Coulter counter
Coulter identified several requirements necessary for practical application of this phenomenon: If multiple particles pass through the constriction simultaneously, their impedance profiles will overlap, resulting in an artifact known as coincidence.
A few of these devices have been commercialized, with the most well-known applications being in the medical industry, particularly in hematology to count and size the various cells that comprise whole blood.
All implementations of the Coulter principle have compromises between sensitivity, noise shielding, solvent compatibility, speed of measurement, sample volume, dynamic range, and reliability of device manufacture.
Coulter was influenced by the atomic bombs dropped on Hiroshima and Nagasaki, which motivated him to improve and streamline complete blood counting for use in large scale screening, as would be necessary in the event of a nuclear war.
The most commercially successful application of the Coulter principle is in hematology, where it is used to obtain information about patients' blood cells.
The amount and quality of data obtained varies greatly as a function of the signal processing circuitry in the Coulter counter.
As electric current detectors became more sensitive and less expensive, the Coulter counter became a common hospital laboratory instrument for quick and accurate analysis of complete blood counts (CBC).
Previously, this procedure involved preparing a peripheral blood smear and manually counting each type of cell under a microscope, a process that typically required a half-hour.
Some flow cytometers continue to utilize the Coulter principle to provide information about cell size and count.
The aperture format is the most-used configuration in commercial Coulter counters, and is suited to testing samples for quality control.
After recording baseline data, the sample to be analyzed is slowly added to the conducting liquid and drawn through the aperture.
This variance is a result of both the physical constriction of the electric field and also the fact that the liquid velocity varies as a function of radial location in the aperture.
For those highly conductive materials that present a problem, the voltage used during a Coulter experiment can be reduced below the breakdown potential (which can be determined empirically).
This leads to some confusion amongst those who are used to optical measurements from microscopes or other systems that only view two dimensions and also show the boundaries of an object.
Subsequent developments were able to extend the information obtained by using alternating current (AC) in order to probe the complex electrical impedance of the cells rather their simply counting their number.
When combined with other technologies such as fluorescence tagging and light scattering, the Coulter principle can help produce a detailed profile of a patient's blood cells.
Coulter counters have been used in a wide variety of fields for their ability to individually measure particles, independent of optical properties, sensitivity, and dependability.
