Coulter counter
A Coulter Counter is a predominantly in medical laboratory diagnostic inserted measuring instrument for determining the number of particles in an electrically conductive liquid. When creating a blood count, it is used, among other things , to automatically determine the number of cells in the blood, for example leukocytes . The underlying Coulter measuring principle is a method from the field of flow cytometry . Other modified measuring devices based on the Coulter measuring principle are used, among other things, in materials technology and in the area of quality control. The Coulter counter and the principle on which it is based were developed by Wallace H. Coulter in the late 1940s and patented in 1953.
Working principle
The principle of the Coulter counter is based on measuring the change in the mean electrical conductivity between two electrodes . These are immersed in an electrically conductive liquid that contains particles with a different conductivity than the liquid. To count the number of particles, the measuring device consists of two measuring chambers, as shown in the schematic diagram on the right. A measuring electrode is immersed in each of the two chambers, which are separated from one another by a narrow opening. The size of the opening depends on the particle size to be measured. Their diameter should be only slightly larger than the maximum particle diameter.
An external pump creates a negative pressure in one of the two chambers for counting. This creates a flow between the two chambers. The particles entrained in the process change the measured electrical resistance between the electrodes as they pass through the opening . The small changes in the measured electrical resistance are electronically amplified and the measurement signal thus formed can be shown directly on a display for control purposes. Particles smaller than the measurement opening only lead to a small signal change, while particles of maximum size lead to a larger signal change. By evaluating the signal strength, the size of the particle when passing through can be classified. For automatic evaluation, the number of pulses within a specific time window is fed to a digital counter and the count is displayed directly. Depending on the scope of the evaluation, several counter displays are used which, depending on the signal strength, only count certain particle sizes and thus also allow a statement to be made about the proportions of the individual particles in the liquid.
Individual evidence
- ↑ RW DeBlois, CP Bean: Counting and sizing of submicron particles by the resistive pulse technique . In: Review of Scientific Instruments . 41, No. 7, 1970, pp. 909-916. doi : 10.1063 / 1.1684724 .
- ↑ Inventor of the Week: Wallace H. Coulter (1913-1998). Massachusetts Institute of Technology (MIT School of Engineering), August 2000, accessed May 5, 2014 .
- ↑ Patent US2656508 : Means for counting particles suspended in a fluid. Applied on August 27, 1949 , published October 20, 1953 , applicant: Wallace H. Coulter, inventor: Wallace H. Coulter.
- ↑ Robert Rath, Dieter Pohl: Particle size determination with the Coulter counter . In: Hazardous substances - keeping the air clean . 34, No. 8, 1974, pp. 292-294.