But What Is a Coulter Counter?

What is a Coulter Counter

For the last couple of years I have been writing posts on Coulter Counter applications, developments and history, some of which have been quite detailed, but this month I thought I would pause and give a simple summary for those who are new to the subject.

In a nutshell, a Coulter Counter is an ingenious analyser that provides us with the most accurate way currently possible of counting and measuring particles. It works by use of the Coulter Principle.

The Coulter Principle involves drawing particles through an aperture, one by one, by applying an electric field across it. To do this the particles must first be suspended in a dilute electrolytic liquid. Electrodes are positioned on each side of the aperture, creating a confined electric field which pulls the particles through.

As each particle moves in this way it displaces a volume of liquid equal to its own volume. The result is a series of pulses. Electronic analysis of these allows determination of the number of particles, their concentration, their volumes and their surface areas.

The Coulter Principle and the Coulter Counter are named after their inventor, Wallace H Coulter, who formulated the idea in the 1940s as a way of quickly counting blood cells for medical purposes. His discovery made cell counts, as well as other particle counts and measurements, into a simple and routine process.

Today Coulter Counters are used for many other kinds of cells and small organisms, as well as a host of non-living particles. Pharmaceuticals, toners, foodstuffs, abrasives, minerals, metals and construction materials are just some of the many particulate substances that we can characterise.

In fact, anything whose particles can be suspended in a conducting liquid may be easily investigated via the Coulter Principle, as long as their diameters are no smaller than 0.4 microns and no larger than 1600 microns.

If you’d like to know more about the applications and particle counting and sizing instruments then please visit the Meritics website.