... Classification and separation of many biological particles are performed using membranes. This technology is presented in Bioseparation Processes. Electronic Particle Counting A suspension of particles in an electrolyte medium is drawn (by vacuum) through a (sapphire) aperture (0.03?1 mm diameter) across which a direct (constant) current is applied. The overall electrical resistance is determined by the dimensions of the aperture. When electrolyte within the aperture is displaced by a non-conducting particle, in transit through the aperture, the resistance increases and the voltage is increased to maintain the current. The amplitude (but not the width) of the resulting voltage pulse is measured, classified and counted using a multi-channel analyser. The pulse amplitude is found to be directly ? to the volume of the particle, over a range of diameters from 5 to 40% of the aperture diameter. The residence time in the aperture (and hence pulse width) depends upon particle trajectory. At high concentrations of ...

See this essay or coursework document in full right now