analyte) is

It works by comparing voltage differences while keeping the current steady.

It follows the Nernst equation, which is a rule that ideal reference electrodes should follow.

Concentration of ions in a solution can be calculated from the measured potential difference between the two electrodes (reference electrode and measuring electrode).

Potentiometry Reference electrodes:

Potentiometry Use:

Reference Electrodes Mercury in contact with a solution of mercurous chloride (calomel) and potassium chloride

Silver electrode in KCl saturated with silver chloride; works better above 60°C but reacts more with sample components than calomel.

It measures the voltage between two parts

A measuring electrode that touches the sample through a special glass that only lets H⁺ (acid) ions through.

A reference electrode that has a stable, known

The tip (bulb) of the electrode is made of special glass with a chloride solution inside.

The difference in voltage between the two electrodes is used to calculate the pH of the sample.

It works like a pH electrode but with a special design.

The pH sensor is placed inside a plastic cover (jacket).

This jacket is filled with a sodium bicarbonate solution and covered by a membrane that lets gases pass through (like CO₂).

It’s mainly used to measure carbon dioxide (CO₂) by detecting pH changes caused by the gas.

It is the first and still the most commonly used electrodes for measuring hydrogen ion activity or pH.

It is an electrochemical transducer capable of responding to one given ion.

Its ionic selectivity depends on the membrane/barrier composition used.

It is very sensitive and measures the activity of one ion (selective)