The Coulter principle is used to count particles suspended in an electrolyte, in a flow cell this would be flow cytometery. This principle applies to cell counting in hematology as well as any small particle counting. Not only are the cells and particles counted but the sizes of the cells and the distribution of the sizes are also determined. The suspended particles are passed through an orifice and an electric charge is passed along the orifice. The change in impedence as the particles pass through is directly related to the volume of the particle. Coulter counters have been available from Beckman Coulter since 1997. A new automated electronic cell counter based on the Coulter principle is being marketed by Orfl0 and is called the Moxi-Z.
The Coulter principle is a more accurate way to count cells than visually. Also the cells do not need to be dyed as they do for cell counting instruments based on visualization. Particle counters using the Coulter principle can count any type of small particles (5 – 25um), not just cells. The particles must be suspended in a conducting solution.